Avelino E Saez

Interests

Research

Water Quality Assessment of Biological and Chemical Contaminants

Courses

Scholarly Contributions

Journals/Publications

• Saez, A. E. (2021). Assessing a Children’s Lead Exposure Uptake Model in an Active Mining Community Using the Integrated Exposure Uptake Biokinetic Model. Exposure and Health, 13, 517-533.
• Saez, A. E. (2021). Foliar Surfaces as Dust and Aerosol Pollution Monitors: An Assessment by a Mining Site,. Science of the Total Environment, 790, 148164.
• Saez, A. E., Saez, A. E., Rodriguez-chavez, T. B., Betterton, E. A., Rine, K. P., Ramirez-andreotta, M. D., O'brien-metzger, R., Ramirez-andreotta, M. D., O'brien-metzger, R., Almusawi, R. M., Rine, K. P., Betterton, E. A., Almusawi, R. M., & Rodriguez-chavez, T. B. (2021). Outdoor/Indoor Contaminant Transport by Atmospheric Dust and Aerosol at an Active Smelter Site. Water Air and Soil Pollution, 232(6), 1-14. doi:10.1007/s11270-021-05168-2
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  Activities associated with mining operations including smelting, ore handling, and mine tailings management have been identified as sources of dust and aerosol that may contain metal and metalloid contaminants, such as lead (Pb) and arsenic (As). Previous studies on contaminant transport have concentrated on the potential impact of these particulate emissions in outdoor environments. The purposes of this study were (i) to quantify the effect of dust and aerosol particle size on contaminant transport from outdoor-to-indoor environments and (ii) to document the changes in particle chemical composition during transport through the outdoor/indoor barrier. Outdoor and indoor particulate samples were collected at a high school equipped with mechanical air filtration systems from 2016 to 2019. The school is located near a set of mine tailings and an active copper smelter in Hayden, Arizona. Particle size segregated samples were collected using a ten-stage micro-orifice uniform deposit impactor (MOUDI). Results show that airborne fine particles (aerodynamic diameters less than 1 micron) can penetrate to the indoor environment but in a reduced amount due to mechanical filtration. Aerosol in the fine fraction particulate air concentrations was around 50% of the corresponding outdoor values, but their mass concentration of contaminants was similar to outdoor values. Indoor coarse particles (> 1 micron) comprised close to 20% of the levels found in outdoor coarse particles. These results highlight the need to consider the impact of particle diameter when assessing indoor exposure and potential health effects in communities living under the direct influence of mining and smelter activities.
• Sierra-alvarez, R., Saez, A. E., Pepel, R. D., Paniego, R., Niu, X., Field, J. A., Chorover, J., & Abrell, L. (2021). Photochemical Fate of Sulfonium Photoacid Generator Cations under Photolithography Relevant UV Irradiation. Journal of Photochemistry and Photobiology A-chemistry, 416. doi:10.1016/j.jphotochem.2021.113324
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  Abstract Onium salts, widely used as photoacid generators (PAGs) in the semiconductor industry, are receiving increased regulatory scrutiny due to their potential hazardous properties. Evaluating the environmental impacts of these chemicals requires knowledge of the fate of the onium species during photolithography steps, which remains unclear for many PAGs. The current study investigated the fate of four representative sulfonium PAGs using an irradiation setup simulating industrial photolithography. The photolytic fate for three of the four selected onium cations is reported for the first time. All onium compounds reacted rapidly under 254 nm irradiation, and their half-lives ranged from 51 to 214 s with high quantum yields (0.23-0.85). Multiple highly aromatic and hydrophobic photoproducts were characterized using HPLC-DAD and GC-MS; eight PAG photoproducts were identified for the first time. Authentic commercial standards of some of the photoproducts were available, enabling quantitative estimates of recoveries. The molar recovery of aromatic rings based on these quantified photoproducts was in the range of 4.9-71.4%. A homolytic reaction mechanisms is proposed and discussed. The results provide insight on the potential environmental impact pertinent to the use of PAGs, e.g., prediction of residual onium levels and the identity of photoproducts in effluents from semiconductor fabrication facilities.
• Stahl, C., Sorooshian, A., Simpas, J. B., Saez, A. E., Macdonald, A. B., Lorenzo, G. R., Gonzalez, M. E., Csavina, J., Cruz, M. T., Cambaliza, M. O., Braun, R. A., Betterton, E. A., Betito, G., Banaga, P. A., & Aghdam, M. A. (2021). Contrasting the size-resolved nature of particulate arsenic, cadmium, and lead among diverse regions. Atmospheric Pollution Research, 12(3), 352-361. doi:10.1016/j.apr.2021.01.002
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  Abstract This study examines the mass size distributions and crustal enrichment factors (EFs) of arsenic (As), cadmium (Cd), and lead (Pb) for diverse regions: coastal marine (Marina, California), arid mining facility (Hayden, Arizona), arid urban (Tucson, Arizona), free troposphere (Mt. Lemmon, Arizona), and coastal urban (Manila, Philippines). Micro-orifice uniform deposit impactor (MOUDI) measurements revealed several notable features. All sites showed a bimodal profile with a peak in the submicrometer and supermicrometer diameter range except for Manila, which peculiarly lacked a peak above 1 μm. Enrichment factor analysis revealed contaminated dust at all sites, even the free tropospheric site, with greater contamination in the submicrometer range. The most extensive dataset in Manila allowed for seasonal analysis, which revealed differences among the same species based on seasonally-dependent transport patterns. Sites experiencing biomass burning influence (Manila and Marina) generally exhibited suppressed concentrations and crustal EFs during burning periods presumably because soil emitted from fires is fresh without extensive processing time to become contaminated. These results have important implications for a variety of aerosol effects dependent on aerosol size (e.g., public health, biogeochemical cycling, heterogeneous chemistry) and underscore the importance of accounting for the coarse aerosol mode as more dust emissions are expected in warmer climate scenarios.
• Alexander-Ozinskas, A., Janes, K., Hils, J., Root, R. A., Saez, A. E., Ramirez, M. D., & Manjon, I. (2020). Ingestion and inhalation of metal(loid)s through preschool gardening: An exposure and risk assessment in legacy mining communities. Science of the Total Environment, 718(134639). doi:10.1016/j.scitotenv.2019.134639
• Saez, A. E. (2020). Environmental monitoring and exposure science dataset to calculate ingestion and inhalation of metal(loid)s through preschool gardening. Data In Brief, 29, 105050.
• Saez, A. E. (2020). Ingestion and Inhalation of Metal(loid)s Through Preschool Gardening: An Exposure and Risk Assessment in Legacy Mining Communities. Science of the Total Environment, 718, 134639.
• Karanikola, V., Moore, S. E., Deshmukh, A., Arnold, R. G., Elimelech, M., & Saez, A. E. (2019). Economic performance of membrane distillation configurations in optimal solar thermal desalination systems. DESALINATION, 472.
• Manjón, I., Ramírez-Andreotta, M. D., Sáez, A. E., Root, R. A., Hild, J., Janes, M. K., & Alexander-Ozinskas, A. (2019). Ingestion and inhalation of metal(loid)s through preschool gardening: An exposure and risk assessment in legacy mining communities. The Science of the total environment, 134639.
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  Children residing in mining towns are potentially disproportionately exposed to metal(loid)s via ingestion and dust inhalation, thus, increasing their exposure when engaging in school or home gardening or playing outside. This citizen science study assessed preschool children's potential arsenic (As), cadmium (Cd), and lead (Pb) exposure via locally grown produce, water, incidental soil ingestion, and dust inhalation at four sites. Participants were trained to properly collect water, soil, and vegetable samples from their preschools in Nevada County, California. As, Cd, and Pb concentrations in irrigation sources did not exceed the U.S. EPA's maximum contaminant and action levels. In general, garden and playground As and Pb soil concentrations exceeded the U.S. EPA Regional Screening Level, CalEPA Human Health Screening Level, and California Department of Toxic Substances Control Screening Level. In contrast, all Cd concentrations were below these recommended screening levels. Dust samples (
• Marquez, I., Hao, V. o., Zhang, T., Barnett, B., Nienhauser, A., Yang, P., Quanrud, D., Arnold, R., & Saez, A. (2019). Photodegradation of trace organic contaminants by singlet oxygen: a kinetic/transport model. ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 257.
• Witten, M. L., Chau, B., Saez, E., Boitano, S., & Lantz, R. C. (2019). Early life inhalation exposure to mine tailings dust affects lung development. TOXICOLOGY AND APPLIED PHARMACOLOGY, 365, 124-132.
• Zhang, T., Marquez-Hernandez, L. I., Arnold, R. G., Diefenthal, G., & Saez, A. E. (2019). Modeling the UV/H2O2 oxidation of phenolic compounds in a continuous-flow reactor with reflective walls. JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, 7(3).
• Gil-Loaiza, J., Field, J. P., White, S. A., Csavina, J., Felix, O., Betterton, E. A., Saez, A. E., & Maier, R. M. (2018). Phytoremediation Reduces Dust Emissions from Metal(Ioid)-Contaminated Mine Tailings. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 52(10), 5851-5858.
• Moore, S. E., Ma, L., Potzler, M., Bish, J., Karanikola, V., Prevatt, J., Arnold, R. G., & Saez, A. E. (2018). Sustainable Struvite Control Using Carbon Dioxide. JOURNAL OF ENVIRONMENTAL ENGINEERING, 144(12).
• Moore, S. E., Mirchandani, S. D., Karanikola, V., Nenoff, T. M., Arnold, R. G., & Saez, A. E. (2018). Process modeling for economic optimization of a solar driven sweeping gas membrane distillation desalination system. DESALINATION, 437, 108-120.
• Thomas, A. N., Root, R. A., & Saez, A. E. (2018). Oxidative Weathering Decreases Bioaccessibility of Toxic Metal(oids) in PM10 Emissions form Sulfide Mine Tailings. GeoHealth, 2, 118-138.
• Cheng, L., Vo, H., Quanrud, D. M., Arnold, R. G., & Saez, A. E. (2017). Effectiveness of engineered and natural wastewater treatment processes for the removal of trace organics in water reuse. Journal of Environmental Engineering, 143, 1-18.
• Saez, A. E. (2017). Effects of Membrane Structure and Operational Variables on Membrane Distillation Performance. Journal of Membrane Science, 524, 87-96.
• Guzman, H., Li, J., Keshta, M., Saez, A. E., & Ela, W. (2016). Release of Arsenic from Metal Oxide Sorbents under Simulated Mature Landfill Conditions. Chemosphere, 151, 84-93.
• Landazuri, A., Saez, A. E., & Anthony, R. (2016). Three-Dimensional Computational Fluid Dynamics Modeling of Particle Uptake by a Horizontally Oriented Occupational Air Sampler. Journal of Aerosol Science, 95, 54-66.
• Li, X., Felix, O., Gonzales, P., Ela, W., & Saez, A. E. (2016). Reconciling PM10 Analyses by Different Sampling Methods for Iron King Mine Tailings Dust. Reviews on Environmental Health, 31, 37-42.
• Stovern, M., Guzman, H., Rine, K., Felix, O., King, M., Ela, W., Betterton, E., & Saez, A. E. (2016). Windblown Dust Deposition Forecasting and Spread of Contamination around Mine Tailings. Atmosphere, 7, 16.
• Arnold, R. G., Ela, W. P., Saez, A. E., Karanikola, V., Corral, A. F., & Jiang, H. (2015). Sweeeping Gas Membrane Distillation: Numerical simulation of mass and heat transfer in a hollow fiber membrane modeual. Journal of Membrane Science, 483, 15-24.
• Arnold, R. G., Saez, A. E., Snyder, S. A., Abrell, L. M., Dong, B., Kahl, A., Wickramasekara, S., Cheng, L., Vo, H., Ruehl, S., Zhang, T., & Quanrud, D. (2015). Fate of Trace Organics in an Effluent Dependent Stream. Science of the Total Environment, 518-19, 479-90.
• Félix, O. I., Csavina, J., Field, J., Rine, K. P., Sáez, A. E., & Betterton, E. A. (2015). Use of lead isotopes to identify sources of metal and metalloid contaminants in atmospheric aerosol from mining operations. Chemosphere, 122, 219-26.
