Reyes Sierra Alvarez

Interests

Research

• Anaerobic waste(water) treatment & biological nutrient removal• Soil/groundwater bioremediation: bioremediation of nitroaromatic explosives and heavy metals • Microbial transformation of hazardous metal and metalloids • Fate and removal of engineered nanomaterials; nanotoxicity• Environmentally technology for semiconductor manufacturing

Teaching

• Environmental engineering• Wastewater treatment• Advanced treatment processes• Environmental microbiology• Bioremediation• Biotransformation of hazardous organic and inorganic compounds

Courses

Scholarly Contributions

Chapters

• Olivares, C. I., Abrell, L., Chorover, J., Simonich, M., Tanguay, R. L., Sierra-Alvarez, R. .., & Field, J. (2016). Identifying toxic biotransformation products of the insensitive munitions compound, 2,4-dinitroanisole (DNAN), using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QToF-MS).. In Towards Harmonized Strategies and Workflows to Assess Transformation Products of Chemicals of Emerging Concern by Non-Target and Suspect Screening, Drewes, J.; Letzel, T., Eds. American Chemical Society: 2016..
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Journals/Publications

• Yu, Y., Root, R. A., Castrejon Miranda, R., Sierra Alvarez, M. R., Chorover, J. D., & Field, J. A. (2024). Abiotic reductive trnasformation of 3-nitro-1,2,4-triazol-5one by zero-valent iron. International journal of Environmental Science and Technology, 21, 25-34. doi:https://doi.org/10.1007/s13762-023-04951-4
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  The military is switching over to insensitive munitions compounds (IMCs) to avoid unintentional detonations during handling and use of explosives. 3-nitro-1,2,4-triazol-5-one (NTO) is an important component of IMCs. NTO may contaminate the subsurface due to its high aqueous solubility. Thus, there is a need to develop remediation technologies for the treatment of NTO-containing (waste) water. This study demonstrated that zero-valent iron (ZVI) reductively transformed NTO to its daughter product, 3-amino-1,2,4-triazol-5-one. The pseudo first-rate constant (k1) of NTO reduction by micron-sized ZVI at pH 3 was 192.6 h−1. Kinetic degradation experiments performed at different pH values showed that ZVI did not effectively reduce NTO at pH 6 (k1 = 0.6 h−1) or higher. The rapid NTO reduction in acidic conditions may be due to dissolution of iron precipitates on the ZVI surface. Additional experiments were conducted to assess the effectiveness of various depassivating pretreatments with deionized water, acetic acid, hydrochloric acid, or bicarbonate. Treatment with 1 M HCl for 15 min was the most effective depassivation method for a ZVI material containing a thick passivating layer (ca. 880 nm), achieving 84.0% NTO removal after 10 min of reaction. On the other hand, a milder treatment involving washing with a diluted bicarbonate solution (60 mM) was sufficient for a ZVI material that was less passivated (estimated thickness of the passivating layer ≈ 300 nm). This study demonstrates that ZVI treatment is a promising approach for the remediation of NTO-contaminated sites or wastewater and provides critical information to optimize this process.
• McCorkel, M., Sherwood, C. L., Borrero, N., Field, J. A., Sierra Alvarez, M. R., & Boitano, S. A. (2017). Sub-cytotoxic hafnium oxide alters cellular signaling in human lung epithelial cells. Toxicological and Applied Pharmacology, In Preparation.
• Niu, X., Abrell, L., Sierra-Alvarez, R., Field, J. A., & Chorover, J. (2022). Analysis of hydrophilic per-and polyfluorinated sulfonates including trifluoromethanesulfonate using solid phase extraction and mixed-mode liquid chromatography-tandem mass spectrometry. Journal of Chromatography A, 462817.
• Jog, K. V., Hess, K. Z., Field, J. A., Krzmarzick, M. J., & Sierra-Alvarez, R. (2021). Aerobic biodegradation of emerging azole contaminants by return activated sludge and enrichment cultures. Journal of Hazardous Materials, 417, 126151.
• Kadoya, W. M., Madeira, C. L., Hoppe-Jones, C., Solsten, T., Snyder, S. A., Root, R. A., Sierra-Alvarez, R., Chorover, J., & Field, J. A. (2021). The Role of Manganese Dioxide in the Natural Formation of Organochlorines. ACS ES&T Water, 1(12), 2523-2530.
• Kadoya, W. M., Sierra-Alvarez, R., Jagadish, B., Wong, S., Abrell, L., Mash, E. A., & Field, J. A. (2021). Covalent bonding of aromatic amine daughter products of 2, 4-dinitroanisole (DNAN) with model quinone compounds representing humus via nucleophilic addition. Environmental Pollution, 268, 115862.
• Lakhey, N., Sierra-Alvarez, R., Couger, M. B., Krzmarzick, M. J., & Field, J. A. (2021). Anammox enrichment culture has unexpected capabilities to biotransform azole contaminants of emerging concern. Chemosphere, 264, 128550.
• Loreto-Muñoz, C., Almendariz-Tapia, F. J., Martin-Garcia, A. R., Sierra-Alvarez, R., Ochoa-Herrera, V., & Monge-Amaya, O. (2021). Sulfate-rich wastewater treatment using an integrated anaerobic/aerobic biological system. Revista Mexicana de Ingeniera Quimica, 20(2), 1005-1017.
• Madeira, C. L., Menezes, O., Park, D., Jog, K. V., Hatt, J. K., Gavazza, S., Krzmarzick, M. J., Sierra-Alvarez, R., Spain, J. C., & Konstantinidis, K. T. (2021). Bacteria Make a Living Breathing the Nitroheterocyclic Insensitive Munitions Compound 3-Nitro-1, 2, 4-triazol-5-one (NTO). Environmental Science & Technology, 55(9), 5806-5814.
• Mendez, G., Trueba, G., Sierra-Alvarez, R., & Ochoa-Herrera, V. (2021). Treatment of acid rock drainage using a sulphate-reducing bioreactor with a limestone precolumn.. Environmental Technology,, 1-12.
• Menezes, O., Kadoya, W. M., Gavazza, S., Sierra-Alvarez, R., Mash, E. A., Abrell, L., & Field, J. A. (2021). Covalent binding with model quinone compounds unveils the environmental fate of the insensitive munitions reduced product 2, 4-diaminoanisole (DAAN) under anoxic conditions. Journal of Hazardous Materials, 413, 125459.
• Menezes, O., Yu, Y., Root, R. A., Gavazza, S., Chorover, J., Sierra-Alvarez, R., & Field, J. A. (2021). Iron (II) monosulfide (FeS) minerals reductively transform the insensitive munitions compounds 2, 4-dinitroanisole (DNAN) and 3-nitro-1, 2, 4-triazol-5-one (NTO). Chemosphere, 285, 131409.
• Munoz, C., Amaya, O., Ochoa-Herrera, V., Sierra-Alvarez, R., & Tapia, F. (2021). Effect of carbon source and metal toxicity for potential acid mine drainage (AMD) treatment with an anaerobic sludge using sulfate-reduction.. Water Science and Technology, 83(11), 2469.
• Muñoz, C., Amaya, O. M., García, A. M., Ochoa-Herrera, V., Sierra-Álvarez, R., & Tapia, F. (2021). Effect of carbon source and metal toxicity for potential acid mine drainage (AMD) treatment with an anaerobic sludge using sulfate-reduction. Water Science and Technology, 83(11), 2469.
• Méndez, G., Trueba, G., Sierra-Alvarez, R., & Ochoa-Herrera, V. (2021). Treatment of acid rock drainage using a sulphate-reducing bioreactor with a limestone precolumn. Environmental Technology, 1-12.
• Niu, X., Field, J. A., Paniego, R., Pepel, R. D., Chorover, J., Abrell, L., & Sierra-Alvarez, R. (2021). Bioconcentration potential and microbial toxicity of onium cations in photoacid generators. Environmental Science and Pollution Research, 28(7), 8915-8921.
• Niu, X., Pepel, R. D., Paniego, R., Field, J. A., Chorover, J., Abrell, L., Sáez, A. E., & Sierra-Alvarez, R. (2021). Photochemical fate of sulfonium photoacid generator cations under photolithography relevant UV irradiation. Journal of Photochemistry and Photobiology A: Chemistry, 416, 113324.
• Olshansky, Y., Gomeniuc, A., Chorover, J., Abrell, L., Field, J. A., Hatton, J., & Sierra-Alvarez, R. (2021). Synthesis and Characterization of Customizable Polyaniline-Derived Polymers and Their Application for Perfluorooctanoic Acid Removal from Aqueous Solution. ACS ES&T Water.
• Zeng, C., Nguyen, C., Boitano, S., Field, J. A., Shadman, F., & Sierra-Alvarez, R. (2021). Toxicity of abrasive nanoparticles (SiO 2, CeO 2, and Al 2 O 3) on Aliivibrio fischeri and human bronchial epithelial cells (16HBE14o-). Journal of Nanoparticle Research, 23(2), 1-12.
• Bueno-Lopez, J. I., Nguyen, C. H., Rangel-Mendez, J. R., Sierra-Alvarez, R. .., Field, J. A., & Cervantes, F. J. (2020). Effects of graphene oxide and reduced graphene oxide on acetoclastic, hydrogenotrophic and methylotrophic methanogenesis. Biodegradation, 31(1-2), 35-45.
• Bueno-López, J. I., Nguyen, C. H., Rangel-Mendez, J. R., Sierra-Alvarez, R., Field, J. A., & Cervantes, F. J. (2020). Effects of graphene oxide and reduced graphene oxide on acetoclastic, hydrogenotrophic and methylotrophic methanogenesis. Biodegradation, 31(1), 35-45.
• Jog, K. V., Sierra-Alvarez, R. .., & Field, J. A. (2020). Rapid biotransformation of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one (NTO), by wastewater sludge. World Journal of Microbiology & Biotechnology, 36(5).
• Jog, K. V., Sierra-Alvarez, R., & Field, J. A. (2020). Rapid biotransformation of the insensitive munitions compound, 3-nitro-1, 2, 4-triazol-5-one (NTO), by wastewater sludge. World Journal of Microbiology and Biotechnology, 36(5), 1-10.
• Lakhey, N., Li, G., Sierra‐Alvarez, R., & Field, J. A. (2020). Toxicity of azoles towards the anaerobic ammonium oxidation (anammox) process. Journal of Chemical Technology & Biotechnology, 95(4), 1057-1063.
• Li, G. B., Field, J. A., Zeng, C., Madeira, C. L., Nguyen, C. H., Jog, K. V., Speed, D., & Sierra-Alvarez, R. .. (2020). Diazole and triazole inhibition of nitrification process in return activated sludge. Chemosphere, 241.
• Li, G., Field, J. A., Zeng, C., Madeira, C. L., Nguyen, C. H., Jog, K. V., Speed, D., & Sierra-Alvarez, R. (2020). Diazole and triazole inhibition of nitrification process in return activated sludge. Chemosphere, 241, 124993.
• Moreno-Andrade, I. .., Regidor-Alfageme, E. .., Durazo, A., Field, J. A., Umlauf, K., & Sierra-Alvarez, R. .. (2020). LC-ICP-OES method for antimony speciation analysis in liquid samples. Journal of Environmental Science and Health Part a-Toxic/Hazardous Substances & Environmental Engineering, 55(4), 457-463.
• Moreno-Andrade, I., Regidor-Alfageme, E., Durazo, A., Field, J. A., Umlauf, K., & Sierra-Alvarez, R. (2020). LC-ICP-OES method for antimony speciation analysis in liquid samples. Journal of Environmental Science and Health, Part A, 55(4), 457-463.
• Nguyen, C. H., Field, J. A., & Sierra-Alvarez, R. (2020). Microbial toxicity of gallium-and indium-based oxide and arsenide nanoparticles. Journal of Environmental Science and Health, Part A, 55(2), 168-178.
• Nguyen, C. H., Field, J. A., & Sierra-Alvarez, R. .. (2020). Microbial toxicity of gallium- and indium-based oxide and arsenide nanoparticles. Journal of Environmental Science and Health Part a-Toxic/Hazardous Substances & Environmental Engineering, 55(2), 168-178.
• Nguyen, C. H., Zeng, C., Boitano, S. A., Field, J. A., & Sierra Alvarez, M. R. (2020). Assessment of Gallium- and Indium-Based Nanoparticles Toward Human Bronchial Epithelial Cells Using an Impedance-Based Real-Time Cell Analyzer. International Journal of Toxicology, 39, 218-231.
• Nguyen, C. H., Zeng, C., Boitano, S., Field, J. A., & Sierra-Alvarez, R. (2020). Cytotoxicity Assessment of Gallium-and Indium-Based Nanoparticles Toward Human Bronchial Epithelial Cells Using an Impedance-Based Real-Time Cell Analyzer. International journal of toxicology, 39(3), 218-231.
• Rios-Valenciana, E. E., Briones-Gallardo, R., Chazaro-Ruiz, L. F., Lopez-Lozano, N. E., Sierra-Alvarez, R., & Celis, L. B. (2020). Dissolution and final fate of arsenic associated with gypsum, calcite, and ferrihydrite: Influence of microbial reduction of As (V), sulfate, and Fe (III). Chemosphere, 239, 124823.
• Rios-Valenciana, E. E., Briones-Gallardo, R., Chazaro-Ruiz, L. F., Lopez-Lozano, N. E., Sierra-Alvarez, R., & Celis, L. B. (2020). Dissolution and final fate of arsenic associated with gypsum, calcite, and ferrihydrite: Influence of microbial reduction of As(V), sulfate, and Fe(III). Chemosphere, 239.
• Fernandez-Gonzalez, N., Sierra-Alvarez, R., Field, J. A., Amils, R., & Sanz, J. L. (2019). Adaptation of granular sludge microbial communities to nitrate, sulfide, and/or p-cresol removal. International Microbiology, 22(3), 305-316.
• Gonzalez-Estrella, J. .., Field, J. A., Ober, C. K., & Sierra-Alvarez, R. (2019). Stability and microbial toxicity of HfO2 and ZrO2 nanoparticles for photolithography. Green Materials, 7(3), 109-117.
• Kadoya, W. M., Sierra-Alvarez, R., Jagadish, B., Wong, S., Abrell, L., Mash, E. A., & Field, J. A. (2019). Coupling reactions between reduced intermediates of insensitive munitions compound analog 4-nitroanisole. Chemosphere, 222, 789-796.
• Li, ., & Sierra-Alvarez, R. .. (2019). [Poster]. A pilot-scale study: Application of Anaerobic Ammonium Oxidation (Anammox) for Side-stream Nitrogen removal in Pima County Wastewater Reclamation Facility (WRF). 2019 Research and Education Conference, Association of Environmental Engineering and Science Professors. May 14-16, 2019. Tempe, AZ..
• Madeira, C. L., Jog, K. V., Vanover, E. T., Brooks, M. D., Taylor, D. K., Sierra-Alvarez, R., Waidner, L. A., Spain, J. C., Krzmarzick, M. J., & Field, J. A. (2019). Microbial enrichment culture responsible for the complete oxidative biodegradation of 3-amino-1, 2, 4-triazol-5-one (ATO), the reduced daughter product of the insensitive munitions compound 3-nitro-1, 2, 4-triazol-5-one (NTO). Environmental science & technology, 53(21), 12648-12656.
• Madeira, C. L., Kadoya, W. M., Li, G., Wong, S., Sierra-Alvarez, R. .., & Field, J. A. (2019). Reductive biotransformation as a pretreatment to enhance in situ chemical oxidation of nitroaromatic and nitroheterocyclic explosives. Chemosphere, 222, 1025-1032.
• Olshansky, Y., Chorover, J., Abrell, L., Field, J. A., Gomeniuc, A., Hatton, J., & Alvarez, R. S. (2019). Sorption of PFAS by Cationic Hydrophobic Polymers. Abstracts of Papers of the American Chemical Society, 257.
• Simon‐Pascual, A., Sierra‐Alvarez, R., & Field, J. A. (2019). Platinum (II) reduction to platinum nanoparticles in anaerobic sludge. Journal of Chemical Technology & Biotechnology, 94(2), 468-474.
• Teran, V., Monge, A. O., Certucha, B., Almendariz, T., Zavala, R. P., & Sierra, A. R. (2019). Bioadsorption of copper and zinc with pre-treated and untreated dry biomass of Escherichia coli. Revista Internacional De Contaminacion Ambiental, 35, 45-55.
• Valdez, D. T., Amaya, O. M., Barragan, M. C., Tapia, F. A., Rivera, P. Z., & Álvarez, Y. S. (2019). Bioadsorption of copper and zinc with pre-treated and untreated dry biomass of Escherichia coli (Estudio de la bioadsorción de cobre y zinc con biomasa seca de escherichia coli pretratada y sin tratar). Revista Internacional de Contaminacion Ambiental, 35, 45-55, DOI: 10.20937/RICA.2019.35.esp03.0.
• Zambrano-Romero, A., Herrera-Moreno, N., Trueba, G., Sierra-Álvarez, R., León-Reyes, A., & Ochoa-Herrera, V. (2019). Construcción y operación de una cámara anaeróbica de bajo costo para la siembra y el cultivo de bacterias sulfato reductoras. CI Avances en Ciencias e Ingenierías, 11(DOI:10.18272/aci.v11i2.1303).
• Ayala-Parra, P., Liu, Y., Sierra-Alvarez, R., & Field, J. A. (2018). Pretreatments to Enhance the Anaerobic Biodegradability of Chlorella Protothecoides Algal Biomass. Environmental Progress & Sustainable Energy, 37(1), 418-424.
• Fernandez-Gonzalez, N. .., Sierra-Alvarez, R. .., Field, J. A., Amils, R., & Sanz, J. L. (2018). Microbial communities and granule structure degradation on sulfide and/or para-cresol denitrifying reactors. International Microbiology. (In press). https://doi.org/10.1007/s10123-018-00050-4.
• Gole, V. L., Fishgold, A., R., S., P., D., & M., K. (2018). Treatment of perfluorooctane sulfonic acid (PFOS) using a large-scale sonochemical reactor. Separation and Purification Technology, 194, 104-110.
• Gole, V. L., Sierra-Alvarez, R., Peng, H., Giesy, J. P., Deymier, P., & Keswani, M. (2018). Sono-chemical treatment of per- and poly-fluoroalkyl compounds in aqueous film-forming foams by use of a large-scale multi-transducer dual-frequency based acoustic reactor. Ultrasonics Sonochemistry, 45, 213-222.
• Gonzalez-Estrella, J. .., Field, J. A., Ober, C. K., & Sierra-Alvarez, R. .. (2018). Stability and microbial toxicity of HfO2 and ZrO2 nanoresists for photolithography.. Green Materials. (In press). https://doi.org/10.1680/jgrma.18.00056.
• Kadoya, W. M., Sierra-Alvarez, R. .., Wong, S., Abrell, L. M., Mash Jr., ,. E., & Field, J. A. (2018). Evidence of Anaerobic Coupling Reactions between Reduced Intermediates of 4-Nitroanisole. Chemosphere, 195, 372-380.
• Khatiwada, R., Abrell, L., Li, G., Root, R. A., Sierra-Alvarez, R., Field, J. A., & Chorover, J. (2018). Adsorption and oxidation of 3-nitro-1,2,4-triazole-5-one (NTO) and its transformation product (3-amino-1,2,4-triazole-5-one, ATO) at ferrihydrite and birnessite surfaces. Environmental Pollution, 240, 200-208.
• Khatiwada, R., Olivares, C., Abrell, L., Root, R. A., Sierra-Alvarez, R., Field, J. A., & Chorover, J. (2018). Oxidation of reduced daughter products from 2,4-dinitroanisole (DNAN) by Mn(IV) and Fe(III) oxides. Chemosphere, 201, 790-798.
• Khatiwada, R., Root, R. A., Abrell, L., Sierra-Alvarez, R., Field, J. A., & Chorover, J. (2018). Abiotic reduction of insensitive munition compounds by sulfate green rust. Environmental Chemistry, 15(5), 259-266.
• Madeira, C. L., Field, J. A., Simonich, M. T., Tanguay, R. L., Chorover, J., & Sierra-Alvarez, R. (2018). Ecotoxicity of the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) and its reduced metabolite 3-amino-1,2,4-triazol-5-one (ATO). Journal of Hazardous Materials, 343(Supplement C), 340-346.
• Ramos-Ruiz, A., Field, J. A., Sun, W., & Sierra-Alvarez, R. (2018). Gallium arsenide (GaAs) leaching behavior and surface chemistry changes in response to pH and O-2. Waste Management, 77, 1-9.
• Simon-Pascual, A., Sierra-Alvarez, R., Ramos-Ruiz, A., & Field, J. A. (2018). Reduction of platinum (IV) ions to elemental platinum nanoparticles by anaerobic sludge. Journal of Chemical Technology and Biotechnology, 93(6), 1611-1617.
• Sun, W., Cho, Y., Krysak, M., Ouyang, C. Y., Sierra-Alvarez, R. .., & Ober, C. K. (2018). Lithography performance and environmental compatibility of PFOS-free photoacid generators. Green Materials (In press) Accepted on 10/26/17 http://dx.doi.org/10.1680/jgrma.17.00020.
• Zeng, C., Chi, N., Boitano, S., Field, J. A., Shadman, F., & Sierra-Alvarez, R. (2018). Cerium dioxide (CeO2) nanoparticles decrease arsenite (As(III)) cytotoxicity to 16HBE14o-human bronchial epithelial cells. Environmental Research, 164, 452-458.
• Ayala-Parra, P. .., Liu, Y. Z., Field, J. A., & Sierra-Alvarez, R. .. (2017). Nutrient recovery and biogas generation from the anaerobic digestion of waste biomass from algal biofuel production. Renewable Energy, 108, 410-416.
• Gonzalez, R. L., Lopez-Honoratob, E. .., Sierra-Alvarez, R. .., & Vela, J. (2017). In Focus: Symposium of Materials and Environment in the International Material Research Congress (IMRC) in Mexico (vol 92, pg 1487, 2017). Journal of Chemical Technology and Biotechnology, 92(10), 2769-2769.
• Gonzalez-Estrella, J. .., Li, G. B., Neely, S. E., Puyol, D., Sierra-Alvarez, R. .., & Field, J. A. (2017). Elemental copper nanoparticle toxicity to anaerobic ammonium oxidation and the influence of ethylene diamine-tetra acetic acid (EDTA) on copper toxicity. Chemosphere, 184, 730-737.
• Li, G. B., Carvajal-Arroyo, J. M., Sierra-Alvarez, R. .., & Field, J. A. (2017). Mechanisms and Control of NO2- Inhibition of Anaerobic Ammonium Oxidation (Anammox). Water Environment Research, 89(4), 330-336.
• Madeira, C. L., Speet, S. A., Nieto, C. A., Abrell, L., Chorover, J., Sierra-Alvarez, R. .., & Field, J. A. (2017). Sequential anaerobic-aerobic biodegradation of emerging insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO). Chemosphere, 167, 478-484.
• Olivares, C. I., Madeira, C. L., Sierra-Alvarez, R. .., Kadoya, W., Abrell, L., Chorover, J., & Field, J. A. (2017). Environmental Fate of C-14 Radiolabeled 2,4-Dinitroanisole in Soil. Microcosms. Environmental Science & Technology, 51(22), 13327-13334.
• Ramos-Ruiz, A. .., Sesma-Martin, J. .., Sierra-Alvarez, R. .., & Field, J. A. (2017). Continuous reduction of tellurite to recoverable tellurium nanoparticles using an upflow anaerobic sludge bed (UASB) reactor. Water Research, 108, 189-196.
• Ramos-Ruiz, A. .., Wilkening, J. V., Field, J. A., & Sierra-Alvarez, R. .. (2017). Leaching of cadmium and tellurium from cadmium telluride (CdTe) thin-film solar panels under simulated landfill conditions. Journal of Hazardous Materials, 336, 57-64.
• Simon-Pascual, A., Sierra-Alvarez, R., Ramos-Ruiz, A., & Field, J. A. (2017). Reduction of platinum(IV) ions to elemental platinum nanoparticles by anaerobic sludge. Journal of Chemical Technology & Biotechnology, in press.
• Zeng, C., Gonzalez-Alvarez, A. .., Orenstein, E., Field, J. A., Shadman, F., & Sierra-Alvarez, R. .. (2017). Ecotoxicity assessment of ionic As(III), As(V), In(III) and Ga(III) species potentially released from novel III-V semiconductor materials. Ecotoxicology and Environmental Safety, 140, 30-36.
• Zeng, C., Shadman, F., & Sierra-Alvarez, R. .. (2017). Transport and abatement of fluorescent silica nanoparticle (SiO2 NP) in granular filtration: effect of porous media and ionic strength. Journal of Nanoparticle Research, 19(3).
• Ayala-Parra, P. .., Sierra-Alvarez, R. .., & Field, J. A. (2016). Algae as an electron donor promoting sulfate reduction for the bioremediation of acid rock drainage. Journal of Hazardous Materials, 317, 335-343.
• Ayala-Parra, P. .., Sierra-Alvarez, R. .., & Field, J. A. (2016). Treatment of acid rock drainage using a sulfate-reducing bioreactor with zero-valent iron. Journal of Hazardous Materials, 308, 97-105.
• Fernandez, N. A., Rodriguez-Freire, L. .., Keswani, M., & Sierra-Alvarez, R. .. (2016). Effect of chemical structure on the sonochemical degradation of perfluoroalkyl and polyfluoroalkyl substances (PFASs). Environmental Science-Water Research & Technology, 2(6), 975-983.
• Gonzalez-Estrella, J. .., Gallagher, S., Sierra-Alvarez, R. .., & Field, J. A. (2016). Iron sulfide attenuates the methanogenic toxicity of elemental copper and zinc oxide nanoparticles and their soluble metal ion analogs. Science of the Total Environment, 548, 380-389.
• Li, G. B., Sierra-Alvarez, R. .., Vilcherrez, D., Weiss, S., Gill, C., Krzmarzick, M. J., Abrell, L., & Field, J. A. (2016). Nitrate Reverses Severe Nitrite Inhibition of Anaerobic Ammonium Oxidation (Anammox) Activity in Continuously-Fed Bioreactors. Environmental Science & Technology, 50(19), 10518-10526.
• Li, G., Vilcherrez, D., Carvajal-Arroyo, J. M., Sierra-Alvarez, R., & Field, J. A. (2016). Exogenous nitrate attenuates nitrite toxicity to anaerobic ammonium oxidizing (anammox) bacteria. Chemosphere, 144, 2360-2367.
• Lopez-Honorato, E. .., Sierra, R., & Gonzalez, R. L. (2016). In Focus: Materials and the Environment Symposium. Journal of Chemical Technology and Biotechnology, 91(8), 2147-2147.
• Mondragon-Solorzano, G. .., Sierra-Alvarez, R. .., Lopez-Honorato, E. .., & Barroso-Flores, J. .. (2016). In silico design of calixarene-based arsenic acid removal agents. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 85(1-2), 169-174.
• Ochoa-Herrera, V. .., Field, J. A., Luna-Velasco, A. .., & Sierra-Alvarez, R. .. (2016). Microbial toxicity and biodegradability of perfluorooctane sulfonate (PFOS) and shorter chain perfluoroalkyl and polyfluoroalkyl substances (PFASs). Environmental Science-Processes & Impacts, 18(9), 1236-1246.
• Olivares, C. I., Abrell, L., Khatiwada, R., Chorover, J., Sierra-Alvarez, R., & Field, J. A. (2016). (Bio)transformation of 2,4-dinitroanisole (DNAN) in soils. Journal of Hazardous Materials, 304, 214-221.
• Olivares, C. I., Field, J. A., Simonich, M., Tanguay, R. L., & Sierra-Alvarez, R. .. (2016). Arsenic (III, V), indium (III), and gallium (III) toxicity to zebrafish embryos using a high-throughput multi-endpoint in vivo developmental and behavioral assay. Chemosphere, 148, 361-368.
• Olivares, C. I., Sierra-Alvarez, R. .., Abrell, L., Chorover, J., Simonich, M., Tanguay, R. L., & Field, J. A. (2016). ZEBRAFISH EMBRYO TOXICITY OF ANAEROBIC BIOTRANSFORMATION PRODUCTS FROM THE INSENSITIVE MUNITIONS COMPOUND 2,4-DINITROANISOLE. Environmental Toxicology and Chemistry, 35(11), 2774-2781.
• Olivares, C. I., Sierra-Alvarez, R. .., Alvarez-Nieto, C. .., Abrell, L., Chorover, J., & Field, J. A. (2016). Microbial toxicity and characterization of DNAN (bio)transformation product mixtures. Chemosphere, 154, 499-506.
• Olivares, C. I., Wang, J., Luna, C. D., Field, J. A., Abrell, L., & Sierra-Alvarez, R. (2016). Continuous treatment of the insensitive munitions compound N-methyl-p-nitro aniline (MNA) in an upflow anaerobic sludge blanket (UASB) bioreactor. Chemosphere, 144, 1116-1122.
• Pat-Espadas, A. M., Field, J. A., Otero-Gonzalez, L., Razo-Flores, E., Cervantes, F. J., & Sierra-Alvarez, R. (2016). Recovery of palladium(II) by methanogenic granular sludge. Chemosphere, 144, 745-753.
• Pat-Espadas, A. M., Field, J. A., Razo-Flores, ., Cervantes, F. J., & Sierra-Alvarez, R. (2016). Continuous removal and recovery of palladium in an upflow anaerobic granular sludge bed (UASB) reactor. Journal of Chemical Technology & Biotechnology, 91, 1183-1189.
• Pat-Espadas, A. M., Field, J. A., Razo-Flores, E. .., Cervantes, F. J., & Sierra-Alvarez, R. .. (2016). Continuous removal and recovery of palladium in an upflow anaerobic granular sludge bed (UASB) reactor. Journal of Chemical Technology and Biotechnology, 91(4), 1183-1189.
• Ramos-Ruiz, A. .., Field, J. A., Wilkening, J. V., & Sierra-Alvarez, R. .. (2016). Recovery of Elemental Tellurium Nanoparticles by the Reduction of Tellurium Oxyanions in a Methanogenic Microbial Consortium. Environmental Science & Technology, 50(3), 1492-1500.
• Ramos-Ruiz, A. .., Zeng, C., Sierra-Alvarez, R. .., Teixeira, L. H., & Field, J. A. (2016). Microbial toxicity of ionic species leached from the II-VI semiconductor materials, cadmium telluride (CdTe) and cadmium selenide (CdSe). Chemosphere, 162, 131-138.
• Rodriguez-Freire, L. .., Abad-Fernandez, N. .., Sierra-Alvarez, R. .., Hoppe-Jones, C. .., Peng, H., Giesy, J. P., Snyder, S., & Keswani, M. (2016). Sonochemical degradation of perfluorinated chemicals in aqueous film-forming foams. Journal of Hazardous Materials, 317, 275-283.
• Rodriguez-Freire, L. .., Moore, S. E., Sierra-Alvarez, R. .., Root, R. A., Chorover, J., & Field, J. A. (2016). Arsenic remediation by formation of arsenic sulfide minerals in a continuous anaerobic bioreactor. Biotechnology and Bioengineering, 113(3), 522-530.
• Rodriguez-Freire, L., Moore, S. E., Sierra-Alvarez, R., Root, R. A., Chorover, J., & Field, J. A. (2016). Arsenic remediation by formation of arsenic sulfide minerals in a continuous anaerobic bioreactor. Biotechnology and Bioengineering, 113, 522-530.
• Gonzalez-Estrella, J., Puyol, D., Gallagher, S., Sierra-Alvarez, R., & Field, J. A. (2015). Elemental copper nanoparticle toxicity to different trophic groups involved in anaerobic and anoxic wastewater treatment processes. Science of the Total Environment, 512, 308-315.
• Gonzalez-Estrella, J., Puyol, D., Sierra-Alvarez, R., & Field, J. A. (2015). Role of biogenic sulfide in attenuating zinc oxide and copper nanoparticle toxicity to acetoclastic methanogenesis. Journal of hazardous materials, 283, 755--763.
• Krzmarzick, M. J., Khatiwada, R., Olivares, C. I., Abrell, L., Sierra-Alvarez, R., Chorover, J., & Field, J. A. (2015). Biotransformation and Degradation of the Insensitive Munitions Compound, 3-Nitro-1,2,4-triazol-5-one, by Soil Bacterial Communities. Environmental science & technology, 49, 5681-8.
• Kzmarzick, M. J., Khatiwada, J. R., Olivares, C. I., Abrell, L., Sierra Alvarez, M. R., Chorover, J. D., & Field, J. A. (2015). Biotransformation and degradation of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one, by soil bacterial communities.. Environ. Sci. Technol., 49, 5681-5688.
• Li, G., Puyol, D., Carvajal-Arroyo, J. M., Sierra-Alvarez, R., & Field, J. A. (2015). Inhibition of anaerobic ammonium oxidation by heavy metals. Journal of Chemical Technology and Biotechnology, 90, 830-837.
• Linker, B. R., Khatiwada, R., Perdrial, N., Abrell, L., Sierra-Alvarez, R., Field, J. A., & Chorover, J. (2015). Adsorption of novel insensitive munitions compounds at clay mineral and metal oxide surfaces. Environmental Chemistry, 12, 74-84.
• Linker, B. R., Khatiwada, R., Perdrial, N., Abrell, L., Sierra-Alvarez, R., Field, J. A., & Chorover, J. (2015). Adsorption of novel insensitive munitions compounds at clay mineral and metal oxide surfaces. Environmental Chemistry.
• López Honorato, E., Navarro Tovar, G., Barroso Flores, J., Sierra-Alvarez, R., & Valdés Pech, M. (2015). Tecnologías para eliminar el arsénico del agua. Revista Ciencia y Desarrollo. July-Aug. 2015. 8 pp..
• Ober, C. K., Jiang, J., Zhang, B., Li, L., Giannelis, E. P., Neisser, M., Chung, J. S., & Sierra-Alvarez, R. (2015). New developments in ligand-stabilized metal oxide nanoparticle photoresists for EUV lithography. In: Proceedings of SPIE International conference on Advanced Lithography, International Society for Optics and Photonics. San Jose, CA. Paper 9422-6..
• Otero-Gonzalez, L., Field, J. A., Calderon, I. A., Aspinwall, C. A., Shadman, F., Zeng, C., & Sierra-Alvarez, R. (2015). Fate of fluorescent core-shell silica nanoparticles during simulated secondary wastewater treatment. Water research, 77, 170-8.
• Rodriguez-Freire, L., Balachandran, R., Sierra-Alvarez, R., & Keswani, M. (2015). Effect of sound frequency and initial concentration on the sonochemical degradation of perfluorooctane sulfonate (PFOS). Journal of Hazardous Materials, 300, 662-669.
• Rodriguez-Freire, L., Moore, S. E., Sierra-Alvarez, R., & Field, J. A. (2015). Adaptation of a Methanogenic Consortium to Arsenite Inhibition. Water Air and Soil Pollution, 226.
• Speed, D., Westerhoff, P., Sierra-Alvarez, R., Draper, R., Pantano, P., Aravamudhan, S., Chen, K. L., Hristovski, K., Herckes, P., Bi, X., Yang, Y., Zeng, C., Otero-Gonzalez, L., Mikoryak, C., Wilson, B. A., Kosaraju, K., Tarannum, M., Crawford, S., Yi, P., , Liu, X., et al. (2015). Physical, chemical, and in vitro toxicological characterization of nanoparticles in chemical mechanical planarization suspensions used in the semiconductor industry: towards environmental health and safety assessments. Environmental Science: Nano, 2, 227-244.
• Zeng, C., Ramos-Ruiz, A., Field, J. A., & Sierra-Alvarez, R. (2015). Cadmium telluride (CdTe) and cadmium selenide (CdSe) leaching behavior and surface chemistry in response to pH and O-2. Journal of Environmental Management, 154, 78-85.
• Zeng, C., Ramos-Ruiz, A., Field, J. A., & Sierra-Alvarez, R. (2015). Response to the comments on "Cadmium telluride leaching behavior: Discussion of Zeng et al. (2015)". Journal of Environmental Management, 164, 65-66.
• Abrell, L. M., Mash, E. A., Field, J. A., Chorover, J. D., Sierra Alvarez, M. R., & Bhumasamudram, J. (2014). Synthesis of 13C and 15N labeled 2,4-dinitroanisole. Journal of Labelled Compounds and Radiopharmaceuticals.
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  Abstract Syntheses of [13C6]-2,4-dinitroanisole (ring-13C6) from [13C6]-anisole (ring-13C6) and[15N2]-2,4-dinitroanisole from anisole using in situ generated acetyl nitrate and [15N]-acetylnitrate, respectively, are described. Treatment of [13C6]-anisole (ring-13C6) with acetyl nitrategenerated in 100% HNO3 gave [13C6]-2,4-dinitroanisole (ring-13C6) in 83% yield. Treatment ofanisole with [15N]-acetyl nitrate generated in 10N [15N]-HNO3 gave [15N2]-2,4-dinitroanisole in44% yield after two cycles of nitration. Byproducts in the latter reaction included [15N]-2-nitroanisole and [15N]-4-nitroanisole.
• Carvajal-Arroyo, J. M., Puyol, D., Guangbin, L. i., Lucero-Acuña, A., Sierra-Álvarez, R., & Field, J. A. (2014). Pre-exposure to nitrite in the absence of ammonium strongly inhibits anammox. Water Research, 48(1), 52-60.
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  Abstract: Anaerobic ammonium oxidizing bacteria (Anammox) are known to be inhibited by their substrate, nitrite. However, the mechanism of inhibition and the physiological conditions under which nitrite impacts the performance of anammox bioreactors are still unknown. This study investigates the role of pre-exposing anammox bacteria to nitrite alone on their subsequent activity and metabolism after ammonium has been added. Batch experiments were carried out with anammox granular biofilm pre-exposed to nitrite over a range of concentrations and durations in the absence of ammonium. The effect of pre-exposure to nitrite alone compared to nitrite simultaneously fed with ammonium was evaluated by measuring the anammox activity and the accumulation of the intermediate, nitric oxide. The results show that the inhibitory effect was more dramatic when bacteria were pre-exposed to nitrite in absence of ammonium, as revealed by the lower activity and the higher accumulation of nitric oxide. The nitrite concentration causing 50% inhibition was 53 and 384mgNL-1 in the absence or the presence of ammonium, respectively. The nitrite inhibition was thus 7.2-fold more severe in the absence of ammonium. Biomass exposure to nitrite (25mgNL-1), in absence of ammonium, led to accumulation of nitric oxide. On the other hand when the biomass was exposed to nitrite in presence of ammonium, accumulation of nitric oxide was only observed at much higher nitrite concentrations (500mgNL-1). The inhibitory effect of nitrite in the absence of ammonium was very rapid. The rate of decay of the anammox activity was equivalent to the diffusion rate of nitrite up to 46% of activity loss. The results taken as a whole suggest that nitrite inhibition is more acute when anammox cells are not actively metabolizing. Accumulation of nitric oxide in the headspace most likely indicates disruption of the anammox biochemistry by nitrite inhibition, caused by an interruption of the hydrazine synthesis step. © 2013 Elsevier Ltd.
• Carvajal-Arroyo, J. M., Puyol, D., Li, G., Sierra-\'Alvarez, R., & Field, J. A. (2014). The intracellular proton gradient enables anaerobic ammonia oxidizing (anammox) bacteria to tolerate NO 2- inhibition. Journal of biotechnology, 192, 265--267.
• Carvajal-Arroyo, J. M., Puyol, D., Li, G., Sierra-\'Alvarez, R., & Field, J. A. (2014). The role of pH on the resistance of resting-and active anammox bacteria to NO2- inhibition. Biotechnology and bioengineering, 111(10), 1949--1956.
• Carvajal-Arroyo, J. M., Puyol, D., Li, G., Swartwout, A., Sierra-\'Alvarez, R., & Field, J. A. (2014). Starved anammox cells are less resistant to inhibition. Water research, 65, 170--176.
• Chorover, J. D., Rodriguez-Freire, L., Sierra Alvarez, M. R., Root, R., & Field, J. A. (2014). Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions. Wat. Res., 66, 242-253.
• Li, G., Puyol, D., Carvajal-Arroyo, J. M., Sierra-Alvarez, R., & Field, J. A. (2014). Inhibition of anaerobic ammonium oxidation by heavy metals. Journal of Chemical Technology and Biotechnology.
• Otero-Gonz\'alez, L., Barbero, I., Field, J. A., Shadman, F., & Sierra-Alvarez, R. (2014). Stability of alumina, ceria, and silica nanoparticles in municipal wastewater. Water Science \& Technology, 70(9), 1533--1539.
• Otero-Gonz\'alez, L., Field, J. A., & Sierra-Alvarez, R. (2014). Inhibition of anaerobic wastewater treatment after long-term exposure to low levels of CuO nanoparticles. Water research, 58, 160--168.
• Otero-González, L., Field, J. A., & Sierra-Alvarez, R. (2014). Fate and long-term inhibitory impact of ZnO nanoparticles during high-rate anaerobic wastewater treatment. Journal of Environmental Management, 135, 110-117.
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  Abstract: The aim of this study was to evaluate the long-term effect of ZnO nanoparticles (NPs) on the performance of high-rate anaerobic bioreactors. Laboratory-scale upflow anaerobic sludge blanket (UASB) reactors were fed with a mixture of volatile fatty acids and exposed to either low (0.32mgZnL-1) or high (34.5mgZnL-1) concentrations of ZnO NPs. Exposure to high NP concentrations caused a rapid and permanent decline in the methane production and the removal of acetate and propionate. In contrast, a gradual and partial inhibitory response was observed in the reactor exposed to low NP concentrations. The long-term effect of the NP exposure was also evident from a decline in the specific methanogenic activity, which was more severe for the acetoclastic compared to the hydrogenotrophic methanogens. ZnO NPs were removed by 62-82% during passage through the UASB reactors. The results taken as a whole indicate that ZnO NPs cause severe inhibition of acetoclastic methanogens. Even sub-ppm levels of the nano-ZnO in the influent had a negative impact on the performance of the UASB reactor due to long-term exposure of methanogens to NPs that accumulated in the sludge bed. © 2014 Elsevier Ltd.
• Puyol, D., Carvajal-Arroyo, J., Garcia, B., Sierra-Alvarez, R., & Field, J. (2014). Kinetics and thermodynamics of anaerobic ammonium oxidation process using Brocadia spp. dominated mixed cultures. Water Science \& Technology, 69(8), 1682--1688.
• Puyol, D., Carvajal-Arroyo, J., Li, G., Dougless, A., Fuentes-Velasco, M., Sierra-Alvarez, R., & Field, J. (2014). High pH (and not free ammonia) is responsible for Anammox inhibition in mildly alkaline solutions with excess of ammonium. Biotechnology letters, 36(10), 1981--1986.
• Puyol, D., Carvajal-Arroyo, J., Sierra-Alvarez, R., & Field, J. A. (2014). Nitrite (not free nitrous acid) is the main inhibitor of the anammox process at common pH conditions. Biotechnology Letters, 36(3), 547-551.
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  Abstract: Nitrite is a substrate but also an inhibitor of anaerobic ammonium oxidation (anammox).There is currently no consensus on whether ionized nitrite (INi) or free nitrous acid (FNA) is the actual inhibitor of the process. The inhibition by INi and FNA on the anammox process has been analysed using a wide range of INi and FNA concentrations and by altering the pH and total nitrite conditions. The inhibitory impacts of both species were quantified through a rational inhibition equation, considering INi and FNA as substrate inhibitor and non-competitive inhibitor, respectively. Inhibitory constants were calculated with strong statistical support as 561 mg INi-N l-1 and 0.117 mg FNA-N l-1. Based on the model, INi is the main inhibiting species of the anammox process at pH > 7.1, which are the most common conditions occurring in field applications of anammox. © 2013 Springer Science+Business Media Dordrecht.
• Carvajal-Arroyo, J. M., Sun, W., Sierra-Alvarez, R., & Field, J. A. (2013). Inhibition of anaerobic ammonium oxidizing (anammox) enrichment cultures by substrates, metabolites and common wastewater constituents. Chemosphere, 91(1), 22-27.
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  PMID: 23245574;Abstract: Anaerobic ammonium oxidation (anammox) is an emerging technology for nitrogen removal that provides a more environmentally sustainable and cost effective alternative compared to conventional biological treatment methods. The objective of this study was to investigate the inhibitory impact of anammox substrates, metabolites and common wastewater constituents on the microbial activity of two different anammox enrichment cultures (suspended and granular), both dominated by bacteria from the genus Brocadia. Inhibition was evaluated in batch assays by comparing the N2 production rates in the absence or presence of each compound supplied in a range of concentrations. The optimal pH was 7.5 and 7.3 for the suspended and granular enrichment cultures, respectively. Among the substrates or products, ammonium and nitrate caused low to moderate inhibition, whereas nitrite caused almost complete inhibition at concentrations higher than 15mM. The intermediate, hydrazine, either stimulated or caused low inhibition of anammox activity up to 3mM. Of the common constituents in wastewater, hydrogen sulfide was the most severe inhibitor, with 50% inhibitory concentrations (IC50) as low as 0.03mM undissociated H2S. Dissolved O2 showed moderate inhibition (IC50=2.3-3.8mgL-1). In contrast, phosphate and salinity (NaCl) posed very low inhibition. The suspended- and granular anammox enrichment cultures had similar patterns of response to the various inhibitory stresses with the exception of phosphate. The findings of this study provide comprehensive insights on the tolerance of the anammox process to a wide variety of potential inhibiting compounds. © 2012 Elsevier Ltd.