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  Mining operations are a potential source of metal and metalloid contamination by atmospheric particulate generated from smelting activities, as well as from erosion of mine tailings. In this work, we show how lead isotopes can be used for source apportionment of metal and metalloid contaminants from the site of an active copper mine. Analysis of atmospheric aerosol shows two distinct isotopic signatures: one prevalent in fine particles (
• Pemberton, J. E., Wang, H., Cheng, L., & Saez, A. E. (2015). Flow Field Penetration in Thin Nanoporous Polymer Films under Laminar Flow by Förster Resonance Energy Transfer Coupled with Total Internal Reflectance Fluorescence Microscopy. Analytical Chemistry, 87, 11746-11754.
• Raghav, M., Saez, A. E., & Ela, W. (2015). Understanding Abiotic Ferrihydrite Remineralization by Ferrous Ions. International Journal of Environmental Science and Technology, 12, 1945-1956.
• Stovern, M., Rine, K., Russell, M., Felix, O., King, M., Saez, A. E., & Betterton, E. (2015). Development of a Dust Deposition Forecasting Model for Mine Tailings Impoundments Using In Situ Observations and Particle Transport Simulations. Aeolian Research, 18, 155-167.
• Wang, H., Cheng, L., Saez, A. E., & Pemberton, J. (2015). Flow Field Penetration in Thin Nanoporous Polymer Films under Laminar Flow by Förster Resonance Energy Transfer Coupled with Total Internal Reflectance Fluorescence Microscopy. Analytical Chemistry, 87, 11746-11754.
• Breshears, D. D., Whicker, J. J., Sáez, A. E., & Field, J. P. (2014). Introduction to a Special Issue of Aeolian Research Airborne mineral dust contaminants: Impacts on human health and the environment. Aeolian research, 14, 1-2.
• Csavina, J., Field, J., Félix, O., Corral-Avitia, A. Y., Sáez, A. E., & Betterton, E. A. (2014). Effect of wind speed and relative humidity on atmospheric dust concentrations in semi-arid climates. The Science of the total environment, 487, 82-90.
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  Atmospheric particulate have deleterious impacts on human health. Predicting dust and aerosol emission and transport would be helpful to reduce harmful impacts but, despite numerous studies, prediction of dust events and contaminant transport in dust remains challenging. In this work, we show that relative humidity and wind speed are both determinants in atmospheric dust concentration. Observations of atmospheric dust concentrations in Green Valley, AZ, USA, and Juárez, Chihuahua, México, show that PM10 concentrations are not directly correlated with wind speed or relative humidity separately. However, selecting the data for high wind speeds (>4m/s at 10 m elevation), a definite trend is observed between dust concentration and relative humidity: dust concentration increases with relative humidity, reaching a maximum around 25% and it subsequently decreases with relative humidity. Models for dust storm forecasting may be improved by utilizing atmospheric humidity and wind speed as main drivers for dust generation and transport.
• Csavina, J., Taylor, M. P., Felix, O., Rine, K., Saez, A. E., & Betterton, E. (2014). Size-Resolved Dust and Aerosol Contaminants Associated with Copper and Lead Smelting Emissions: Implications for Emissions Management and Human Health. Science of the Total Environment, 493, 750-756.
• Gonzales, P., Felix, O., Alexander, C., Lutz, E., & Saez, A. E. (2014). Laboratory Dust Generation and Size-dependent Characterization of Metal and Metalloid-contaminated Mine Tailings Deposits. Journal of Hazardous Materials, 280, 619-626.
• Sherwood, D. J., & Sáez, A. E. (2014). The start of ebullition in quiescent, yield-stress fluids. Nuclear Engineering and Design, 270, 101-108.
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  Abstract: Non-Newtonian rheology is typical for the high-level radioactive waste (HLW) slurries to be processed in the Hanford Tank Waste Treatment and Immobilization Plant (WTP). Hydrogen and other flammable gases are generated in the aqueous phase by radiolytic and chemical reactions. HLW slurries have a capacity for retaining gas characterized by the shear strength holding the bubbles still. The sizes and degassing characteristics of flammable gas bubbles in the HLW slurries, expected to be processed by the WTP are important considerations for designing equipment and operating procedures. Slurries become susceptible to degassing as the bubble concentration increases over a maximum value that depends on shear strength. This susceptibility and the process of ebullitive bubble enlargement are described here. When disturbed, the fluid undergoes localized flow around neighboring bubbles which are dragged together and coalesce, producing an enlarged bubble. For the conditions considered in this work, bubble size increase is enough to displace the weight required to overcome the fluid shear strength and yield the surroundings. The buoyant bubble ascends and accumulates others within a zone of influence, enlarging by a few orders of magnitude. This process describes how the first bubbles appear on the surface of a 7 Pa shear strength fluid a few seconds after being jarred. © 2014 Elsevier B.V.
• Stovern, M., Betterton, E. A., Sáez, A. E., Villar, O. I., Rine, K. P., Russell, M. R., & King, M. (2014). Modeling the emission, transport and deposition of contaminated dust from a mine tailing site. Reviews on environmental health, 29(1-2), 91-4.
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  Mining operations are potential sources of airborne particulate metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern US by climate models may make contaminated atmospheric dust and aerosols increasingly important, due to potential deleterious effects on human health and ecology. Dust emissions and dispersion of contaminants from the Iron King Mine tailings in Dewey-Humboldt, Arizona, a Superfund site, are currently being investigated through in situ field measurements and computational fluid dynamics modeling. These tailings are significantly contaminated with lead and arsenic with an average soil concentration of 1616 and 1420 ppm, respectively. Similar levels of these contaminants have also been measured in soil samples taken from the area surrounding the mine tailings. Using a computational fluid dynamics model, we have been able to model dust transport from the mine tailings to the surrounding region. The model includes a distributed Eulerian model to simulate fine aerosol transport and a Lagrangian approach to model fate and transport of larger particles. In order to improve the accuracy of the dust transport simulations both regional topographical features and local weather patterns have been incorporated into the model simulations.
• Stovern, M., Felix, O., Csavina, J., Rine, K. P., Russell, M. R., Jones, R. M., King, M., Betterton, E. A., & Sáez, A. E. (2014). Simulation of windblown dust transport from a mine tailings impoundment using a computational fluid dynamics model. Aeolian research, 14, 75-83.
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  Mining operations are potential sources of airborne particulate metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern US by climate models may make contaminated atmospheric dust and aerosols increasingly important, due to potential deleterious effects on human health and ecology. Dust emissions and dispersion of dust and aerosol from the Iron King Mine tailings in Dewey-Humboldt, Arizona, a Superfund site, are currently being investigated through in situ field measurements and computational fluid dynamics modeling. These tailings are heavily contaminated with lead and arsenic. Using a computational fluid dynamics model, we model dust transport from the mine tailings to the surrounding region. The model includes gaseous plume dispersion to simulate the transport of the fine aerosols, while individual particle transport is used to track the trajectories of larger particles and to monitor their deposition locations. In order to improve the accuracy of the dust transport simulations, both regional topographical features and local weather patterns have been incorporated into the model simulations. Results show that local topography and wind velocity profiles are the major factors that control deposition.
• Raghav, M., Shan, J., Sáez, A. E., & Ela, W. P. (2013). Scoping candidate minerals for stabilization of arsenic-bearing solid residuals. Journal of Hazardous Materials, 263, 525-532.
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  PMID: 24231323;PMCID: PMC3984437;Abstract: Arsenic Crystallization Technology (ACT) is a potentially eco-friendly, effective technology for stabilization of arsenic-bearing solid residuals (ABSRs). The strategy is to convert ABSRs generated by water treatment facilities into minerals with a high arsenic capacity and long-term stability in mature, municipal solid waste landfills. Candidate minerals considered in this study include scorodite, arsenate hydroxyapatites, ferrous arsenates (symplesite-type minerals), tooeleite, and arsenated-schwertmannite. These minerals were evaluated as to ease of synthesis, applicability to use of iron-based ABSRs as a starting material, and arsenic leachability. The Toxicity Characteristic Leaching Procedure (TCLP) was used for preliminary assessment of candidate mineral leaching. Minerals that passed the TCLP and whose synthesis route was promising were subjected to a more aggressive leaching test using a simulated landfill leachate (SLL) solution. Scorodite and arsenate hydroxyapatites were not considered further because their synthesis conditions were not found to be favorable for general application. Tooeleite and silica-amended tooeleite showed high TCLP arsenic leaching and were also not investigated further. The synthesis process and leaching of ferrous arsenate and arsenated-schwertmannite were promising and of these, arsenated-schwertmannite was most stable during SLL testing. The latter two candidate minerals warrant synthesis optimization and more extensive testing. © 2013 Elsevier B.V.
• Rojas, M. R., Leung, C., Bonk, F., Zhu, Y., Edwards, L., Arnold, R. G., Sáez, A. E., & Klečka, G. (2013). Assessment of the effectiveness of secondary wastewater treatment technologies to remove trace chemicals of emerging concern. Critical Reviews in Environmental Science and Technology, 43(12), 1281-1314.
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  Abstract: This work presents the results of a literature review and statistical analysis of removals of chemicals of emerging concern (CECs) during conventional wastewater treatment. Process-dependent attenuations are examined for the 42 most frequently measured and reported CECs. Biological treatment processes contributing to the review include conventional activated sludge, membrane bioreactors, trickling filters, sequencing batch reactors, and lagoons. Also summarized are compound-specific physical characteristics and biodegradability data that are potential determinants of removal. As anticipated, results of the statistical analysis point to biodegradability and hydrophobicity as the most important contributing factors for removal. Supplemental materials are available for this article. Go to the publisher's online edition of Critical Reviews in Environmental Science and Technology to view the supplemental file. © 2013 Copyright Taylor and Francis Group, LLC.
• Arnold, R. G., Saez, A. E., Snyder, S., Maeng, S. K., Lee, C., Woods, G. J., Li, X., & Choi, H. (2012). Direct potable reuse of reclaimed wastewater: it is time for a rational discussion. Reviews on environmental health, 27(4), 197-206.
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  Water shortage arising from rapid population growth and relocation has produced an unprecedented degree of stress on regional water resources. Engineered solutions to relieve water stress are frequently based on the use of water of impaired initial quality. Chief among these impaired waters is reclaimed wastewater. For the most part, however, the breadth of both acceptable uses and use-dependent degree of treatment for reclaimed wastewater remain to be established.The chief advantages of direct potable reuse (DPR) relative to other forms of wastewater reclamation and reuse are that(i) all wastewater reclaimed for DPR can be readily used in water-stressed areas and (ii) delivery to points of use does not require a separate distribution system. The drawbacks are related to the need for highly competent, continuous on-line verification of water quality and the cost of treating all reclaimed wastewater to meet potable use requirements when only a small fraction will be used for potable purposes.We have attempted to explore those differences, providing quantitative comparisons where possible, to support selection among water reuse options in water-stressed areas.
• Beamer, P. I., Luik, C. E., Abrell, L., Campos, S., Martinez, M. E., & Saez, A. E. (2012). Concentration of Trichloroethylene in Breast Milk and Household Water from Nogales, Arizona. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 46(16), 9055-9061.
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  The United States Environmental Protection Agency has identified quantification of trichloroethylene (TCE), an industrial solvent, in breast milk as a high priority need for risk assessment. Water and milk samples were collected from 20 households by a lactation consultant in Nogales, Arizona. Separate water samples (including tap, bottled, and vending machine) were collected for all household uses: drinking, bathing, cooking, and laundry. A risk factor questionnaire was administered. Liquid liquid extraction with diethyl ether was followed by GC-MS for TCE quantification in water. Breast milk underwent homogenization, lipid hydrolysis, and centrifugation prior to extraction. The limit of detection was 1.5 ng/mL. TCE was detected in 7 of 20 mothers' breast milk samples. The maximum concentration was 6 ng/mL, TCE concentration in breast milk was significantly correlated with the concentration in water used for bathing (p = 0.59, p = 0.008). Detection of TCE in breast milk was more likely if the infant had a body mass index
• Beamer, P. I., Luik, C. E., Abrell, L., Campos, S., Martínez, M. E., & Sáez, A. E. (2012). Concentration of trichloroethylene in breast milk and household water from Nogales, Arizona. Environmental Science and Technology, 46(16), 9055-9061.
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  PMID: 22827160;PMCID: PMC3699401;Abstract: The United States Environmental Protection Agency has identified quantification of trichloroethylene (TCE), an industrial solvent, in breast milk as a high priority need for risk assessment. Water and milk samples were collected from 20 households by a lactation consultant in Nogales, Arizona. Separate water samples (including tap, bottled, and vending machine) were collected for all household uses: drinking, bathing, cooking, and laundry. A risk factor questionnaire was administered. Liquid-liquid extraction with diethyl ether was followed by GC-MS for TCE quantification in water. Breast milk underwent homogenization, lipid hydrolysis, and centrifugation prior to extraction. The limit of detection was 1.5 ng/mL. TCE was detected in 7 of 20 mothers' breast milk samples. The maximum concentration was 6 ng/mL. TCE concentration in breast milk was significantly correlated with the concentration in water used for bathing (ρ = 0.59, p = 0.008). Detection of TCE in breast milk was more likely if the infant had a body mass index
• Beamer, P. I., Luik, C. E., Abrell, L., Campos, S., Martínez, M. E., & Sáez, A. E. (2012). Concentration of trichloroethylene in breast milk and household water from Nogales, Arizona. Environmental science & technology, 46(16), 9055-61.
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  The United States Environmental Protection Agency has identified quantification of trichloroethylene (TCE), an industrial solvent, in breast milk as a high priority need for risk assessment. Water and milk samples were collected from 20 households by a lactation consultant in Nogales, Arizona. Separate water samples (including tap, bottled, and vending machine) were collected for all household uses: drinking, bathing, cooking, and laundry. A risk factor questionnaire was administered. Liquid-liquid extraction with diethyl ether was followed by GC-MS for TCE quantification in water. Breast milk underwent homogenization, lipid hydrolysis, and centrifugation prior to extraction. The limit of detection was 1.5 ng/mL. TCE was detected in 7 of 20 mothers' breast milk samples. The maximum concentration was 6 ng/mL. TCE concentration in breast milk was significantly correlated with the concentration in water used for bathing (ρ = 0.59, p = 0.008). Detection of TCE in breast milk was more likely if the infant had a body mass index
• Beamer, P. I., Luik, C. E., Abrell, L., Campos, S., Martínez, M. E., & Sáez, A. E. (2012). Erratum: Concentration of trichloroethylene in breast milk and household water from Nogales, Arizona (Environmental Science and Technology 46:16 (9055-9061) DOI:10.1021/es301380d). Environmental Science and Technology, 46(20), 11483-.
• Csavina, J., Field, J., Taylor, M. P., Gao, S., Landazuri, A., Betterton, E. A., & Saez, A. E. (2012). A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations.
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  Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport. (C) 2012 Elsevier B.V. All rights reserved.
• Csavina, J., Field, J., Taylor, M. P., Gao, S., Landázuri, A., Betterton, E. A., & Sáez, A. E. (2012). A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations. Science of the Total Environment, 433, 58-73.
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  PMID: 22766428;PMCID: PMC3418464;Abstract: Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport. © 2012 Elsevier B.V.
• Csavina, J., Field, J., Taylor, M. P., Gao, S., Landázuri, A., Betterton, E. A., & Sáez, A. E. (2012). A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations. The Science of the total environment, 433, 58-73.
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  Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.
• Rivero, D., Gouveia, L. M., Müller, A. J., & Sáez, A. (2012). Shear-thickening behavior of high molecular weight poly(ethylene oxide) solutions. Rheologica Acta, 51(1), 13-20.
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  Abstract: Simple shear rheological properties of solutions of a high molecular weight (8 × 10 6 g/mol) poly(ethylene oxide) (PEO) and its mixtures with sodium dodecyl sulfate (SDS) have been studied. Shear-thickening effects set in at a critical shear rate for PEO solutions. This particular behavior has not been reported for aqueous solutions of PEO, to our knowledge. The effect is attributed to PEO flow-induced self-aggregation. The experiments were performed in different operation modes (strain rate and stress controlled) and with different geometries (double wall Couette and Couette) and identical viscosities were obtained, which rules out flow instabilities as possible cause for the shear-thickening effect. Shear thickening was observed in the temperature range 15-50°C. Flow-induced PEO degradation occurs for shear rates in the shear-thickening regime, which indicates substantial chain deformation and accumulated stresses in the molecule when shear thickening occurs. Addition of SDS to the PEO solutions induces the formation of surfactant polymer complexes that preserve the characteristic shear-thickening effect. © 2011 Springer-Verlag.
• Rojas, M. R., & Saez, A. E. (2012). Two-Layer Model for Horizontal Pipe Flow of Newtonian and Non-Newtonian Settling Dense Slurries. INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 51(20), 7095-7103.
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  The steady-state flow of Newtonian and non-Newtonian dense aqueous slurries in horizontal pipes has been analyzed using a two-layer model, consisting of a top layer of flowing suspension and a bottom bed of stationary or moving particles. The coarse solids used have a wide range of particle density and particle size distributions. The fluids studied were designed to simulate U.S. Department of Energy Hanford site waste slurries. The most important changes from previous models include an independent settling analysis for different particle size fractions, effects of particle shape on settling velocity, and a new correlation for the turbulent particle dispersivity. The results indicate that the turbulent dispersivity of settling particles is sensitive to particle size and density. The model gives good estimation of the critical deposition velocity as the minimum of the pressure drop versus superficial slurry velocity relation. The existence of a stationary layer can be observed and predicted by the model under laminar and turbulent flow conditions.
• Rojas, M. R., & Sáez, A. E. (2012). Two-layer model for horizontal pipe flow of newtonian and non-newtonian settling dense slurries. Industrial and Engineering Chemistry Research, 51(20), 7095-7103.
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  Abstract: The steady-state flow of Newtonian and non-Newtonian dense aqueous slurries in horizontal pipes has been analyzed using a two-layer model, consisting of a top layer of flowing suspension and a bottom bed of stationary or moving particles. The coarse solids used have a wide range of particle density and particle size distributions. The fluids studied were designed to simulate U.S. Department of Energy Hanford site waste slurries. The most important changes from previous models include an independent settling analysis for different particle size fractions, effects of particle shape on settling velocity, and a new correlation for the turbulent particle dispersivity. The results indicate that the turbulent dispersivity of settling particles is sensitive to particle size and density. The model gives good estimation of the critical deposition velocity as the minimum of the pressure drop versus superficial slurry velocity relation. The existence of a stationary layer can be observed and predicted by the model under laminar and turbulent flow conditions. © 2012 American Chemical Society.
• Sorooshian, A., Csavina, J., Shingler, T., Dey, S., Brechtel, F. J., Saez, A. E., & Betterton, E. A. (2012). Hygroscopic and Chemical Properties of Aerosols Collected near a Copper Smelter: Implications for Public and Environmental Health. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 46(17), 9473-9480.
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  Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 mu m) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 mu m). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.
• Sorooshian, A., Csavina, J., Shingler, T., Dey, S., Brechtel, F. J., Sáez, A. E., & Betterton, E. A. (2012). Hygroscopic and chemical properties of aerosols collected near a copper smelter: implications for public and environmental health. Environmental science & technology, 46(17), 9473-80.
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  Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 μm) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 μm). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.
• Arnold, R. G., Heyworth, J., Sáez, A. E., Rodriguez, C., Weinstein, P., Ling, B., & Memon, S. (2011). The status of water and sanitation among Pacific Rim nations. Reviews on Environmental Health, 26(1), 17-30.
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  PMID: 21714378;Abstract: Analysis of relationships among national wealth, access to improved water supply and sanitation facilities, and population health indices suggests that the adequacy of water resources at the national level is a poor predictor of economic development - namely, that low water stress is neither necessary nor sufficient for economic development at the present state of water stress among Pacific Rim nations. Although nations differ dramatically in terms of priority provided to improved water and sanitation, there is some level of wealth (per capita GNP) at which all nations promote the development of essential environmental services. Among the Pacific Rim countries for which there are data, no nation with a per capita GNP < US$18,000 per year has failed to provide near universal access to improved water supply and sanitation. Below US$18,000/person-year, however, there are decided differences in the provision of sanitary services (improved water supply and sanitation) among nations with similar economic success. There is a fairly strong relationship between child mortality/life expectancy and access to improved sanitation, as expected from the experiences of developed nations. Here no attempt is made to produce causal relationships among these data. Failure to meet Millennium Development Goals for the extension of improved sanitation is frequently evident in nations with large rural populations. Under those circumstances, capital intensive water and sanitation facilities are infeasible, and process selection for water/wastewater treatment requires an adaptation to local conditions, the use of appropriate materials, etc., constraints that are mostly absent in the developed world. Exceptions to these general ideas exist in water-stressed parts of developed countries, where water supplies are frequently augmented by water harvesting, water reclamation/reuse, and the desalination of brackish water resources. Each of these processes involves public acceptance of water resources that are at least initially of inferior quality. Despite predictions of looming increases in water stress throughout the world, adaptation and resourcefulness generally allow us to meet water demand while pursuing rational economic development, even in the most water-stressed areas of the Pacific Rim.
• Csavina, J., Landázuri, A., Wonaschütz, A., Rine, K., Rheinheimer, P., Barbaris, B., Conant, W., Sáez, A. E., & Betterton, E. A. (2011). Metal and metalloid contaminants in atmospheric aerosols from mining operations. Water, Air, and Soil Pollution, 221(1-4), 145-157.
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  Abstract: Mining operations are potential sources of airborne metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern USA by climate models may make contaminated atmospheric dust and aerosols increasingly important, with potential deleterious effects on human health and ecology. Fine particulates such as those resulting from smelting operations may disperse more readily into the environment than coarser tailings dust. Fine particles also penetrate more deeply into the human respiratory system and may become more bioavailable due to their high specific surface area. In this work, we report the size-fractionated chemical characterization of atmospheric aerosols sampled over a period of a year near an active mining and smelting site in Arizona. Aerosols were characterized with a ten-stage (0.054 to 18 μm aerodynamic diameter) multiple orifice uniform deposit impactor (MOUDI), a scanning mobility particle sizer (SMPS), and a total suspended particulate collector. The MOUDI results show that arsenic and lead concentrations follow a bimodal distribution, with maxima centered at approximately 0.3 and 7.0 μm diameter. We hypothesize that the sub-micron arsenic and lead are the product of condensation and coagulation of smelting vapors. In the coarse size, contaminants are thought to originate as Aeolian dust from mine tailings and other sources. Observation of ultrafine particle number concentration (SMPS) show the highest readings when the wind comes from the general direction of the smelting operations site. © 2011 Springer Science+Business Media B.V.
• Ela, W. P., Sedlak, D. L., Barlaz, M. A., Henry, H. F., Muir, D. C., Swackhamer, D. L., Weber, E. J., Arnold, R. G., Ferguson, P. L., Field, J. A., Furlong, E. T., Giesy, J. P., Halden, R. U., Henry, T., Hites, R. A., Hornbuckle, K. C., Howard, P. H., Luthy, R. G., Meyer, A. K., , Sáez, A. E., et al. (2011). Toward identifying the next generation of superfund and hazardous waste site contaminants. Environmental Health Perspectives, 119(1), 6-10.
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  PMID: 21205582;PMCID: PMC3018501;Abstract: Background: This commentary evolved from a workshop sponsored by the National Institute of Environmental Health Sciences titled "Superfund Contaminants: The Next Generation" held in Tucson, Arizona, in August 2009. All the authors were workshop participants. obBjectives: Our aim was to initiate a dynamic, adaptable process for identifying contaminants of emerging concern (CECs) that are likely to be found in future hazardous waste sites, and to identify the gaps in primary research that cause uncertainty in determining future hazardous waste site contaminants. Superfund-relevant CECs can be characterized by specifc attributes: Tey are persistent, bioaccumulative, toxic, occur in large quantities, and have localized accumulation with a likelihood of exposure. Although still under development and incompletely applied, methods to quantify these attributes can assist in winnowing down the list of candidates from the universe of potential CECs. Unfortunately, signifcant research gaps exist in detection and quantifcation, environ mental fate and transport, health and risk assessment, and site exploration and remediation for CECs. Addressing these gaps is prerequisite to a preventive approach to generating and managing hazardous waste sites. A need exists for a carefully considered and orchestrated expansion of programmatic and research eforts to identify, evaluate, and manage CECs of hazardous waste site relevance, including developing an evolving list of priority CECs, intensifying the identifcation and monitoring of likely sites of present or future accumulation of CECs, and implementing eforts that focus on a holistic approach to prevention.
• Rodríguez, M., Xue, J., Gouveia, L. M., Müller, A. J., Sáez, A. E., Rigolini, J., & Grassl, B. (2011). Shear rheology of anionic and zwitterionic modified polyacrylamides. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 373(1-3), 66-73.