• Gonzalez-Estrella, J., Sierra-Alvarez, R., & Field, J. A. (2013). Toxicity assessment of inorganic nanoparticles to acetoclastic and hydrogenotrophic methanogenic activity in anaerobic granular sludge. Journal of Hazardous Materials, 260, 278-285.
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  PMID: 23770618;Abstract: Release of engineered nanoparticles (NPs) to municipal wastewater from industrial and residential sources could impact biological systems in wastewater treatment plants. Methanogenic inhibition can cause failure of anaerobic waste(water) treatment. This study investigated the inhibitory effect of a wide array of inorganic NPs (Ag0, Al2O3, CeO2, Cu0, CuO, Fe0, Fe2O3, Mn2O3, SiO2, TiO2, and ZnO supplied up to 1500mgL-1) to acetoclastic and hydrogenotrophic methanogenic activity of anaerobic granular sludge. Of all the NPs tested, only Cu0 and ZnO caused severe methanogenic inhibition. The 50% inhibiting concentrations determined towards acetoclastic and hydrogenotrophic methanogens were 62 and 68mgL-1 for Cu0 NP; and 87 and 250mgL-1 for ZnO NP, respectively. CuO NPs also caused inhibition of acetoclastic methanogens. Cu2+ and Zn2+ salts caused similar levels of inhibition as Cu0 and ZnO NPs based on equilibrium soluble metal concentrations measured during the assays, suggesting that the toxicity was due to the release of metal ions by NP-corrosion. A commercial dispersant, Dispex, intended to increase NP stability did not affect the inhibitory impact of the NPs. The results taken as a whole suggest that Zn- and Cu-containing NPs can release metal ions that are inhibitory for methanogenesis. © 2013 Elsevier B.V.
• Hernández, S. M., Sun, W., Sierra-Alvarez, R., & Field, J. A. (2013). Toluene-nitrite inhibition synergy of anaerobic ammonium oxidizing (anammox) activity. Process Biochemistry, 48(5-6), 926-930.
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  Abstract: Anammox process is emerging as a promising biotechnology to remove ammonium (NH4+) from wastewater. Co-existing organic matters such as toluene could pose potential inhibitions on this process. In this study, the mechanisms of toluene-nitrite (NO2-) inhibition synergy of anammox activity (AA) was investigated in batch culture. In results, the AA (mmolN2-NLliquid-1h-1) in reference assays achieved values of 0.21 ± 0.0078. The toluene (0.1-3.0 mM) demonstrated different inhibitory effects on the AA and caused 50% inhibition (IC50) at 0.79 mM. The pre-exposure to toluene and NO2- or NO 2- alone in the absence of NH4+ demonstrated a much severer inhibition, compared to toluene alone. The IC 50 of the AA due to pre-exposure to NO2- lacking NH4+ was of 6.25 mM NO2-. These results indicated that toluene by itself did not severely inhibit the anammox process but did so in the presence of NO2-. © 2013 Elsevier Ltd. All rights reserved.
• Liang, J., Olivares, C., Field, J. A., & Sierra-Alvarez, R. (2013). Microbial toxicity of the insensitive munitions compound, 2,4-dinitroanisole (DNAN), and its aromatic amine metabolites. Journal of Hazardous Materials, 262, 281-287.
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  PMID: 24041820;Abstract: 2,4-Dinitroanisole (DNAN) is an insensitive munitions compound considered to replace conventional explosives such as 2,4,6-trinitrotoluene (TNT). DNAN undergoes facile microbial reduction to 2-methoxy-5-nitroaniline (MENA) and 2,4-diaminoanisole (DAAN). This study investigated the inhibitory effect of DNAN, MENA, and DAAN toward various microbial targets in anaerobic (acetoclastic methanogens) and aerobic (heterotrophs and nitrifiers) sludge, and the bioluminescent bacterium, Aliivibrio fischeri, used in the Microtox assay. Aerobic heterotrophic and nitrifying batch experiments with DAAN could not be performed because the compound underwent extensive autooxidation in these assays. DNAN severely inhibited methanogens, nitrifying bacteria, and A. fischeri (50% inhibitory concentrations (IC50) ranging 41-57μM), but was notably less inhibitory to aerobic heterotrophs (IC50>390μM). Reduction of DNAN to MENA and DAAN lead to a marked decrease in methanogenic inhibition (i.e., DNAN>MENA≈DAAN). Reduction of all nitro groups in DNAN also resulted in partial detoxification in assays with A. fischeri. In contrast, reduction of a single nitro group did not alter the inhibitory impact of DNAN toward A. fischeri and nitrifying bacteria given the similar IC50 values determined for MENA and DNAN in these assays. These results indicate that reductive biotransformation could reduce the inhibitory potential of DNAN. © 2013 Elsevier B.V.
• Olivares, C., Liang, J., Abrell, L., Sierra-Alvarez, R., & Field, J. A. (2013). Pathways of reductive 2,4-dinitroanisole (DNAN) biotransformation in sludge. Biotechnology and Bioengineering, 110(6), 1595-1604.
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  PMID: 23280483;Abstract: As the use of the insensitive munition compound 2,4-dinitroanisole (DNAN) increases, releases to the environment may pose a threat to local ecosystems. Little is known about the environmental fate of DNAN and the conversions caused by microbial activity. We studied DNAN biotransformation rates in sludge under aerobic, microaerophilic, and anaerobic conditions, detected biotransformation products, and elucidated their chemical structures. The biotransformation of DNAN was most rapid under anaerobic conditions with H2 as a cosubstrate. The results showed that the ortho nitro group in DNAN is regioselectively reduced to yield 2-methoxy-5-nitroaniline (MENA), and then the para nitro group is reduced to give 2,4-diaminoanisole (DAAN). Both MENA and DAAN were identified as important metabolites in all redox conditions. Azo and hydrazine dimer derivatives formed from the coupling of DNAN reduction products in anaerobic conditions. Secondary pathways included acetylation and methylation of amine moieties, as well as the stepwise O-demethylation and dehydroxylation of methoxy groups. Seven unique metabolites were identified which enabled elucidation of biotransformation pathways. The results taken as a whole suggest that reductive biotransformation is an important fate of DNAN leading to the formation of aromatic amines as well as azo and hydrazine dimeric metabolites. © 2012 Wiley Periodicals, Inc.
• Otero-González, L., García-Saucedo, C., Field, J. A., & Sierra-Álvarez, R. (2013). Toxicity of TiO₂, ZrO₂, Fe⁰, Fe₂O₃, and Mn₂O₃ nanoparticles to the yeast, Saccharomyces cerevisiae. Chemosphere, 93(6), 1201-1206.
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  PMID: 23886442;Abstract: The growing application of engineered nanomaterials is leading to an increased occurrence of nanoparticles (NPs) in the environment. Thus, there is a need to better understand their potential impact on the environment. This study evaluated the toxicity of nanosized TiO2, ZrO2, Fe0, Fe2O3, and Mn2O3 towards the yeast Saccharomyces cerevisiae based on O2 consumption and cell membrane integrity. In addition, the state of dispersion of the nanoparticles in the bioassay medium was characterized.All the nanomaterials showed high tendency to aggregate in the bioassay medium. A non-toxic polyacrylate dispersant was used to improve the NP dispersion stability and test the influence of the aggregation state in their toxicity. Mn2O3 NPs showed the highest inhibition of O2 consumption (50% at 170mgL-1) and cell membrane damage (approximately 30% of cells with compromised membrane at 1000mgL-1), while the other NPs caused low (Fe0) or no toxicity (TiO2, ZrO2, and Fe2O3) to the yeast. Dispersant supplementation decreased the inhibition caused by Mn2O3 NPs at low concentrations, which could indicate that dispersant association with the particles may have an impact on the interaction between the NPs and the cells. © 2013 Elsevier Ltd.
• Rottman, J., Platt, L. C., Sierra-Alvarez, R., & Shadman, F. (2013). Removal of TiO₂ nanoparticles by porous media: Effect of filtration media and water chemistry. Chemical Engineering Journal, 217, 212-220.
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  Abstract: The use of nanoparticles in manufacturing as well as in commercial products continues to rise despite concerns over the environmental release and potentially negative ecological and health effects. Some aqueous waste streams carry a large fraction of released nanoparticles and thus should be targeted for treatment. Conventional porous media filtration has focused on sand as the bed material with discouraging results. This study investigated the effectiveness of three different bed materials, namely, sand, activated carbon, and diatomaceous earth, on the removal of nano-TiO2 from aqueous streams. Additionally, the impact of solution chemistry (a commercial dispersant and the two organic compounds lysozyme and glycine) on nanoparticle retention by the various bed materials was evaluated. Diatomaceous earth displayed great promise in nanoparticle capture, providing full retention of a 50mg TiO2L-1 stream for the 30 bed volumes tested as compared to zero and only 20% TiO2 capture for sand and activated carbon, respectively. Batch isotherms showed that diatomaceous earth, with specific loading capacities exceeding 25mg TiO2 gmedium-1, has a high affinity for nano-TiO2. This loading capacity is 20- and 1000-fold higher compared to activated carbon and sand, respectively. The solution contaminants investigated had varying effects on nano-TiO2 retention depending on the bed material, indicating the need for investigation of co-contaminants and their role on nanoparticle filtration. This study demonstrates the superiority of diatomaceous earth as a filtration material compared to conventional sand and indicates its suitability as a new material for the removal of nanoparticles in porous media filtration. © 2012 Elsevier B.V.
• Rottman, J., Sierra-Alvarez, R., & Shadman, F. (2013). Real-time monitoring of nanoparticle retention in porous media. Environmental Chemistry Letters, 11(1), 71-76.
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  Abstract: Nanoparticles are not specifically targeted in conventional treatment schemes; consequently, typical wastewater treatment systems are ineffective for nanoparticles removal. With rapidly increasing concern over their health effects, improved understanding of nanoparticle transport and retention in porous media filters is critical because of its application in new wastewater treatment methods and for assessment of the fate of the discharged nanoparticles in soil. In this study, a unique and robust integrated method is developed and validated. Experimentally, this approach uses an on-line, real-time, and in situ method for measuring nanoparticle retention dynamics, eliminating the laborious and less accurate sampling and off-line analysis. The data analysis part is a process simulator which provides both kinetic properties of the retention process as well as the overall capacity and loading. This technique is validated by application to the transport and retention of TiO2 nanoparticles in two vastly different porous filtration media-activated carbon and sand. TiO2 retained concentrations ranged from 0. 24 to 0. 37 mg g-1 for activated carbon and 0. 01-0. 014 mg g-1 for sand. The integrated method presented here is useful for both comparison of the filtration effectiveness of various porous materials as well as for process optimization and scale-up for industrial applications. © 2012 Springer-Verlag.
• Sierra Alvarez, M., Liang, J., Olivares, C., Field, J. A., & Sierra Alvarez, M. R. (2013). Microbial toxicity of the insensitive munitions compound, 2,4-dinitroanisole (DNAN), and its aromatic amine metabolites. Journal of hazardous materials, 262C.
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  2,4-Dinitroanisole (DNAN) is an insensitive munitions compound considered to replace conventional explosives such as 2,4,6-trinitrotoluene (TNT). DNAN undergoes facile microbial reduction to 2-methoxy-5-nitroaniline (MENA) and 2,4-diaminoanisole (DAAN). This study investigated the inhibitory effect of DNAN, MENA, and DAAN toward various microbial targets in anaerobic (acetoclastic methanogens) and aerobic (heterotrophs and nitrifiers) sludge, and the bioluminescent bacterium, Aliivibrio fischeri, used in the Microtox assay. Aerobic heterotrophic and nitrifying batch experiments with DAAN could not be performed because the compound underwent extensive autooxidation in these assays. DNAN severely inhibited methanogens, nitrifying bacteria, and A. fischeri (50% inhibitory concentrations (IC50) ranging 41-57μM), but was notably less inhibitory to aerobic heterotrophs (IC50>390μM). Reduction of DNAN to MENA and DAAN lead to a marked decrease in methanogenic inhibition (i.e., DNAN>MENA≈DAAN). Reduction of all nitro groups in DNAN also resulted in partial detoxification in assays with A. fischeri. In contrast, reduction of a single nitro group did not alter the inhibitory impact of DNAN toward A. fischeri and nitrifying bacteria given the similar IC50 values determined for MENA and DNAN in these assays. These results indicate that reductive biotransformation could reduce the inhibitory potential of DNAN.
• Sierra Alvarez, M., Sun, W., Gamez, V. M., Otero-Gonzalez, L., Cho, Y., Ober, C. K., & Sierra Alvarez, M. R. (2013). Biodegradability, cytotoxicity, and physicochemical treatability of two novel perfluorooctane sulfonate-free photoacid generators. Archives of environmental contamination and toxicology, 64(2).
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  There is a need for effective, environmentally compatible photoacid generators (PAGs) for application in photolithography for microelectronic device fabrication. Perfluoroalkyl sulfonates (PFAS) used in conventional PAG formulations, such as perfluorooctane sulfonate (PFOS), are under increasing scrutiny due to their widespread environmental distribution and toxicity. Recently, two new PFAS-free, PAG anions with semifluorinated sulfonate anions containing biomolecules (γ-butyrolactone or D-glucose groups) were successfully applied as PAGs. In this study, the biodegradation potential, cytotoxicity, and physicochemical treatability of the new PAG anions was evaluated. PFOS and perfluorobutane sulfonate (PFBS) were used as reference materials in all of the assays. The new PAGs were susceptible to partial degradation by microorganisms in aerobic activated sludge, and these were also readily removed by chemical oxidative treatment with Fenton's reagent [H(2)O(2)/Fe(II)]. In contrast, the compounds were resistant to microbial and chemical attack under reductive conditions as indicated by the low removal efficiencies observed with anaerobic biodegradation assays and chemical assays with zero-valent iron, respectively. The enhanced biodegradation potential and treatability make of the new PAGs attractive materials to resolve current issues related to the lithographic performance and environmental concerns.
• Sun, W., Gamez, V. M., Otero-Gonzalez, L., Cho, Y., Ober, C. K., & Sierra-Alvarez, R. (2013). Biodegradability, cytotoxicity, and physicochemical treatability of two novel perfluorooctane sulfonate-free photoacid generators. Archives of Environmental Contamination and Toxicology, 64(2), 187-197.
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  PMID: 23104522;Abstract: There is a need for effective, environmentally compatible photoacid generators (PAGs) for application in photolithography for microelectronic device fabrication. Perfluoroalkyl sulfonates (PFAS) used in conventional PAG formulations, such as perfluorooctane sulfonate (PFOS), are under increasing scrutiny due to their widespread environmental distribution and toxicity. Recently, two new PFAS-free, PAG anions with semifluorinated sulfonate anions containing biomolecules (γ-butyrolactone or d-glucose groups) were successfully applied as PAGs. In this study, the biodegradation potential, cytotoxicity, and physicochemical treatability of the new PAG anions was evaluated. PFOS and perfluorobutane sulfonate (PFBS) were used as reference materials in all of the assays. The new PAGs were susceptible to partial degradation by microorganisms in aerobic activated sludge, and these were also readily removed by chemical oxidative treatment with Fenton's reagent [H 2O2/Fe(II)]. In contrast, the compounds were resistant to microbial and chemical attack under reductive conditions as indicated by the low removal efficiencies observed with anaerobic biodegradation assays and chemical assays with zero-valent iron, respectively. The enhanced biodegradation potential and treatability make of the new PAGs attractive materials to resolve current issues related to the lithographic performance and environmental concerns. © 2012 Springer Science+Business Media New York.
• Sun, W., Luna-Velasco, A., Sierra-Alvarez, R., & Field, J. A. (2013). Assessing protein oxidation by inorganic nanoparticles with enzyme-linked immunosorbent assay (ELISA). Biotechnology and Bioengineering, 110(3), 694-701.
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  PMID: 23055386;Abstract: Growth in the nanotechnology industry is leading to increased production of engineered nanoparticles (NPs). This has given rise to concerns about the potential adverse and toxic effects to biological system and the environment. An important mechanism of NP toxicity is oxidative stress caused by the formation of reactive oxygen species (ROS) or via direct oxidation of biomolecules. In this study, a protein oxidation assay was developed as an indicator of biomolecule oxidation by NPs. The oxidation of the protein, bovine serum albumin (BSA) was evaluated with an enzyme-linked immunosorbent assay (ELISA) to measure the protein carbonyl derivatives formed from protein oxidation. The results showed that some NPs such as Cu(0), CuO, Mn2O3, and Fe(0) caused oxidation of BSA; whereas, many of the other NPs tested were not reactive or very slowly reactive with BSA. The mechanisms involved in the oxidation of BSA protein by the reactive NPs could be attributed to the combined effects of ROS-dependent and direct protein oxidation mechanisms. The ELISA assay is a promising method for the assessment of protein oxidation by NPs, which can provide insights on NP toxicity mechanisms. © 2012 Wiley Periodicals, Inc.
• Gómez-Rivera, F., Field, J. A., Brown, D., & Sierra-Alvarez, R. (2012). Fate of cerium dioxide (CeO ₂) nanoparticles in municipal wastewater during activated sludge treatment. Bioresource Technology, 108, 300-304.
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  PMID: 22265985;Abstract: This study investigated the fate of nano-CeO 2 during municipal wastewater treatment using a laboratory-scale activated sludge (A/S) system fed with primarily-treated municipal wastewater and nano-CeO 2 (55.0mg Ce/L). Nano-CeO 2 was highly removed during A/S treatment (96.6% total Ce). Extensive removal of CeO 2
• Otero-González, L., Sierra-Alvarez, R., Boitano, S., & Field, J. A. (2012). Application and validation of an impedance-based real time cell analyzer to measure the toxicity of nanoparticles impacting human bronchial epithelial cells. Environmental Science and Technology, 46(18), 10271-10278.
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  PMID: 22916708;Abstract: Nanomaterials are increasingly used in a variety of industrial processes and consumer products. There are growing concerns about the potential impacts for public health and environment of engineered nanoparticles. The aim of this work was to evaluate a novel impedance-based real time cell analyzer (RTCA) as a high-throughput method for screening the cytotoxicity of nanoparticles and to validate the RTCA results using a conventional cytotoxicity test (MTT). A collection of 11 inorganic nanomaterials (Ag0, Al2O 3, CeO2, Fe0, Fe2O3, HfO2, Mn2O3, SiO2, TiO2, ZnO, and ZrO2) were tested for potential cytotoxicity to a human bronchial epithelial cell, 16HBE14o-. The data collected by the RTCA system was compared to results obtained using a more traditional methyl tetrazolium (MTT) cytotoxicity assay at selected time points following application of nanomaterials. The most toxic nanoparticles were ZnO, Mn2O 3 and Ag0, with 50% response at concentrations lower than 75 mg/L. There was a good correlation in cytotoxicity measurements between the two methods; however, the RTCA method maintained a distinct advantage in continually following cytotoxicity over time. The results demonstrate the potential and validity of the impedance-based RTCA technique to rapidly screen for nanoparticle toxicity. © 2012 American Chemical Society.
• Rodríguez-Freire, L., Sun, W., Sierra-Alvarez, R., & Field, J. A. (2012). Flexible bacterial strains that oxidize arsenite in anoxic or aerobic conditions and utilize hydrogen or acetate as alternative electron donors. Biodegradation, 23(1), 133-143.
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  PMID: 21706372;PMCID: PMC3604901;Abstract: Arsenic is a carcinogenic compound widely distributed in the groundwater around the world. The fate of arsenic in groundwater depends on the activity of microorganisms either by oxidizing arsenite (As III), or by reducing arsenate (As V). Because of the higher toxicity and mobility of As III compared to As V, microbial-catalyzed oxidation of As III to As V can lower the environmental impact of arsenic. Although aerobic As III-oxidizing bacteria are well known, anoxic oxidation of As III with nitrate as electron acceptor has also been shown to occur. In this study, three As III-oxidizing bacterial strains, Azoarcus sp. strain EC1-pb1, Azoarcus sp. strain EC3-pb1 and Diaphorobacter sp. strain MC-pb1, have been characterized. Each strain was tested for its ability to oxidize As III with four different electron acceptors, nitrate, nitrite, chlorate and oxygen. Complete As III oxidation was achieved with both nitrate and oxygen, demonstrating the novel ability of these bacterial strains to oxidize As III in either anoxic or aerobic conditions. Nitrate was only reduced to nitrite. Different electron donors were used to study their suitability in supporting nitrate reduction. Hydrogen and acetate were readily utilized by all the cultures. The flexibility of these As III-oxidizing bacteria to use oxygen and nitrate to oxidize As III as well as organic and inorganic substrates as alternative electron donors explains their presence in non-arsenic-contaminated environments. The findings suggest that at least some As III-oxidizing bacteria are flexible with respect to electron-acceptors and electron-donors and that they are potentially widespread in low arsenic concentration environments. © 2011 Springer Science+Business Media B.V.
• Rottman, J., Shadman, F., & Sierra-Alvarez, R. (2012). Interactions of inorganic oxide nanoparticles with sewage biosolids. Water Science and Technology, 66(9), 1821-1827.
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  PMID: 22925851;Abstract: The use of nanoparticles (NPs) in manufacturing continues to increase despite the growing concern over their potential environmental and health effects. Understanding the interaction of NPs and sewage sludge is crucial for determining the ultimate fate of NPs released to municipal wastewater treatment plants (WWTPs) as those interactions will determine whether the bulk of the material is retained in the sludge or released in the effluent stream. Analyzing the affinity of aluminum oxide, cerium oxide, and silicon oxide NPs, which are commonly used in semiconductor manufacturing processes, for biosolids used in municipal WWTPs provides a basis for estimating their removal efficiency. Batch studies were performed and the NPs were shown to partition onto the cellular surface. At the maximum equilibrium values tested (75-92 mg nanoparticles/L), the concentration of Al2O3, CeO2 and SiO 2 associated with the sludge was 137, 238, and 28 mg/g-sludge VSS, respectively. These results suggest that electrostatic interactions play a major role in determining NP association with biosolids. © IWA Publishing 2012.
• Sierra Alvarez, M., Gómez-Rivera, F., Field, J. A., Brown, D., & Sierra Alvarez, M. R. (2012). Fate of cerium dioxide (CeO2) nanoparticles in municipal wastewater during activated sludge treatment. Bioresource technology, 108.
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  This study investigated the fate of nano-CeO(2) during municipal wastewater treatment using a laboratory-scale activated sludge (A/S) system fed with primarily-treated municipal wastewater and nano-CeO(2) (55.0 mg Ce/L). Nano-CeO(2) was highly removed during A/S treatment (96.6% total Ce). Extensive removal of CeO(2)
• Sierra Alvarez, M., Rottman, J., Shadman, F., & Sierra Alvarez, M. R. (2012). Interactions of inorganic oxide nanoparticles with sewage biosolids. Water science and technology : a journal of the International Association on Water Pollution Research, 66(9).
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  The use of nanoparticles (NPs) in manufacturing continues to increase despite the growing concern over their potential environmental and health effects. Understanding the interaction of NPs and sewage sludge is crucial for determining the ultimate fate of NPs released to municipal wastewater treatment plants (WWTPs) as those interactions will determine whether the bulk of the material is retained in the sludge or released in the effluent stream. Analyzing the affinity of aluminum oxide, cerium oxide, and silicon oxide NPs, which are commonly used in semiconductor manufacturing processes, for biosolids used in municipal WWTPs provides a basis for estimating their removal efficiency. Batch studies were performed and the NPs were shown to partition onto the cellular surface. At the maximum equilibrium values tested (75-92 mg nanoparticles/L), the concentration of Al(2)O(3), CeO(2) and SiO(2) associated with the sludge was 137, 238, and 28 mg/g-sludge VSS, respectively. These results suggest that electrostatic interactions play a major role in determining NP association with biosolids.
• Tapia-Rodríguez, A., Luna-Velasco, A., Field, J. A., & Sierra-Alvarez, R. (2012). Toxicity of uranium to microbial communities in anaerobic biofilms. Water, Air, and Soil Pollution, 223(7), 3859-3868.
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  Abstract: Microbial processes have shown promise for the remediation of uranium and nitrate in groundwater impacted by uranium mine tailings. This study investigated the inhibitory impact of uranium(VI) towards different microbial populations in anaerobic biofilms, including methanogenic, denitrifying, and uranium-reducing microorganisms, which are commonly found at uranium bioremediation sites. Results of batch activity bioassays indicated a very distinct level of toxicity depending on the targeted microbial community. U(VI) caused severe inhibition of acetoclastic methanogenesis as indicated by a 50 % inhibiting concentration (IC 50) of only 0.16 mM. Denitrifying populations were also impacted by uranium, but their sensitivity depended on the electron donor utilized. Sulfur-oxidizing denitrifiers were the least affected (IC 50 for denitrification activity∈=∈0.32 mM), followed by H 2- and acetate-utilizing denitrifiers (IC 50 of 0.20 and 0.15 mM, respectively). In contrast, exposure to U(VI) concentrations up to 1.0 mM did not inhibit the rate of U(VI) bioreduction with H 2 as electron donor in the presence or absence of nitrate. On the contrary, a considerable increase in the uranium-reducing activity of the denitrifying and methanogenic mixed cultures was observed with increasing uranium concentrations. The results suggest that microorganisms responsible for U(V) reduction could tolerate much higher uranium concentrations compared to the other microbial populations assayed. © 2012 Springer Science+Business Media B.V.
• Blowers, P., Field, J. A., Ogden, K., Sáez, A. E., & Sierra, R. (2011). ChE at... The university of Arizona. Chemical Engineering Education, 45(1), 2-7.
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  Abstract: Chemical engineering at the University of Arizona that was founded in 1957 as part of the School of Mines now has 15 full-time faculty members who contribute to the academic and researches conducted in the campus. The department has strong involvement or leadership positions in two prominent research centers that include the Semiconductor Research Center (SRC)/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing. The center is led by Farhang Shadman, who originally founded the center with collaborators at Stanford and another center is MIT through the NSF Engineering Research Center initiatives. The chemical engineering courses is supported by many electives, with offerings in rheology, surface science, atmospheric science, semiconductor manufacturing, and bioreactor design. Several classes are offered in water chemistry, wastewater treatment, hazardous waste management, and pollution control.
• Cho, Y., Ouyang, C. Y., Krysak, M., Sun, W., Gamez, V., Sierra-Alvarez, R., & Ober, C. K. (2011). Environmentally friendly natural materials based photoacid generators for next generation photolithography. Proceedings of SPIE - The International Society for Optical Engineering, 7972.
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  Abstract: We describe the development of new triphenylsulfonium photoacid generators (TPS PAGs) with semifluorinated sulfonate anions containing glucose or other natural product groups, and their successful application to patterning sub-100 nm features using 254 nm and e-beam lithography. The TPS PAGs with functionalized octafluoro-3-oxapentanesulfonate were synthesized efficiently in high purity and high yield by utilizing simple and unique chemistries on 5-iodooctafluoro-3-oxapentanesulfonyl fluoride. The PAGs has been fully evaluated in terms of chemical properties, lithographic performance, environmental friendliness or toxicological impact. The PAGs are non-toxic and it is susceptible to chemical degradation and to microbial attack under aerobic/anaerobic conditions. These new PAGs are very attractive materials for high resolution photoresist applications and they are particularly useful in addressing the environmental concerns caused by PFOS and other perfluoroalkyl surfactants. © 2011 SPIE.
• Field, J. A., Luna-Velasco, A., Boitano, S. A., Shadman, F., Ratner, B. D., Barnes, C., & Sierra-Alvarez, R. (2011). Cytotoxicity and physicochemical properties of hafnium oxide nanoparticles. Chemosphere, 84(10), 1401-1407.
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  PMID: 21605889;Abstract: Nano-sized hafnium oxide (HfO 2) particles are being considered for applications within the semiconductor industry. However, little is known about their cytotoxicity. The objective of this work was to assess several HfO 2 nanoparticles (NPs) samples for their acute cytotoxicity. Dynamic light scattering analysis of the samples indicated that the average particle size of the HfO 2 in aqueous dispersions was in the submicron range with a fraction of particles having nano-dimensions. The media used in the toxicity assays decreased or increased the average particle size of HfO 2 NPs due to dispersion or agglomeration. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed numerous surface contaminants on the NPs. Only one HfO 2 sample caused moderate cytotoxicity to human cell lines. The inhibitory sample caused a 50% response in the Live/Dead assay with HaCaT skin cells at 2200mgL -1; and a 50% response in the mitochondrial toxicity test at 300mgL -1. A microbial inhibition assay based on methanogenic activity also revealed that another HFO 2 sample caused moderate inhibition. The difference in toxicity between samples could not be attributed to size. Instead the difference in toxicity was likely due to differences in the contaminants of the HfO 2. The ToF-SIMS analysis indicated unique signatures of Br and P in the sample toxic to human cell lines suggesting a distinct synthesis was used for that sample which may have been accompanied by inhibitory impurities. The results taken as a whole indicate that HfO 2 itself is relatively non-toxic. © 2011 Elsevier Ltd.
• García-Saucedo, C., Field, J. A., Otero-Gonzalez, L., & Sierra-Álvarez, R. (2011). Low toxicity of HfO₂, SiO₂, Al₂O₃ and CeO₂ nanoparticles to the yeast, Saccharomyces cerevisiae. Journal of Hazardous Materials, 192(3), 1572-1579.
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  PMID: 21782338;Abstract: Increasing use of nanomaterials necessitates an improved understanding of their potential impact on environment health. This study evaluated the cytotoxicity of nanosized HfO2, SiO2, Al2O3 and CeO2 towards the eukaryotic model organism Saccharomyces cerevisiae, and characterized their state of dispersion in bioassay medium. Nanotoxicity was assessed by monitoring oxygen consumption in batch cultures and by analysis of cell membrane integrity.CeO2, Al2O3, and HfO2 nanoparticles were highly unstable in yeast medium and formed micron-sized, settleable agglomerates. A non-toxic polyacrylate dispersant (Dispex A40) was used to improve nanoparticle stability and determine the impact of enhanced dispersion on toxicity. None of the NPs tested without dispersant inhibited O2 uptake by yeast at concentrations as high as 1000mg/L. Dispersant supplementation only enhanced the toxicity of CeO2 (47% at 1000mg/L). Dispersed SiO2 and Al2O3 (1000mg/L) caused cell membrane damage, whereas dispersed HfO2 and CeO2 did not cause significant disruption of membrane integrity at the same concentration. These results suggest that the O2 uptake inhibition observed with dispersed CeO2 NPs was not due to reduced cell viability. This is the first study evaluating toxicity of nanoscale HfO2, SiO2, Al2O3 and CeO2 to S. cerevisiae. Overall the results obtained demonstrate that these nanomaterials display low or no toxicity to yeast. © 2011 Elsevier B.V.
• Luna-Velasco, A., Field, J. A., Cobo-Curiel, A., & Sierra-Alvarez, R. (2011). Inorganic nanoparticles enhance the production of reactive oxygen species (ROS) during the autoxidation of l-3,4-dihydroxyphenylalanine (l-dopa). Chemosphere, 85(1), 19-25.
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  PMID: 21737115;Abstract: Public concerns over the toxicity of nanoparticles (NPs) are growing due to the rapid development of nanotechnology. An important mechanism of nanotoxicity is oxidative stress resulting from reactive oxygen species (ROS). In this study, the chemical production of ROS by inorganic NPs oxidizing the mammalian phenolic compound, l-3,4-dihydroxyphenylalanine (l-dopa) was evaluated using a ROS sensitive dye, 2',7'-diclorodihydrofluorescin (DCFH). CeO 2, Fe 2O 3 and Fe 0 NPs enhanced ROS production during the autoxidation of l-dopa by more than four-fold in reactions that were dependent on O 2. This is the first report of chemical ROS production due to interaction of phenolic compounds with NPs. Mn 2O 3 oxidized DCFH in a reaction that did not require O 2 or l-dopa, suggesting a direct redox reaction between the Mn 2O 3 and the dye. CeO 2, Mn 2O 3 and to a lesser extent Fe 0 formed clear electron paramagnetic resonance (EPR) signature for hydroxyl radicals when incubated in aerobic aqueous suspensions with spin traps. The results indicate that NPs can generate ROS via chemical reactions with medium components and biomolecules susceptible to oxidation, such as l-dopa. NPs were reactive whereas micron-sized particles were not. The combined assay with l-dopa and DCFH is a method proposed to screen for chemical ROS production by NPs. © 2011.
• Ochoa-Herrera, V., León, G., Banihani, Q., Field, J. A., & Sierra-Alvarez, R. (2011). Toxicity of copper(II) ions to microorganisms in biological wastewater treatment systems. Science of the Total Environment, 412-413, 380-385.
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  PMID: 22030247;Abstract: Copper is an essential element, however, this heavy metal is an inhibitor of microbial activity at relatively low concentrations. The objective of this study was to evaluate the inhibitory effect of copper(II) towards various microbial trophic groups responsible for the removal of organic constituents and nutrients in wastewater treatment processes. The results of the batch bioassays indicated that copper(II) caused severe inhibition of key microbial populations in wastewater treatment systems. Denitrifying bacteria were found to be very sensitive to the presence of copper(II). The concentrations of copper(II) causing 50% inhibition (IC 50) on the metabolic activity of denitrifiers was 0.95mgL -1. Copper was also inhibitory to fermentative bacteria, aerobic glucose-degrading heterotrophs, and nitrifying bacteria (IC 50 values=3.5, 4.6 and 26.5mgL -1, respectively). Nonetheless, denitrifying and nitrifying bacteria showed considerable recovery of their metabolic activity after only several days of exposure to high copper levels (up to 25 and 100mg Cu(II) L -1 for denitrification and nitrification, respectively). The recovery could be due to attenuation of soluble copper or to microbial adaptation. © 2011 Elsevier B.V..
• Sierra Alvarez, M., Luna-Velasco, A., Field, J. A., Cobo-Curiel, A., & Sierra Alvarez, M. R. (2011). Inorganic nanoparticles enhance the production of reactive oxygen species (ROS) during the autoxidation of L-3,4-dihydroxyphenylalanine (L-dopa). Chemosphere, 85(1).
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  Public concerns over the toxicity of nanoparticles (NPs) are growing due to the rapid development of nanotechnology. An important mechanism of nanotoxicity is oxidative stress resulting from reactive oxygen species (ROS). In this study, the chemical production of ROS by inorganic NPs oxidizing the mammalian phenolic compound, L-3,4-dihydroxyphenylalanine (l-dopa) was evaluated using a ROS sensitive dye, 2',7'-diclorodihydrofluorescin (DCFH). CeO(2), Fe(2)O(3) and Fe(0) NPs enhanced ROS production during the autoxidation of L-dopa by more than four-fold in reactions that were dependent on O(2). This is the first report of chemical ROS production due to interaction of phenolic compounds with NPs. Mn(2)O(3) oxidized DCFH in a reaction that did not require O(2) or L-dopa, suggesting a direct redox reaction between the Mn(2)O(3) and the dye. CeO(2), Mn(2)O(3) and to a lesser extent Fe(0) formed clear electron paramagnetic resonance (EPR) signature for hydroxyl radicals when incubated in aerobic aqueous suspensions with spin traps. The results indicate that NPs can generate ROS via chemical reactions with medium components and biomolecules susceptible to oxidation, such as L-dopa. NPs were reactive whereas micron-sized particles were not. The combined assay with L-dopa and DCFH is a method proposed to screen for chemical ROS production by NPs.
• Sierra Alvarez, M., Ochoa-Herrera, V., León, G., Banihani, Q., Field, J. A., & Sierra Alvarez, M. R. (2011). Toxicity of copper(II) ions to microorganisms in biological wastewater treatment systems. The Science of the total environment, 412-413.
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  Copper is an essential element, however, this heavy metal is an inhibitor of microbial activity at relatively low concentrations. The objective of this study was to evaluate the inhibitory effect of copper(II) towards various microbial trophic groups responsible for the removal of organic constituents and nutrients in wastewater treatment processes. The results of the batch bioassays indicated that copper(II) caused severe inhibition of key microbial populations in wastewater treatment systems. Denitrifying bacteria were found to be very sensitive to the presence of copper(II). The concentrations of copper(II) causing 50% inhibition (IC(50)) on the metabolic activity of denitrifiers was 0.95 mg L(-1). Copper was also inhibitory to fermentative bacteria, aerobic glucose-degrading heterotrophs, and nitrifying bacteria (IC(50) values=3.5, 4.6 and 26.5 mg L(-1), respectively). Nonetheless, denitrifying and nitrifying bacteria showed considerable recovery of their metabolic activity after only several days of exposure to high copper levels (up to 25 and 100mg Cu(II) L(-1) for denitrification and nitrification, respectively). The recovery could be due to attenuation of soluble copper or to microbial adaptation.