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  Abstract: Two groups of copolymers were synthesized from high molecular weight polyacrylamides. One group of copolymers consisted of sulfonated, anionic copolymers (PAM-S) of acrylamide with the sodium salt of 2-acryloamido-2-methyl-1-propane sulfonic acid, and the other consisted of zwitterionic copolymers (PAM-Z) of acrylamide with a sulfobetaine methacrylate monomer. The shear rheology of aqueous solutions of the copolymers and their mixtures was studied experimentally. Solutions of both copolymers exhibit shear thinning behavior in the range of concentrations explored. Solutions of mixtures of two copolymers (PAM-Z and PAM-S) exhibited a slight viscosity synergy at high relative contents of PAM-S. Addition of a relatively high concentration of an electrolyte (0.3. M NaCl) induces decreases in viscosity due to coil contraction and eliminates the synergy of the mixtures. Mixtures of the zwitterionic copolymer and a cationic surfactant, cetyl trimethylammonium p-toluene sulfonate (CTAT), were also studied. These solutions exhibit a strong synergistic effect at low-shear rates when the surfactant forms wormlike micelles. In addition, oscillatory shear measurements demonstrate that PAM-Z/CTAT mixtures are significantly more elastic than CTAT solutions, which indicates that PAM-Z is effective in promoting micelle entanglements, as reflected by the increase in relaxation time with PAM-Z content. © 2010 Elsevier B.V.
• Rojas, M. R., Leung, C., Whitley, D., Zhu, Y., Arnold, R. G., & Sáez, A. E. (2011). Advanced oxidation of trace organics in water by hydrogen peroxide solar photolysis. Industrial and Engineering Chemistry Research, 50(22), 12479-12487.
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  Abstract: Solar-UV/H2O2 advanced oxidation for destruction of trace organics was investigated under a variety of operating conditions in homogeneous, laboratory-scale batch reactor experiments. Fluorescein and p-cresol were selected as representative targets in the experiments. Half times for degradation of p-cresol ranged between 500 min with 2 mM H2O 2 and 20 min with 50 mM H2O2 during high-solar irradiance experiments (around noon on July 15th). A kinetic model, previously developed for monochromatic light, was adapted for use with solar UV irradiance, using (i) calculated ground-level solar spectral irradiance for the date and time of the experiments and (ii) wavelength-dependent light attenuation in the reaction mixture. The model accurately represents experimental data without adjustable parameters. Model output included the time-dependent pH arising from complete mineralization of the targets. Observed radical scavenging effects were correctly predicted by the kinetic model. Contaminant transformation was also measured in a municipal secondary wastewater effluent matrix. Here, 2-D fluorescence spectroscopy was used as a measure of the time-dependent bulk organic characteristics in treated wastewater. Results indicated that solar-UV/H2O2 advanced oxidation is capable of eliminating or drastically reducing the concentrations of organic constituents that remain in conventionally treated municipal wastewater effluent. © 2011 American Chemical Society.
• Csavina, J., Sáez, A., Betterton, E. A., Barbaris, B., Rine, K., Campillo, A., Rheinheimer, P., Landázuri, A., Wonaschutz, A., & Conant, W. (2010). Modeling and characterization of aerosol emissions from mining operations. AIChE Annual Meeting, Conference Proceedings.
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  Abstract: Problem statement: Mining operations are important sources of airborne metal and metalloid contaminants: smelting may lead to emissions of metals and metalloids, while wind erosion of mine tailings mobilizes dust particles containing trace metals. Contaminant transport by atmospheric aerosols in arid and semiarid climates, such as the Southwestern US, may become increasingly important with predicted regional climate change, with potential deleterious effects on human health and ecology. Fine particulates (size
• Rojas, M. R., Müller, A. J., & Sáez, A. E. (2010). Effect of ionic environment on the rheology of wormlike micelle solutions of mixtures of surfactants with opposite charge. Journal of Colloid and Interface Science, 342(1), 103-109.
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  PMID: 19879593;Abstract: This work reports on the rheological characterization of aqueous solutions of mixtures of a cationic surfactant (hexadecyltrimethylammonium p-toluenesulfonate, CTAT), capable of forming wormlike micelles, and an anionic surfactant (sodium dodecylsulfate, SDS) when the ionic environment of the solution is altered by the addition of electrolytes. Previous work showed that mixtures CTAT/SDS exhibit a strong rheological synergy in shear flows caused by promotion of interaction between wormlike micelles by the presence of the dodecylsulfate anion. In this work, we explore the CTAT/SDS synergy in the presence of electrolytes. The effect of the added electrolyte varies with wormlike micelle concentration range and type of flow. In simple shear flows and relatively low wormlike micelle concentrations (dilute regime), electrolyte addition inhibits the shear thickening effect observed in CTAT/SDS solution. In porous media flows, which have an important elongational component, electrolyte addition results in an appreciable increase in apparent viscosity at low electrolyte concentrations. In the semi-dilute regime, electrolyte addition at low concentrations strengthens the synergy between CTAT and SDS, leading to higher shear viscosities, especially at low-shear rates. An important consequence of these results is the potential for manipulation of the rheology of solutions of wormlike micelles by induction of intermicelle associations and/or promotion of conformational changes by electrolyte addition. © 2009 Elsevier Inc. All rights reserved.
• Rojas, M. R., Pérez, F., Whitley, D., Arnold, R. G., & Sáez, A. E. (2010). Modeling of advanced oxidation of trace organic contaminants by hydrogen peroxide photolysis and fentons reaction. Industrial and Engineering Chemistry Research, 49(22), 11331-11343.
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  Abstract: The kinetics of nonylphenol and p-cresol destruction by hydrogen peroxide photolysis and Fentons reaction was investigated under a variety of operating conditions in homogeneous, laboratory-scale batch reactor experiments. Models with no adjustable parameters successfully accounted for radical initiation by photolysis of H2O2 or radical initiation by Fentons mechanism, reaction of organic targets with hydroxyl radical, and radical scavenging and recombination mechanisms, as well as changes in solution pH due to evolution of carbon dioxide because of target mineralization. Simulations of the UV/H2O2 and Fenton-based models can be used to anticipate the kinetics of advanced oxidation involving any target compound for which there is a known apparent second-order rate constant for reaction with hydroxyl radical. The presence of radical scavengers was successfully treated by the model, suggesting that the model can be generalized to the treatment of complex matrixes. © 2010 American Chemical Society.
• Shan, J., Sáez, A. E., & Ela, W. P. (2010). Evaluating the mobility of arsenic in synthetic iron-containing solids u sing a modified sequential extraction method. Journal of Environmental Engineering, 136(2), 238-245.
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  Abstract: Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing residuals which are disposed in nonhazardous landfills. Previous works have established that many of these residuals will release arsenic to a much greater extent than predicted by standard regulatory leaching tests (e.g., the toxicity characteristic leaching procedure) and, consequently, require stabilization to ensure benign behavior after disposal. In this work, a four-step sequential extraction method was developed in an effort to determine the proportion of arsenic in various phases in untreated as well as stabilized iron-based solid matrices. The solids synthesized using various potential stabilization techniques included: amorphous arsenic-iron sludge (ASL), reduced ASL via reaction with zero valent iron (RASL), amorphous ferrous arsenate (PFA), a mixture of PFA and SL (M1), crystalline ferrous arsenate (HPFA), and a mixture of HPFA and SL (M2). The overall arsenic mobility of the tested samples increased in the following order: ASL>RASL>PFA>M>1>HPFA>M >2. © 2010 ASCE.
• Amundarain, J. L., Castro, L. J., Rojas, M. R., Siquier, S., Ramírez, N., Müller, A., & Sáez, A. (2009). Solutions of xanthan gum/guar gum mixtures: Shear rheology, porous media flow, and solids transport in annular flow. Rheologica Acta, 48(5), 491-498.
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  Abstract: Mixtures of xanthan and guar gum in aqueous solution were studied in two flow situations: simple shear and porous media. In addition, solids transport in vertical annular flow of sand suspensions was explored. The zero shear rate viscosity of the solutions displayed a pronounced synergy: the viscosity of the mixture is higher than that of the polymer solutions in a wide range of relative concentrations of the two polymers, in agreement with previous literature. However, at relatively high shear rates, the viscosity approaches the value of the more viscous xanthan gum solutions at mass fractions of xanthan gum between 0.1 and 0.15, and the degree of synergy substantially decreases. Stress relaxation experiments in simple shear indicate that the polymer mixtures exhibit a well-defined yield stress after relaxation that is absent in solutions of pure polymers. In porous media flow experiments, a synergistic behavior mimicking the shear flow results was obtained for the polymer mixtures at low shear rates. However, at a critical shear rate, the apparent viscosity in porous media flows exceeds the shear viscosity due to the elongational nature of flow in the pores. The solids transport capacity in annular flows is well-represented by trends in shear viscosity and stress relaxation behavior. However, the lack of viscosity synergy at high shear rates limits the applicability of the mixtures as a way to improve solids suspension capacity in annular flows. © Springer-Verlag 2008.
• Calderón, M., Velasco, M. I., Strumia, M. C., Lorenzo, A. T., Müller, A. J., Rojas, M. R., & Sáez, A. E. (2009). Synthesis of amphiphilic dendrons and their interactions in aqueous solutions with cetyltrimethylammonium p-toluenesulfonate (CTAT). Journal of Colloid and Interface Science, 336(2), 462-469.
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  PMID: 19427644;Abstract: In this work, we report synthesis and rheology of an interesting structured fluid based on the self-assembly of amphiphilic dendrons and wormlike micelles. Two amphiphilic dendrons were synthesized by the combination of aliphatic chains and polar dendritic heads. They showed different degrees of hydrophobicity and formed micelles in aqueous solution at critical micelle concentrations (CMC) of 25 and 125 ppm. The dendrons were soluble in water up to a concentration of approximately 1200 ppm, and produced no measurable increase in the viscosity of the solvent. The rheology of solutions of mixtures of each dendron with cetyltrimethylammonium p-toluenesulfonate (CTAT, a cationic surfactant) was characterized in simple shear flow. In the concentration range in which CTAT forms semidilute solutions of wormlike micelles, dendron addition produced a substantial synergy in zero-shear rate viscosity. Parallel-plate oscillatory shear measurements demonstrated that the CTAT/dendron mixtures are significantly more elastic than CTAT solutions. The viscosity synergy occurs at dendron concentrations lower than their CMC, and it is stronger for the more hydrophobic dendron. This suggests that the interactions between dendrons and wormlike micelles are basically hydrophobic, which implies attachment of dendron micelles to wormlike CTAT micelles in a manner similar to micellization of surfactants on polyelectrolytes. © 2009 Elsevier Inc. All rights reserved.
• Rupp, E. C., Betterton, E. A., Arnold, R. G., & Sáez, A. E. (2009). Interaction of perchloroethylene with cerium oxide in three-way catalysts. Catalysis Letters, 132(1-2), 153-158.
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  Abstract: The role of cerium oxide on direct oxidation of perchloroethylene (PCE) by a three-way catalyst was explored. In the absence of an external oxidizing agent, PCE was oxidized over an alumina supported Pt/Rh three-way catalyst. We hypothesize that the chlorine atoms in the adsorbed PCE interact with oxygen in CeO2, reducing the cerium to create CeCl3. © 2009 Springer Science+Business Media, LLC.
• Willinger, M., Rupp, E., Barbaris, B., Gao, S., Arnold, R., Betterton, E., & Sáez, A. E. (2009). Thermocatalytic destruction of gas-phase perchloroethylene using propane as a hydrogen source. Journal of Hazardous Materials, 167(1-3), 770-776.
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  PMID: 19217713;PMCID: PMC2693271;Abstract: The use of propane in combination with oxygen to promote the destruction of perchloroethylene (PCE) over a platinum (Pt)/rhodium (Rh) catalyst on a cerium/zirconium oxide washcoat supported on an alumina monolith was explored. Conversions of PCE were measured in a continuous flow reactor with residence times less than 0.5 s and temperatures ranging from 200 to 600 °C. The presence of propane was shown to increase significantly the conversion of PCE over oxygen-only conditions. Conversions close to 100% were observed at temperatures lower than 450 °C with 20% oxygen and 2% propane in the feed, which makes this process attractive from a practical standpoint. In the absence of oxygen, PCE conversion is even higher, but the catalyst suffers significant deactivation in less than an hour. Even though results show that oxygen competes with reactants for active sites on the catalyst, the long-term stability that oxygen confers to the catalyst makes the process an efficient alternative to PCE oxidation. A Langmuir-Hinshelwood competitive adsorption model is proposed to quantify PCE conversion. © 2009 Elsevier B.V. All rights reserved.
• Arnold, R. G., Teske, S., Tomanek, M., Engstrom, J., Leung, C., Zhang, J., Banihani, Q., Quanrud, D., Ela, W. P., & Sáez, A. E. (2008). Fate of polybrominated diphenyl ethers during wastewater treatment/polishing and sludge stabilization/disposal. Annals of the New York Academy of Sciences, 1140, 394-411.
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  PMID: 18991940;Abstract: Large quantities of polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in clothing and plastic products since the 1970s. A small fraction of the PBDEs in manufactured products subsequently enters municipal wastewater. Nevertheless, the resistance of these compounds to chemical and biochemical transformations provides opportunities for accumulation in sediments that are in contact with wastewater effluent and agricultural soils that are amended with biosolids derived from wastewater treatment. Balances developed for PBDE congeners indicate that conventional wastewater treatment processes and soil infiltration of treated wastewater in recharge operations do not discriminate significantly among the major congeners in commercially available PBDE products. Accumulation of PBDEs at near part-per-million levels was measured in the surface sediments at the Sweetwater Recharge Facility in Tucson, Arizona, during 10-15 years of operation. Half-lives for loss of major PBDE congeners from sediments were decades or longer. Local agricultural soils amended with biosolids over a 20-year period showed similar accumulation of PBDEs. The widespread use of PBDEs in commercial products, compound persistence, and toxicity indicate that additional effort is warranted to better understand fate-determining processes for PBDEs in the environment. © 2008 New York Academy of Sciences.
• Daniel, R. C., Poloski, A. P., & Sáez, A. (2008). Vane rheology of cohesionless glass beads. Powder Technology, 181(3), 237-248.
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  Abstract: The rheology of a single coarse granular powder has been studied with shear vane rotational viscometry. The torque required to maintain constant rotation of a vane tool in a loose bed of glass beads (with a mean particle size of 203 μm) is measured as a function of vane immersion depth and rotational speed. The resulting torque profiles exhibit both Coulombic behavior at low rotational rates and fluid-like, collisional behavior at high rotational rates. Analyzing vane shaft and end effects allows the flow dynamics at the cylindrical and top and bottom disk surfaces of vane rotation to be determined. Disk surfaces show a uniform torque profile consistent with Coulombic friction over most of the rotational rates studied. In contrast, cylindrical surfaces show both frictional and collisional torque contributions, with significant dynamic torque increases at deep immersion depths and fast vane rotation. © 2007.
• Gao, S., Rupp, E., Bell, S., Willinger, M., Foley, T., Barbaris, B., Sáez, A. E., Arnold, R. G., & Betterton, E. (2008). Mixed redox catalytic destruction of chlorinated solvents in soils and groundwater: From the laboratory to the field. Annals of the New York Academy of Sciences, 1140, 435-445.
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  PMID: 18991945;PMCID: PMC2867620;Abstract: A new thermocatalytic method to destroy chlorinated solvents has been developed in the laboratory and tested in a pilot field study. The method employs a conventional Pt/Rh catalyst on a ceramic honeycomb. Reactions proceed at moderate temperatures in the simultaneous presence of oxygen and a reductant (mixed redox conditions) to minimize catalyst deactivation. In the laboratory, stable operation with high conversions (above 90% at residence times shorter than 1 s) for perchloroethylene (PCE) is achieved using hydrogen as the reductant. A molar ratio of H2/O2 = 2 yields maximum conversions; the temperature required to produce maximum conversions is sensitive to influent PCE concentration. When a homologous series of aliphatic alkanes is used to replace hydrogen as the reductant, the resultant mixed redox conditions also produce high PCE conversions. It appears that the dissociation energy of the C-H bond in the respective alkane molecule is a strong determinant of the activation energy, and therefore the reaction rate, for PCE conversion. This new method was employed in a pilot field study in Tucson, Arizona. The mixed redox system was operated semicontinuously for 240 days with no degradation of catalyst performance and complete destruction of PCE and trichloroethylene in a soil vapor extraction gas stream. Use of propane as the reductant significantly reduced operating costs. Mixed redox destruction of chlorinated solvents provides a potentially viable alternative to current soil and groundwater remediation technologies. © 2008 New York Academy of Sciences.
• Mukiibi, M., Ela, W. P., & Sáez, A. E. (2008). Effect of ferrous iron on arsenate sorption to amorphous ferric hydroxide. Annals of the New York Academy of Sciences, 1140, 335-345.
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  PMID: 18991933;Abstract: Amorphous ferric hydroxide (AFH) sorbents are commonly used for removal of arsenate from water. When disposed in microbially active, reducing environments, such as landfills, Fe(II) will be generated by reductive dissolution of the AFH surface and arsenate will be desorbed. However, the observed ratio of arsenate (and, in fact, total arsenic) to total iron in the leachate is not consistent with the original ratio of arsenate to iron on the AFH. Work to determine if ferrous iron re-adsorption to the AFH can partially explain this inconsistency is described. As pH increases above 7, Fe(II) increasingly sorbs onto the AFH surface. This sorption is largely independent of ionic strength and somewhat irreversible at high pH. In contrast, arsenate partitioning to AFH decreases with increasing pH. However, over the pH range from 5 to 9, the presence of Fe(II) sorbed to the AFH surface increases the capacity for arsenate sorption. In addition, when no Fe(II) is present, arsenate binding is largely to surface sites inaccessible to Fe(II) binding. The results are also consistent with Fe(II) sorption to AFH sites, otherwise unfavorable to arsenate binding and transformation of those sites into arsenate-amenable binding sites. © 2008 New York Academy of Sciences.
• Orbay, Ö., Gao, S., Barbaris, B., Rupp, E., Sáez, A. E., Arnold, R. G., & Betterton, E. A. (2008). Catalytic dechlorination of gas-phase perchloroethylene under mixed redox conditions. Applied Catalysis B: Environmental, 79(1), 43-52.
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  Abstract: The validity of a new method to destroy gas-phase perchloroethylene (PCE) is demonstrated at bench scale using a fixed-bed reactor that contains a Pt/Rh catalyst. Hydrogen and oxygen were simultaneously fed to the reactor together with PCE. The conversion efficiencies of PCE were sensitive to H2/O2 ratio and reactor temperature. When the temperature was ≥400 °C and H2/O2 was ≥2.15, PCE conversion efficiency was maintained at ≥90%. No catalyst deactivation was observed for over 2 years, using only mild, convenient regeneration procedures. It is likely that PCE reduction steps precede oxidation reactions and that the importance of oxidation lies in its elimination of intermediates that would otherwise lead to catalyst poisoning. In practice, this catalytic dechlorination method holds potential for low-cost, large-scale field operation. © 2007 Elsevier B.V. All rights reserved.
• Rojas, M. R., Müller, A. J., & Sáez, A. E. (2008). Shear rheology and porous media flow of wormlike micelle solutions formed by mixtures of surfactants of opposite charge. Journal of Colloid and Interface Science, 326(1), 221-226.
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  PMID: 18674777;Abstract: The rheology of solutions of wormlike micelles formed by oppositely charged surfactant mixtures (cationic cetyl trimethylammonium p-toluene sulfonate, CTAT, and anionic sodium dodecyl sulfate, SDS), in the dilute and semi-dilute regimes, were studied under simple shear and porous media flows. Aqueous mixtures of CTAT and SDS formed homogeneous solutions for SDS/CTAT molar ratios below 0.12. Solutions of mixtures exhibited a strong synergistic effect in shear viscosity, especially in the semi-dilute regime with respect to wormlike micelles, reaching a four order of magnitude increase in the zero-shear rate viscosity for solutions with 20 mM CTAT. Oscillatory shear results demonstrated that the microstructure of CTAT wormlike micelles is sensitive to SDS addition. The cross-over relaxation times of wormlike micelles of 20 mM CTAT solutions increased by three orders of magnitude with the addition of up to 2 mM of SDS, and the solutions became increasingly elastic. The shear thickening process observed in shear rheology became more pronounced in porous media flow due to the formation of stronger cooperative structures induced by the extensional component of the flow. © 2008 Elsevier Inc. All rights reserved.
• Rojas, M. R., Müller, A., & Sáez, A. (2008). Synergistic effects in flows of mixtures of wormlike micelles and hydroxyethyl celluloses with or without hydrophobic modifications. Journal of Colloid and Interface Science, 322(1), 65-72.
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  PMID: 18384803;Abstract: This work presents experimental results on simple shear and porous media flow of aqueous solutions of two hydroxyethyl celluloses (HEC) and two hydrophobically modified hydroxyethyl celluloses (HMHEC) with different molecular weights. Mixtures of these polymers with a cationic surfactant, cetyltrimethylammonium p-toluenesulfonate (CTAT) were also studied. Emphasis was given to the range of surfactant concentrations in which wormlike micelles are formed. The presence of hydrophobic groups, the effect of the molecular weight of the polymers, the surfactant and polymer concentrations, and the effect of the flow field type (simple shear versus porous media flow) were the most important variables studied. The results show that the shear viscosity of HEC/CTAT solutions is higher than the viscosities of surfactant and polymer solutions at the same concentrations, but surface tension measurements indicate that no complex formation occurs between CTAT and HEC. On the other hand, a complex driven by hydrophobic interactions was detected by surface tension measurements between CTAT and HMHEC. In this case, the viscosity of the mixture increases significantly more (up to four orders of magnitude at high CTAT concentrations) in comparison with HEC/CTAT aqueous solutions. Increments in the molecular weight of the polymers increase the interaction with CTAT and the shear viscosity of the solution, but make phase separation more feasible. In porous media flow, the polymer/CTAT mixtures exhibited higher apparent viscosities than in simple shear flows. This result suggests that the extensional component of the flow field in porous media flows leads to a stronger interaction between the polymer and the wormlike micelles, probably as a consequence of change of conformation and growth of the micelles. © 2008 Elsevier Inc. All rights reserved.
• Rojas, M., Andará, O., Müller, A., Siquier, S., Ramírez, N., & Sáez, E. (2008). Transport of solids in solutions of biopolymer mixtures and improvements to their distribution in a flow simulator in vertical conduits with annular cross section. Revista de la Facultad de Ingenieria, 23(3), 43-51.
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  Abstract: This paper compares the results on suspension and transport of solids in two experimental flow simulators in vertical ducts with annular cross section. In both cases, non-Newtonian biopolymer solutions were used as the liquid phase. The biopolymers used were xanthan gum and guar gum, and the solid phase was silica sand with an average particle size of 250 μm. The first experimental system used was based on a 3-m height concentric pipe with a 0.15 m hydraulic diameter. The second equipment was built by changing the dimensions of the first system to a height of 6 m and a 0.10 m hydraulic diameter. These changes were made so that the solid phase would distribute better throughout the whole system. Both units simulate a well drilling process at room temperature and without the effect of drill bit rotation. The most important variables studied were annular velocity and polymer concentration. Significant improvements were obtained in solids transport when changing the solids distribution pattern in the system and the geometrical characteristics of the annulus. Furthermore, the xanthan-guar gum mixture solutions with a higher proportion of guar gum have a higher solids transport capacity than pure polymer solutions; there is an important synergistic effect from the point of view of the use of these polymers as viscosifying additives for drilling fluids.
• Shaw, J. K., Fathordoobadi, S., Zelinski, B. J., Ela, W. P., & Sáez, A. (2008). Stabilization of arsenic-bearing solid residuals in polymeric matrices. Journal of Hazardous Materials, 152(3), 1115-1121.
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  PMID: 17825487;Abstract: This research investigates the use of polymeric matrices to encapsulate solid sorbents used to remove arsenic from drinking water. Arsenic-containing granular ferric oxy/hydroxide and ferric hydroxide amended alumina residuals were encapsulated in a polymeric matrix using a novel aqueous-based manufacturing process. The polymer was a blend of poly(styrene butadiene) and an epoxy resin. The polymeric waste forms produced were capable of containing more than 60 wt% of sorbent (dry basis), while keeping good mechanical properties. Arsenic leaching from encapsulated and unencapsulated residuals was evaluated using the standard toxicity characteristic leaching procedure (TCLP) and the California Waste Extraction Test (CA-WET). The results show that waste forms of the polymer-encapsulated residuals crushed for testing retain good leaching resistance when evaluated with the more aggressive CA-WET test, yielding leachate arsenic concentrations below the toxicity characteristic (TC) standard of 5 mg/L. When residuals were preprocessed and encapsulated in a polymer form that avoided the size reduction required by leaching protocols, arsenic leached up to 700 times less than that from the unencapsulated residuals. Comparison of the waste form developed here with conventional cement matrices containing the same residuals show that the polymeric matrices were capable of encapsulating appreciably more material and leached arsenic at concentration levels that were more than an order of magnitude lower than cement. © 2007 Elsevier B.V. All rights reserved.