• Sierra Alvarez, M., Tapia-Rodriguez, A., Tordable-Martinez, V., Sun, W., Field, J. A., & Sierra Alvarez, M. R. (2011). Uranium bioremediation in continuously fed upflow sand columns inoculated with anaerobic granules. Biotechnology and bioengineering, 108(11).
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  Reductive precipitation of soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) containing minerals is one of the more promising approaches to uranium remediation. The objective of this study was to evaluate the long-term performance of methanogenic granules for the continuous treatment of U(VI). For this purpose, three sand-packed columns inoculated with anaerobic biofilm were operated with or without ethanol and one column was exposed to nitrate co-contamination. The columns were operated for 373 days and efficiently removed U (24 mg L(-1)) in excess of 99.8%. No long-term benefit of ethanol addition was observed, suggesting that endogenous substrates in the biofilm were sufficient to drive the reduction reactions. Nitrate addition was found to inhibit U(VI) reduction and cause re-oxidation of some U(IV) deposited in the column. Taken as a whole, the results indicate that methanogenic biofilms can be reliably applied in bioreactor technology for sustained U removal from groundwater.
• Sun, W., Banihani, Q., Sierra-Alvarez, R., & Field, J. A. (2011). Stoichiometric and molecular evidence for the enrichment of anaerobic ammonium oxidizing bacteria from wastewater treatment plant sludge samples. Chemosphere, 84(9), 1262-1269.
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  PMID: 21620436;Abstract: Anammox enrichments were readily developed from seven municipal wastewater treatment plants (WWTPs) sludge, but not with methanogenic granular sludge from two agro-industrial WWTPs. Only 50. d was required for the first evidence of anammox activity from a return activated sludge obtained from a WWTP operated for nutrient removal. The molar ratios of nitrite and ammonium consumption of approximately 1.32 as well as nitrate and dinitrogen gas product ratios of approximately 0.095 provided evidence of the anammox reaction. The presence of anammox was confirmed by polymerase chain reaction (PCR) using primer sets (PLA46F and AMX820R) specific for anammox bacteria. The 16S rRNA gene fragment of anammox bacteria was detected in seven enrichment cultures (ECs) with demonstrated anammox activity but not in the original inocula from which the ECs were derived and also not in the two methanogenic sludge samples, which indicates the PCR predicted the anammox activity. Two genera, Brocadia and Kuenenia, were successfully identified as the Planctomycetes occurring in the clone libraries of successful anammox enrichments. Brocadia dominated in cultures that were respiked extensively; whereas Kuenenia predominated in cultures that were less aggressively respiked. These findings indicate that respiking management may play an important role on selecting the genus of anammox bacteria. The batch enrichment results clearly illustrate that anammox can be readily enriched from municipal sludge from a wide variety of process operations at WWTPs. © 2011 Elsevier Ltd.
• Sun, W., Sierra-Alvarez, R., & Field, J. A. (2011). Long term performance of an arsenite-oxidizing-chlorate-reducing microbial consortium in an upflow anaerobic sludge bed (UASB) bioreactor. Bioresource Technology, 102(8), 5010-5016.
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  PMID: 21333531;PMCID: PMC3081540;Abstract: A chlorate (ClO3-) reducing microbial consortium oxidized arsenite (As(III)) to arsenate (As(V)) in an upflow anaerobic sludge-bed bioreactor over 550days operation. As(III) was converted with high conversion efficiencies (>98%) at volumetric loadings ranging from 0.45 to 1.92mmol As/(Lreactord). The oxidation of As(III) was linked to the complete reduction of ClO3- to Cl- and H2O, as demonstrated by a molar ratio of approximately 3.0mol As(III) oxidized per mole of Cl- formed and by the greatly lowered ClO3--reducing capacity without As(III) feeding. An autotrophic enrichment culture was established from the bioreactor biofilm. A 16S rRNA gene clone library indicated that the culture was dominated by Dechloromonas, and Stenotrophomonas as well as genera within the family Comamonadaceae. The results indicate that the oxidation of As(III) to less mobile As(V) utilizing ClO3- as a terminal electron acceptor provides a sustainable bioremediation strategy for arsenic contamination in anaerobic environments. © 2011 Elsevier Ltd.
• Tapia-Rodriguez, A., Tordable-Martinez, V., Sun, W., Field, J. A., & Sierra-Alvarez, R. (2011). Uranium bioremediation in continuously fed upflow sand columns inoculated with anaerobic granules. Biotechnology and Bioengineering, 108(11), 2583-2591.
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  PMID: 21656705;Abstract: Reductive precipitation of soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) containing minerals is one of the more promising approaches to uranium remediation. The objective of this study was to evaluate the long-term performance of methanogenic granules for the continuous treatment of U(VI). For this purpose, three sand-packed columns inoculated with anaerobic biofilm were operated with or without ethanol and one column was exposed to nitrate co-contamination. The columns were operated for 373 days and efficiently removed U (24mgL -1) in excess of 99.8%. No long-term benefit of ethanol addition was observed, suggesting that endogenous substrates in the biofilm were sufficient to drive the reduction reactions. Nitrate addition was found to inhibit U(VI) reduction and cause re-oxidation of some U(IV) deposited in the column. Taken as a whole, the results indicate that methanogenic biofilms can be reliably applied in bioreactor technology for sustained U removal from groundwater. © 2011 Wiley Periodicals, Inc.
• Chairez, M., Luna-Velasco, A., Field, J. A., Xiumin, J. u., & Sierra-Alvarez, R. (2010). Reduction of bromate by biogenic sulfide produced during microbial sulfur disproportionation. Biodegradation, 21(2), 235-244.
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  PMID: 19763846;Abstract: Bromate (BrO3-) is a carcinogenic contaminant formed during ozonation of waters that contain trace amounts of bromide. Previous research shows that bromate can be microbially reduced to bromide using organic (i. e. acetate, glucose, ethanol) and inorganic (H2) electron-donating substrates. In this study, the reduction of bromate by a mixed microbial culture was investigated using elemental sulfur (S0) as an electron donor. In batch bioassays performed at 30°C, bromate (0. 30 mM) was completely converted to bromide after 10 days and no accumulation of intermediates occurred. Bromate was also reduced in cultures supplemented with thiosulfate and hydrogen sulfide as electron donor. Our results demonstrated that S0-disproportionating microorganisms were responsible for the reduction of bromate in cultures spiked with S0 through an indirect mechanism involving microbial formation of sulfide and subsequent abiotic reduction of bromate by the biogenic sulfide. Confirmation of this mechanism is the fact that bromate was shown to undergo rapid chemical reduction by sulfide (but not S0 or thiosulfate) in abiotic experiments. Bromate concentrations above 0. 30 mM inhibited sulfide formation by S0-disproportionating bacteria, leading to a decrease in the rate of bromate reduction. The results suggest that biological formation of sulfide from by S0 disproportionation could support the chemical removal of bromate without having to directly use sulfide as a reagent. © Springer Science+Business Media B.V. 2009.
• Gomez-Rivera, F., Brown, D., Field, J., Shadman, F., & Sierra-Alvarez, R. (2010). Fate of CeO₂ nanoparticles during laboratory-scale activated sludge treatment. SESHA Journal: Semiconductor Environmental Safety and Health Association, 810.
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  Abstract: The semiconductor industry is a major consumer of engineered nanoparticles since slurries containing silica, alumina, and ceria oxides are utilized extensively for the chemical-mechanical planarization (CMP) of wafers. Little is known about the fate of abrasive CMP nanoparticles during conventional wastewater treatment. With the objective to get a better understanding of the behavior of nanoparticles during biological treatment of wastewater, a laboratory-scale aerobic activated sludge treatment was set up to evaluate the fate of cerium oxide nanoparticles. The results obtained show that only a small fraction of the cerium oxide nanoparticles entering the treatment system escaped with the treated effluent (< 4.5%). Mechanisms contributing to the removal of the ceria included partitioning onto the microbial sludge floccules as well as destabilization of the nanoparticle dispersions by constituents present in the wastewater.Copyright © SESHA.
• Luna-Velasco, A., Sierra-Alvarez, R., Castro, B., & Field, J. A. (2010). Removal of nitrate and hexavalent uranium from groundwater by sequential treatment in bioreactors packed with elemental sulfur and zero-valent iron. Biotechnology and Bioengineering, 107(6), 933-942.
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  PMID: 20661908;Abstract: The bioreduction of soluble hexavalent uranium (UVI) to insoluble tetravalent uranium (UIV) is an attractive bioremediation strategy for the clean-up of contaminated groundwater. High levels of the common occurring co-contaminant, nitrate (NO3-), can potentially interfere with uranium bioremediation. this study, treatment of a synthetic groundwater containing a mixture of NO3- and UVI was investigated in a sulfur-limestone autotrophic denitrifying (SLAD) bioreactor that was coupled in series with a bioreactor packed with zero-valent iron (Fe0, ZVI) and sand. An additional aim of the study was to explore the possible role of biological activity in enhancing the reduction of UVI by Fe0. The SLAD reactor removed NO3- efficiently (99.8%) at loadings of up to 20 mmol NO3- L r-1 d-1, with near stoichiometric conversion to benign dinitrogen gas (N2). The ZVI bioreactor subsequently removed uranium (99.8%) at high (0.22 mM) and low (0.02 mM) influent concentrations of the radionuclide. Aqueous uranium was reliably eliminated to below the maximum contaminant level of 30 μg L-1 (0.13 μM) when the ZVI reactor was operated at average empty bed hydraulic retention times as low as 2.3 h, demonstrating the feasibility of the sequential treatment strategy in packed bed bioreactors. Sequential extraction of the ZVI reactor packing confirmed that uranium was immobilized as UIV. Uranium removal was enhanced by microbial activity as confirmed by the increased rate of uranium removal in batch assays inoculated with effluent from the ZVI bioreactor and spiked with Fe0 compared to abiotic controls. © 2010 Wiley Periodicals, Inc.
• Rottman, J., Shadman, F., & Sierra-Alvarez, R. (2010). Interactions of CMP nanoparticles and sewage sludge. SESHA Journal: Semiconductor Environmental Safety and Health Association, 810.
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  Abstract: The use of nanoparticles (NPs) in semiconductor manufacturing continues to increase despite the growing concern over the potential environmental and health effects. The interaction of NPs and sewage sludge is an integral part of determining the ultimate fate of NPs released to municipal wastewater treatment plants (WWTP) as it will determine whether the bulk of the material is contained in the sludge or released in the effluent stream. Analyzing the affinity of aluminum oxide, cerium oxide, and silicon oxide NPs, which are commonly used in chemical mechanical planarization (CMP) processes, for biosolids used in municipal wastewater treatment plants provides a basis for estimating their removal efficiency. Batch studies were performed and the NPs were shown to partition to the cellular surface. It is expected that significant removal of the cerium oxide NPs will be achieved during conventional biological wastewater treatment. Copyright © SESHA.
• Sierra Alvarez, M., Chairez, M., Luna-Velasco, A., Field, J. A., Ju, X., & Sierra Alvarez, M. R. (2010). Reduction of bromate by biogenic sulfide produced during microbial sulfur disproportionation. Biodegradation, 21(2).
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  Bromate (BrO(3) (-)) is a carcinogenic contaminant formed during ozonation of waters that contain trace amounts of bromide. Previous research shows that bromate can be microbially reduced to bromide using organic (i.e. acetate, glucose, ethanol) and inorganic (H(2)) electron-donating substrates. In this study, the reduction of bromate by a mixed microbial culture was investigated using elemental sulfur (S(0)) as an electron donor. In batch bioassays performed at 30 degrees C, bromate (0.30 mM) was completely converted to bromide after 10 days and no accumulation of intermediates occurred. Bromate was also reduced in cultures supplemented with thiosulfate and hydrogen sulfide as electron donor. Our results demonstrated that S(0)-disproportionating microorganisms were responsible for the reduction of bromate in cultures spiked with S(0) through an indirect mechanism involving microbial formation of sulfide and subsequent abiotic reduction of bromate by the biogenic sulfide. Confirmation of this mechanism is the fact that bromate was shown to undergo rapid chemical reduction by sulfide (but not S(0) or thiosulfate) in abiotic experiments. Bromate concentrations above 0.30 mM inhibited sulfide formation by S(0)-disproportionating bacteria, leading to a decrease in the rate of bromate reduction. The results suggest that biological formation of sulfide from by S(0) disproportionation could support the chemical removal of bromate without having to directly use sulfide as a reagent.
• Sierra Alvarez, M., Tapia-Rodriguez, A., Luna-Velasco, A., Field, J. A., & Sierra Alvarez, M. R. (2010). Anaerobic bioremediation of hexavalent uranium in groundwater by reductive precipitation with methanogenic granular sludge. Water research, 44(7).
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  Uranium has been responsible for extensive contamination of groundwater due to releases from mill tailings and other uranium processing waste. Past evidence has confirmed that certain bacteria can enzymatically reduce soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) under anaerobic conditions in the presence of appropriate electron donors. This paper focuses on the evaluation of anaerobic granular sludge as a source of inoculum for the bioremediation of uranium in water. Batch experiments were performed with several methanogenic anaerobic granular sludge samples and different electron donors. Abiotic controls consisting of heat-killed inoculum and non-inoculated treatments confirmed the biological removal process. In this study, unadapted anaerobic granular sludge immediately reduced U(VI), suggesting an intrinsic capacity of the sludge to support this process. The high biodiversity of anaerobic granular sludge most likely accounts for the presence of specific microorganisms capable of reducing U(VI). Oxidation by O(2) was shown to resolubilize the uranium. This observation combined with X-ray diffraction evidence of uraninite confirmed that the removal during anaerobic treatment was due to reductive precipitation. The anaerobic removal activity could be sustained after several respikes of U(VI). The U(VI) removal was feasible without addition of electron donors, indicating that the decay of endogenous biomass substrates was contributing electron equivalents to the process. Addition of electron donors, such as H(2) stimulated the removal of U(VI) to varying degrees. The stimulation was greater in sludge samples with lower endogenous substrate levels. The present work reveals the potential application of anaerobic granular sludge for continuous bioremediation schemes to treat uranium-contaminated water.
• Sierra-Alvarez, R., Cortinas, I., & Field, J. A. (2010). Methanogenic inhibition by roxarsone (4-hydroxy-3-nitrophenylarsonic acid) and related aromatic arsenic compounds. Journal of Hazardous Materials, 175(1-3), 352-358.
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  PMID: 19889499;PMCID: PMC2815220;Abstract: Roxarsone (4-hydroxy-3-nitro-phenylarsonic acid) and p-arsanilic acid (4-aminophenylarsonic acid) are feed additives widely used in the broiler and swine industry. This study evaluated the inhibitory effect of roxarsone, p-arsanilic, and other phenylarsonic compounds on the activity of acetate- and H2-utilizing methanogenic microorganisms. Roxarsone, p-arsanilic, and 4-hydroxy-3-aminophenylarsonic acid (HAPA) inhibited acetoclastic and hydrogenotrophic methanogens when supplemented at concentrations of 1 mM, and their inhibitory effect increased sharply with incubation time. Phenylarsonic acid (1 mM) inhibited acetoclastic but not H2-utilizing methanogens. HAPA, a metabolite from the anaerobic biodegradation of roxarsone, was found to be sensitive to autooxidation by oxygen. The compound (2.6 mM) caused low methanogenic inhibition (only 14.2%) in short-term assays of 12 h when autooxidation was prevented by supplementing HAPA solutions with ascorbate. However, ascorbate-free HAPA solutions underwent spontaneous autooxidation in the presence of oxygen, leading to the formation of highly inhibitory compounds. These results confirm the microbial toxicity of organoarsenic compounds, and they indicate that biotic as well as abiotic transformations can potentially impact the fate and microbial toxicity of these contaminants in the environment. © 2009 Elsevier B.V. All rights reserved.
• Sun, W., Sierra-Alvarez, R., & Field, J. A. (2010). The role of denitrification on arsenite oxidation and arsenic mobility in an anoxic sediment column model with activated alumina. Biotechnology and Bioengineering, 107(5), 786-794.
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  PMID: 20662039;Abstract: Arsenite (As(III)) is the predominant arsenic (As) species in reducing environments. As(III) is less strongly adsorbed than As(V) at circumneutral pH conditions by common non-iron metal oxides in sediments such as those of aluminum. Therefore, oxidation of As(III) to As(V) could contribute to an improved immobilization of As and thus help mitigate As contamination in groundwater. Microbial oxidation of As(III) is known to readily under aerobic conditions, however, the dissolved oxygen (O2) concentration in groundwater may be limited due to the poor solubility of O2 and its high chemical reactivity with reduced compounds. Nitrate, can be considered as an alternative electron acceptor, which can support oxidation of As(III) to As(V) by denitrifying bacteria. In this study, two up-flow sediment columns packed with activated alumina (AA) were utilized to demonstrate the role of denitrification on the oxidation of As(III) to As(V) and its contribution to improved As adsorption onto AA. One column was supplied with (C1) and its performance was compared with a control column lacking (C2). During most of the operation when the pH was in the circumneutral range (days 50-250), the release of arsenic was greater from C2 compared to C1. The effluent As concentrations started increasing on days 60 and 100 in C2 and C1, respectively. Complete breakthrough started on day 200 in C2; whereas in C1, complete breakthrough was never achieved. The effluent and solid phase As speciation was dominated by As(V) in C1, indicating the occurrence of As(III) oxidation due to whereas in C2, only As(III) was dominant. This study illustrates a bioremediation or natural attenuation process based on anoxic microbial -dependent oxidation of As(III) to more readily adsorbed As(V) as a means to enhance the immobilization of As on alumina oxide particles in subsurface environments. © 2010 Wiley Periodicals, Inc.
• Sun, W., Sierra-Alvarez, R., Hsu, I., Rowlette, P., & Field, J. A. (2010). Anoxic oxidation of arsenite linked to chemolithotrophic denitrification in continuous bioreactors. Biotechnology and Bioengineering, 105(5), 909-917.
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  PMID: 19953675;Abstract: In this study, the anoxic oxidation of arsenite (As(III)) linked to chemolithotrophic denitrification was shown to be feasible in continuous bioreactors. Biological oxidation of As(III) was stable over prolonged periods of operation ranging up to 3 years in continuous denitrifying bioreactors with granular biofilms. As(III) was removed with a high conversion efficiency (>92%) to arsenate (As(V)) in periods with high volumetric loadings (e.g., 3.5-5.1 mmol As Lreactor-1 day-1). The maximum specific activity of sampled granular sludge from the bioreactors was 0.98±0.04 mmol As(V) formed g-1 VSS day-1 when determined at an initial concentration of 0.5mM As(III). The microbial population adapted to high influent concentrations of As(III) up to 5.2 mM. However, the As(III) oxidation process was severely inhibited when 7.6-8.1mMAs(III) was fed. Activity was restored upon lowering the As(III) concentration to 3.8 mM. Several experimental strategies were utilized to demonstrate a dependence of the nitrate removal on As(III) oxidation as well as a dependence of the As(III) removal on nitrate reduction. The molar stoichiometric ratio of As(V) formed to nitrate removed (corrected for endogenous denitrification) in the bioreactors approximated 2.5, indicating complete denitrification was occurring. As(III) oxidation was also shown to be linked to the complete denitrification of NO3- to N 2 gas by demonstrating a significantly enhanced production of N 2 beyond the background endogenous production in a batch bioassay spiked with 3.5mM As(III). The N2 production also corresponded closely to the expected stoichiometry of 2.5 mol As(III) mol-1 N 2-N for complete denitrification. © 2009 Wiley Periodicals, Inc.
• Sun, W., Sierra-Alvarez, R., Milner, L., & Field, J. A. (2010). Anaerobic oxidation of arsenite linked to chlorate reduction. Applied and Environmental Microbiology, 76(20), 6804-6811.
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  PMID: 20729322;PMCID: PMC2953025;Abstract: Microorganisms play a significant role in the speciation and mobility of arsenic in the environment. In this study, the oxidation of arsenite [As(III)] to arsenate [As(V)] linked to chlorate (ClO3-)- reduction was shown to be catalyzed by sludge samples, enrichment cultures (ECs), and pure cultures incubated under anaerobic conditions. No activity was observed in treatments lacking inoculum or with heat-killed sludge, or in controls lacking ClO3- The As(III) oxidation waslinked to the complete reduction of ClO3- to Cl- and the molar ratio of As(V) formed to ClO3- consumed approached the theoretical value of 3:1 assuming the e equivalents from As(III) were used to completely reduce ClO3-. In keeping with O2 as a putative intermediate of ClO3- reduction, the ECs could also oxidize As(III) to As(V) with O2 at low concentrations. Low levels of organic carbon were essential in heterotrophic ECs but not in autotrophic ECs. 16S rRNA gene clone libraries indicated that the ECs were dominated by clones of Rhodocyclaceae (including Dechloromonas, Azospira, and Azonexus phylotypes) and Stenotrophomonas under autotrophic conditions. Additional phylotypes (Alicycliphilus, Agrobacterium, and Pseudoxanthomonas) were identified in heterotrophic ECs.Two isolated autotrophic pure cultures, Dechloromonas sp. strain ECC1-pb1 and Azospira sp. strain ECC1-pb2, were able to grow by linking the oxidationof As(III) to As(V) with the reduction of ClO 3-. Thepresence of the arsenite oxidase subunit A (aroA) gene was demonstrated with PCR in the ECs and pure cultures. This study demonstrates thatClO3- is an alternative electron acceptor to support the microbial oxidation of As(III). © 2010, American Society for Microbiology.
• Tapia-Rodriguez, A., Luna-Velasco, A., Field, J. A., & Sierra-Alvarez, R. (2010). Anaerobic bioremediation of hexavalent uranium in groundwater by reductive precipitation with methanogenic granular sludge. Water Research, 44(7), 2153-2162.
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  PMID: 20060558;Abstract: Uranium has been responsible for extensive contamination of groundwater due to releases from mill tailings and other uranium processing waste. Past evidence has confirmed that certain bacteria can enzymatically reduce soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) under anaerobic conditions in the presence of appropriate electron donors. This paper focuses on the evaluation of anaerobic granular sludge as a source of inoculum for the bioremediation of uranium in water. Batch experiments were performed with several methanogenic anaerobic granular sludge samples and different electron donors. Abiotic controls consisting of heat-killed inoculum and non-inoculated treatments confirmed the biological removal process. In this study, unadapted anaerobic granular sludge immediately reduced U(VI), suggesting an intrinsic capacity of the sludge to support this process. The high biodiversity of anaerobic granular sludge most likely accounts for the presence of specific microorganisms capable of reducing U(VI). Oxidation by O2 was shown to resolubilize the uranium. This observation combined with X-ray diffraction evidence of uraninite confirmed that the removal during anaerobic treatment was due to reductive precipitation. The anaerobic removal activity could be sustained after several respikes of U(VI). The U(VI) removal was feasible without addition of electron donors, indicating that the decay of endogenous biomass substrates was contributing electron equivalents to the process. Addition of electron donors, such as H2 stimulated the removal of U(VI) to varying degrees. The stimulation was greater in sludge samples with lower endogenous substrate levels. The present work reveals the potential application of anaerobic granular sludge for continuous bioremediation schemes to treat uranium-contaminated water. © 2009 Elsevier Ltd. All rights reserved.
• Banihani, Q., Sierra-Alvarez, R., & Field, J. A. (2009). Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges. Biodegradation, 20(6), 801-812.
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  PMID: 19449209;Abstract: Anaerobic bioreactors that can support simultaneous microbial processes of denitrification and methanogenesis are of interest to nutrient nitrogen removal. However, an important concern is the potential toxicity of nitrate (NO3-) and nitrite (NO2-) to methanogenesis. The methanogenic toxicity of the NOx- compounds to anaerobic granular biofilms and municipal anaerobic digested sludge with two types of substrates, acetate and hydrogen, was studied. The inhibition was the severest when the NOx- compounds were still present in the media (exposure period). During this period, 95% or greater inhibition of methanogenesis was evident at the lowest concentrations of added NO2- tested (7.6-10.2 mg NO2--N l-1) or 8.3-121 mg NO3--N l-1 of added NO3-, depending on substrate and inoculum source. The inhibition imparted by NO3- was not due directly to NO3- itself, but instead due to reduced intermediates (e.g., NO2-) formed during the denitrification process. The toxicity of NOx- was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NOx- concentrations; whereas the recovery was only partial at high added NOx- concentrations. The recovery is attributed to the metabolism of the NOx- compounds. The assay substrate had a large impact on the rate of NO2- metabolism. Hydrogen reduced NO2- slowly such that NO2- accumulated more and as a result, the toxicity was greater compared to acetate as a substrate. The final methane yield was inversely proportional to the amount of NOx- compounds added indicating that they were the preferred electron acceptors compared to methanogenesis. © Springer Science+Business Media B.V. 2009.
• Beristain-Cardoso, R., Texier, A., Sierra-Álvarez, R., Razo-Flores, E., Field, J. A., & Gómez, J. (2009). Effect of initial sulfide concentration on sulfide and phenol oxidation under denitrifying conditions. Chemosphere, 74(2), 200-205.
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  PMID: 18990426;Abstract: The objective of this work was to evaluate the effect of the initial sulfide concentration on the kinetics and metabolism of phenol and sulfide in batch bioassays using nitrate as electron acceptor. Complete oxidation of sulfide (20 mg L-1 of S2-) and phenol (19.6 mg L-1) was linked to nitrate reduction when nitrate was supplemented at stoichiometric concentrations. At 32 mg L-1 of sulfide, oxidation of sulfide and phenol by the organo-lithoautotrophic microbial culture was sequential; first sulfide was rapidly oxidized to elemental sulfur and afterwards to sulfate; phenol oxidation started once sulfate production reached a maximum. When the initial sulfide concentration was increased from 20 to 26 and finally to 32 mg L-1, sulfide oxidation was inhibited. In contrast phenol consumption by the denitrifying culture was not affected. These results indicated that sulfide affected strongly the sulfide oxidation rate and nitrate reduction. © 2008 Elsevier Ltd. All rights reserved.
• Fernandez, N., Sierra-Alvarez, R., Amils, R., Field, J. A., & Sanz, J. L. (2009). Compared microbiology of granular sludge under autotrophic, mixotrophic and heterotrophic denitrification conditions. Water Science and Technology, 59(6), 1227-1236.
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  PMID: 19342820;Abstract: Water contamination by nitrate is a wideworld extended phenomena. Biological autotrophic denitrification has a real potential to face this problem and presents less drawbacks than the most extended heterotrophic denitrification. Three bench-scale UASB reactors were operated under autotrophic (R1, H2S as electron donor), mixotrophic (R2, H2S plus p-cresol as electron donors) and heterotrophic (R3, p-cresol as electron donor) conditions using nitrate as terminal electron acceptor. 16S rDNA genetic libraries were built up to compare their microbial biodiversity. Six different bacteria phyla and three archaeal classes were observed. Proteobacteria was the main phyla in all reactors standing out the presence of denitrifiers. Microorganisms similar to Thiobacillus denitrificans and Acidovorax sp. performed the autotrophic denitification. These OTUs were displaced by chemoheterotrophic denitrifiers, especially by Z./mr?otoacter-like and Offoi/wa-like OTUs. Other phyla were Bacteroidetes, Chloroflexi, Firmicutes and Actinobacteria that- as well as Archaea members- were implicated in the degradation of organic matter, as substrate added as coming from endogenous sludge decay under autotrophic conditions. Archaea diversity remained low in all the reactors being Methanosaeta concilil the most abundant one.© IWA Publishing 2009.
• Gámez, V. M., Sierra-Alvarez, R., Waltz, R. J., & Field, J. A. (2009). Anaerobic degradation of citrate under sulfate reducing and methanogenic conditions. Biodegradation, 20(4), 499-510.
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  PMID: 19089588;Abstract: Citrate is an important component of metal processing effluents such as chemical mechanical planarization wastewaters of the semiconductor industry. Citrate can serve as an electron donor for sulfate reduction applied to promote the removal of metals, and it can also potentially be used by methanogens that coexist in anaerobic biofilms. The objective of this study was to evaluate the degradation of citrate with sulfate-reducing and methanogenic biofilms. During batch bioassays, the citrate, acetate, methane and sulfide concentrations were monitored. The results indicate that independent of the biofilm or incubation conditions used, citrate was rapidly fermented with specific rates ranging from 566 to 720 mg chemical oxygen demand (COD) consumed per gram volatile suspended solids per day. Acetate was found to be the main fermentation product of citrate degradation, which was later degraded completely under either methanogenic or sulfate reducing conditions. However, if either sulfate reduction or methanogenesis was infeasible due to specific inhibitors (2-bromoethane sulfonate), absence of sulfate or lack of adequate microorganisms in the biofilm, acetate accumulated to levels accounting for 90-100% of the citrate-COD consumed. Based on carbon balances measured in phosphate buffered bioassays, acetate, CO2 and hydrogen are the main products of citrate fermentation, with a molar ratio of 2:2:1 per mol of citrate, respectively. In bicarbonate buffered bioassays, acetogenesis of H2 and CO2 increased the yield of acetate. The results taken as a whole suggest that in anaerobic biofilm systems, citrate is metabolized via the formation of acetate as the main metabolic intermediate prior to methanogenesis or sulfate reduction. Sulfate reducing consortia must be enriched to utilize acetate as an electron donor in order to utilize the majority of the electron-equivalents in citrate. © 2008 Springer Science+Business Media B.V.
• Ochoa-Herrera, V., Banihani, Q., León, G., Khatri, C., Field, J. A., & Sierra-Alvarez, R. (2009). Toxicity of fluoride to microorganisms in biological wastewater treatment systems. Water Research, 43(13), 3177-3186.
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  PMID: 19457531;Abstract: Fluoride is a common contaminant in a variety of industrial wastewaters. Available information on the potential toxicity of fluoride to microorganisms implicated in biological wastewater treatment is very limited. The objective of this study was to evaluate the inhibitory effect of fluoride towards the main microbial populations responsible for the removal of organic constituents and nutrients in wastewater treatment processes. The results of short-term batch bioassays indicated that the toxicity of sodium fluoride varied widely depending on the microbial population. Anaerobic microorganisms involved in various metabolic steps of anaerobic digestion processes were found to be very sensitive to the presence of fluoride. The concentrations of fluoride causing 50% metabolic inhibition (IC50) of propionate- and butyrate-degrading microorganisms as well as mesophilic and thermophilic acetate-utilizing methanogens ranged from 18 to 43 mg/L. Fluoride was also inhibitory to nitrification, albeit at relatively high levels (IC50 = 149 mg/L). Nitrifying bacteria appeared to adapt rapidly to fluoride, and a near complete recovery of their metabolic activity was observed after only 4 d of exposure to high fluoride levels (up to 500 mg/L). All other microbial populations evaluated in this study, i.e., glucose fermenters, aerobic glucose-degrading heterotrophs, denitrifying bacteria, and H2-utilizing methanogens, tolerated fluoride at very high concentrations (>500 mg/L). © 2009 Elsevier Ltd. All rights reserved.
• Sierra Alvarez, M., & Sierra Alvarez, M. R. (2009). Removal of copper, chromium and arsenic from preservative-treated wood by chemical extraction-fungal bioleaching. Waste management (New York, N.Y.), 29(6).
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  Large volumes of preservative-treated wood containing toxic Cr, Cu and As salts are decommissioned worldwide. This study investigated the effectiveness of solid-state fermentation with copper-tolerant brown-rot fungi for the remediation of wood treated with chromated copper arsenate (CCA) and acid copper chromate (ACC) formulations. Treatment of CCA- and ACC-wood with the most effective strain, Antrodia vaillantii FRLP-14G, attained extensive leaching of As and/or Cr, but Cu elimination was poor (
• Sierra Alvarez, M., Ochoa-Herrera, V., Banihani, Q., León, G., Khatri, C., Field, J. A., & Sierra Alvarez, M. R. (2009). Toxicity of fluoride to microorganisms in biological wastewater treatment systems. Water research, 43(13).
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  Fluoride is a common contaminant in a variety of industrial wastewaters. Available information on the potential toxicity of fluoride to microorganisms implicated in biological wastewater treatment is very limited. The objective of this study was to evaluate the inhibitory effect of fluoride towards the main microbial populations responsible for the removal of organic constituents and nutrients in wastewater treatment processes. The results of short-term batch bioassays indicated that the toxicity of sodium fluoride varied widely depending on the microbial population. Anaerobic microorganisms involved in various metabolic steps of anaerobic digestion processes were found to be very sensitive to the presence of fluoride. The concentrations of fluoride causing 50% metabolic inhibition (IC(50)) of propionate- and butyrate-degrading microorganisms as well as mesophilic and thermophilic acetate-utilizing methanogens ranged from 18 to 43 mg/L. Fluoride was also inhibitory to nitrification, albeit at relatively high levels (IC(50)=149 mg/L). Nitrifying bacteria appeared to adapt rapidly to fluoride, and a near complete recovery of their metabolic activity was observed after only 4d of exposure to high fluoride levels (up to 500 mg/L). All other microbial populations evaluated in this study, i.e., glucose fermenters, aerobic glucose-degrading heterotrophs, denitrifying bacteria, and H(2)-utilizing methanogens, tolerated fluoride at very high concentrations (>500 mg/L).
• Sierra-Alvarez, R. (2009). Preface. Reviews in Environmental Science and Biotechnology, 8(4), 289-290.
• Sierra-Alvarez, R. (2009). Removal of copper, chromium and arsenic from preservative-treated wood by chemical extraction-fungal bioleaching. Waste Management, 29(6), 1885-1891.
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  PMID: 19136247;Abstract: Large volumes of preservative-treated wood containing toxic Cr, Cu and As salts are decommissioned worldwide. This study investigated the effectiveness of solid-state fermentation with copper-tolerant brown-rot fungi for the remediation of wood treated with chromated copper arsenate (CCA) and acid copper chromate (ACC) formulations. Treatment of CCA- and ACC-wood with the most effective strain, Antrodia vaillantii FRLP-14G, attained extensive leaching of As and/or Cr, but Cu elimination was poor (
• Sun, W., Sierra-Alvarez, R., Fernandez, N., Sanz, J. L., Amils, R., Legatzki, A., Maier, R. M., & Field, J. A. (2009). Molecular characterization and in situ quantification of anoxic arsenite-oxidizing denitrifying enrichment cultures. FEMS Microbiology Ecology, 68(1), 72-85.
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  PMID: 19187211;Abstract: To explore the bacteria involved in the oxidation of arsenite (As(III)) under denitrifying conditions, three enrichment cultures (ECs) and one mixed culture (MC) were characterized that originated from anaerobic environmental samples. The oxidation of As(III) (0.5 mM) was dependent on NO3- addition and N2 formation was dependent on As(III) addition. The ratio of N2-N formed to As(III) fed approximated the expected stoichiometry of 2.5. A 16S rRNA gene clone library analysis revealed three predominant phylotypes. The first, related to the genus Azoarcus from the division Betaproteobacteria, was found in the three ECs. The other two predominant phylotypes were closely related to the genera Acidovorax and Diaphorobacter within the Comamonadaceae family of Betaproteobacteria, and one of these was present in all of the cultures examined. FISH confirmed that Azoarcus accounted for a large fraction of bacteria present in the ECs. The Azoarcus clones had 96% sequence homology with Azoarcus sp. strain DAO1, an isolate previously reported to oxidize As(III) with nitrate. FISH analysis also confirmed that Comamonadaceae were present in all cultures. Pure cultures of Azoarcus and Diaphorobacter were isolated and shown to be responsible for nitrate-dependent As(III) oxidation. These results, taken as a whole, suggest that bacteria within the genus Azoarcus and the family Comamonadaceae are involved in the observed anoxic oxidation of As(III). © 2009 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.
• Sun, W., Sierra-Alvarez, R., Milner, L., Oremland, R., & Field, J. A. (2009). Arsenite and ferrous iron oxidation linked to chemolithotrophic denitrification for the immobilization of arsenic in anoxic environments. Environmental Science and Technology, 43(17), 6585-6591.