• Shaw, J., Pepe, L., Ela, W., & Sáez, A. E. (2008). Damage control: Managing the residuals generated during arsenic treatment. Water Quality Technology Conference and Exposition 2008, 2762-2768.
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  Abstract: The recently reduced USEPA Maximum Contaminant Level (MCL) for arsenic in drinking water has forced facilities to either implement new or modifying existing arsenic removal technologies to meet the 10 μg/L MCL. The favored EPA-identified treatment option is adsorption onto solid media. These treatment processes generate arsenic-bearing solid residuals (ABSR) that must be tested and potentially treated prior to disposal. A growing body of research has demonstrated that these residuals may pose an unacceptable risk if disposed untreated in non-hazardous landfills. This risk motivated the development of an innovative stabilization method: polymeric encapsulation. Polymeric encapsulation out-performs the only reported alternative encapsulation technique, cement stabilization, with respect to both residual loading capacity (greater than 3-fold increase) and leach resistance. Another way to reduce the risk of ABSR disposal is to reduce the amount of ABSR generated, which could be achieved through the use of regenerable media. However, regeneration produces an arsenic-laden brine that must then be treated prior to disposal. This research investigated the use of less common, non-iron-based adsorption media for the treatment regenerate brine waste streams. Four media types (lanthanum hydroxide, ferric/lanthanum hydroxide, zirconium dioxide, and titanium oxide composition) were identified as potential treatment options based on their ability to retain relatively high arsenic capacities relative to traditional iron-based media. © 2008 American Water Works Association.
• Szidarovszky, M., Heckel, K., Sáez, A. E., & Ela, W. (2008). Removal of arsenate ions from water using micellar enhanced ultrafiltration. AIChE Annual Meeting, Conference Proceedings.
• Torres, M. F., Müller, A. J., Szidarovszky, M. A., & Sáez, A. E. (2008). Shear and extensional rheology of solutions of mixtures of poly(ethylene oxide) and anionic surfactants in ionic environments. Journal of Colloid and Interface Science, 326(1), 254-260.
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  PMID: 18684464;Abstract: Interactions between a high molecular weight poly(ethylene oxide) (PEO) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions were investigated by shear and extensional rheometry. Results for mixtures between PEO and sodium dodecyl sulfate (SDS) are also presented for comparison purposes. Addition of anionic surfactants to PEO solutions above the critical aggregation concentration (CAC), at which micellar aggregates attach to the polymer chain, results in an increase in shear viscosity due to PEO coil expansion, and a strengthening of interchain interactions. In extensional flows, these interactions result in a decrease of the critical shear rate for the onset of the characteristic extension thickening of the PEO solutions that is due to transient entanglements of polymer molecules. The relaxation times associated with these transient entanglements are not directly proportional to the shear viscosity of the solutions, but rather vary more rapidly with surfactant concentration. In the presence of an electrolyte, coil contraction results in lower shear viscosities and a decrease in the extension thickening effects at surfactant concentrations just beyond the CAC. The relaxation times associated with transient entanglement reach a minimum at the same surfactant concentration as the shear viscosity, which indicates that coil contraction is responsible for the observed effects in both types of flow. However, the increase in extensional-flow entanglement relaxation times is much more abrupt than the decrease in shear viscosity. All these results point to a greater sensitivity of extensional flows on the molecular conformation of PEO/surfactant complexes. © 2008 Elsevier Inc. All rights reserved.
• Zhang, J., Tomanek, M., Dong, H., Arnold, R. G., Ela, W. P., Quanrud, D. M., & Sáez, A. E. (2008). Fate of polybrominated diphenyl ethers, nonylphenol, and estrogenic activity during managed infiltration of wastewater effluent. Journal of Environmental Engineering, 134(6), 433-442.
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  Abstract: About a billion cubic meters of wastewater effluent are artificially recharged annually in the United States for maintenance of groundwater levels and prevention of seawater intrusion. There is concern that trace contaminants, including various endocrine disrupting compounds (EDCs), are not completely removed during infiltration, leading to deterioration of groundwater quality. In this work, we investigate the mechanisms and efficiency of EDC removal at the Sweetwater Recharge Facility, which is used to recharge secondary effluent from the Roger Road Wastewater Treatment Plant in Tucson, Ariz. Material was collected from the top meter of sediments in two infiltration basins and analyzed for extractable nonylphenol (NP), polybrominated diphenyl ethers (PBDE) and total estrogenic activity. The basins differed significantly in length of service (7 versus 15 years). Nevertheless, profiles of extractable contaminants and estrogenic activity were similar in the two basins. Results suggest that hydrophobic determinants of estrogenic activity are efficiently retained in surface sediments during soil-aquifer treatment. However, measurable levels of PBDEs, NP, and estrogenic activity are present in infiltrate that reaches the local unconfined aquifer at ∼40 m below land surface. © 2008 ASCE.
• Conroy, O., Sáez, A. E., Quanrud, D., Ela, W., & Arnold, R. G. (2007). Changes in estrogen/anti-estrogen activities in ponded secondary effluent. Science of the Total Environment, 382(2-3), 311-323.
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  PMID: 17543371;Abstract: Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decreased from 60 pM (equivalent 17α-ethinylestradiol concentration) to an estimated 1.4 pM during a 24-hour period in which secondary effluent was held in a shallow infiltration basin. Over the same period, anti-estrogenic activity, measured as an equivalent concentration of tamoxifen, increased from 35 to 260 nM, suggesting that antagonists produced during secondary effluent storage played a role in the apparent loss of estrogenic activity. Androgenic activity, measured over the same 24-hour period using the yeast androgen screen, was near or below the method detection limit (0.7 pM as testosterone). However, the same pond samples were clearly anti-androgenic. When whole-sample extracts were separated via adsorption and stepwise elution in alcohol/water solutions consisting of 20, 40 and 100% ethanol, the sum of estrogenic activities in derived fractions was always lower than the measured estrogenic activity in the whole-sample extracts. Summed anti-estrogenic activities in the same fractions, however, always exceeded values for corresponding whole-sample extracts. Results reinforce the importance of sample preparation steps (concentration of organics followed by estrogen/anti-estrogen separation) when measuring endocrine-related activities in chemically complex samples such as wastewater effluent. The potential complexity of relationships among estrogens, anti-estrogens and matrix organics suggests that additive models are of questionable validity for estimating whole-sample estrogenic activity from measurements involving sample fractions. © 2007 Elsevier B.V. All rights reserved.
• Daniel, R. C., Poloski, A. P., & Sáez, A. E. (2007). A continuum constitutive model for cohesionless granular flows. Chemical Engineering Science, 62(5), 1343-1350.
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  Abstract: A constitutive model is developed to represent shear granular flows of cohesionless solids. The model is based on the postulate that the friction coefficient and the solids fraction in a moving granular material are exclusive functions of the inertial number, which represents the ratio of inertial to normal stress forces. The constitutive equation obtained has the same form as a multidimensional Bingham fluid model, albeit with apparent viscosity and yield stress that depend on the vertical normal stress. The model is applied to previously published experimental results dealing with shear flows of granular beds made up of cohesionless spherical particles. The first case analyzed corresponds to a granular bed moving on top of a rotating disk. The model captures the main trends of the velocity profiles with a single adjustable parameter. The second case is a conventional Couette flow, for which the model is capable of representing the velocity and solids fraction profiles measured experimentally. © 2006 Elsevier Ltd. All rights reserved.
• Penott-Chang, E. K., Gouveia, L., Fernández, I. J., Müller, A. J., Díaz-Barrios, A., & Sáez, A. E. (2007). Rheology of aqueous solutions of hydrophobically modified polyacrylamides and surfactants. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 295(1-3), 99-106.
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  Abstract: Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using as hydrophobic monomers n-decylacrylamide and t-octyl-acrylamide. The synthesized polymers contained between 0.5 and 1.5 mol.% of the hydrophobic groups. Shear rheology experiments showed a viscosity enhancement for most copolymers in comparison with the homopolymers due to intermolecular hydrophobic associations, which lead to shear thickening for copolymers with 1 mol.% or more hydrophobic groups. An increase in the ionic strength of the solutions strengthens these hydrophobic associations. The addition of an anionic surfactant (sodium dodecyl sulfate, SDS) produced viscosity increases due to intermolecular bridging caused by the formation of mixed micelles between the hydrophobic groups and the surfactant. Higher surfactant concentrations lead to a viscosity reduction due to electrostatic screening of associations between hydrophobic side groups of different chains. The same behavior was observed in the spherical micelle concentration regime for the cationic surfactant cetyltrimethylammonium p-toluenesulfonate (CTAT), but at higher surfactant concentrations, entanglements between the copolymers and worm-like micelles lead to further increases in solution viscosity. © 2006 Elsevier B.V. All rights reserved.
• Torres, M. F., González, J. M., Rojas, M. R., Müller, A. J., Sáez, A. E., Löf, D., & Schillén, K. (2007). Effect of ionic strength on the rheological behavior of aqueous cetyltrimethylammonium p-toluene sulfonate solutions. Journal of Colloid and Interface Science, 307(1), 221-228.
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  PMID: 17118386;Abstract: The influence of ionic environment on the rheological properties of aqueous cetyltrimethylammonium p-toluene sulfonate (CTAT) solutions has been studied under three different flow fields: simple shear, opposed-jets flow and porous media flow. Emphasis was placed in the experiments on a range of CTAT concentration in which wormlike micelles were formed. It is known that these solutions exhibit shear thickening in the semi-dilute regime, which has been explained in terms of the formation of shear-induced, cooperative structures involving wormlike micelles. In simple shear flow, the zero shear viscosity exhibits first an increase with salt addition followed by a decrease, while the critical shear rate for shear thickening increases sharply at low salt contents and tends to saturate at relatively high ionic strengths. The results are explained in terms of a competition between micellar growth induced by salt addition and changes in micellar flexibility caused by ionic screening effects. Dynamic light scattering results indicate that micelles grow rapidly upon salt addition but eventually achieve a constant size under static conditions. These observations suggest that the wormlike micelles continuously grow with salt addition, but, as they become more flexible due to electrostatic screening, the wormlike coils tend to adopt a more compact conformation. The trends observed in the apparent viscosities measured in porous media flows seem to confirm these hypotheses-but viscosity increases in the shear thickening region-and are magnified by micelle deformation induced by the elongational nature of the local flow in the pores. In opposed-jets flow, the solutions have a behavior that is close to Newtonian, which suggests that the range of strain rates employed makes the flow strong enough to destroy or prevent the formation of cooperative micellar structures. © 2006.
• De, C., Bishop, K. G., Bercik, L. M., Johnson, M., Potzler, M., Ela, W. P., Sáez, A., Huling, S. G., & Arnold, R. G. (2006). In-place regeneration of granular activated carbon using fenton's reagents. ACS Symposium Series, 940, 43-65.
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  Abstract: The feasibility of using Fenton's reagents for in-place recovery of spent granular activated carbon (GAC) was investigated. Fenton's reagents were cycled through spent GAC to degrade sorbed chlorinated hydrocarbons. Little carbon adsorption capacity was lost in the process. Seven chlorinated compounds were tested to determine compound-specific effectiveness for GAC regeneration. The contaminant with the weakest adsorption characteristics, methylene chloride, was 89% lost from the carbon surface during a 14-hour regeneration period. Results suggest that intraparticle mass transport limits carbon recovery kinetics, as opposed to the rate of oxidation of the target contaminants. Fenton-dependent recovery of GAC was also evaluated at a field site at which GAC was used to separate tetrachloroethylene (PCE) and trichloroethylene (TCE) from contaminated soil vapors. In the field, up to 95% of the sorbed TCE was removed from GAC during regeneration periods of 50-60 hours. Recovery of PCE was significantly slower. Although the process was not proven to be cost effective relative to thermal regeneration or carbon replacement, straightforward design and operational changes can lower process costs significantly. © 2006 American Chemical Society.
• Ghosh, A., Mukiibi, M., Sáez, A. E., & Ela, W. P. (2006). Leaching of arsenic from granular ferric hydroxide residuals under mature landfill conditions. Environmental Science and Technology, 40(19), 6070-6075.
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  PMID: 17051802;PMCID: PMC2536495;Abstract: Most arsenic bearing solid residuals (ABSR) from water treatment will be disposed in nonhazardous landfills. The lack of an appropriate leaching test to predict arsenic mobilization from ABSR creates a need to evaluate the magnitude and mechanisms of arsenic release under landfill conditions. This work studies the leaching of arsenic and iron from a common ABSR, granular ferric hydroxide, in a laboratory-scale column that simulates the biological and physicochemical conditions of a mature, mixed solid waste landfill. The column operated for approximately 900 days and the mode of transport as well as chemical speciation of iron and arsenic changed with column age. Both iron and arsenic were readily mobilized under the anaerobic, reducing conditions. During the early stages of operation, most arsenic and iron leaching (80% and 65%, respectively) was associated with suspended particulate matter, and iron was lost proportionately faster than arsenic. In later stages, while the rate of iron leaching declined, the arsenic leaching rate increased greater than 7-fold. The final phase was characterized by dissolved species leaching. Future work on the development of standard batch leaching tests should take into accountthe dominant mobilization mechanisms identified in this work: solid associated transport, reductive sorbent dissolution, and microbially mediated arsenic reduction. © 2006 American Chemical Society.
• Ghosh, A., Sáez, A. E., & Ela, W. (2006). Effect of pH, competitive anions and NOM on the leaching of arsenic from solid residuals. Science of the Total Environment, 363(1-3), 46-59.
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  PMID: 16239021;Abstract: Implementation of the new arsenic MCL in 2006 will lead to the generation of an estimated 6 million pounds of arsenic-bearing solid residuals (ABSRs) every year, which will be disposed predominantly in non-hazardous landfills. The Toxicity Characteristic Leaching Procedure (TCLP) is typically used to assess whether a waste is hazardous and most solid residuals pass the TCLP. However, recent research shows the TCLP significantly underestimates arsenic mobilization in landfills. A variety of compositional dissimilarities between landfill leachates and the TCLP extractant solution likely play a role. Among the abiotic factors likely to play a key role in arsenic remobilization/leaching from solid sorbents are pH, and the concentrations of natural organic matter (NOM) and anions like phosphate, bicarbonate, sulfate and silicate. This study evaluates the desorption of arsenic from actual treatment sorbents, activated alumina (AA) and granular ferric hydroxide (GFH), which are representative of those predicted for use in arsenic removal processes, and as a function of the specific range of pH and concentrations of the competitive anions and NOM found in landfills. The influence of pH is much more significant than that of competing anions or NOM. An increase in one unit of pH may increase the fraction of arsenic leached by 3-4 times. NOM and phosphate replace arsenic from sorbent surface sites up to three orders of magnitude more than bicarbonate, sulfate and silicate, on a per mole basis. Effects of anions are neither additive nor purely competitive. Leaching tests, which compare the fraction of arsenic mobilized by the TCLP vis-a-vis an actual or more realistic synthetic landfill leachate, indicate that higher pH, and greater concentrations of anions and NOM are all factors, but of varying significance, in causing higher extraction in landfill and synthetic leachates than the TCLP. © 2005 Elsevier B.V. All rights reserved.
• Poloski, A. P., Bredt, P. R., Daniel, R. C., & Saez, A. E. (2006). The contribution of frictional contacts to the shear strength of coarse glass bead powders and slurries. Rheologica Acta, 46(2), 249-259.
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  Abstract: This paper investigates the use of the shear vane technique as a means of determining frictional and cohesive interparticle force contributions to the shear strength of coarse glass bead powders and slurries. To this end, the shear strength of 203-μm glass beads in air and slurried in water and kaolinite suspensions was determined as a function of vane immersion depth, vane geometry, and container size. Both vane immersion depth and container diameter are found to significantly impact the shear strength measured using the vane technique. An equation describing interparticle frictional and cohesive contributions to shear vane measurements was derived in an effort to describe the experimental results. A Janssen stress distribution model for granular materials forms the basis for this equation and appears to explain the behavior of shear strength measurements at varying immersion depths. The presence of the Janssen stress distribution can affect the interpretation of shear vane results. Rather than shear strength being a material property, as is the case with flocculated colloid slurries and polymer solutions, shear strength becomes a process property where vane depth, container size, and container material can result in significant measurement variations. Such parameters should be considered before using the shear vane results on applications involving granular material components. © Springer-Verlag 2006.
• Rojas, M. R., Mendoza, C. E., Siquier, S., Ramírez, N., Müller, A., & Sáez, A. (2006). Transport of solids in a non-newtonian annular vertical flow of biopolymer solutions. Revista de la Facultad de Ingenieria, 21(1), 57-69.
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  Abstract: This work presents an experimental study of solids suspension in upward annular flow using non-Newtonian biopolymer solutions as liquid phases. The biopolymers employed were xanthan and guar gums, and the solid phase consisted of silica sand with a mean particle size of 250 μm. The experimental equipment is a vertical concentric pipe system, with 3 m of height and a hydraulic diameter of 0.15 m, simulating the drilling process at room temperature without the drill rotation effects. The annular velocity, concentration of load and polymer were the most important variables studied. It was found that the transport ratio allows a simple quantification of the effects of the polymer as a viscosifying additive in drilling muds, independently of the solids loading, xanthan gum provides a better suspension capacity than Guar gum at similar concentrations, especially at low flow velocities, while at high velocities the solids transport is similar for both polymeric solutions, due to their pseudoplasticity.
• Xiumin, J. u., Hecht, M., Galhotra, R. A., Ela, W. P., Betterton, E. A., Arnold, R. G., & Sáez, A. E. (2006). Destruction of gas-phase trichloroethylene in a modified fuel cell. Environmental Science and Technology, 40(2), 612-617.
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  PMID: 16468410;Abstract: A conventional fuel cell was used as a catalytic reactor to treat soil vapor extraction (SVE) gases contaminated with trichloroethylene (TCE). The SVE gases are fed to the cathode side of the fuel cell, where TCE is reduced to ethane and hydrochloric acid. The results obtained suggest that TCE reduction occurs by a catalytic reaction with hydrogen that is re-formed on the cathode's surface beyond a certain applied cell potential. Substantial conversion of TCE is obtained, even when competing oxygen reduction occurs in the cathode. The process has been modeled successfully by conceptualizing the flow passage in the fuel cell as a plug flow reactor. © 2006 American Chemical Society.
• González, J. M., Müller, A. J., Torres, M. F., & Sáez, A. E. (2005). The role of shear and elongation in the flow of solutions of semi-flexible polymers through porous media. Rheologica Acta, 44(4), 396-405.
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  Abstract: The rheological behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) and xanthan gum solutions has been characterized in simple shear flow, opposed-jets flow, and flow through porous media. Both polymers exhibit shear thinning in simple shear flow and apparent shear thinning in flow through porous media. Analysis of the results shows there is a direct correspondence between shear viscosities determined in simple shear experiments and apparent viscosities in porous media flow at relatively low shear rates. At high shear rates the extensional component of the flow in porous media appreciably increases the apparent viscosity over the simple shear values. This increase is shown to correlate with results obtained in opposed-jets experiments, and is attributed to formation of transient entanglements. © Springer-Verlag 2004.
• Rengifo, F., Garbo, B., Quach, A., Ela, W. P., Sáez, A., III, D. B., Franks, C., Zelinski, B. J., Smith, H., & Smith, G. (2005). Stabilization of arsenic-bearing iron hydroxide solid wastes in polymeric matrices. Ceramic Transactions, 168, 99-108.
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  Abstract: This work explores the use of an aqueous-based emulsion process to create an epoxy/rubber matrix for separating and encapsulating waste components from salt-laden, arsenic-contaminated, amorphous iron hydrate sludges. Such sludges are generated from conventional water purification precipitation/adsorption processes, used to convert aqueous brine streams to semi-solid waste streams, such as ion exchange/membrane separations, and from other precipitative heavy metal removal operations. In this study, epoxy resin and polystyrene butadiene (PSB) rubber emulsions are mixed together, combined with residual sludge, and cured and dried at 80°C to remove water. The microstructure of the resulting waste form is characterized by scanning electron microscopy (SEM), which confirms that the epoxy/PSB matrix surrounds and encapsulates the arsenic-laden amorphous iron hydrate phase, while allowing the salt to migrate to internal and external surfaces of the sample. Soluble salts leach from the sample at a rate given by diffusion coefficients of the order of 10 -8 cm 2/s. Long-term leaching studies reveal no evidence of iron migration and, by inference, arsenic migration, and demonstrate that diffusivities of the unextracted salt yield teachability indices within regulations for non-hazardous landfill disposal.
• Evans, R., Quach, A., Xia, G., J., B., Ela, W. P., P., D., Sáez, A. E., Smith, H. D., & Smith, G. L. (2004). Microstructure of emulsion-based polymeric waste forms for encapsulating low-level, radioactive and toxic metal wastes. Ceramic Transactions, 155, 331-340.
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  Abstract: Developed technologies in vitrification, cement, and polymeric materials manufactured using flammable organic solvents have been used to encapsulate solid wastes, including low-level radioactive materials, but are impractical for high salt-content waste streams. 1 In this work, we investigate an emulsification process for producing an aqueous-based polymeric waste form consisting of epoxy resin and polystyrene-butadiene (PSB) latex that is non-flammable, light weight and of relatively low cost. Sodium nitrate was used as a model for the salt waste. The microstructure and composition of the samples were probed using SEM/EDS techniques and salt extraction. The results show that some portion of the salt migrates towards the exterior surfaces of the waste forms during the curing process. The portion of the salt in the interior of the sample is contained in polymer corpuscles or sacs. These sacs are embedded in a polymer matrix phase that contains fine, well-dispersed salt crystals. A companion paper describes work in which small-scale samples were manufactured and analyzed using leach tests designed to measure the diffusion coefficient and leachability index for the fastest diffusing species in the waste form, the salt ions. 2.
• Jiahan, H. e., Arnold, R. G., Sáez, A. E., Betterton, E. A., & Ela, W. P. (2004). Removal of aqueous phase trichloroethylene using membrane air stripping contactors. Journal of Environmental Engineering, 130(11), 1232-1241.
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  Abstract: This work investigates the use of membrane air-stripping (MAS) contactors containing microporous polypropylene hollow-fiber membranes to remove volatile organic compounds from water into the gas phase. Experiments using countercurrent and cross-flow flow configurations to remove trichloroethylene (TCE) from water into air were performed. The effects of influent TCE concentration, liquid and gas flow rates, and air-to-water ratio were investigated. In each case studied, it was found that mass transfer in MAS contactors is controlled by liquid-phase resistance. Maximum removal of TCE was obtained at air-to-water ratios that were significantly lower than those required for conventional packed-tower stripping. Mathematical models based on empirical correlations for the liquid-phase convective mass transfer coefficients were developed and validated with experimental data, and subsequently used to perform simulations of full-scale MAS contactors. At the operating conditions explored, full-scale cross-flow contactors were shown to be superior to countercurrent-flow contactors: for the same gas and liquid flow rates and number of fibers, cross-flow contactors removed more than 95% of the original TCE in the feed liquid whereas countercurrent-flow contactors removed less than 50%. In comparison with packed-tower stripping, MAS contactors are shown to be an alternative feasible technology. © ASCE / NOVEMBER 2004.
• Jiahan, H. e., Ela, W. P., Betterton, E. A., Arnold, R. G., & Sáez, A. E. (2004). Reductive dehalogenation of aqueous-phase chlorinated hydrocarbons in an electrochemical reactor. Industrial and Engineering Chemistry Research, 43(25), 7965-7974.
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  Abstract: This work describes the reductive dehalogenation of carbon tetrachloride (CT) in a novel liquid-phase electrochemical reactor. The reactor consists of a cylindrical porous copper cathode with a concentric carbon-cloth anode wrapped around the cathode. The results show that CT destruction can be achieved, even in low conductivity solutions (i.e., deionized water), reaching 80% conversion of CT with a residence time of 10 min when a cathode potential of -0.4 V (versus a standard hydrogen electrode) is used. A mathematical model was formulated to simulate reactor performance. The model accounted for CT reductive dechlorination, hydrogen evolution on the cathode surface, and CT mass-transfer limitations. The equilibrium potential for CT reduction on the cathode surface was the only adjustable parameter. The model adequately represented experimental data under high-conductivity (2.2 S/m) and low-conductivity (0.05 S/m) conditions. The model results and experimental observations suggest that the entire cathode was active during CT reduction experiments, i.e., solution potential did not render portions of the cathode nonreactive, even in the low-conductivity experiments.