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  PMID: 19764221;Abstract: The objective of this study was to explore a bioremediation strategy based on injecting NO3- to support the anoxic oxidation of ferrous iron (Fe(II)) and arsenite (As(III)) in the subsurface as a means to immobilize As in the form of arsenate (As(V)) adsorbed onto biogenic ferric (Fe(III)) (hydr)oxides. Continuous flows and filled columns were used to simulate a natural anaerobic groundwater and sediment system with co-occurring As(III) and Fe(II) in the presence (column SF1) or absence (column SF2) of nitrate, respectively. During operation for 250 days, the average influent arsenic concentration of 567 μg L-1 was reduced to 10.6 (±9.6) μg L-1 in the effluent of column SF1. The cumulative removal of Fe(II) and As(III) in SF1 was 6.5 to 10-fold higher than that in SF2. Extraction and measurement of the mass of iron and arsenic immobilized on the sand packing of the columns were close to the iron and arsenic removed from the aqueous phase during column operation. The dominant speciation of the immobilized iron and arsenic was Fe(III) and As(V) in SF1, compared with Fe(II) and As(III) in SF2. The speciation was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that microbial oxidation of As(III) and Fe(II) linked to denitrification resulted in the enhanced immobilization of aqueous arsenic in anaerobic environments by forming Fe(III) (hydr)oxide coated sands with adsorbed As(V). © 2009 American Chemical Society.
• Torres, F. J., Ochoa-Herrera, V., Blowers, P., & Sierra-Alvarez, R. (2009). Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers. Chemosphere, 76(8), 1143-1149.
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  PMID: 19428046;Abstract: Structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its trifluoromethyl-branched isomers (i.e. 1-CF3- to 6-CF3-PFOS) were theoretically studied by means of ab initio density functional theory (DFT) calculations with the B3LYP functional and a 6-31++G(d,p) basis set. The anionic form of linear PFOS and its trifluromethyl-branched isomers were considered for the initial construction of the computational models; subsequently, H+, Li+, and Na+ were added as counter-ions to study their effect on the properties under investigation. Insignificant changes with respect to the anions were observed in the structure of both the protonated and salt forms due to the presence of these counter-ions. However, important differences in the electrostatic potential maps as well as HOMO and LUMO molecular orbitals were observed for the various forms of PFOS. The linear and branched PFOS ions were identified as the most suitable compounds for interacting with charged species. Furthermore, in the linear anion, it was observed that the LUMO orbital is diffused along the whole fluoro-carbon chain, whereas it is localized to the region close to the ternary carbon in the 4-CF3-PFOS, 5-CF3-PFOS, and 6-CF3-PFOS isomers. The higher accessibility of the LUMO orbital in these branched anions suggests that they have a higher probability of reacting with free radicals when compared with the linear counterpart. This behavior is reflected in the experimental observation that only the branched PFOS isomers were susceptible to reductive defluorination by reduced vitamin B12 as we previously reported. The relative stability of the linear and branched PFOS in their different forms computed by comparing their calculated Gibbs free energy showed that 1-CF3-, 6-CF3-, and linear PFOS are the most favorable structures from a thermodynamic point of view. © 2009 Elsevier Ltd. All rights reserved.
• Torres, F. J., Ochoa-Herrera, V., Blowers, P., & Sierra-Alvarez, R. (2009). Response to Comment by Sierra Rayne and Kaya Forest on ''Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers" [Chemosphere 76 (8) (2009) 1143-1149]. Chemosphere, 77(10), 1457-1458.
• Yi, Y. i., Ayothi, R., Wang, Y., Mingqi, L. i., Barclay, G., Sierra-Alvarez, R., & Ober, C. K. (2009). Sulfonium salts of alicyclic group functionalized semifluorinated alkyl ether sulfonates as photoacid generators. Chemistry of Materials, 21(17), 4037-4046.
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  Abstract: We describe new sulfonium salts incorporating semifluorinated sulfonate anions and their successful application as photoacid generators (PAGs) intended to solve the environmental problems caused by perfluorooctyl sulfonate (PFOS). By utilizing simple and unique chemistries based on 5-iodooctafluoro-3- oxapentanesulfonyl fluoride, a series of alicyclic-group functionalized octafluoro-3-oxapentanesulfonate anions were prepared in high purity and high yield. Triphenylsulfonium (TPS) salts of norbornyl and γ-butyrolactone groups functionalized octafluoro-3-oxapentanesulfonates were extensively studied. They have excellent thermal stability and good solubility in various polar solvents. Their optical and thermal properties were thoroughly investigated. Angle resolved X-ray photoelectron spectroscopy (XPS) analysis confirmed that the new TPS salts are uniformly distributed in polymer films, whereas TPS PFOS is heavily segregated to a polymer film surface. Lithographic performance of the new salts together with TPS PFOS and triphenylsulfonium perfluorobutyl sulfonate (TPS PFBS) in model positive tone resists was evaluated and compared at 193 nm (both dry and immersion) and extreme ultraviolet (EUV) wavelengths. Resist compositions containing the new salts are capable of resolving sub-100 nm dense lines and spaces at both tested wavelengths. Especially, a pattern of 42 nm dense lines was successfully demonstrated in 193 nm immersion exposures. A specific TPS salt of monosaccharide-functionalized octafluoro-3-oxapentanesulfonate, a "sweet" PAG, was also synthesized and studied. This PAG is capable of resolving 90 nm lines in 193 nm lithography. These new PAGs show comparable performance with TPS PFBS and better performance than TPS PFOS, which makes them very promising environmentally friendly candidates for high resolution lithography applications. © 2009 American Chemical Society.
• Beristain-Cardoso, R., Texier, A., Sierra-Álvarez, R., Field, J. A., Razo-Flores, E., & Gómez, J. (2008). Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor. Journal of Chemical Technology and Biotechnology, 83(9), 1197-1203.
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  Abstract: Background: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO-/ NO3- molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). Results: Three molar ratios of CH3COO-/NO3- (0.85, 0.72 and 0.62) with a constant S2-/NO3- molar ratio of 0.13 were evaluated. At a CH3COO-/NO3- molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g-1 NO3- -N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic-C g-1 CH3COO- -C consumed. Sulfide was partially oxidized to S0, and 71% of the S2- consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO-/ NO3- molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic-C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g S042- -S g-1 S2- consumed. Conclusions: The CH3COO-/NO3- molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. © 2008 Society of Chemical Industry.
• Cortinas, I., Sierra-Alvarez, R., & Field, J. A. (2008). Biologically mediated mobilization of arsenic from granular ferric hydroxide in anaerobic columns fed landfill leachate. Biotechnology and Bioengineering, 101(6), 1205-1213.
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  PMID: 18980210;Abstract: To gain insight on the fate of arsenic (As) from drinking water treatment residuals in landfills, the mobilization of arsenate adsorbed onto granular ferric hydroxide (GFH) was studied in continuous anaerobic columns fed with a synthetic landfill leachate. The release of As was compared in biologically active and abiotic columns. More than 150 days of incubation were required before noteworthy As release occurred. After 400 days of operation, 19% of the As was mobilized as identified species in the biologically active column, which was 25.5-fold greater than that of the abiotic column. Fine colloids accounted for up to 81% of the As released. Arsenite was the predominant species identified in filtered (0.45 μm) effluent samples. Dimethylarsinic acid and monomethylarsonic acid were also observed as metabolites. During column operation, approximately 30% of the iron (hydr)oxide mass was lost and most of the mass loss was attributed to changes in iron mineralogy that could be demonstrated in a batch bioassay. The results indicate that As-laden GFH residuals from drinking water treatment are subject to mobilization in municipal landfills and that biologically mediated changes in the iron mineralogy may play an important role in the mobilization mechanism. © 2008 Wiley Periodicals, Inc.
• Fernández, N., Sierra-Alvarez, R., Field, J. A., Amils, R., & Sanz, J. L. (2008). Microbial community dynamics in a chemolithotrophic denitrification reactor inoculated with methanogenic granular sludge. Chemosphere, 70(3), 462-474.
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  PMID: 17689587;Abstract: Denitrification is applied in the tertiary treatment of wastewater to reduce nitrogen pollution. Fluorescence in situ hybridization (FISH), catalyzed reporter deposition (CARD)-FISH, cloning, and scanning electron microscopy (SEM) were applied to follow the evolution of the microbial composition and structure of granular sludge in chemolithotrophic denitrifying bioreactors fed with nitrate and thiosulfate. FISH oligonucleotide probes for the chemolitoautotrophic denitrifiers Thiobacillus denitrificans and Thiomicrospira denitrificans were designed and their utility tested. CARD-FISH and cloning data showed that bacterial diversity in the biofilms changed during the reactor operation. Chemoorganotrophic fermentative Gram-positive strains in the phyla, Actinobacteria and Firmicutes, were dominant in the methanogenic inoculum, both in terms of biodiversity and in number. Other significant phyla were Bacteroidetes and Chloroflexi. After 6 months of operation, Proteobacteria became dominant (83% of the clones). The diversity of Gram-positive bacteria was partially maintained although their abundance decreased notably. After 110 d of operation, the abundance of Tb. denitrificans cells increased considerably, from 1% to 35% of total DAPI-stained cells and from no isolated clones to 15% of the total clones. Tm. denitrificans only represented a minor fraction of the microorganisms in the sludge (1-4% of the DAPI-stained cells). These findings confirm that Tb. denitrificans was the dominant chemolitoautotrophic denitrifying microorganism in the bioreactors. The Archaeal diversity remained almost unchanged and it was represented mostly by Methanosaeta soehngenii. SEM results indicated a considerable loss in the integrity of the sludge granules during the operation, with risk of sludge buoyancy. © 2007 Elsevier Ltd. All rights reserved.
• Field, J. A., & Sierra-Alvarez, R. (2008). Microbial degradation of chlorinated benzenes. Biodegradation, 19(4), 463-480.
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  PMID: 17917704;Abstract: Chlorinated benzenes are important industrial intermediates and solvents. Their widespread use has resulted in broad distribution of these compounds in the environment. Chlorobenzenes (CBs) are subject to both aerobic and anaerobic metabolism. Under aerobic conditions, CBs with four or less chlorine groups are susceptible to oxidation by aerobic bacteria, including bacteria (Burkholderia, Pseudomonas, etc.) that grow on such compounds as the sole source of carbon and energy. Sound evidence for the mineralization of CBs has been provided based on stoichiometric release of chloride or mineralization of 14C-labeled CBs to 14CO2. The degradative attack of CBs by these strains is initiated with dioxygenases eventually yielding chlorocatechols as intermediates in a pathway leading to CO2 and chloride. Higher CBs are readily reductively dehalogenated to lower chlorinated benzenes in anaerobic environments. Halorespiring bacteria from the genus Dehalococcoides are implicated in this conversion. Lower chlorinated benzenes are less readily converted, and mono-chlorinated benzene is recalcitrant to biotransformation under anaerobic conditions. © 2007 Springer Science+Business Media B.V.
• Field, J. A., & Sierra-Alvarez, R. (2008). Microbial degradation of chlorinated dioxins. Chemosphere, 71(6), 1005-1018.
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  PMID: 18083210;Abstract: Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were introduced into the biosphere on a large scale as by-products from the manufacture of chlorinated phenols and the incineration of wastes. Due to their high toxicity they have been the subject of great public and scientific scrutiny. The evidence in the literature suggests that PCDD/F compounds are subject to biodegradation in the environment as part of the natural chlorine cycle. Lower chlorinated dioxins can be degraded by aerobic bacteria from the genera of Sphingomonas, Pseudomonas and Burkholderia. Most studies have evaluated the cometabolism of monochlorinated dioxins with unsubstituted dioxin as the primary substrate. The degradation is usually initiated by unique angular dioxygenases that attack the ring adjacent to the ether oxygen. Chlorinated dioxins can also be attacked cometabolically under aerobic conditions by white-rot fungi that utilize extracellular lignin degrading peroxidases. Recently, bacteria that can grow on monochlorinated dibenzo-p-dioxins as a sole source of carbon and energy have also been characterized (Pseudomonas veronii). Higher chlorinated dioxins are known to be reductively dechlorinated in anaerobic sediments. Similar to PCB and chlorinated benzenes, halorespiring bacteria from the genus Dehalococcoides are implicated in the dechlorination reactions. Anaerobic sediments have been shown to convert tetrachloro- to octachlorodibenzo-p-dioxins to lower chlorinated dioxins including monochlorinated congeners. Taken as a whole, these findings indicate that biodegradation is likely to contribute to the natural attenuation processes affecting PCDD/F compounds. © 2007 Elsevier Ltd. All rights reserved.
• Field, J. A., & Sierra-Alvarez, R. (2008). Microbial degradation of chlorinated phenols. Reviews in Environmental Science and Biotechnology, 7(3), 211-241.
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  Abstract: Chlorophenols have been introduced into the environment through their use as biocides and as by-products of chlorine bleaching in the pulp and paper industry. Chlorophenols are subject to both anaerobic and aerobic metabolism. Under anaerobic conditions, chlorinated phenols can undergo reductive dechlorination when suitable electron-donating substrates are available. Halorespiring bacteria are known which can use both low and highly chlorinated congeners of chlorophenol as electron acceptors to support growth. Many strains of halorespiring bacteria have the capacity to eliminate ortho-chlorines; however only bacteria from the species Desulfitobacterium hafniense (formerly frappieri) can eliminate para- and meta-chlorines in addition to ortho-chlorines. Once dechlorinated, the phenolic carbon skeletons are completely converted to methane and carbon dioxide by other anaerobic microorganisms in the environment. Under aerobic conditions, both lower and higher chlorinated phenols can serve as sole electron and carbon sources supporting growth. The best studied strains utilizing pentachlorophenol belong to the genera Mycobacterium and Sphingomonas. Two main strategies are used by aerobic bacteria for the degradation of chlorophenols. Lower chlorinated phenols for the most part are initially attacked by monooxygenases yielding chlorocatechols as the first intermediates. On the other hand, polychlorinated phenols are converted to chlorohydroquinones as the initial intermediates. Fungi and some bacteria are additionally known that cometabolize chlorinated phenols. © 2007 Springer Science+Business Media B.V.
• Field, J. A., & Sierra-Alvarez, R. (2008). Microbial transformation and degradation of polychlorinated biphenyls. Environmental Pollution, 155(1), 1-12.
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  PMID: 18035460;Abstract: This paper reviews the potential of microorganisms to transform polychlorinated biphenyls (PCBs). In anaerobic environments, higher chlorinated biphenyls can undergo reductive dehalogenation. Meta- and para-chlorines in PCB congeners are more susceptible to dechlorination than ortho-chlorines. Anaerobes catalyzing PCB dechlorination have not been isolated in pure culture but there is strong evidence from enrichment cultures that some Dehalococcoides spp. and other microorganisms within the Chloroflexi phylum can grow by linking the oxidation of H2 to the reductive dechlorination of PCBs. Lower chlorinated biphenyls can be co-metabolized aerobically. Some aerobes can also grow by utilizing PCB congeners containing only one or two chlorines as sole carbon/energy source. An example is the growth of Burkholderia cepacia by transformation of 4-chlorobiphenyl to chlorobenzoates. The latter compounds are susceptible to aerobic mineralization. Higher chlorinated biphenyls therefore are potentially fully biodegradable in a sequence of reductive dechlorination followed by aerobic mineralization of the lower chlorinated products. © 2007 Elsevier Ltd. All rights reserved.
• Field, J. A., & Sierra-Alvarez, R. (2008). Microbial transformation of chlorinated benzoates. Reviews in Environmental Science and Biotechnology, 7(3), 191-210.
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  Abstract: Chlorinated benzoates enter the environment through their use as herbicides or as metabolites of other halogenated compounds. Ample evidence is available indicating biodegradation of chlorinated benzoates to CO2 and chloride in the environment under aerobic as well as anaerobic conditions. Under aerobic conditions, lower chlorinated benzoates can serve as sole electron and carbon sources supporting growth of a large list of taxonomically diverse bacterial strains. These bacteria utilize a variety of pathways ranging from those involving an initial degradative attack by dioxygenases to those initiated by hydrolytic dehalogenases. In addition to monochlorinated benzoates, several bacterial strains have been isolated that can grow on dichloro-, and trichloro- isomers of chlorobenzoates. Some aerobic bacteria are capable of cometabolizing chlorinated benzoates with simple primary substrates such as benzoate. Under anaerobic conditions, chlorinated benzoates are subject to reductive dechlorination when suitable electron-donating substrates are available. Several halorespiring bacteria are known which can use chlorobenzoates as electron acceptors to support growth. For example, Desulfomonile tiedjei catalyzes the reductive dechlorination of 3-chlorobenzoate to benzoate. The benzoate skeleton is mineralized by other microorganisms in the anaerobic environment. Various dichloro- and trichlorobenzoates are also known to be dechlorinated in anaerobic sediments. © 2008 Springer Science+Business Media B.V.
• Freeman, S. A., Sierra-Alvarez, R., Altinbas, M., Hollingsworth, J., J., A., & Smidt, H. (2008). Molecular characterization of mesophilic and thermophilic sulfate reducing microbial communities in expanded granular sludge bed (EGSB) reactors. Biodegradation, 19(2), 161-177.
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  PMID: 17479349;Abstract: The microbial communities established in mesophilic and thermophilic expanded granular sludge bed reactors operated with sulfate as the electron acceptor were analyzed using 16S rRNA targeted molecular methods, including denaturing gradient gel electrophoresis, cloning, and phylogenetic analysis. Bacterial and archaeal communities were examined over 450 days of operation treating ethanol (thermophilic reactor) or ethanol and later a simulated semiconductor manufacturing wastewater containing citrate, isopropanol, and polyethylene glycol 300 (mesophilic reactor), with and without the addition of copper(II). Analysis, of PCR-amplified 16S rRNA gene fragments using denaturing gradient gel electrophoresis revealed a defined shift in microbial diversity in both reactors following a change in substrate composition (mesophilic reactor) and in temperature of operation from 30°C to 55°C (thermophilic reactor). The addition of copper(II) to the influent of both reactors did not noticeably affect the composition of the bacterial or archaeal communities, which is in agreement with the very low soluble copper concentrations (3-310 μg l-1) present in the reactor contents as a consequence of extensive precipitation of copper with biogenic sulfides. Furthermore, clone library analysis confirmed the phylogenetic diversity of sulfate-reducing consortia in mesophilic and thermophilic sulfidogenic reactors operated with simple substrates. © 2007 Springer Science+Business Media B.V.
• Ochoa-Herrera, V., & Sierra-Alvarez, R. (2008). Removal of perfluorinated surfactants by sorption onto granular activated carbon, zeolite and sludge. Chemosphere, 72(10), 1588-1593.
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  PMID: 18511099;Abstract: Perfluorinated surfactants are emerging pollutants of increasing public health and environmental concern due to recent reports of their world-wide distribution, environmental persistence and bioaccumulation potential. Treatment methods for the removal of anionic perfluorochemical (PFC) surfactants from industrial effluents are needed to minimize the environmental release of these pollutants. Removal of PFC surfactants from aqueous solutions by sorption onto various types of granular activated carbon was investigated. Three anionic PFC surfactants, i.e., perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS), were evaluated for the ability to adsorb onto activated carbon. Additionally, the sorptive capacity of zeolites and sludge for PFOS was compared to that of granular activated carbon. Adsorption isotherms were determined at constant ionic strength in a pH 7.2 phosphate buffer at 30 °C. Sorption of PFOS onto activated carbon was stronger than PFOA and PFBS, suggesting that the length of the fluorocarbon chain and the nature of the functional group influenced sorption of the anionic surfactants. Among all adsorbents evaluated in this study, activated carbon (Freundlich KF values = 36.7-60.9) showed the highest affinity for PFOS at low aqueous equilibrium concentrations, followed by the hydrophobic, high-silica zeolite NaY (Si/Al 80, KF = 31.8), and anaerobic sludge (KF = 0.95-1.85). Activated carbon also displayed a superior sorptive capacity at high soluble concentrations of the surfactant (up to 80 mg l-1). These findings indicate that activated carbon adsorption is a promising treatment technique for the removal of PFOS from dilute aqueous streams. © 2008 Elsevier Ltd. All rights reserved.
• Ochoa-Herrera, V., Sierra-Alvarez, R., Somogyi, A., Jacobsen, N. E., Wysocki, V. H., & Field, J. A. (2008). Reductive defluorination of perfluorooctane sulfonate. Environmental Science and Technology, 42(9), 3260-3264.
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  PMID: 18522103;Abstract: Perfluorooctane sulfonate (PFOS) is under increased scrutiny as an environmental pollutant due to recent reports of its worldwide distribution, environmental persistence, and bioaccumulation potential. The susceptibility of technical PFOS and PFOS branched isomers to chemical reductive dehalogenation with vitamin B 12 (260 μ.M) as catalyst and Ti(lll)-citrate (36 mM) as bulk reductant in anoxic aqueous solution at 70 °C and pH 9 was evaluated in this study. Defluorination was confirmed by fluoride release measurements of 18% in technical PFOS, equivalent to the removal 3 mol F -/mol PFOS, and 71% in PFOS branched isomers equivalent to the removal of 12 mol F -/mol PFOS. Degradation of PFOS was further confirmed by monitoring the disappearance of PFOS compounds with reaction time by suppressed conductivity ion chromatography, LC-MS/MS, and 19F NMR studies. The PFOS compounds differed in their susceptibility to reductive degradation by vitamin B 12/Ti(lll) citrate. Chromatographic peaks corresponding to branched PFOS isomers disappeared whereas the peak corresponding to linear PFOS was stable. To our knowledge this is the first report of reductive dehalogenation of PFOS catalyzed by a biomolecule. © 2008 American Chemical Society.
• Sierra Alvarez, M., Field, J. A., & Sierra Alvarez, M. R. (2008). Microbial degradation of chlorinated benzenes. Biodegradation, 19(4).
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  Chlorinated benzenes are important industrial intermediates and solvents. Their widespread use has resulted in broad distribution of these compounds in the environment. Chlorobenzenes (CBs) are subject to both aerobic and anaerobic metabolism. Under aerobic conditions, CBs with four or less chlorine groups are susceptible to oxidation by aerobic bacteria, including bacteria (Burkholderia, Pseudomonas, etc.) that grow on such compounds as the sole source of carbon and energy. Sound evidence for the mineralization of CBs has been provided based on stoichiometric release of chloride or mineralization of (14)C-labeled CBs to (14)CO(2). The degradative attack of CBs by these strains is initiated with dioxygenases eventually yielding chlorocatechols as intermediates in a pathway leading to CO(2) and chloride. Higher CBs are readily reductively dehalogenated to lower chlorinated benzenes in anaerobic environments. Halorespiring bacteria from the genus Dehalococcoides are implicated in this conversion. Lower chlorinated benzenes are less readily converted, and mono-chlorinated benzene is recalcitrant to biotransformation under anaerobic conditions.
• Sierra Alvarez, M., Field, J. A., & Sierra Alvarez, M. R. (2008). Microbial degradation of chlorinated dioxins. Chemosphere, 71(6).
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  Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were introduced into the biosphere on a large scale as by-products from the manufacture of chlorinated phenols and the incineration of wastes. Due to their high toxicity they have been the subject of great public and scientific scrutiny. The evidence in the literature suggests that PCDD/F compounds are subject to biodegradation in the environment as part of the natural chlorine cycle. Lower chlorinated dioxins can be degraded by aerobic bacteria from the genera of Sphingomonas, Pseudomonas and Burkholderia. Most studies have evaluated the cometabolism of monochlorinated dioxins with unsubstituted dioxin as the primary substrate. The degradation is usually initiated by unique angular dioxygenases that attack the ring adjacent to the ether oxygen. Chlorinated dioxins can also be attacked cometabolically under aerobic conditions by white-rot fungi that utilize extracellular lignin degrading peroxidases. Recently, bacteria that can grow on monochlorinated dibenzo-p-dioxins as a sole source of carbon and energy have also been characterized (Pseudomonas veronii). Higher chlorinated dioxins are known to be reductively dechlorinated in anaerobic sediments. Similar to PCB and chlorinated benzenes, halorespiring bacteria from the genus Dehalococcoides are implicated in the dechlorination reactions. Anaerobic sediments have been shown to convert tetrachloro- to octachlorodibenzo-p-dioxins to lower chlorinated dioxins including monochlorinated congeners. Taken as a whole, these findings indicate that biodegradation is likely to contribute to the natural attenuation processes affecting PCDD/F compounds.
• Sierra Alvarez, M., Field, J. A., & Sierra Alvarez, M. R. (2008). Microbial transformation and degradation of polychlorinated biphenyls. Environmental pollution (Barking, Essex : 1987), 155(1).
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  This paper reviews the potential of microorganisms to transform polychlorinated biphenyls (PCBs). In anaerobic environments, higher chlorinated biphenyls can undergo reductive dehalogenation. Meta- and para-chlorines in PCB congeners are more susceptible to dechlorination than ortho-chlorines. Anaerobes catalyzing PCB dechlorination have not been isolated in pure culture but there is strong evidence from enrichment cultures that some Dehalococcoides spp. and other microorganisms within the Chloroflexi phylum can grow by linking the oxidation of H(2) to the reductive dechlorination of PCBs. Lower chlorinated biphenyls can be co-metabolized aerobically. Some aerobes can also grow by utilizing PCB congeners containing only one or two chlorines as sole carbon/energy source. An example is the growth of Burkholderia cepacia by transformation of 4-chlorobiphenyl to chlorobenzoates. The latter compounds are susceptible to aerobic mineralization. Higher chlorinated biphenyls therefore are potentially fully biodegradable in a sequence of reductive dechlorination followed by aerobic mineralization of the lower chlorinated products.
• Sierra Alvarez, M., Ochoa-Herrera, V., & Sierra Alvarez, M. R. (2008). Removal of perfluorinated surfactants by sorption onto granular activated carbon, zeolite and sludge. Chemosphere, 72(10).
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  Perfluorinated surfactants are emerging pollutants of increasing public health and environmental concern due to recent reports of their world-wide distribution, environmental persistence and bioaccumulation potential. Treatment methods for the removal of anionic perfluorochemical (PFC) surfactants from industrial effluents are needed to minimize the environmental release of these pollutants. Removal of PFC surfactants from aqueous solutions by sorption onto various types of granular activated carbon was investigated. Three anionic PFC surfactants, i.e., perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS), were evaluated for the ability to adsorb onto activated carbon. Additionally, the sorptive capacity of zeolites and sludge for PFOS was compared to that of granular activated carbon. Adsorption isotherms were determined at constant ionic strength in a pH 7.2 phosphate buffer at 30 degrees C. Sorption of PFOS onto activated carbon was stronger than PFOA and PFBS, suggesting that the length of the fluorocarbon chain and the nature of the functional group influenced sorption of the anionic surfactants. Among all adsorbents evaluated in this study, activated carbon (Freundlich K(F) values=36.7-60.9) showed the highest affinity for PFOS at low aqueous equilibrium concentrations, followed by the hydrophobic, high-silica zeolite NaY (Si/Al 80, K(F)=31.8), and anaerobic sludge (K(F)=0.95-1.85). Activated carbon also displayed a superior sorptive capacity at high soluble concentrations of the surfactant (up to 80 mg l(-1)). These findings indicate that activated carbon adsorption is a promising treatment technique for the removal of PFOS from dilute aqueous streams.
• Sun, W., Sierra, R., & Field, J. A. (2008). Anoxic oxidation of arsenite linked to denitrification in sludges and sediments. Water Research, 42(17), 4569-4577.
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  PMID: 18762312;PMCID: PMC2614353;Abstract: In this study, denitrification linked to the oxidation of arsenite (As(III)) to arsenate (As(V)) was shown to be a widespread microbial activity in anaerobic sludge and sediment samples that were not previously exposed to arsenic contamination. When incubated with 0.5 mM As(III) and 10 mM NO3-, the anoxic oxidation of As(III) commenced within a few days, achieving specific activities of up to 1.24 mmol As(V) formed g-1 volatile suspended solids d-1 due to growth (doubling times of 0.74-1.4 d). The anoxic oxidation of As(III) was partially to completely inhibited by 1.5 and 5 mM As(III), respectively. Inhibition was minimized by adding As(III) adsorbed onto activated aluminum (AA). The oxidation of As(III) was shown to be linked to the complete denitrification of NO3- to N2 by demonstrating a significantly enhanced production of N2 beyond the background endogenous production as a result of adding As(III)-AA to the cultures. The N2 production corresponded closely the expected stoichiometry of the reaction, 2.5 mol As(III) mol-1 N2-N. The oxidation of As(III) linked to the use of common-occurring nitrate as an electron acceptor may be an important missing link in the biogeochemical cycling of arsenic. © 2008 Elsevier Ltd. All rights reserved.
• Xiumin, J. u., Sierra-Alvarez, R., Field, J. A., Byrnes, D. J., Bentley, H., & Bentley, R. (2008). Microbial perchlorate reduction with elemental sulfur and other inorganic electron donors. Chemosphere, 71(1), 114-122.
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  PMID: 17988714;Abstract: ClO4- has recently been recognized as a widespread contaminant of surface and ground water. This research investigated chemolithotrophic perchlorate reduction by bacteria in soils and sludges utilizing inorganic electron-donating substrates such as hydrogen, elemental iron, and elemental sulfur. The bioassays were performed in anaerobic serum bottles with various inocula from anaerobic or aerobic environments. All the tested sludge inocula were capable of reducing perchlorate with H2 as electron donor. Aerobic activated sludge was evaluated further and it supported perchlorate reduction with Fe0 and S0 additions under anaerobic conditions. Heat-killed sludge did not convert ClO4-, confirming the reactions were biologically catalyzed. ClO4- (3 mM) was almost completely removed by the first sampling time on d 8 with H2 (≥0.37 mM d-1), after 22 d with S0 (0.18 mM d-1) and 84% removed after 37 d with Fe0 additions (0.085 mM d-1). Perchlorate-reduction occurred at a much faster rate (1.12 mM d-1), when using an enrichment culture developed from the activated sludge with S0 as an electron donor. The enrichment culture also utilized S2- and S2 O32 - as electron-donating substrates to support ClO4- reduction. The mixed cultures also catalyzed the disproportionation of S0 to S2- and SO42 -. Evidence is presented demonstrating that S0 was directly utilized by microorganisms to support perchlorate-reduction. In all the experiments, ClO4- was stoichiometrically converted to chloride. The study demonstrates that microorganisms present in wastewater sludges can readily use a variety of inorganic compounds to support perchlorate reduction. © 2007 Elsevier Ltd. All rights reserved.
• A., T., Claassen, F. W., Dorado, J., Godejohann, M., Sierra-Alvarez, R., & B., J. (2007). Fungal biotransformation products of dehydroabietic acid. Journal of Natural Products, 70(2), 154-159.
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  PMID: 17315956;Abstract: Dehydroabietic acid (DHA) (1) is one of the main compounds in Scots pine wood responsible for aquatic and microbial toxicity. The degradation of 1 by Trametes versicolor and Phlebiopsis gigantea in liquid stationary cultures was followed by HPLC-DAD-ELSD. Both fungi rapidly degraded DHA relative to a control. More breakdown products were observed for T. versicolor than for P. gigantea. After 13 days, four compounds were identified by means of spectroscopic methods in P. gigantea cultures: 1β-hydroxy-DHA (2), 1β,7α-dihydroxy-DHA (3), 1β,16-dihydroxy-DHA (5), and tentatively 1β-hydroxy-7-oxo-DHA (4). In T. versicolor cultures, 1β,16-dihydroxy-DHA (5), 7β,16-dihydroxy-DHA (6), 1β,7β,16- trihydroxy-DHA (7), 1β,16-dihydroxy-7-oxo-DHA (8), 1β,15-dihydroxy-DHA (9), and 1β,7α,16-trihydroxy-DHA (10) were identified after 9 days of incubation. Thus the biotransformation of 1 by the two fungi was different, with only 5 being produced by both strains. Compounds 3, 7, 8, and 10 are reported for the first time as natural products. © 2007 American Chemical Society and American Society of Pharmacognosy.
• A., T., Kuster, B., Claassen, F. W., Tienvieri, T., Bertaud, F., Lenon, G., Petit-Conil, M., & Sierra-Alvarez, R. (2007). Fungal bio-treatment of spruce wood with Trametes versicolor for pitch control: Influence on extractive contents, pulping process parameters, paper quality and effluent toxicity. Bioresource Technology, 98(2), 302-311.
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  PMID: 16517156;Abstract: Lipophilic low molar-mass constituents in wood chips for the paper industry result in low quality pulp, pitch deposition, and effluent toxicity. New biotechnological solutions such as fungal pre-treatment of wood chips can reduce pitch problems. This laboratory-scale study focuses on the potential and limitations of a fungal bio-treatment of Norway spruce chips with the white-rot fungus Trametes versicolor. Different fungal treatment conditions were compared. A 4-week fungal treatment reduced the concentration of resin acids and triglycerides by 40% and 100%, respectively, but neither lowered the energy requirements of the TMP process nor significantly affected the morphological fiber characteristics and the physical pulp properties. The pre-treatment led to slightly poorer optical properties. The Trametes versicolor fungal treatment contributed to a less toxic effluent and improved the biodegradability. A treatment of 2-3 weeks appears optimal. © 2006 Elsevier Ltd. All rights reserved.
• Shaw, J. R., Glaholt, S. P., Greenberg, N. S., Sierra-Alvarez, R., & Folt, C. L. (2007). Acute toxicity of arsenic to Daphnia pulex: Influence of organic functional groups and oxidation state. Environmental Toxicology and Chemistry, 26(7), 1532-1537.
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  PMID: 17665696;Abstract: Investigations were conducted to determine the influence of organic functional groups (i.e., methyl, phenyl) and valence state (i.e., III, V) on acute (48-h) arsenic toxicity in Daphnia pulex. These included toxicity texts with a suite of inorganic (arsenite, arsenate) and organic arsenicals (trivalent and pentavalent methylated arsenicals, roxarsone, p-arsanilic acid). Toxicity, based on median lethal concentrations (LC50 values), clustered the arsenicals into three groups and followed the order (most toxic to least toxic) of monomethylarsonous acid (MMAIII), 120 μg/L > inorganic arsenic, 2,500 to 3,900 μg/L > pentavalent methylated arsenicals and phenylarsonic compounds, 13,800 to 15,700 μg/L. Pentavalent organic arsenicals were less toxic than inorganic forms regardless of functional group. In contrast, the trivalent organic species (MMAIII) was the most toxic arsenical studied. These findings, which are the first to include an aquatic organism, add to the growing body of evidence that find that MMAIII is an extremely toxic intermediate of arsenic methylation and contradict theories of arsenic toxicity that regard methylation as a detoxication event. © 2007 SETAC.
• Sierra-Alvarez, R. (2007). Fungal bioleaching of metals in preservative-treated wood. Process Biochemistry, 42(5), 798-804.
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  Abstract: Twenty-four brown-rot and 10 white-rot fungi were screened to evaluate their applicability for detoxification of preservative-treated wood impregnated with copper and chromium (CC) salts. Brown-rot fungi generally showed higher tolerance towards copper inhibition than white-rot fungi. Additionally, brown-rot fungi were found to accumulate considerable quantities of oxalic acid (up to 44.3 mM) in liquid medium, while white-rot fungi generally accumulated only traces of this organic acid. Oxalic acid is a strong organic acid capable of complexing a variety of heavy metals. Four Antrodia vaillantii and two Poria placenta brown-rot strains that displayed both a high copper tolerance and a high oxalic acid production were selected for further study. The brown-rot fungi effectively decayed wood containing up to 4.4% CC causing corrected mass losses of up to 24.3% in 4 weeks. Fungal treatment was also found to promote extensive leaching of chromium (up to 52.4%), but only moderate leaching of copper (15.6% or less). These results indicate the potential of solid-state fermentation with copper-tolerant fungi for the remediation of preservative-treated wood. Improving the solubility of copper will be an important challenge for future research. © 2007 Elsevier Ltd. All rights reserved.
• Sierra-Alvarez, R., Beristain-Cardoso, R., Salazar, M., Gómez, J., Razo-Flores, E., & Field, J. A. (2007). Chemolithotrophic denitrification with elemental sulfur for groundwater treatment. Water Research, 41(6), 1253-1262.
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  PMID: 17296214;Abstract: Denitrification for the treatment of nitrates in wastewater typically relies on organic electron donating substrates. However, for groundwater treatment, inorganic compounds such as elemental sulfur (S0) are being considered as alternative electron donars in order to overcome concerns that residual organics can cause biofouling. In this study, a packed-bed bioreactor supplied with S0:limestone granules (1:1, v/v) was started up utilizing a chemolithotrophic denitrifying enrichment culture in the form of biofilm granules that was pre-cultivated on thiosulfate. The granular enrichment culture enabled a rapid start-up of the bioreactor. A nearly complete removal of nitrate (7.3 mM) was NO3-attained by the bioreactor at nitrate loading rates of up to 21.6 mmol/(Lreactor d). With lower influent concentrations (1.3 mM nitrate) comparable to those found in contaminated groundwater, high nitrate loads of 18.1 mmol/(Lreactor d) were achieved with an average nitrate removal efficiency of 95.9%. The recovery of nitrogen as benign N2 gas was nearly stoichiometric. The concentration of undesirable products from S0-based denitrification such as nitrite and sulfide were low. Comparison of bioreactor results with batch kinetic studies revealed that denitrification rates were dependent on the surface area of the added S0. The surface area normalized denitrification rate was determined to be 26.4 mmol /(m2 S0 d). © 2007 Elsevier Ltd. All rights reserved.
• Sierra-Alvarez, R., Hollingsworth, J., & Zhou, M. S. (2007). Removal of copper in an integrated sulfate reducing bioreactor- crystallization reactor system. Environmental Science and Technology, 41(4), 1426-1431.
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  PMID: 17593752;Abstract: Removal of copper was investigated using an innovative water treatment system integrating a sulfidogenic bioreactor with a fluidized-bed crystallization reactor containing fine sand to facilitate the recovery of copper as a purified copper-sulfide mineral. The performance of the system was tested using a simulated semiconductor manufacturing wastewater containing high levels of Cu2+ (4-66 mg/L), sulfate, and a mixture of citrate, isopropanol, and polyethylene glycol (Mn 300). Soluble copper removal efficiencies exceeding 99% and effluent copper concentrations averaging 89 μg/L were demonstrated in the two-stage system, with near complete metal removal occurring in the crystallizer. Copper crystals deposited on sand grains were identified as covellite (CuS). The removal of organic constituents did not exceed 70% of the initial chemical oxygen demand due to incomplete degradation of isopropanol and its breakdown product (acetone). Taken as a whole, these results indicate the potential of this novel reactor configuration for the simultaneous removal of heavy metals and organic constituents. The ability of this process to recover heavy metals in a purified form makes it particularly attractive for the treatment of contaminated aqueous streams, including industrial wastewaters and acid mine drainage. © 2007 American Chemical Society.
• Xiumin, J. u., Field, J. A., Sierra-Alvarez, R., Salazar, M., Bentley, H., & Bentley, R. (2007). Chemolithotrophic perchlorate reduction linked to the oxidation of elemental sulfur. Biotechnology and Bioengineering, 96(6), 1073-1082.
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  PMID: 17009322;Abstract: Perchlorate (ClO4-) contamination of ground and surface water has been recently recognized as a widespread environmental problem. Biological methods offer promising perspectives of perchlorate remediation. Facultative anaerobic bacteria couple the oxidation of organic and inorganic electron-donating substrates to the reduction of perchlorate as a terminal electron acceptor, converting it completely to the benign end-product, chloride. Insoluble inorganic substrates are of interest for low maintenance bioreactor or permeable reactive barrier systems because they can provide a long-term supply of electron donor without generating organic residuals. The main objective of this research was to investigate the feasibility of utilizing elemental sulfur (S0) as an insoluble electron donor for the biological reduction of perchlorate. A chemolithotrophic enrichment culture derived from aerobic activated sludge was obtained which effectively coupled the oxidation of elemental sulfur to sulfate with the reduction of perchlorate to chloride and gained energy from the process for cell growth. The enrichment culture grew at a rate of 0.41 or 0.81 1/d in the absence and presence of added organic carbon for cell growth, respectively. The enrichment culture was also shown to carry out sulfur disproportionation to a limited extent as evidenced by the formation of sulfide and sulfate in the absence of added electron acceptor. When nitrate and perchlorate were added together, the two electron acceptors were removed simultaneously after an initial partial decrease in the nitrate concentration. © 2006 Wiley Periodicals, Inc.
• Belmonte, M., Xavier, C., Decap, J., Martinez, M., Sierra-Alvarez, R., & Vidal, G. (2006). Improved aerobic biodegradation of abietic acid in ECF bleached kraft mill effluent due to biomass adaptation. Journal of Hazardous Materials, 135(1-3), 256-263.
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  PMID: 16386835;Abstract: Kraft pulp mill effluents contain elevated concentrations of resin acids, chiefly abietic and dehydroabietic acid, and other lipophilic wood constituents. Resin acids, if not efficiently removed during wastewater treatment, can be responsible for chronic toxicity in aquatic systems. The objective of this study was to investigate the biological removal of abietic acid (AbA) during the treatment of elemental chlorine free (ECF) kraft mill effluents in aerobic lagoons and to assess its improvement with time as a result of biomass adaptation. Under these conditions, the average removal efficiencies of AbA and BOD5 attained in the aerobic lagoon were high and exceeded 80% and 95%, respectively. Microbial inhibition of non-acclimated and acclimated biomass by AbA was not detected in batch bioassays. Kinetic studies showed that the Ks and Vm values equalled 76.7 mg AbA/l and 0.011 l/h, respectively, for the non-acclimated biomass, and 1678 mg AbA/l and 0.13 l/h, respectively, for the acclimated biomass. © 2005 Elsevier B.V. All rights reserved.
• Cardoso, R. B., Sierra-Alvarez, R., Rowlette, P., Flores, E. R., Gómez, J., & Field, J. A. (2006). Sulfide oxidation under chemolithoautotrophic denitrifying conditions. Biotechnology and Bioengineering, 95(6), 1148-1157.
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  PMID: 16807929;Abstract: Chemolithoautotrophic denitrifying microorganisms oxidize reduced inorganic sulfur compounds coupled to the reduction of nitrate as an electron acceptor. These denitrifiers can be applied to the removal of nitrogen and/or sulfur contamination from wastewater, groundwater, and gaseous streams. This study investigated the physiology and kinetics of chemolithotrophic denitrification by an enrichment culture utilizing hydrogen sulfide, elemental sulfur, orthiosulfate as electron donor. Complete oxidation of sulfide to sulfate was observed when nitrate was supplemented at concentrations equal or exceeding the stoichiometric requirement. In contrast, sulfide was only partially oxidized to elemental sulfur when nitrate concentrations were limiting. Sulfide was found to inhibit chemolithotrophic sulfoxidation, decreasing rates by approximately 21-fold when the sulfide concentration increased from 2.5 to 10.0 mM, respectively. Addition of low levels of acetate (0.5 mM) enhanced denitrification and sulfate formation, suggesting that acetate was utilized as a carbon source by chemolithotrophic denitrifiers. The results of this study indicate the potential of chemolithotrophic denitrification for the removal of hydrogen sulfide. The sulfide/nitrate ratio can be used to control the fate of sulfide oxidation to either elemental sulfur or sulfate. © 2006 Wiley Periodicals, Inc.
• Cortinas, I., Field, J. A., Kopplin, M., Garbarino, J. R., Gandolfi, A. J., & Sierra-Alvarez, R. (2006). Anaerobic biotransformation of roxarsone and related N-substituted phenylarsonic acids. Environmental Science and Technology, 40(9), 2951-2957.
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  PMID: 16719096;Abstract: Large quantities of arsenic are introduced into the environment through land application of poultry litter containing the organoarsenical feed additive roxarsone (3-nitro-4-hydroxyphenylarsonic acid). The objective of this study was to evaluate the bioconversion of roxarsone and related N-substituted phenylarsonic acid derivatives under anaerobic conditions. The results demonstrate that roxarsone is rapidly transformed in the absence of oxygen to the corresponding aromatic amine, 4-hydroxy-3-aminophenylarsonic acid (HAPA). The formation of HAPA is attributable to the facile reduction of the nitro group. Electron-donating substrates, such as hydrogen gas, glucose, and lactate, stimulated the rate of nitro group reduction, indicating a microbial role. During long-term incubations, HAPA and the closely related 4-aminophenylarsonic acid (4-APA) were slowly biologically eliminated by up to 99% under methanogenic and sulfate-reducing conditions, whereas little or no removal occurred in heat-killed inoculum controls. Arsenite and, to a lesser extent, arsenate were observed as products of the degradation. Freely soluble forms of the inorganic arsenical species accounted for 19-28% of the amino-substituted phenylarsonic acids removed. This constitutes the first report of a biologically catalyzed rupture of the phenylarsonic group under anaerobic conditions. © 2006 American Chemical Society.
• Fernández, N., Gómez, R., Amils, R., Sierra-Alvarez, R., Field, J. A., & Sanz, J. L. (2006). Microbiological and structural aspects of granular sludge from autotrophic denitrifying reactors. Water Science and Technology, 54(2), 11-17.
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  PMID: 16939078;Abstract: Denitrification is applied in the tertiary treatment of wastewater to reduce N-pollutants. Fluorescence in situ hybridisation (FISH), CARD (catalyzed reporter deposition)-FISH, cloning, and scanning electron microscopy (SEM) were applied to follow the evolution of the microbial composition and structure of granular sludge in autotrophic denitrifying bioreactors fed with nitrate and thiosulfate. With this goal, FISH oligonucleotide probes for the autotrophic denitrifiers, Thiobacillus denitrificans and Thiomicrospira denitrificans, were designed and their utility tested. CARD-FISH and cloning data showed that bacterial diversity changed with bioreactor operation time. After 110 days of operation, the abundance of Thiobacillus denitrificans cells increased considerably: from 1 to 35% of total DAPI-stained cells and from no isolated clones to 30% of the total positives clones. This fact strongly suggests that this microorganism played a dominant role in the autotrophic denitrification. The Archaeal diversity remained almost unchanged and it was mainly represented by Methanosaeta soehngenii. Scanning electron microscopy results indicated a considerable loss in the integrity of the sludge granules during the operation, with risk of sludge buoyancy. © IWA Publishing 2006.
• Karri, S., Sierra-Alvarez, R., & Field, J. A. (2006). Toxicity of copper to acetoclastic and hydrogenotrophic activities of methanogens and sulfate reducers in anaerobic sludge. Chemosphere, 62(1), 121-127.
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  PMID: 15936054;Abstract: Heavy metals could potentially negatively impact microorganisms in anaerobic sulfate reducing bioreactors. The objective of this is study was to evaluate the inhibitory effect of copper to acetoclastic and hydrogenotrophic activities of methanogens and sulfate reducers in sludge obtained from a full-scale sulfate reducing bioreactor. The 50% inhibiting concentration (50%IC) of Cu2+ to acetoclastic and hydrogenotrophic methanogens was 20.7 and 8.9 mg l-1, respectively. The 50%IC of Cu2+ to acetoclastic sulfate reduction was 32.3 mg l-1. The hydrogenotrophic sulfate reducers were only inhibited by 27% at the highest concentration of Cu2+ tested, 200 mg l-1, indicating a high level of tolerance. The soluble Cu2+ was observed to decrease rapidly in both the methanogenic and sulfate reducing assays. The highest level of decrease was observed in the hydrogenotrophic sulfate reducing assay which was over 99% in 5 h. The results of this study indicate that sulfate reducing biotechnologies would be robust at relatively high inlet concentrations of Cu2+. © 2005 Elsevier Ltd. All rights reserved.
• Sierra Alvarez, M., Cortinas, I., Field, J. A., Kopplin, M., Garbarino, J. R., Gandolfi, A. J., & Sierra Alvarez, M. R. (2006). Anaerobic biotransformation of roxarsone and related N-substituted phenylarsonic acids. Environmental science & technology, 40(9).
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  Large quantities of arsenic are introduced into the environment through land application of poultry litter containing the organoarsenical feed additive roxarsone (3-nitro-4-hydroxyphenylarsonic acid). The objective of this study was to evaluate the bioconversion of roxarsone and related N-substituted phenylarsonic acid derivatives under anaerobic conditions. The results demonstrate that roxarsone is rapidly transformed in the absence of oxygen to the corresponding aromatic amine, 4-hydroxy-3-aminophenylarsonic acid (HAPA). The formation of HAPA is attributable to the facile reduction of the nitro group. Electron-donating substrates, such as hydrogen gas, glucose, and lactate, stimulated the rate of nitro group reduction, indicating a microbial role. During long-term incubations, HAPA and the closely related 4-aminophenylarsonic acid (4-APA) were slowly biologically eliminated by up to 99% under methanogenic and sulfate-reducing conditions, whereas little or no removal occurred in heat-killed inoculum controls. Arsenite and, to a lesser extent, arsenate were observed as products of the degradation. Freely soluble forms of the inorganic arsenical species accounted for 19-28% of the amino-substituted phenylarsonic acids removed. This constitutes the first report of a biologically catalyzed rupture of the phenylarsonic group under anaerobic conditions.
• Sierra-Alvarez, R., Karri, S., Freeman, S., & Field, J. A. (2006). Biological treatment of heavy metals in acid mine drainage using sulfate reducing bioreactors. Water Science and Technology, 54(2), 179-185.
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  PMID: 16939100;Abstract: The uncontrolled release of acid mine drainage (AMD) from abandoned mines and tailing piles threatens water resources in many sites worldwide. AMD introduces elevated concentrations of sulfate ions and dissolved heavy metals as well as high acidity levels to groundwater and receiving surface water. Anaerobic biological processes relying on the activity of sulfate reducing bacteria are being considered for the treatment of AMD and other heavy metal containing effluents. Biogenic sulfides form insoluble complexes with heavy metals resulting in their precipitation. The objective of this study was to investigate the remediation of AMD in sulfate reducing bioreactors inoculated with anaerobic granular sludge and fed with an influent containing ethanol. Biological treatment of an acidic (pH 4.0) synthetic AMD containing high concentrations of heavy metals (100 mg Cu2+l-1; 10 mg Ni2+l-1, 10 mg Zn2+l-1) increased the effluent pH level to 7.0-7.2 and resulted in metal removal efficiencies exceeding 99.2%. The highest metal precipitation rates attained for Cu, Ni and Zn averaged 92.5, 14.6 and 15.8 mg metal l-1 of reactor d-1. The results of this work demonstrate that an ethanol-fed sulfidogenic reactor was highly effective to remove heavy metal contamination and neutralized the acidity of the synthetic wastewater. © IWA Publishing 2006.
• Sierra-Alvarez, R., Yenal, U., Feld, J. A., Kopplin, M., Gandolfi, A. J., & Garbarino, J. R. (2006). Anaerobic biotransformation of organoarsenical pesticides monomethylarsonic acid and dimethylarsinic acid. Journal of Agricultural and Food Chemistry, 54(11), 3959-3966.
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  PMID: 16719521;Abstract: Monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV) are extensively utilized as pesticides, introducing large quantities of arsenic into the environment. Once released into the environment, these organoarsenicals are subject to microbial reactions. Aerobic biodegradation of MMAV and DMAV has been evaluated, but little is known about their fate in anaerobic environments. The objective of this study was to evaluate the biotransformation of MMAV and DMAV in anaerobic sludge. Biologically mediated conversion occurred under methanogenic or sulfate-reducing conditions but not in the presence of nitrate. Monomethylarsonous acid (MMAIII) was consistently observed as an important metabolite of MMAV degradation, and it was recovered in molar yields ranging from 5 to 47%. The main biotransformation product identified from DMAV metabolism was MMAV, which was recovered in molar yields ranging from 8 to 65%. The metabolites indicate that reduction and demethylation are important steps in the anaerobic bioconversion of MMAV and DMAV, respectively. © 2006 American Chemical Society.
• Hollingsworth, J. R., Sierra Alvarez, R., Zhou, M., Ogden, K. L., & Field, J. A. (2005). Anaerobic biodegradability and methanogenic toxicity of key constituents in copper chemical mechanical planarization effluents of the semiconductor industry. Chemosphere, 59, 1219-1228.
• Hollingsworth, J., Sierra-Alvarez, R., Zhou, M., Ogden, K. L., & Field, J. A. (2005). Anaerobic biodegradability and methanogenic toxicity of key constituents in copper chemical mechanical planarization effluents of the semiconductor industry. Chemosphere, 59(9), 1219-1228.
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  PMID: 15857633;Abstract: Copper chemical mechanical planarization (CMP) effluents can account for 30-40% of the water discharge in semiconductor manufacturing. CMP effluents contain high concentrations of soluble copper and a complex mixture of organic constituents. The aim of this study is to perform a preliminary assessment of the treatability of CMP effluents in anaerobic sulfidogenic bioreactors inoculated with anaerobic granular sludge by testing individual compounds expected in the CMP effluents. Of all the compounds tested (copper (II), benzotriazoles, polyethylene glycol (Mn 300), polyethylene glycol (Mn 860) monooleate, perfluoro-1-octane sulfonate, citric acid, oxalic acid and isopropanol) only copper was found to be inhibitory to methanogenic activity at the concentrations tested. Most of the organic compounds tested were biodegradable with the exception of perfluoro-1-octane sulfonate and benzotriazoles under sulfate reducing conditions and with the exception of the same compounds as well as Triton X-100 under methanogenic conditions. The susceptibility of key components in CMP effluents to anaerobic biodegradation combined with their low microbial inhibition suggest that CMP effluents should be amenable to biological treatment in sulfate reducing bioreactors. © 2004 Elsevier Ltd. All rights reserved.
• Karri, S., Sierra-Alvarez, R., & Field, J. A. (2005). Zero valent iron as an electron-donor for methanogenesis and sulfate reduction in anaerobic sludge. Biotechnology and Bioengineering, 92(7), 810-819.
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  PMID: 16136594;Abstract: Zero valent iron (ZVI) is a reactive media commonly utilized in permeable reactive barriers (PRBs). Sulfate reducing bacteria are being considered for the immobilization of heavy metals in PRBs. The purpose of this study was to evaluate the potential of ZVI as an electron donor for sulfate reduction in natural mixed anaerobic cultures. The ability of methanogens to utilize ZVI as an electron-donor was also explored since these microorganisms often compete with sulfate reducers for common substrates. Four grades of ZVI of different particle sizes (1.120, 0.149, 0.044, and 0.010 mm diameter) were compared as electron donor in batch bioassays inoculated with anaerobic bioreactor sludge. Methanogenesis was evaluated in mineral media lacking sulfate. Sulfate reduction was evaluated in mineral media containing sulfate and the specific methanogenic inhibitor, 2-bromoethane sulfonate. ZVI contributed to significant increases in methane production and sulfate reduction-compared to endogenous substrate controls. The rates of methane formation or sulfate reduction were positively correlated with the surface area of ZVI. The highest rates of 0.310 mmol CH 4 formed/mol Fe0·day and 0.804 mmol SO 42 reduced/ mol Fe0·day were obtained with the finest grade of ZVI (0.01 mm). The results demonstrate that ZVI is readily utilized as a slow-release electron donor for methanogenesis and sulfate reduction in anaerobic sludge; and therefore, has a promising potential in bioremediation applications. © 2005 Wiley Periodicals, Inc.
• Sierra-Alvarez, R., Field, J. A., Cortinas, I., Feijoo, G., Moreira, M. T., Kopplin, M., & Gandolfi, A. J. (2005). Anaerobic microbial mobilization and biotransformation of arsenate adsorbed onto activated alumina. Water Research, 39(1), 199-209.
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  PMID: 15607178;Abstract: Due to the enactment of a stricter drinking water standard for arsenic in the United States, larger quantities of arsenic will be treated resulting in larger volumes of treatment residuals. The current United States Environmental Protection Agency recommendation is to dispose spent adsorbent residuals from arsenic treatment into non-hazardous municipal solid waste (MSW) landfills. The potential of microorganisms to alter the speciation affecting the mobility of arsenic in the disposal environment is therefore a concern. The purpose of this paper was to evaluate the potential of an anaerobic microbial consortium to biologically mobilize arsenate (As(V)) adsorbed onto activated alumina (AA), a common adsorbent used for treating arsenic in drinking water. Three anaerobic columns (0.27 l) packed with 100 g dry weight of AA containing 0.657 mg adsorbed As(V) (expressed as arsenic) per gram dry weight were continuously flushed with synthetic landfill leachate for 257 days. The fully biologically active column was inoculated with methanogenic anaerobic sludge (10 g volatile suspended solids l -1 column) and was operated with a mixture of volatile fatty acids (VFA) in the feed (2.5 g chemical oxygen demand l -1 feed). At the end of the experiment, 37% of the arsenic was removed from the column, of which 48% was accounted for by arsenical species identified in the column effluent. The most important form of arsenic eluted was arsenite (As(III)), accounting for nearly all of the identified arsenic in periods of high mobilization. Additionally, two methylated metabolites, methylarsonic acid and dimethylarsinic acid were observed. Mobilization of arsenic is attributed to the biological reduction of As(V) to As(III) since literature data indicates that As(III) is more weakly adsorbed to AA compared to As(V). Batch and continuous assays confirmed that VFA, present in landfill leachates, served as an electron donating substrate supporting enhanced rates of As(V) reduction to As(III). Two control columns, lacking inoculum and/or VFA in the feed displayed low mobilization of arsenic compared to the fully biologically active column. Therefore, leachates generated in MSW landfills could potentially result in the biologically catalyzed mobilization of arsenic from As(V)-laden drinking water residuals. © 2004 Elsevier Ltd. All rights reserved.
• Sierra-Alvarez, R., Guerrero, F., Rowlette, P., Freeman, S., & Field, J. A. (2005). Comparison of chemo-, hetero- and mixotrophic denitrification in laboratory-scale UASBs. Water Science and Technology, 52(1-2), 337-342.
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  PMID: 16180447;Abstract: This study investigated removal of sulfide and p-cresol linked to denitrification in laboratory-scale upflow anaerobic granular sludge bed (UASB) bioreactors. Three parallel denitrification bioreactors were run for nine months, which were operated under chemolithoautotrophic conditions (i.e., using sulfide as electron donor -e-donor- and bicarbonate as C source); heterotrophic conditions (with p-cresol as e-donor and C source), and mixotrophic conditions (utilizing both sulfide and p-cresol as electron donors), respectively. The average hydraulic retention time and nitrate load applied to the bioreactors was 13.4 h and 1,240 mg N-NO3/l/day, respectively. The nitrate removal efficiency was 89, 95 and 99%, respectively, for the chemo-, hetero- and mixotrophic reactors. The mixotrophic UASB removed both sulfide and p-cresol almost completely, indicating that simultaneous removal of the inorganic and organic e-donors occurred. Nitrite was seldom observed as an intermediate. N2O gas and methane concentrations in the biogas were also negligible. These results indicate that mixotrophic denitrification with phenols and sulfide is feasible in high rate UASB reactors. © IWA Publishing 2005.
• Field, J. A., & Sierra-Alvarez, R. (2004). Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds. Reviews in Environmental Science and Biotechnology, 3(3), 185-254.
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  Abstract: The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d -1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions. © Springer 2004.
• Field, J. A., Sierra-Alvarez, R., Cortinas, I., Feijoo, G., Moreira, M. T., Kopplin, M., & Gandolfi, A. J. (2004). Facile reduction of arsenate in methanogenic sludge. Biodegradation, 15(3), 185-196.
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  PMID: 15228076;Abstract: Due to the recent enactment of a stricter drinking water standard for arsenate, large quantities of arsenate-laden drinking water residuals will be disposed in municipal landfills. The objective of this study was to determine the role of methanogenic consortia on the conversion of arsenate. Methanogenic conditions commonly occur in mature municipal solid waste landfills. The results indicate the rapid and facile reduction of arsenate to arsenite in methanogenic sludge. Endogenous substrates in the sludge were sufficient to support the reductive biotransformation. However the rates of arsenate reduction were stimulated by the addition of exogenous electron donating substrates, such as H2, lactate or a mixture of volatile fatty acids. A selective methanogenic inhibitor stimulated arsenate reduction in microcosms supplied with H2, suggesting that methanogens competed with arsenate reducers for the electron donor. Rates of arsenate reduction increased with arsenate concentration up to 2 mM, higher concentrations were inhibitory. The electron shuttle, anthraquinone-2,6-disulfonate, used as a model of humic quinone moieties, was shown to significantly increase rates of arsenate reduction at substoichiometric concentrations. The presence of sulfur compounds, sulfate and sulfide, did not affect the rate of arsenate transformation but lowered the yield of soluble arsenite, due to the precipitation of arsenite with sulfides. The results taken as a whole suggest that arsenate disposed into anaerobic environments may readily be converted to arsenite increasing the mobility of arsenic. The extent of the increased mobility will depend on the concentration of sulfides generated from sulfate reduction.
• Machek, L., Edlund, M. -., Sierra-Alvarez, R., & Militz, H. (2004). A non-destructive approach for assessing decay in preservative treated wood. Wood Science and Technology, 37(5), 411-417.
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  Abstract: This study investigated the suitability of the non-destructive vibration-impulse excitation technique to assess the attack of preservative-treated wood in contact with the ground. Small stakes (10×5×100 mm3) of treated and untreated Scots pine sapwood were exposed to decay in laboratory-scale terrestrial ecosystems. Different soils were used to prove the influence of different types of wood destroying micro-organisms. Wood decay was monitored periodically for one year by determining mass losses and changes in dynamic modulus of elasticity. The results show a large variability in resistance against attacking fungi, depending on wood preservative and soil type. The non-destructive approach using the dynamic modulus of elasticity proved to be a good and sensitive tool for assessing the attack of stakes in laboratory soil testing.
• Sierra-Alvarez, R., Cortinas, I., Yenal, U., & Field, J. A. (2004). Methanogenic inhibition by arsenic compounds. Applied and Environmental Microbiology, 70(9), 5688-5691.
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  PMID: 15345461;PMCID: PMC520875;Abstract: The acute acetoclastic methanogenic inhibition of several inorganic and organic arsenicals was assayed. Trivalent species, i.e., methylarsonous acid and arsenite, were highly inhibitory, with 50% inhibitory concentrations of 9.1 and 15.0 μM, respectively, whereas pentavalent species were generally nontoxic. The nitrophenylarsonate derivate, roxarsone, displayed moderate toxicity.
• Acker, J. V., Stevens, M., Carey, J., Sierra-Alvarez, R., Militz, H., Bayon, I. L., Kleist, G., & Peek, R. (2003). Biological durability of wood in relation to end-use. Holz als Roh - und Werkstoff, 61(1), 35-45.
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  Abstract: The determination of biological durability of wood is an issue requiring sufficient reliability regarding end-use related prediction of performance. Five test institutes joined efforts to check standard test methods and to improve methodology and data interpretation for assessment of natural durability of timber species. A range of softwood and hardwood species was tested using both basidiomycete and soil soft rot testing. Based on combined processing of all data collected, an improved and simplified durability classification system was established. The test methods and the interpretation of results are proposed to be used to assess suitability and service life for applications under European hazard class 3 and 4. The methodology for basidiomycete testing only requires two test fungi and allows direct classification based on median mass loss, while for soil bed testing, which is only required when hazard class 4 applications are envisaged, a slightly more complicated approach proved to be necessary mainly due to variation in test soil parameters. Since service life can be based on natural durability classes, it is evident that these are identified differently for uses in or out of ground contact and for softwoods or hardwoods.
• Dorado, J., Almendros, G., Field, J. A., & Sierra-Alvarez, R. (2001). Infrared spectroscopy analysis of hemp (Cannabis sativa) after selective delignification by Bjerkandera sp. at different nitrogen levels. Enzyme and Microbial Technology, 28(6), 550-559.
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  Abstract: Fourier-transform infrared (FT-IR) spectroscopy has been used to monitor changes in C/N-modified lignocellulosic substrates from Cannabis sativa L. in a 7-week solid-state fermentation with the white-rot fungus Bjerkandera sp. strain BOS55. The microbial transformation of hemp was considered as a pretreatment to pulping processes in paper industries. Special emphasis was paid on the N-content of the substrate, which was modified by: (i) external ammonium inputs, (ii) water extraction, and (iii) protease treatment. Selective delignification in the N-limited media was observed. The most diagnostic FT-IR spectral bands in relation to changes in the lignocellulosic substrate were those corresponding to alkyl structures (2920, 1460 cm-1), carboxyl groups (1720 cm-1), amides (1650, 1540 cm-1) and carbohydrate (mainly 1030 cm-1). Simple and multiple regression functions revealed the potential of FT-IR in accurately reflecting substrate composition features previously determined by wet chemical methods. Correspondence analysis suggests C/N-dependent degradation patterns, and discriminant analysis confirmed that the differences between N-limited, N-enriched and the original substrate were significant (P < 0.05) in terms of the intensities of five FT-IR diagnostic bands (1030, 1130, 1270, 1540 and 1650 cm-1). The results suggest that, in the system studied, the FT-IR spectroscopy is a reliable alternative to wet chemical analyses in the routine monitoring of the success of the biologic process since it reflects both qualitative and quantitative changes and it is very sensitive to lignin alteration and to carbohydrate and protein concentration. © 2001 Elsevier Science Inc.
• Dorado, J., Beek, T. V., Claassen, F. W., & Sierra-Alvarez, R. (2001). Degradation of lipophilic wood extractive constituents in Pinus sylvestris by the white-rot fungi Bjerkandera sp. and Trametes versicolor. Wood Science and Technology, 35(1-2), 117-125.
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  Abstract: The white-rot fungi Trametes versicolor and Bjerkandera spp. are among the most frequent decomposers of angiosperm wood in forest ecosystems and in wood products in service. Wood extractives have a major impact on wood properties and wood utilization. This work evaluated the ability of two white-rot fungal strains (Bjerkandera sp. strain BOS55 and T. versicolor strain LaVec94-6) to degrade the main lipophilic extractive constituents in Scots pine (Pinus sylvestris L.). The time course of wood decay and wood extractive degradation was monitored in stationary batch assays incubated for eight weeks. The strains tested eliminated high levels of total resin, 34 to 51% in two weeks. Wood triglycerides were the most readily degraded extractive components (over 93% elimination in only two weeks). Free fatty acids and resin acids, which are potential fungal inhibitors, were also rapidly decomposed by the fungal strains. Sterols were used more slowly, nonetheless, the fungal degradation of this extractive fraction ranged from 50 to 88% after four weeks.
• Dorado, J., Field, J. A., Almendros, G., & Sierra-Alvarez, R. (2001). Nitrogen-removal with protease as a method to improve the selective delignification of hemp stemwood by the white-rot fungus Bjerkandera sp. strain BOS55. Applied Microbiology and Biotechnology, 57(1-2), 205-211.
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  PMID: 11693922;Abstract: Certain white-rot fungi cause selective removal of lignin from woody substrates. Selective delignification can potentially be applied to biopulping and upgrading animal feeds. Nitrogen nutrient limitation is known to enhance the selectivity of lignin degradation. The relatively high N-content of annual fiber crops is an important drawback for utilizing white-rot fungi for their selective delignification. In this study, removal of N from hemp stemwood with protease was explored as a means of improving the selectivity of lignin degradation by the white-rot fungus Bjerkandera sp. strain BOS55. Various protease treatments followed by hot-water extraction were found to be suitable in lowering the N-content of hemp stemwood by up to 70%. The removal was significantly higher than with hot-water extraction alone, which caused a 39% N-removal. The selectivity of lignin degradation was compared in protease-treated, hot-water treated, untreated and ammonium-spiked hemp stemwood, providing N levels that were, respectively, 0.32-, 0.61-, 1.0- and 5.0-fold relative to the natural N-content in the substrate. Removal of N by hot-water extraction alone or in combination with protease greatly protected the holocellulose fraction from excessive decay during 10 weeks of solid state fermentation. However, the selectivity of lignin decay was only greatly enhanced (three-fold) by the protease treatment, due mostly to a highly improved lignin degradation at the lowest N-level.
• Dorado, J., Sierra-Alvarez, R., Claassen, F. W., & A., T. (2001). Utilization of white-rot fungi for pitch control in pulp and paper manufacturing. Afinidad, 58(493), 175-180.
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  Abstract: This research investigated the ability of two different white-rot fungi, Bjerkandera sp. and Trametes versicolor, to reduce the lipid fraction (resin or extractives) in industrial chips of Scots pine (Pinus sylvestris) as well as in the pulps and effluents obtained upon mechanical pulping of the biotreated chips. Wood lipids are known to cause pitch problems in pulp and paper manufacturing that are characterized by the formation of troublesome deposits in manufacturing equipment, and spots and other quality defects in the paper sheet. Extractive components in wood chips and mechanical pulps were obtained by Sohxlet extraction with acetone, while the lipid fraction in pulping effluents was isolated by liquid-liquid extraction with tertbutylmethylether. The lipophilic extractives were then analyzed by HPLC. Fungal treatment of the wood chips during four weeks resulted in extensive degradation of the extractive components associated with the formation of pitch in softwoods, chiefly triglycerides and diglycerides. The total elimination of these compound classes by T. versicolor averaged 86% in chips, 100% in pulp and 84% in effluents; while their removal by Bjerkandera sp. was 83% in chips, 100% in pulp and 57% in the effluents. In addition, both strains cause substantial reduction in the level of fatty acids, that are among the pitch constituents contributing to effluent toxicity. In contrast with these results, and in spite of the high levels of resin acid degradation attained in previous studies conducted in our laboratory with pine wood meal, the reduction of these inhibitory extractives during the treatment of industrial wood chips by Bjerkandera sp. and T. versicolor was low.
• Machek, L., Militz, H., & Sierra-Alvarez, R. (2001). The use of an acoustic technique to assess wood decay in laboratory soil-bed tests. Wood Science and Technology, 34(6), 467-472.
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  Abstract: This study assesses the changes in elastic behaviour (i.e. modulus of elasticity - MOE) and mass loss of different hardwood and softwood species exposed to decay in laboratory soil-bed tests. Elasticity moduli were determined using conventional static methods as well as a dynamic method based on flexural vibration. The results obtained show a high correlation between dynamic and static bending measurements for all the timber species tested at different stages of fungal decay. Furthermore, the non-destructive MOE assessment proved to be a good tool for the early detection of wood decay.
• Moreira, M. T., Sierra-Alvarez, R., Lema, J. M., Feijoo, G., & Field, J. A. (2001). Oxidation of lignin in eucalyptus kraft pulp by manganese peroxidase from Bjerkandera sp. strain BOS55. Bioresource Technology, 78(1), 71-79.
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  PMID: 11265791;Abstract: The white rot fungus Bjerkandera sp. strain BOS55 was shown in previous studies to cause high levels of kraft pulp bleaching and delignification under culture conditions in which manganese peroxidase (MnP) occurs as the dominant oxidative enzyme. In this study, the MnP of Bjerkandera was isolated and tested in vitro with eucalyptus oxygen-delignified kraft pulp (ODKP) based on measuring the reduction in kappa number as an indicator of lignin oxidation. The MnP preparation applied at 60 U/g pulp for 6 h caused a significant decrease of 11-13% in the kappa number in the ODKP under optimal conditions compared to parallel-incubated controls lacking enzyme. The effects of MnP dosage, Mn2+ concentration, organic acid buffer selection, pH and H2O2 addition were evaluated. The optimal Mn2+ concentration range for lignin oxidation in ODKP was 100-500 μM. In the presence of low oxalate concentrations (0.3-2 mM), the Bjerkandera MnP also significantly reduced the kappa number of ODKP by 6% without any Mn. This observation is in agreement with the fact that purified Bjerkandera MnP has Mn-independent activities. Under incubation conditions with added Mn2+, buffers composed of metal-complexing organic acids provided two-fold better kappa number reductions compared to the inert acetic acid. The optimal H2O2 dosage was found to be 0.017 μmol/min ml when added as semi-continuous pulses (every 30 min) or 0.2 μmol/min ml when generated continuously by glucose oxidase. Excess H2O2 caused severe inactivation of MnP during the incubations. Factors that improved the turnover of the enzyme, such as Mn2+ and metal-chelating acids, stabilized MnP against rapid inactivation. Copyright © 2001 Elsevier Science Ltd.
• Claassen, F. W., Van, C., A., T., Dorado, J., Martínez-Iñigo, M., & Sierra-Alvarez, R. (2000). Rapid analysis of apolar low molecular weight constituents in wood using high pressure liquid chromatography with evaporative light scattering detection. Phytochemical Analysis, 11(4), 251-256.
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  Abstract: A new high pressure liquid chromatographic method with evaporative light scattering detection was developed for the qualitative and quantitative analysis of apolar, low molecular weight constituents in wood. The wood extractives were obtained by means of a 6 h Soxhlet extraction with acetone. The extract was quantitatively analysed on an end-capped C18 column eluted with a gradient of acetonitrile:water:acetic acid. The crude sample was directly injected following dissolution in acetonitrile:methanol:dichloromethane (60:8:40) and filtration through a 0.45 μm membrane filter. No other time consuming fractionation or derivatisation steps were required prior to the analysis. The main apolar, low molecular weight constituents of pinewood are free fatty acids, resin acids, sterols and triglycerides. With this method, individual free fatty acids, sterols and triglycerides are well separated. Resin acids, with the exception of dehydroabietic acid, are not separated and co-elute. The method does not require any sample clean-up steps except filtration and it is compatible with other softwood and hardwood wood species. Copyright (C) 2000 John Wiley and Sons, Ltd.
• Dorado, J., Claassen, F. W., A., T., Lenon, G., Wijnberg, J. B., & Sierra-Alvarez, R. (2000). Elimination and detoxification of softwood extractives by white-rot fungi. Journal of Biotechnology, 80(3), 231-240.
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  PMID: 10949313;Abstract: The ability of several white-rot fungal strains to remove and detoxify acetone extractives (pitch or resin) in Scots pine sapwood was investigated in stationary laboratory batch assays. Fungal pretreatment provided up to 62% total pitch reduction and significant decreases in pitch toxicity. The best strains were Bjerkandera sp. strain BOS55, Stereum hirsutum and Trametes versicolor that eliminated over 93% of the problematic triglyceride fraction and 58-87% of other lipophilic extractive classes in only 2 weeks. Fungal removal of the wood extractives was accompanied by a 7.4-16.9-fold decrease in their inhibitory effect, as determined in the Microtox bioassay. Wood pretreatment by Bjerkandera sp. and T. versicolor caused limited losses of woody mass (less than 4% in 4 weeks); whereas S. hirsutum led to somewhat higher mass losses (7% in 4 weeks). These results indicate the potential of white rot fungi to control pitch deposition problems in pulping and to reduce the aquatic toxicity caused by naturally-occurring lipophilic extractives in forest industry effluents. (C) 2000 Elsevier Science B.V.
• Dorado, J., Claassen, F. W., Lenon, G., A., T., Wijnberg, J. B., & Sierra-Alvarez, R. (2000). Degradation and detoxification of softwood extractives by sapstain fungi. Bioresource Technology, 71(1), 13-20.
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  Abstract: Wood extractives (resin) cause pitch deposition problems and effluent toxicity in pulp and papermaking. The ability of six sapstaining fungi to degrade and detoxify extractive constituents in Scots pine sapwood was examined, and the results were compared with those obtained with the commercial depitching fungus Cartapip (Ophiostoma piliferum). Pestalotiopsis crassiuscula and O. piliferum were the best strains and they provided high reductions of total resin (50-60% in 6 weeks). Both strains were highly effective in the degradation of individual extractive components including triglycerides, diglycerides and free fatty acids. Although all strains displayed moderate to high pitch degradation, their detoxifying capacity was limited. Two important exceptions were Ceratocystis deltoideospora and O. piliferum that caused a 11-14-fold decrease in toxicity (Microtox bioassay). These results indicate the potential of wood pretreatment with the selected sapstain fungi for minimizing pitch problems and decreasing effluent toxicity in pulping.
• Martínez-Iñigo, M., Claassen, F. W., Joseleau, B., Beek, T. V., Lenon, G., & Sierra-Alvarez, R. (2000). Evaluation of fungal capacity for detoxification of extractives in Scots pine sapwood. Environmental Technology, 21(5), 569-575.
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  Abstract: Ninety wood-inhabiting fungi were screened for their ability to degrade and detoxify acetone extractives in Scots pine (Pinus sylvestris L.) sapwood under solid-state fermentation conditions. Fungal degradation of resin acids and long-chain fatty acids was investigated by high pressure liquid chromatography with evaporative light scattering detection (HPLC-ELSD) and the toxicity of the acetone soluble fraction of wood measured by Microtox assay. Discriminant analysis of data showed different patterns of extractive detoxification for white-rot basidiomycetes and sapstain fungi. The major detoxification skills of basidiomycetes appeared to be related to the highest degradation of resin acids, and particularly dehydroabietic acid. Among them, Ischnoderma benzoinum, Stereum sanguinolentum and Trametes versicolor greatly reduced the sapwood toxicity due to acetone extractives from the EC50 value of 0.08 mg wood ml-1 to levels between 5-10 mg wood ml-1.
• Sierra-Alvarez, R., Claassen, F. W., Dorado, J., A., T., Lenon, G., & Wijnberg, H. B. (2000). Removal and transformation of toxic resin acids by wood-inhabiting fungi. TAPPI Pulping/Process and Product Quality Conference, 1241-1245.
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  Abstract: Resin acids, major components in the lipophilic extractives of many coniferous pulpwood species, are known to display high acute toxicity against aquatic organisms and bacteria in wastewater treatment systems. In the present study we examined the ability of several white-rot fungal strains to degrade different resin acids. Results obtained in solid-state fermentation studies with Scots pine wood as well as in liquid culture experiments with resin model compounds show the high effectiveness of fungal treatment to reduce the content and/or the acute inhibitory effect (Microtox assay) displayed by toxic pitch constituents. Several (novel) metabolites of the fungal transformation of dehydroabietic acid were isolated and identified. These included polar intermediates, mainly hydroxylated-, dihydroxylated and hydroxyl-oxodehydroabietic acids.
• Sierra-Alvarez, R., Dorado, J., & Field, J. A. (2000). Effect of nitrogen on biopulping of non-woody plant species. TAPPI Pulping/Process and Product Quality Conference, 1207-1210.
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  Abstract: This work considered the effect of the nitrogen content in non-woody fiber crops on the extent of decay and selectivity of lignin degradation by the white-rot fungus Bjerkandera sp. strain BOS55. Solid-state fermentation studies were conducted with three different lignocellulosic materials including, hemp (Cannabis sativa), miscanthus (Miscanthus sinensis) and wheat straw (Triticum aestivum) as well as with the hardwood birch (Betula sp.). Fungal decay studies were also performed with hemp stemwood containing different amounts of nitrogen, including N-reduced and N-amended treatments. The results show that the extent of fungal decay was positively correlated with the N-content in the various feedstocks. Protease pretreatment combined with hot-water extraction proved effective to reduce N-levels in hemp stemwood and led to a considerable increase of the lignin degradation selectivity.
• Martínez-Iñigo, M. J., Immerzeel, P., Gutierrez, A., Carlos, J., & Sierra-Alvarez, R. (1999). Biodegradability of extractives in sapwood and heartwood from Scots pine by sapstain and white rot fungi. Holzforschung, 53(3), 247-252.
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  Abstract: The fungal degradation of lipophilic extractives in sapwood and heartwood from Scots pine (Pinus sylvestris) was studied. In sapwood, the white rot fungi, Bjerkandera sp. and Funalia trogii, removed higher amounts of extractives than the sapstain strains, Ophiostoma ainoae and Ceratocystis allantospora. Triglycerides, long chain fatty acids, steryl esters and waxes in pine sapwood were almost completely degraded by all the fungi. Sterols and resin acids were also extensively degraded by the white rot strains; however, these components were not or only poorly removed by the sapstain fungi. The removal of total extractives by all the fungal strains was higher in sapwood as compared to heartwood. The highly concentrated extractive fraction in pine heartwood mainly consists of resin acids. As observed in sapwood, sapstain were also poorly effective in the degradation of the resin acids present in heartwood. The fungal degradation of heartwood extractives was not only limited by the degradative ability of the various test microorganisms, but also by the inhibitory effect exerted by the extractive fraction. The white rot fungus F. trogii was particularly inhibited on heartwood. Bjerkandera sp. showed a higher tolerance to toxic extractives and was the most efficient fungus in degrading extractive constituents in both Scots pine heartwood and sapwood. Therefore, Bjerkandera sp. strain BOS55 should be considered as a potential agent for pitch control in pulp and paper manufacture.
• Moreira, M. T., Feijoo, G., Sierra-Alvarez, R., & Field, J. A. (1999). Reevaluation of the manganese requirement for the biobleaching of kraft pulp by white rot fungi. Bioresource Technology, 70(3), 255-260.
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  Abstract: Manganese dependent peroxidase (MnP) is the main enzyme implicated in the biobleaching of kraft pulps by white rot fungi. The goal of this study was to evaluate the Mn requirement for biobleaching of eucalyptus oxygen delignified kraft pulp (OKP) by various white rot fungi: Trametes versicolor, Phanerochaete sordida, Phlebia radiata, Stereum hirsutum and Bjerkandera sp. strain BOS55. All of the strains tested produced MnP and provided extensive bleaching of OKP when 33 μM Mn was included in the medium. Bjerkandera sp. strain BOS55 was the only strain that also displayed MnP production and biobleaching activity of EDTA-extracted OKP in the complete absence of Mn. However, MnP and biobleaching activity in the absence of Mn was dependent on the presence of organic acids in the medium. The fact the biobleaching was correlated to MnP activity irrespective of whether Mn was present or absent suggests that there may be roles for MnP in Bjerkandera under Mn-deficient conditions. Although manganese-independent peroxidase (MIP) and lignin peroxidase (LiP) were also detected, the titres were much smaller in comparison with those of MnP, so their relative role in biobleaching can be predicted to have a minor importance in comparison with MnP. Only in the case of Bjerkandera, was the expression of LiP stimulated in the presence of oxalate but final brightness was not substantially affected.
• Claassen, F. W., van, C., A., T., Martinez-Inigo, M. J., Dorado, J., & Sierra-Alvarez, R. (1998). HPLC analysis of low molecular weight constituents in wood. Proceedings of the International Conference on Biotechnology in the Pulp and Paper Industry, 2, B45-B47.
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  Abstract: This study reports on the use of high pressure liquid chromatography with evaporative light scattering detection for the analysis of low molecular weight constituents in sterile and fungal treated pinewood. The analytical method used requires minimal sample preparation and enables the quantification of the main apolar constituents without derivatization in one run. The main constituents, i.e., individual free fatty acids, sterols and triglycerides are well separated. Resin acids, with the exception of dehydroabietic acid, are not separated and co-elute.
• Dorado, J., Martinez-Inigo, M. J., Claassen, F. W., A., T., Wijnberg, H. B., Lenon, G., & Sierra-Alvarez, R. (1998). Degradation and detoxification of pitch constituents in Scots pine by white-rot fungi. Proceedings of the International Conference on Biotechnology in the Pulp and Paper Industry, 2, B41-B44.
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  Abstract: The ability of various white-rot fungi to degrade and detoxify pitch in Scots pine sapwood was investigated in stationary batch assays. Fungal pretreatment provided up to 60% total pitch reduction and significant decreases in pitch toxicity. The best strains degraded over 96% of the problematic triglyceride fraction and between 71% to 87% of other identified resin compounds in only 2 weeks. These results indicate the potentials of white-rot fungi for wood depitching and biodetoxification.
• Feijoo, G., Mester, T., Field, J. A., Moreira, M., & Alvarez, R. S. (1998). Pulp biobleaching and MnP production by the white rot fungus Bjerkandera BOS55 in the absence of manganese. Proceedings of the International Conference on Biotechnology in the Pulp and Paper Industry, 1, A139-A141.
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  Abstract: Manganese and manganese peroxidase (MnP) are considered essential for kraft pulp biobleaching by white rot fungi. However, biobleaching of EDTA extracted eucalyptus oxygen delignified kraft pulp by the white rot fungus Bjerkandera sp. BOS55 does not require Mn. Fungal organic acid metabolites (e.g. oxalate and glycolate) added to the Mn-free culture medium were found to be stimulatory for brightness gains, delignification and MnP production.
• Martinez-Inigo, M., Joseleau, B., Claassen, F. W., Lenon, G., Beek, T. A., & Sierra-Alvarez, R. (1998). Detoxification of extractive constituents in pine wood by sapstain fungi. TAPPI Proceedings - Environmental Conference & Exhibit, 1, 177-181.
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  Abstract: The toxicity of forest industry effluents to aquatic ecosystems can largely be attributed to lipophilic wood extractives, particularly resin acids and long chain fatty acids. This research examined the ability of ten sapstain fungi to degrade toxic extractive constituents in Scots pine (Pinus sylvestris) pulpwood. After 6 weeks under solid-state fermentation conditions, wood meal samples were extracted with acetone to determine wood extractive losses. The acute toxicity of the acetone extracts was evaluated using the Microtox bioassay. The fungal strains differed greatly in their ability to degrade and detoxify pine wood extractives. The best strain, Ceratocystis conicola, was able to remove up to 55% of the wood extractives and caused a 29-fold decrease in toxicity. The rest of the strains seemed to have limited detoxifying capacity.
• Mester, T., Sierra-Alvarez, R., & Field, J. A. (1998). Peroxidase and Aryl Metabolite Production by the White Rot Fungus Bjerkandera sp. Strain BOS55 during Solid State Fermentation of Lignocellulosic Substrates. Holzforschung, 52(4), 351-358.
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  Abstract: Ligninolytic enzymes and secondary metabolite production by Bjerkandera sp. strain BOS 55 were monitored during solid state fermentation (SSF) on two lignocellulosic substrates, beech wood and hemp stem wood (HSW). After 6 weeks of SSF, the fungus was responsible for removing 27 and 39% of the Klason lignin as well as 43 and 70% of the apolar extractives on beech and HSW, respectively. The lignin degradation during beech wood decay was very selective. On both substrates, high activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) were detected. The peak activity of LiP was 660nmol ml-1 min.-1 on HSW and that of MnP was 1320nmol ml-1 min.-1 on beech wood. The presence of several LiP and MnP isoenzymes at different times during the SSF was demonstrated by FPLC profiles of these heme proteins. The production of the secondary aryl metabolites, veratryl alcohol and 3-chloro-p-anisaldehyde, reached peak concentrations of 820 and 90μM, respectively. The enhanced production of these secondary metabolites compared to defined liquid cultures is suggested to be due to the release of lignin degradation products serving as alternative precursors for their biosynthesis. The high production of veratryl alcohol, which is a cofactor known to protect LiP from inactivation by physiological levels of H2O2, may account for the high production of active LiP on the lignocellulosic substrates.
• Moreira, M. T., Feijoo, G., Mester, T., Mayorga, P., Sierra-Alvarez, R., & Field, J. A. (1998). Role of organic acids in the manganese-independent biobleaching system of bjerkandera sp. Strain BOS55. Applied and Environmental Microbiology, 64(7), 2409-2417.
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  Abstract: Bjerkandera sp. strain BOS55 is a white rot fungus that can bleach EDTA- extracted eucalyptus oxygen. delignified kraft pulp (OKP) without any requirement for manganese. Under manganese-free conditions, additions of simple physiological organic acids (e.g., glycolate, glyoxylate, oxalate, and others) at 1 to 5 mM stimulated brightness gains and pulp delignification two- to threefold compared to results for control cultures not receiving acids. The role of the organic acids in improving the manganese-independent biobleaching was shown not to be due to pH-buffering effects. Instead, the stimulation was attributed to enhanced production of manganese peroxidase (MnP) and lignin peroxidase (LIP) as well as increased physiological concentrations of veratryl alcohol and oxalate. These factors contributed to greatly improved production of superoxide anion radicals, which may have accounted for the more extensive biobleaching. Optimum biobleaching corresponded most to the production of MnP. These results suggest that MnP from Bjerkandera is purposefully produced in the absence of manganese and can possibly function independently of manganese in OKP delignification. LiP probably also contributed to OKP delignification when it was present.
• Moreira, M., Sierra-Alvarez, R., Feijoo, G., & Field, J. A. (1998). Evaluation of the manganese requirement for biobleaching by white rot fungi. Proceedings of the International Conference on Biotechnology in the Pulp and Paper Industry, 2, B229-B231.
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  Abstract: Mn-requirement for biobleaching by various white rot fungi, Trametes versicolor, Phanerochaete sordida, Phlebia radiata, Stereum hirsutum and Bjerkandera sp. strain BOS55, was analyzed. All the strains bleached kraft pulp with the Mn-containing medium. In Mn-deficient conditions, bleaching was only observed with Bjerkandera sp. strain BOS55, and this only occurred in the presence of organic acids.
• Feijoo, G., Moreira, M. T., Sierra-Alvarez, R., Field, J. A., & Lema, J. M. (1997). Kraft paste bleaching with ligninolitic fungi. Afinidad, 54(470), 321-326.
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  Abstract: There have been proposed the biotechnological processes as an alternative to the chemical bleaching sequences of Kraft cellulose paste (Kraft pulp), either for a reduction in the use of chemical compounds (prebleaching with hemicellulasas) or as a procedure able to carry out the bleaching in an ecological way (bleaching with ligninolitic fungi and their oxidative enzymes). The industrial application of the latter depends mostly on the deep knowledge of the bleaching mechanisms, where extracellular peroxidases and oxidases, produced by fungi and other environmetal factors are jointly implied, as for example, Mn2+ and organic acids concentration, oxygen pressure, etc. With the aim to analyze every factor about the biobleaching of Eucaliptus globulus Kraft paste, it was studied the effect of adding different organic acid concentrations (oxalic and glycolic acids) for different Mn+2 concentrations, the influence of the oxygenation through air or oxygen and the effect of fungus morphology, as free or immobilized mycelium, on the enzymatic activity and the final whiteness of the paste.
• Moreira, M. T., Feijoo, G., Sierra-Alvarez, R., Lema, J., & Field, J. A. (1997). Biobleaching of oxygen delignified kraft pulp by several white rot fungal strains. Journal of Biotechnology, 53(2-3), 237-251.
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  Abstract: Twenty-five white rot fungal strains were tested for their ability to bleach Eucalyptus globulus oxygen delignified kraft pulp (OKP). Under nitrogen-limited culture conditions, eight outstanding biobleaching strains were identified that increased the brightness of OKP by more than 10 ISO units compared to pulp incubated in sterile control medium. The highest brightness gain of approximately 13 ISO units was obtained with Bjerkandera sp. strain BOS55, providing a high final brightness of 82% ISO. This strain also caused the greatest level of delignification, decreasing the kappa number of OKP by 29%. When the white rot fungal strains were tested in nitrogen-sufficient medium, the extracellular activities of laccase and peroxidases increased in many strains; nonetheless, the pulp handsheets were either destroyed or brightness gains were lower than those obtained under nitrogen-limitation. The titer of ligninolytic enzymes was not found to be indicative of biobleaching potential. However, the best biobleaching strains were generally characterized by a predominance of manganese dependent peroxidase (MnP) activity compared to other ligninolytic enzymes and by a high decolorizing activity towards the polyanthraquinone ligninolytic indicator dye, Poly R-478.
• Moreira, M. T., Feijoo, G., Sierra-Alvarez, R., Lema, J., & Field, J. A. (1997). Manganese is not required for biobleaching of oxygen-delignified kraft pulp by the white rot fungus Bjerkandera sp. Strain BOS55. Applied and Environmental Microbiology, 63(5), 1749-1755.
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  PMID: 16535591;PMCID: PMC1389146;Abstract: The white rot fungus Bjerkandera sp. strain BOS55 extensively delignified and bleached oxygen-delignified eucalyptus kraft pulp handsheets. Biologically mediated brightness gains of up to 14 ISO (International Standards Organization units) were obtained, providing high final brightness values of up to 80% ISO. In nitrogen-limited cultures (2.2 mM N), manganese (Mn) greatly improved manganese-dependent peroxidase (MnP) production. However, the biobleaching was not affected by the Mn nutrient regimen, ranging from 1,000 μM added Mn to below the detection limit of 0.26 μM Mn in EDTA-extracted pulp medium. The lowest Mn concentration tested was at least several orders of magnitude lower than the K(m) known for MnP. Consequently, it was concluded that Mn is not required for biobleaching in Bjerkandera sp. strain BOS55. Nonetheless, fast protein liquid chromatography profiles indicated that MnP was the predominant oxidative enzyme produced even under culture conditions in the near absence of manganese. High nitrogen (22 mM N) and exogenous veratryl alcohol (2 mM) repressed biobleaching in Mn- deficient but not in Mn-sufficient culture medium. No correlation was observed between the titers of extracellular peroxidases and the biobleaching. However, the decolorization rate of the polyaromatic dye Poly R-478 was moderately correlated to the biobleaching under a wide range of Mn and N nutrient regimens.
• E., M., & Sierra-Alvarez, R. (1996). Brightness improvement of Douglas fir thermomechanical pulp by EDTA and ascorbic acid treatments on chips. Journal of Wood Chemistry and Technology, 16(2), 155-167.
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  Abstract: This investigation studies the use of Douglas fir wood as feedstock for thermomechanical pulp (TMP). Douglas fir wood extractives include flavonoids and other polyphenolic compounds, which make the pulp susceptible to discolouration. Pulp darkening is promoted by the formation of metal-chelates and phenolic oxidation products. The effectiveness of various wood pretreatment s to prevent the discoloration of polyphenolic extractives in Douglas fir wood was investigated in lab-scale experiments. Iron-mediated brightness losses (up to 5.1% ISO) could be prevented by wood pretreatment with 0.2% EDTA. Treatment of wood meal slurries at temperature levels comparable to those applied in thermomechanical pulping caused wood discoloration due to polyphenol oxidation. The brightness losses could be reduced by the addition of 0.5% ascorbic acid. The anti-oxidizing agent was more effective with sapwood compared to heartwood. EDTA pretreatment allowed an increase in the proportion of heartwood from 12% to 39% (w/w) that could be tolerated as feedstock for the production of dithionite bleached TMP with a brightness of 60% ISO. Wood chip impregnation with both EDTA and ascorbic acid only proved advantageous over EDTA alone in Douglas fir samples consisting almost exclusively of sapwood.
• Moreira, M. T., Feijoo, G., Lema, J., Field, J. A., & Sierra-Alvarez, R. (1996). Oxalic acid extraction as a posttreatment to increase the brightness of kraft pulps bleached by white-rot fungi. Biotechnology Techniques, 10(8), 559-564.
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  Abstract: Pulp brightness gains obtained by fungal biobleaching are often decreased by dark MnO2 deposits which are formed by the biologically- mediated oxidation of Mn(II). Oxalic acid extraction of O2-delignified kraft pulps bleached by several white-rot fungi was found to increase pulp brightness by up to 9.7 ISO points due to MnO2 dissolution. These results indicate that pulp extraction with oxalic acid can be used in order to accurately assess the net brightness gains achieved by fungal biobleaching.
• Sierra-Alvarez, R., Field, J. A., Kortekaas, S., & Lettinga, G. (1994). Overview of the anaerobic toxicity caused by organic forest industry wastewater pollutants. Water Science and Technology, 29(5-6), 353-363.
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  Abstract: Numerous types of organic environmental pollutants are encountered in forest industry effluents which potentially could inhibit consortia of anaerobic bacteria. The purpose of this study was to collect anaerobic bioassay data from the literature to better estimate the impact of these pollutants on anaerobic wastewater treatment systems. The most important methanogenic inhibitors in forest industry wastewaters are wood resin, chlorophenols and tannins. These compounds account for toxicity in alkaline pulping liquors, bleaching effluents and debarking wastewaters, respectively. Adaptation to chlorophenol toxicity can be expected since they are eventually degraded in anaerobic systems. Wood resin compounds, on the other hand, are not biodegraded anaerobically and therefore their toxicity is persistent. Toxicity in forest industry wastewaters does not necessarily preclude anaerobic treatment. A variety of techniques can be employed to diminish inhibition, such as dilution and detoxification treatments.
• Field, J., Leyendeckers, J. H., Sierra-Alvarez, R., Lettinga, G., & Habets, L. H. (1991). Continuous anaerobic treatment of autoxidized bark extracts in laboratory-scale columns. Biotechnology and Bioengineering, 37(3), 247-255.
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  PMID: 18597362;Abstract: Debarking wastewaters of the forest industry contain high concentrations of tannins that are inhibitory to methane bacteria. The tannins can be polymerized to nontoxic colored compounds by the applications of an autoxidation pretreatment, enabling the anaerobic treatment of easily biodegradable components in the wastewater. The continuous anaerobic treatment of untreated and autoxidized pine bark extract was studied in laboratory-scale columns packed with a granular sludge bed. The autoxidation doubled the conversion efficiency of bark extract COD to methane (from 19 to 40%). After 5 months of operation, anaerobic treatment of the autoxidized extracts was feasible at high influent concentrations (14 g COD/L) and loading rates (26 g biodegradable COD/L · d) with 98% elimination of the biodegradable fraction. The detoxification pretreatment polymerized the toxic tannins to poorly biodegradable high molecular weight tannins and humic compounds which were not eliminated during anaerobic treatment. Although the original tannins of the untreated extract were eliminated by 60%, they were not biodegraded to volatile fatty acids and methane but instead were transformed to phenolic degradation intermediates (phenol, p-cresol, 3-phenylpropionate, and carboxycyclohexane). Therefore, the autoxidation pretreatment did not decrease the content of readily biodegradable substrates which accounted for 53% of the extract COD. The recalcitrant COD expected in the effluents of reactors treating autoxidized debarking wastewater can be effectively separated by calcium precipitation prior to anaerobic treatment.
• Lettinga, G., Field, J. A., Sierra-Alvarez, R., Lier, J. V., & Rintala, J. (1991). Future perspectives for the anaerobic treatment of forest industry wastewaters. Water Science and Technology, 24(3-4), 91-102.
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  Abstract: Anaerobic treatment systems have been successfully applied over the last decade for combating wastewater pollution loads in the forest industry. However, anaerobic treatment of certain paper mill waste streams is limited by the presence of toxic and recalcitrant organic compounds, high concentrations of sulfur and in some cases high wastewater temperatures. Nonetheless, the future perspectives for the anaerobic treatment of difficult forest industry wastewaters are encouraging. This paper discusses a variety of measures available to anaerobic treatment technologies for dealing with the aforementioned limitations.
• Sierra-Alvarez, R., & Lettinga, G. (1991). The effect of aromatic structure on the inhibition of acetoclastic methanogenesis in granular sludge. Applied Microbiology and Biotechnology, 34(4), 544-550.
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  Abstract: Benzene derivatives are important constituents of certain effluents discharged by pulp and paper, petrochemical and chemical industries. The anaerobic treatment of these waste-waters can be limited due to methanogenic inhibition exerted by aromatic compounds. The objective of this study was to evaluate the effect of aromatic structure on acetoclastic methanogenic inhibition. The toxicity to acetoclastic methanogens was assayed in serum flasks utilizing granular sludge as inoculum. Among the monosubstituted benzenes, chlorobenzene, methoxybenzene and benzaldehyde were the most toxic with 50% inhibition occurring at concentrations of 3.4, 4.2 and 5.2 m m, respectively. In contrast, benzoate was the least inhibitory: concentrations up to 57.3 m m were non-toxic. In general, the toxicity of aromatic compounds increased with increasing length of aliphatic side-chains, increasing the number of alkyl or chlorine groups. The logarithm of the partition coefficient octanol/water (log P), an indicator of hydrophobicity, was observed to be positively correlated with the methanogenic inhibition. The results indicate that hydrophobicity is an important factor contributing to the high toxicity of the most inhibitory aromatic compounds. © 1991 Springer-Verlag.
• Sierra-Alvarez, R., & Lettinga, G. (1991). The methanogenic toxicity of wastewater lignins and lignin related compounds. Journal of Chemical Technology and Biotechnology, 50(4), 443-455.
• Sierra-Alvarez, R., Kortekaas, S., Eekert, M. V., & Lettinga, G. (1991). The anaerobic biodegradability and methanogenic toxicity of pulping wastewaters. Water Science and Technology, 24(3-4), 113-125.
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  Abstract: The objective of this study was to evaluate the effect of various pulping conditions and different lignocellulosic feedstocks on the anaerobic treatability of pulping wastewaters. Wastewaters were prepared from lignocellulosic feedstocks commonly used in the forest industry, namely, pine, spruce and birch wood, and wheat straw. The pulping conditions used were representative of those applied in TMP and soda pulping processes. The anaerobic biodegradability and the methanogenic toxicity of the various wastewaters were evaluated in standardized batch bioassays using anaerobic granular sludge. The acidification of the TMP wastewaters (conversion to CH4 and VFA) ranged from 68 to 87% of the total COD, indicating their high anaerobic biodegradability. TMP wastewaters were non-toxic to methane bacteria at concentrations expected in paper mill wastewaters. No inhibition was observed at 10 g COD/l. In contrast, wastewaters prepared in alkaline conditions were poorly biodegradable (approx. 50% acidification) and they caused severe inhibition of the methanogenic activity. The 50% inhibitory concentrations ranged from 2.1 to 5.4 g COD/l. Additional experiments showed that wood resin components, poorly solubilized at acidic to neutral pH, but easily extractable in alkali, are responsible for most of the methanogenic toxicity observed in alkaline pulping wastewaters. These results indicated that contact of wood with alkali contributes significantly to increase the methanogenic toxicity of the pulping wastewater.
• Field, J. A., Sierra-Alvarez, R., & Lettinga, G. (1990). Oxidative detoxification of aqueous bark extracts. Part II: Alternative methods. Journal of Chemical Technology and Biotechnology, 49(1), 35-53.
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  Abstract: The most important problem associated with the high-pH autoxidative detoxification of methanogenic toxins in debarking wastewater was its limited application to the aqueous extractives of bark from specific species. The autoxidative polymerization of coniferous bark extracts exhausted prior to complete removal of the toxic oligomeric tannins. As a result, highly toxic spruce bark extracts were only partly detoxified. Birch bark extracts were not detoxified, even though effective polymerization of the oligomeric tannins occurred. The nontannin toxins in birch bark extracts and toxic intermediates produced by high-pH autoxidation of these extracts were responsible for the poor detoxification results. These problems can potentially be resolved by applying alternative oxidation methods. In this study a high level of detoxification was obtained for all bark species tested by short-term destructive oxidations with H2O2, or by long-term aerobic biological treatments which caused high levels of polymerization. The applicability of high-pH autoxidation was also made feasible for all species of bark by applying a granular active carbon treatment after the autoxidation. The active carbon was able to adsorb the residual toxic oligomeric tannins of autoxidized spruce bark extracts and the non-tannin toxins in autoxidized birch bark extracts.
• Sierra-Alvarez, R., & Lettinga, G. (1990). The methanogenic toxicity of wood resin constituents. Biological Wastes, 33(3), 211-226.
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  Abstract: The purpose of this study was to evaluate the inhibitory effect of representative wood resin compounds on the activity of methanogenic bacteria. Resin is by definition the mixture of wood components that are extractable with apolar solvents. Major resin constituents are long-chain fatty acids, terpenes, resin acids, lignans and apolar phenols. The methanogenic inhibition was determined at a temperature of 30°C in standardized toxicity assays utilizing anaerobic granular sludge. An apolar phenol, 4-hydroxystilbene, was the most toxic of the compounds studied, with a 50% inhibiting concentration of 20 mg/litre. Resin acids and volatile terpenes were also highly toxic to methanogenic activity. Concentrations causing 50% inhibition ranged from 43 to 330 mg/litre. In contrast, triterpenes were non-toxic at relatively high concentrations, 1000-1300 mg/litre. These results suggest that wood resin constituents play an important role in the anaerobic inhibition exerted by several forest industry wastewaters. © 1990.
• Sierra-Alvarez, R., Harbrecht, J., Kortekaas, S., & Lettinga, G. (1990). The continuous anaerobic treatment of pulping wastewaters. Journal of Fermentation and Bioengineering, 70(2), 119-127.
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  Abstract: The anaerobic treatability of thermomechanical pulping (TMP) effluents and soda pulping liquors was evaluated in this study. Continuous experiments were conducted in laboratory scale UASB reactors inoculated with anaerobic granular sludge at 30±2°C. TMP wastewaters were found highly suitable for anaerobic treatment. The application of high organic loadings (31 g COD·l-1·d-1) was feasible by the end of the continuous experiment with TMP wastewaters, with 68 and 98%, total COD and blodegradable COD elimination efficiencies, respectively. Unlike TMP effluents, soda pulping wastewaters were highly inhibitory to methanogenic bacteria and they contained important fractions of recalcitrant organic matter. Wood resin constituents were shown to be responsible for most of the methanogenic inhibition in these wastewaters. Nonetheless, anaerobic wastewater treatment was feasible for removing the biodegradable substrate in soda pulping wastewaters if the wastewaters were diluted to subtoxic levels or detoxified by pretreatment with the adsorbent Amberlite XAD-2 prior to biological treatment. Low COD removal efficiencies were observed during the continuous experiment (45 to 50%) with soda pulping liquors, due to the high amounts of recalcitrant lignin in these wastewaters. The elimination of UV280 absorbance (15 to 20%) indicated partial removal of some lignin components by anaerobic treatment. The lignic fraction removed or biotransformed anaerobically corresponded to low molecular weight lignin derivatives as confirmed by gel chromatography results. © 1990.
• Sierra-Alvarez, R., Kato, M., & Lettinga, G. (1990). The anaerobic biodegradability of paper mill wastewater constituents. Environmental Technology, 11(10), 891-898.
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  Abstract: The biodegradability of ten paper mill wastewater constituents under methanogenic conditions was evaluated in this study. The compounds studied included wood resin constituents and low molecular weight lignin derivatives. Biodegradation was assessed in batch bioassays inoculated with anaerobic granular sludge at 30 ± 2°C. The assays were supplied with low concentrations of the test chemicals (35-200 mg l-1) to prevent methanogenic inhibition. The long chain fatty acids, oleic and linoleic acid, were readily biodegradable under anaerobic conditions. Guaiacol was also mineralized after a 40 days lag period. However, no indication of methanogenic degradation was obtained with eugenol, benzene, the resin acids (abietic and dehydroabietic acid), the volatile terpenes (pinene and limonene) and the unsaturated hydrocarbon squalene.
• Field, J. A., Leyendekers, M. J., Alvarez, R. S., Lettinga, G., & Habets, L. H. (1988). Methanogenic toxicity of bark tannins and the anaerobic biodegradability of water soluble bark matter. Water Science and Technology, 20(1), 219-240.
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  Abstract: The 50 percent inhibitory concentration of bark tannins averaged approximately 600 mg COD L-1. The toxicity caused by the resin fraction of bark was demonstrated not to be very important to the methanogenic toxicity of aqueous extracts. While tree resin compounds were found to be very toxic to methanogenic bacteria, the solubility of the resin fraction was very poor due to the low natural pH during the aqueous extraction. Additionally, those compounds aqueous extracted from tree resin at the natural pH were not as toxic as all the tree resin compounds solubilized by alkali and supplied at similar concentrations. Anaerobic biodegradability results indicated that 30 to 50 percent of the bark water soluble COD can be acidified to methanogenic substrates during short term digestion. Additional study results are discussed.

Proceedings Publications

• Olshansky, Y., Chorover, J., Abrell, L., Field, J. A., Gomeniuc, A., Hatton, J., & Alvarez, R. S. (2022). Sorption of PFAS by Cationic Hydrophobic Polymers. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 257.
• Olshansky, Y., Chorover, J., Abrell, L., Field, J. A., Gomeniuc, A., Hatton, J., & Alvarez, R. S. (2020). Sorption of PFAS by Cationic Hydrophobic Polymers. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 257.
• Olshansky, Y., Chorover, J., Abrell, L., Field, J. A., Gomeniuc, A., Hatton, J., & Sierra-Alvarez, R. .. (2019, Spring). Sorption of PFAS by Cationic Hydrophobic Polymers. In 2019 spring American Chemical Society National Meeting. March 31 - April 4, 2019. Orlando, FL..
• Field, J. A. (2017, Fall). Energy savings with anaerobic ammonium oxidation. In Technology and Research Initiative Fund: Water, Environmental, and Energy Solutions: Funding for Research and Equipment, A Faculty and Researcher Informational Meeting. Feb. 15th, 2017.
• Field, J. A., Ramos Ruiz, A., Simon Pascual, A., Zhu, K., & Sierra Alvarez, R. (2017, Fall). Recovery of Critical Metal and Metalloid Resources by Anaerobic Processes. In The 14th International Water Association, Leading Edge Conference on Water and Wastewater Technologies. Innovative technology solutions to address challenges at the water-energy-food interface. May 29th – June 2nd, 2017.
• Field, J. A., Rodriguez-Freire, L. .., & Sierra-Alvarez, R. .. (2017, Spring). Biorremediacon anaerobia de aguas contaminadas con arsenico. In Simposio Internacional: Ri­o Tinto, aspectos fundamentales y aplicados de un analogo terrestre de Marte. June 6-7, 2017.
• Field, J. A., Sierra-Alvarez, R. .., & Ayala, P. (2017, Fall). Novel electron donors for bioremediation of acid rock drainage. In Water Reuse Monitoring and Treatment Technologies. May 17th -19th.
• Sierra-Alvarez, R. .., Nguyen, C. H., Westerhoff, P., Field, J. A., Shadman, F., Zeng, C., & Bi, X. (2017, Spring). Aquatic fate and toxicity of III/V semiconductor materials in the presence of chemical mechanical planarization nanoparticles. In 2017 Annual Engineering Research Center (ERC) in Environmentally Benign Semiconductor Manufacturing. April 12, 2017.

Presentations

• Madeira, C., Menezes, O., Park, D., Jog, K., Hatt, J., Gavazza, S., Krzmarzick, M., Sierra-Alvarez, R., Spain, J., Konstantinidis, K., & Field, J. A. (2021). Bacteria make a living breathing the nitro-heterocyclic insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO).. American Chemical Society Fall Meeting, 2021, Atlanta. American Chemical Society Fall Meeting. Atlanta: ACS, 2021..
• Menezes, O., Kadoya, W., Gavazza, S., Sierra-Alvarez, R., Mash, E., Abrell, L., & Field, J. A. (2021). Dead end for nitroaromatic explosives: Incorporation of the 2,4-dinitroanisole (DNAN) reduced daughter product into quinone moieties of natural organic matter. American Chemical Society Fall Meeting, 2021, Atlanta. American Chemical Society Fall Meeting. Atlanta: ACS, 2021..
• Field, J. A., Jog, K., Sierra-Alvarez, R. .., Nguyen, C., & Vanover, E. (2019, Summer). Biodegradability and Microbial Toxicity of Azoles, the Forgotten Class of Emerging Contaminants. [Oral presentation], Association of Environmental Engineering and Science Professors (AEESP) Research and Education Conference; 2019 May 14-16; Tempe, AZ..
• Field, J. A., Sierra-Alvarez, R. .., Jog, K., Nguyen, C. H., Vanover, E., & Li, J. A. (2019, Summer). Biodegradability and Toxicity of Ubiquitous Azoles to Anaerobic and Post-Treatment Processes. [Oral Poster IWA Anaerobic Digestion Conference AD16, Accelerating natural cycles Delft University of Technology, 23-27 June 2019, Delft, The Netherlands.
• Kadoya, W. M., Sierra-Alvarez, R. .., Jagadish, B., Wong, S., Abrell, L., Mash, E. A., & Field, J. A. (2019, Summer). Mechanism of Covalent Incorporation of Nitroaromatic Contaminants into Natural Organic Matter.. [Oral presentation] Association of Environmental Engineering and Science Professors (AEESP) Research and Education Conference; 2019 May 14-16; Tempe, AZ..
• Kalyani, V. J., Vanover, E., Chi, H. N., He, C., Field, J. A., & Sierra-Alvarez, R. (2019, Fall). Mechanisms of Nitrification Inhibition by Azoles: A Framework to Promote Azole Detoxification, Biodegradation and Green Chemistry. [Oral Presentation] Semiconductor Research Corporation (SRC) Environment, Safety and Health (ESH) Review, Tucson, AZ, Nov 05, 2019..
• Lakhey, N., Sierra-Alvarez, R. .., & Field, J. A. (2019, Fall). The interactions of azole compounds with an anammox enrichment culture: toxicity and biotransformation. [Oral Presentation] SETAC North America 40th annual meeting, November, 3-7, 2019, Toronto, Ontario, Canada..
• Li., G., Field, J. A., Prevatt, J., McMurray, M. R., Smutzer, J., King, I., Shiroma, J., & Sierra-Alvarez, R. .. (2019, summer). [Oral presentation]. Performance of Pilot-scale Anaerobic Ammonium Oxidation (Anammox) Reactors in Treating Ammonium Rich Wastewater for Pima County Wastewater Reclamation Facility (WRF).. Nutrient Removal and Recovery Symposium 2019: July 23 -25, 2019. Minneapolis, Minnesota, USA.
• Madeira, C. L., Kadoya, W. M., Li, G., Wong, S., Sierra-Alvarez, R. .., & Field, J. A. (2019, Summer). Biological Pretreatment to Enhance In Situ Chemical Oxidation of Insensitive Munitions Compounds. [Oral presentation] Association of Environmental Engineering and Science Professors (AEESP) Research and Education Conference; 2019 May 14-16; Tempe, AZ..
• Niu, X. Z., Abrell, L., Sierra-Alvarez, R. .., Field, J. A., & Chorover, J. (2019, Fall). Environmental, Safety & Health Properties of Onium Photoacid Generators and their Photodegradation Products.. [Oral Presentation] Semiconductor Research Corporation (SRC) Environment, Safety and Health (ESH) Review, Tucson, AZ, Nov 05, 2019..
• Olshansky, Y., Chorover, J., Abrell, L., Field, J. A., Gomeniuc, A., Hatton, J., & Sierra-Alvarez, R. .. (2019, Spring). Sorption of PFAS by Cationic Hydrophobic Polymers. [Oral Presentation] 2019 spring American Chemical Society National Meeting. March 31 - April 4, 2019. Orlando, FL..
• Sierra-Alvarez, R. .. (2019, Fall). [Oral presentation]. Remediation of PFAS contaminated water.. University of Arizona Water & Energy Sustainable Technology (WEST) Center 2019 Industry Meeting and Research Symposium, Nov. 18th. Tucson, AZ..
• Sierra-Alvarez, R. .. (2019, Summer). [Oral presentation]. Mechanisms of Nitrification Inhibition by Azoles: A Framework to Promote Azole Detoxification, Biodegradation and Green Chemistry.. Semiconductor Research Corporation ESH e-Workshop. June 5, 2019.
• Sierra-Alvarez, R., Olshansky, Y., Field, J. A., Abrell, L., Hatton, J., Gomeniuc, A., Schirn, G., & Chorover, J. (2019, Summer). Remediation of Per- and Polyfluoroalkyl Contaminated Groundwater Using Cationic Hydrophobic Polymers as Ultra-High Affinity Sorbents (ER18-1052).. [Oral Presentation] SERDP & ESTCP PFAS Project Meeting, July 30 -August 1, 2019.
• Ayala-Parra, P. .., Field, J. A., & Sierra-Alvarez., R. 2. (2018, Fall). Nutrient recovery and biogas generation from the anaerobic digestion of waste biomass from algal biofuel production.. Sixth Int. Symp. On Environmental Biotechnology and Engineering. Ciudad Obregon, Sonora, Mexico. Nov. 5-9. [oral presentation].
• Boitano, S. A., McCorkel, M., Sherwood, C. L., Borrero, N., Zeng, C., Nguyne, C. H., Field, J. A., & Sierra Alvarez, M. R. (2018, Spring). Nanoparticle toxicity: cytotoxic and sub-cytotoxic measurements using xCELLigence real time cell analysis. 4th Conference on Impedance-Based Cellular Assays, 6th-8th June 2018 (Oral presentation). Edinburgh, UK.
• Field, J. A., & Sierra-Alvarez, R. .. (2018, Spring). Methanogenic granular sludge for the bioremediation and biorecovery of priority inorganic pollutants. IWA Biofilms: Granular Sludge Conference , March 18-21, 2018, Delft, The Netherlands [oral talk & won best speaker award]. IWA Biofilms: Granular Sludge Conference , March 18-21, 2018, Delft, The Netherlands [oral talk & won best speaker award].
• Kadoya, W. M., Sierra, R., Jagadish, B., Wong, S., Abrell, L., Mash, E. A., & Field, J. A. (2018, Fall). Anaerobic Adduct Formation between Reduced Intermediates of 2,4-Dinitroanisole (DNAN) and Humic Model Compounds. Poster presented at: Symposium of the Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP); November 27-29; Washington, DC [poster]. Symposium of the Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP); November 27-29; Washington, DC [poster].
• Loreto, M., Monge Amaya, O., Almendariz, T., Ochoa-Herrera, V. .., & Sierra Alvarez, R. (2018, Fall). Caracterización de un inóculo microbiano con diferentes fuentes de electrones para el posible tratamiento de DAMS. XXVII International Conference of Extractive Metallurgy: Advances in Metallurgy, Materials and the Environment; April 23-27. Zacatecas, Az., Mexico. [ORAL].. XXVII International Conference of Extractive Metallurgy: Advances in Metallurgy, Materials and the Environment; April 23-27. Zacatecas, Az., Mexico. [ORAL]..
• Matalgah, A., Li, G., Field, J. A., & Sierra-Alvarez, R. .. (2018, Spring). Anaerobic Ammonium Oxidation For Nitrogen Removal (Anammox). UA/NASA Space Grant Program, April 14, 2018, Tucson, AZ..
• Sierra-Alvarez, R. .., Field, J. A., Chorover, J., Abrell, L., Niu, X., & Wang, A. (2018, Fall). Environmental, safety & health properties of "onium" photoacid generators and their photodegradation products. Semiconductor Research Corporation (SRC) Annual Executive Review. Sept. 11-13, 2018. Intel, Hillsborough, OR..
• Sierra-Alvarez, R. .., Olshansky, Y., Field, J. A., Abrell, L., Hatton, J., Gomeniuc, A., & Chorover, J. (2018, Fall). ER18-1052: Remediation of Per- and Polyfluoroalkyl Contaminated Groundwater Using Cationic Hydrophobic Polymers as Ultra-High Affinity Sorbents. SERDP/ESTCP Environmental Technology Technical Symposium & Workshop. Nov. 27-30, 2018. Washington DC. [Oral Presentation].
• Field, J. A., Simon-Pascual, A. .., Zhu, K., & Sierra-Alvarez, R. .. (2017, Fall). Recovery of platinum group metals (PGM) utilizing anaerobic microbial consortia.. 15th IWA World Conference on Anaerobic Digestion. Oct. 17-20, 2017.
• Madeira, C. .., Chorover, J., Sierra-Alvarez, R. .., & Field, J. A. (2017, Spring). Biodegradation of the emerging insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) by soil microorganisms. Platform presentation at Battelle's Fourth International Symposium on Bioremediation and Sustainable Environmental Technologies. May 22-25, 2017.
• Moreno-Andrade, I. .., Regidor, E., Ramos-Ruiz, A. .., Field, J. A., & Sierra-Alvarez, R. .. (2017, Spring). Toxicity of antimony on anaerobic microorganisms. 90th Annual Arizona Water Conference & Exhibition. May. 3-5, 2017.
• Regidor, E., Moreno-Andrade, I. .., Field, J. A., & Sierra-Alvarez, R. .. (2017, Fall). Anaerobic microorganisms are capable of reducing antimony (V) to antimony (III). 10th World Congress of Chemical Engineering. Oct. 1-5, 2017.
• Sierra-Alvarez, R. .. (2017, Spring). Onium compound persistence, bioaccumulation and toxicity (PBT) characteristics. ESH Aspects of Semiconductor Manufacturing Research Needs and Opportunities Workshop - Semiconductor Research Corporation. April 12-13, 2017.
• Sierra-Alvarez, R. .., & Celis, B. (2017, Spring). Bioremediation of arsenic contaminated water in arid zones by formation of arsenic-sulfide minerals. CAZMEX Science Crossing Borders Summit (Cumbre de Ciencia Cruzando Fronteras). May 5-6, 2017 [ORAL].
• Zeng, C., Zeng, C., Nguyen, C. H., Nguyen, C. H., Boitano, S., Boitano, S., Field, J. A., Field, J. A., Shadman, F., Shadman, F., Sierra-Alvarez, R., & Sierra-Alvarez, R. (2017, Spring). Impacts of CMP nanoparticles on the cytotoxicity of soluble III/V species to human lung cells. Semiconductor Research Corporation-GRC Technology Transfer e-Workshop. March 1st, 2017.
• Field, J. A., Li, G., & Sierra-Alvarez, R. .. (2016, December). Anammox for nutrient nitrogen removal from sludge liquors. The UA WEST Center. Annual Conference and Industrial Advisory Board Meeting Dec 12 & 13, 2016, Tucson, AZ. [Invited Talk]. UA WEST Center. Annual Conference and Industrial Advisory Board Meeting Dec 12 & 13, 2016, Tucson, AZ. [Invited Talk].
• Field, J. A., Madeira, C. L., Kadoya, W., Speet, S., Sierra-Alvarez, R., Abrell, L., Chorover, J., & Krzmarzick, M. (2016, June). Biodegradation of insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one (NTO), to mineral products via 3-amino-1,2,4-triazol-5-one (ATO) as the central intermediate. SERDP and ESTCP Webinar Series #34, Insensitive Munitions: Environmental Health Criteria, Fate and Transport, June 2nd [Invited Talk]. SERDP and ESTCP Webinar Series #34, Insensitive Munitions: Environmental Health Criteria, Fate and Transport, June 2nd [Invited Talk].
• Field, J. A., Madeira, C., Olivares, C., Abrell, L., Krzmarzick, M., Chorover, J., & Sierra-Alvarez, R. (2016, August). Biotransformation and biodegradation of insensitive munitions compounds in soil. Environmental Chemistry Session, Microbial and Molecular Tools to Determine the Fate and Biotransformation of Emerging Contaminants. 252nd American Chemical Society National Meeting , August 21-25, 2016, Philadelphia, PA [Keynote talk]. 252nd American Chemical Society National Meeting , August 21-25, 2016,. Philadelphia, PA.
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  Biotransformation and biodegradation of insensitive munitions compounds in soil. Environmental Chemistry Session, Microbial and Molecular Tools to Determine the Fate and Biotransformation of Emerging Contaminants. 252nd American Chemical Society National Meeting , August 21-25, 2016, Philadelphia, PA [Keynote talk]
• Field, J. A., Rodriguez-Freire, L. .., & Sierra-Alvarez, R. (2016, April). Arsenic remediation by formation of arsenic sulfide minerals in a continuous anaerobic bioreactor. Department of Metallurgical and Materials Engineering and the Department of Sanitation and Environmental Engineering, Universidade Federal Minas Gerais, , Belo Horizonte, Brazil April 7th, 2016 [Invited Talk]. Department of Metallurgical and Materials Engineering and the Department of Sanitation and Environmental Engineering, Universidade Federal Minas Gerais, , Belo Horizonte, Brazil April 7th, 2016 [Invited Talk]. Belo Horizonte, Brazil.
• Li, G., Carvajal-Arroyo, J. M., Sierra-Alvarez, R., & Field, J. A. (2016, July). Mechanisms and control of nitrite inhibition of anaerobic ammonium oxidation (anammox). Water Environmental Federation/International Water Association, Nutrient Removal and Recovery Conference. Denver, CO, USA, July 10-13, 2016 [Oral Presentation]. Water Environmental Federation/International Water Association, Nutrient Removal and Recovery Conference. Denver, CO, USA, July 10-13, 2016 [Oral Presentation]. Denver. CO.
• McCorkel, M., Sherwood, C., Borrego, N., Zeng, C., Nguyen, C., Field, J., Sierra-Alvarez, R., & Boitano, S. (2016, Fall). Nanoparticle toxicity: cytotoxic and sub-cytotoxic measurements using xCELLigence real time cell analysis. 3rd Conference on Impedance-based cellular assays, Aug. 9-12, 2016. Regensburg, Germany. [ORAL].. 3rd Conference on Impedance-based cellular assays, Aug. 9-12, 2016.. Regensburg, Germany.
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  McCorkel, M., Sherwood, CL, Borrero, NG., Zeng, C., Nguyen, C.H., Field, JA., Sierra-Alvarez, R. and Boitano, S. 2016. Nanoparticle toxicity: cytotoxic and sub-cytotoxic measurements using xCELLigence real time cell analysis. 3rd Conference on Impedance-based cellular assays, Aug. 9-12, 2016. Regensburg, Germany. [ORAL].
• Olivares, C. I., Field, J. A., Sierra-Alvarez, R., Krzmarzick, M., Madeira, C. L., & Chorover, J. (2016, July). Invited Talk: Biotransformation pathways dictating the fate in soil of insensitive munition compounds, 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazole-5-one (NTO). Session on the Bioremediation of Explosive-Contaminated Soil and Water at the Society of Industrial Microbiology and Biotechnology Annual Meeting in New Orleans, LA July 24-28, 2016. [Invited Talk]. Session on the Bioremediation of Explosive-Contaminated Soil and Water at the Society of Industrial Microbiology and Biotechnology Annual Meeting in New Orleans, LA July 24-28, 2016. New Orleans, LA.
• Sierra-Alvarez, R., Rodriguez-Freire, L., Chorover, J., & Field, J. A. (2016, Fall). Anaerobic bioremediation of arsenic in contaminated water by formation of arsenic-sulfide minerals. CRHIAM-INOVAGRI Conference on Leading Technologies For Water Management. Oct. 24-26, 2016. [Keynote speaker]. Concepcion, Chile.
• Sierra-Alvarez, R., Westerhoff, P., Field, J., Shadman, F., Zeng, C., Nguyen, C. H., & Bi, X. (2016, August). Microbial toxicity of Ga2O3, In2O3, GaAs, and InAs nanoparticles in semiconductor manufacturing effluents. 11th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, (ICEENN 2016). August 14 - 18, 2016. Colorado School of Mines, Golden, CO. [ORAL].. 11th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, (ICEENN 2016). August 14 - 18, 2016. Colorado School of Mines, Golden, CO.. Golden, CO.
• Sierra-Alvarez, R., Westerhoff, P., Field, J., Shadman, F., Zeng, C., Nguyen, C. H., & Bi, X. (2016, Fall). Aquatic Fate and Toxicity of III/V Semiconductor Materials in the Presence of CMP Nanoparticles. Semiconductor Research Corporation (SRC) Annual Executive Review. Sept. 8-9, 2016. Intel, Sept. 8-9, 2016. Hillsborough, OR..
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  . Semiconductor Research Corporation (SRC) Annual Executive Review. Sept. 8-9, 2016. Intel, Hillsborough, OR. Sept. 8-9, 2016

Poster Presentations

• Lakhey, N., Swartzendruber, D., Ding, H., Sierra-Alvarez, R. .., & Field, J. A. (2019, Summer). Effects of common wastewater constituents and environmental conditions on Anammox bacterial growth kinetics. [Poster Presentation], 2019 AEESP Research and Education Conference, May 14-16; 2019, Tempe, AZ, USA..
• Madeira, C. L., Menezes, O., Kalyani, V. J., Brooks, M., Park, D., Konstantinidis, K., Krzmarzick, M. J., Spain, J. C., Sierra-Alvarez, R., & Field, J. A. (2019, Fall). Complete Biodegradation of Insensitive High Explosive Compounds. [Poster]. 2019 SERDP and ESTCP Symposium, Dec 3 - Dec 5, 2019, Washington DC..
• Menezes, O., Florencio, L., Kato, M., Sierra-Alvarez, R., Field, J. A., & Gavazza., S. (2019, summer). [Poster]. Biodegradation of 2,4-Diaminoanisole (DAAN), a reduced product of an insensitive munition compound, under different electron acceptor conditions. 2019 Research and Education Conference, Association of Environmental Engineering and Science Professors. May 14-16, 2019. Tempe, AZ..
• Moreno-Andrade, I., Carrillo-Reyes, J., Field, J., & Sierra-Alvarez., R. (2019, Summer). [Poster]. Microbial reduction of antimony by anaerobic microorganisms.. 16th IWA World Conference on Anaerobic digestion 23-27 June 2019, Delft, The Netherlands.
• Nguyen, ., & Sierra-Alvarez, R. .. (2019, Summer). [Poster]. Effects of common wastewater constituents and environmental conditions on Anammox bacterial growth kinetics. 2019 Research and Education Conference, Association of Environmental Engineering and Science Professors. May 14-16, 2019. Tempe, AZ..
• Olshansky, R. (2019, Summer). [Poster]. Remediation of per- and polyfluoroalkyl contaminated groundwater using cationic hydrophobic polymers as ultra-high affinity sorbents.. 2019 Research and Education Conference, Association of Environmental Engineering and Science Professors. May 14-16, 2019. Tempe, AZ..
• Olshansky, Y., Sierra-Alvarez, R., Field, J. A., Abrell, L., Hatton, J., Gomeniuc, A., Jones, S. L., & Chorover, J. (2019, Fall). Remediation of Per- and Polyfluoroalkyl Contaminated Groundwater Using Cationic Hydrophobic Polymers as Ultra-High Affinity Sorbents (ER18-1052). [Poster Presentation] at the 2019 SERDP and ESTCP Symposium, Dec 3 - Dec 5, 2019, Washington DC..
• Valdivielso, J. (2019, Summer). [Poster]. Detection of onium compounds used in semiconductor photolithography with liquid-chromatograph-high resolution mass spectrometry. 2019 Research and Education Conference, Association of Environmental Engineering and Science Professors. May 14-16, 2019. Tempe, AZ..
• Vanover, E., Jog, K., Nguyen, C. H., He, C., Field, J. A., & Sierra-Alvarez, R. .. (2019, Summer). [Poster]. Impact of azole compounds on the nitrification process in wastewater treatment. Semiconductor Environmental Safety & Health Conference (SESHA)/ Semiconductor Industry Association (SIA) International High Technology ESH Symposium and Exhibition, April 16-20, Scottsdale, AZ. Honorable mention.
• Yu, Y., Castrejon, M. R., Madeira, C. L., Sierra-Alvarez, R., Field, J. A., Chorover, J., & Root, R. (2019, Fall). High rate degradation of 3-Nitro-1,2,4-triazol-5-one (NTO) to environmentally benign end products in sequential reducing-oxidizing reactive mineral packed bed reactors. [Poster Presentation]. 2019 SERDP and ESTCP Symposium, Dec 3 - Dec 5, 2019, Washington DC.
• Abrell, L., Kadoya, W. M., Madeira, C. L., Sierra-Alvarez, R. .., Wong, S., Mash Jr, ,. E., Field, J. A., & ., . (2018, fall). Nitroaromatic pollutants environmental fate characterized by HRAM; Understanding anaerobic formation of azo coupling products. 66th Am. Soc. For Mass Spectrometry (ASMS) Conference on Mass Spectrometry and Allied Topics. June 2-3, San Diego, CA. [poster].
• Jog, K., Speed, D., Li, G., Nguyen, C. H., Field, J. A., & Sierra-Alvarez, R. .. (2018, Fall). Azoles as emerging contaminants and their role in nitrification inhibition. Semiconductor Environmental Safety & Health Conference (SESHA)/ Semiconductor Industry Association (SIA) International High Technology ESH Symposium and Exhibition, April 16-20, Scottsdale, Arizona. [Poster, 3rd prize].
• Madeira, C. L., Jog, K. V., Vanover, E. T., Brooks, M. D., Taylor, D. K., Sierra-Alvarez, R., Spain, J. C., Krzmarzick, M. J., & Field, J. A. (2018, Spring). Enrichment culture that biodegrades the reduced metabolite of the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) to inorganic products. SERDP/ESTCP Environmental Technology Technical Symposium & Workshop. Nov. 27-30, 2018. Washington DC. [poster]. SERDP/ESTCP Environmental Technology Technical Symposium & Workshop. Nov. 27-30, 2018. Washington DC. [poster].
• Madeira, C. L., Kadoya, W. M., Li, G., Wong, S., Sierra-Alvarez, R. .., & Field, J. (2018, Fall). Reductive Biological Pretreatment to Enhance In Situ Chemical Oxidation of Insensitive Munitions Compounds. SERDP/ESTCP Environmental Technology Technical Symposium & Workshop. Nov. 27-30, Washington DC. [poster].
• Nguyen, C. H., Zeng, C., Boitano, S., Shadman, F., Field, J. A., & Sierra-Alvarez, R. .. (2018, Spring). Cytotoxicity of gallium arsenide (GaAs) and indium arsenide (InAs) nanoparticles to human lung epithelial cells. Semiconductor Environmental Safety & Health Conference (SESHA)/ Semiconductor Industry Association (SIA) International High Technology ESH Symposium and Exhibition, April 16-20, Scottsdale, Arizona. [Poster award, 1st prize]..
• Vanover, E., Madeira, C. L., Speet, S. A., Abrell, A., Chorover, J., Sierra-Alvarez, R. .., & Field, J. A. (2018, Spring). Remediation of Insensitive Munitions Compound 3-nitro-1,2,4-triazol-5-one (NTO). 2018 Student Western Alliance to Expand Student Opportunity (WAESO) Conference. March 2nd. Tempe, AZ. [poster, 3rd prize].
• I., M., E., R., A., F. J., & R.., S. (2017, Fall). Microbial inhibition by antimony compounds. AZ Water research Committee Building Our Sustainable water Future Workshop. Oct. 1, 2017.
• Kadoya, W. M., Sierra-Alvarez, R. .., S., W., Abrell, L., Mash, G., & Field, J. A. (2017, Fall). Anaerobic coupling reactions between reduced intermediates of 2,4-dinitroanisole (DNAN). Battelle's Fourth International Symposium on Bioremediation and Sustainable Environmental Technologies. May 22-25, 2017.
• Kadoya, W. M., Sierra-Alvarez, R. .., S., W., Abrell, L., Mash, G., & Field, J. A. (2017, Spring). Anaerobic coupling reactions between reduced intermediates of 2,4-dinitroanisole (DNAN). 90th Annual Conference of AZ Water Association. May 4, 2017.
• Kadoya, W. M., Sierra-Alvarez, R. .., S., W., Abrell, L., Mash, G., & Field, J. A. (2017, Spring). Evidence of anaerobic coupling reactions between reduced intermediates of 2,4-dinitroanisole (DNAN). Proc. Society of Environmental Toxicology and Chemistry, North America 38th Annual Meeting. 12th-16th Nov. 2017.
• Lee, J. W., & Sierra-Alvarez, R. .. (2017, Spring). Adsorption of toxic metals and metalloids onto engineered nanomaterials. NASA Research program Symposium. April 22, 2017.
• Li, G., Carvajal-Arroyo, J. M., Neely, S., Vilcherrez, D., Sierra-Alvarez, R. .., & field, J. A. (2017, Fall). How to recover a failing anaerobic ammonium oxidation (anammox) reactor with nitrate. 15th IWA World Conference on Anaerobic Digestion. Oct. 17-20, 2017.
• Madeira, C. L., Simonich, M. T., Tanguay, R. L., Chorover, J., & Sierra-Alvarez, R. .. (2017, Fall). Ecotoxicity of the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) and its reduced metabolite 3-amino-1,2,4-triazol-5-one (ATO). Proc. Society of Environmental Toxicology and Chemistry, North America 38th Annual Meeting. 12-16 Nov. 2017.
• Moreno-Andrade, I. .., Regidor, E., Ramos-Ruiz, A. .., Field, J. A., & Sierra-Alvarez, R. .. (2017, Fall). Microbial reduction of antimony by anaerobic microorganisms. 15th IWA World Conference on Anaerobic Digestion. Oct. 17-20, 2017.
• Nguyen, C. H., Field, J. A., & Sierra-Alvarez, R. .. (2017, Fall). Microbial toxicity of Ga2O3, In2O3, GaAs, and InAs nanoparticles in semiconductor manufacturing effluents. Proc. Society of Environmental Toxicology and Chemistry, North America 38th Annual Meeting. 12–16 Nov. 2017.
• Regidor, E., Moreno-Andrade, I. .., Field, J. A., & Sierra-Alvarez, R. (2017, Spring). Anaerobic microorganisms are capable of reducing antimony (V). The University of Arizona Showcase. Feb. 2nd, 2017.
• Abrell, L., Olivares, C. I., Chorover, J., & Sierra-Alvarez, R. .. (2016, June). Field, J. A. New 2,4-dinitroanisole (DNAN; munitions chemical) (bio)transformation products discovered and bioassayed using high resolution UPLC-QToFMS. 64th ASMS Conference on Mass Spectrometry, San Antonio, TX, USA, Jun 5-9, 2016 [Poster]. 64th ASMS Conference on Mass Spectrometry, San Antonio, TX, USA, Jun 5-9, 2016.
• Madeira, C. L., Speet, S. A., Abrell, L., Chorover, J., Sierra-Alvarez, R. .., & Field, J. A. (2016, November). Biodegradation of the Insensitive Munitions Compound 3-nitro-1,2,4-triazol-5-one (NTO). 7th SETAC World Congress/37th SETAC North America Annual Meeting, Nov. 6-10, 2016. Orlando, FL [Poster]. 7th SETAC World Congress/37th SETAC North America Annual Meeting, Nov. 6-10, 2016. Orlando, FL [Poster]. Orlando. FL.
• Zeng, C., Nguyen, C. H., Boitano, S., Field, J., Shadman, F., & Sierra-Alvarez, R. (2016, August). Dynamic Monitoring Cytotoxicity of Nanoscale III-V Materials and CMP Nanoparticles. 11th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, (ICEENN 2016). August 14 - 18, 2016. Colorado School of Mines, Golden, CO. [POSTER].. 11th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, (ICEENN 2016). August 14 - 18, 2016. Colorado School of Mines, Golden, CO.. Golden, CO.