• Jiahan, H. e., Sáez, A. E., Ela, W. P., Betterton, E. A., & Arnold, R. G. (2004). Destruction of Aqueous-Phase Carbon Tetrachloride in an Electrochemical Reactor with a Porous Cathode. Industrial and Engineering Chemistry Research, 43(4), 913-923.
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  Abstract: In this work we investigate the use of a continuous-flow, laboratory-scale electrochemical reactor for the destruction of aqueous-phase carbon tetrachloride (CT). The reactor consists of a porous copper foam cathode and a carbon-cloth anode section located downstream from the cathode. Experimental results show that appreciable conversions of CT can be obtained in the reactor, as long as the electrical conductivity of the liquid exceeds 1 S/m. At lower conductivities, most of the cathode exhibits low reactivity for CT-destruction due to relatively low charge transfer overpotentials. A mathematical model was formulated to predict reactor performance. The model takes into account the CT-reduction reaction and the hydrogen evolution reaction on the cathode surface as well as mass transfer limitations. Using the equilibrium potential for CT reduction as the only adjustable parameter, the model adequately represents experimental data for highly conductive solutions.
• L., C., Bishop, K. G., Bercik, L. M., Ela, W. P., Sáez, A. E., Huling, S. G., & Arnold, R. G. (2004). In-place regeneration of SVE-loaded GAC using Fenton's reagents. ACS, Division of Environmental Chemistry - Preprints of Extended Abstracts, 44(2), 648-653.
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  Abstract: The feasibility of Fenton's reaction as an in-place chemical regeneration process for granular activated carbon (GAC) was studied. Methods were investigated for enhancing the rate of Fenton-dependent regeneration of halogenated VOC-loaded GAC. The target organic compounds (methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, trichloroethylene (TCE), and tetrachloroethylene (PCE)) were analyzed by GC-ECD according to a modified version of EPA method 551.1. For each of the compounds tested, the rate of disappearance of the adsorbed contaminant was approximately proportional to its adsorbed concentration. All compounds exhibited pseudo first-order kinetics through much of their observed range. However, the observed pseudo first-order reaction rate constant for TCE was 0.045/hr, or less than one-third that of methylene chloride. The observed reaction rate constants were strongly correlated to contaminant solubility. The most soluble, methylene chloride, was 89% degraded during a 14-hr regeneration period. In the field trials, the halogenated organics (predominantly TCE and PCE) sorbed out of a gas-phase soil vapor extraction stream onto the GAC in a packed bed. Upon saturation, the GAC was regenerated (analogous to the laboratory trials) using Fenton's reagents in an aqueous-stream capable of expanding the bed in an up-flow mode. Preliminary results at the field site using the Fenton treatment indicated that at least 80% TCE destruction is achieved during a 6-hr regeneration period. Preliminary results indicated that H2O2 usage in the field is higher than expected from the laboratory trials. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).
• Müller, A., Torres, M. F., & Sáez, A. (2004). Effect of the flow field on the rheological behavior of aqueous cetyltrimethylammonium p-toluenesulfonate solutions. Langmuir, 20(10), 3838-3841.
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  PMID: 15969367;Abstract: It is well-known that solutions of cetyltrimethylammonium p-toluenesulfonate in water exhibit a pronounced shear-thickening phenomenon in a specific concentration range (0.1-0.8%) when they are subjected to simple-shear flows, as a consequence of flow-induced self-assembly of wormlike micelles. This work shows that a strong elongational flow field (opposed-jets flow), applied to the same solutions, does not lead to extension thickening because the extensional flow prevents or destroys micellar association. In flow through a porous medium, a substantial increase in apparent viscosity is observed beyond a critical apparent shear rate, which surpasses increases observed in simple-shear flows. This is explained as the result of a synergistic effect of shear and relatively weak elongation on the solution microstructure.
• Pérez, R., Siquier, S., Ramírez, N., Müller, A., & Sáez, A. (2004). Non-Newtonian annular vertical flow of sand suspensions in aqueous solutions of guar gum. Journal of Petroleum Science and Engineering, 44(3-4), 317-331.
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  Abstract: In this work we present an experimental study of non-Newtonian solid-liquid suspension flow in the annular space of a concentric-pipe system that simulates the geometry of wells during drilling for petroleum exploration and production, excluding effects of drill rotation. The liquids used were solutions of biodegradable guar gum at various concentrations and the solid phase was siliceous sand. We studied how the mean annular velocity, polymer concentration and degree of polymer cross-linking affect axial solids distribution. The results show that the solids suspension capacity of the solutions is enhanced by the presence of polymer: the addition of guar gum decreases the minimum annular velocity needed to achieve a homogeneous axial solids distribution in the annular region. However, the amount of solids that is carried by the solutions is not always increased in the presence of polymer. The chemical cross-linking of guar gum with borax promotes a substantial increase of transported solids in the annular space. Overall, the results presented show that relatively high viscosities, high polymer relaxation times under shear flow and non-zero residual shear stresses are desired rheological characteristics for a drilling fluid to obtain a uniform solids distribution in the annulus, as well as high solids carrying capacity. © 2004 Elsevier B.V. All rights reserved.
• Quach, A., Xia, G., Evans, R., Sáez, A. E., Zelinski, B. J., Smith, H., Smith, G., P., D., & Ela, W. P. (2004). Leach resistance of encapsulated salts in polymeric waste forms fabricated using an aqueous-based route. Ceramic Transactions, 155, 341-349.
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  Abstract: The leaching behavior of a highly-soluble salt (sodium nitrate) encapsulated in novel polymeric waste forms was investigated. The waste forms are solid monoliths composed of cured blends of polystyrene-butadiene and an epoxy resin. The synthesis and encapsulation process are accomplished simultaneously via an aqueous-based route recently developed. Leaching of the salt was carried out by exposing sections of the waste forms to large volumes of well-stirred water. The measured time dependence of the leaching process is described quantitatively by a model based on the diffusion of the salt through the waste form. The results obtained suggest that diffusion occurs through limited but significant continuous porosity. Preliminary experiments indicate that this porosity may be reduced to improve leach resistance by the use of a post-curing heat treatment.
• Rengifo, F., Sáez, A. E., Ela, W. P., Quach, A., Garbo, B., Franks, C., Zelinski, B. J., P., D., Smith, H. D., & Smith, G. L. (2004). Microstructure and leaching behavior of polymer composites for encapsulating toxic solid wastes. Industrial and Engineering Chemistry Research, 43(23), 7492-7499.
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  Abstract: This work presents a water-based process for the manufacture of a polymeric waste form for the encapsulation of soluble toxic salts. The process is based on the elaboration of an aqueous emulsion in which polymeric precursors are mixed with the waste. Upon drying and curing, the emulsion inverts to form a waste form with mechanical integrity that stabilizes the toxic salt. The final polymer matrix is a mixture of an epoxy resin and poly(styrene butadiene) (PSB). Sodium nitrate was used as a model salt waste. The microstructure and composition of the samples were examined using scanning electron microscopy, osmium tetroxide staining, and salt extraction. The results show that the epoxy resin is dispersed in a continuous PSB phase, and the encapsulated salt is distributed throughout the matrix. Leaching tests were carried out by exposing sections of the waste forms to large volumes of well-stirred water. The measured time dependence of the leaching process is described quantitatively by a model based on the diffusion of the salt through the waste form. Effective diffusivities of the salt in the polymeric matrix ranged between 10-8 and 10-7 cm2/s. The results suggest that diffusion occurs through limited but significant continuous porosity.
• Xiumin, J. u., Sáez, A. E., Ela, W. P., Arnold, R. G., Betterton, E. A., Wallen, M., Candillo, K., Barbaris, B., & Orbay, O. (2004). Reductive and oxidative destruction of chlorinated hydrocarbons in gas-phase catalytic reactors: Packed-beds and modified fuel cells. ACS National Meeting Book of Abstracts, 228(1), ENVR-135.
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  Abstract: The catalytic destruction of trichloroethylene and perchloroethylene was studied in a packed-bed reactor (Pt/alumina) and a modified fuel cell (Pt/carbon cloth) to treat soil-vapor extraction gases. Mechanisms and conditions for which reductive dehalogenation and oxidation of the targets occur when both hydrogen and oxygen are present in the reactive mixture were established. Low temperatures (< 200°C) favored reductive dehalogenation of the targets and produced ethane, while higher temperatures (between 200° and 400°C) favored oxidative dehalogenation and produced CO 2. Reductive dehalogenation of the targets was achieved in the cathode of the modified fuel cell using cell potential (0.1-0.4 v cathode relative to anode) to control the supply of hydrogen for the reaction by reformation of hydrogen gas in the cathode from protons produced in the anode. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).
• Xiumin, J. u., Sáez, A. E., Ela, W. P., Arnold, R. G., Betterton, E. A., Wallen, M., Candillo, K., Barbaris, B., & Orbay, O. (2004). Reductive and oxidative destruction of chlorinated hydrocarbons in gas-phase catalytic reactors: Packed-beds and modified fuel cells. ACS, Division of Environmental Chemistry - Preprints of Extended Abstracts, 44(2), 452-457.
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  Abstract: The thermochemical destruction of TCE, a major contaminant of soil and groundwater, was studied using a packed-bed reactor to establish the ranges of temperature and H2/O2 ratio at which oxidative destruction and reductive chlorination occur. At H2/O2 ratios of 2:1 and 3:1, TCE conversion increased with temperature, reaching 100% at ≥ 150°C. When excess hydrogen was present, the main reaction product was ethane. These results showed that the reduction reaction is more efficient for TCE conversion at lower temperatures (50°-200°C) than the oxidation reaction. There was clear evidence of a change in conversion mechanism as the temperature increased; at low temperatures, TCE was converted primarily to ethane. At higher temperatures, ethane yield decreased while C02 production increased. The effluent flow rate and cell current increased as the potential decreased although the influent flow rate was constant. Performance of the modified fuel cell reactor was also evaluated in the presence of 21% oxygen in the influent gas stream. An inhibition of TCE conversion was expected in the presence of oxygen due to a lower availability of hydrogen caused by reduction of oxygen to water. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).
• Müller, A. J., Garcés, Y., Torres, M., Scharifker, B., & Sáez, A. E. (2003). Interactions between high-molecular-weight poly(ethylene oxide) and sodium dodecyl sulfate. Progress in Colloid and Polymer Science, 122, 73-81.
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  Abstract: In this work, we study interactions between poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS) in aqueous solutions, using surface tension, electrical conductivity and shear rheometry. The main distinguishing feature of this investigation with respect to previous works is the use of high-molecular-weight PEOs (up to 8 × 106 g/mol). The aggregation pattern of the surfactant in the form of micellar aggregates attached to the polymer chain causes specific changes in surface tension, electrical conductivity and zero-shear-rate viscosity that qualitatively resemble those found previously for lower-molecular-weight PEOs when no additional electrolytes are present in the solution. In the presence of 0.1 M NaCl and for PEOs with molecular weights of 600,000 g/mol and more, the electrical conductivity and surface tension of the solutions remain constant when surfactant is added beyond the critical aggregation concentration, until saturation of the polymer with micellar aggregates is achieved. This behavior indicates complete complexation of the dodecyl sulfate ions into micellar aggregates attached to the polymer, as well as a strong binding of the counterions to the PEO/SDS complex.
• Littlejohn, F., Grant, C. S., Wong, Y. L., & Sáez, A. E. (2002). Effect of poly(aspartic acid) on the removal rates of brushite deposits from stainless steel tubing in turbulent flow. Industrial and Engineering Chemistry Research, 41(18), 4576-4584.
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  Abstract: This research investigates the effect of poly(aspartic acid) (PASP) and its sodium salt on the removal of brushite (dicalcium phosphate dihydrate, DCPD) deposits from stainless steel tubing in turbulent flows. In the absence of PASP, DCPD removal is dominated by the abrasion of solid particles from the deposit by fluid shear and is influenced by the kinetics of the interfacial dissolution process. The presence of PASP promotes DCPD removal for pHs between 4 and 10, with an optimum enhancement at pH 5. A decrease in the sensitivity of the removal rate to shear forces indicates that PASP inhibits solids detachment from the deposit for pH < 5. At higher pHs, PASP appears to reduce the shear stress required to remove particles from the deposit. A model for the interfacial dissolution process that includes mass transfer, adsorption equilibria, and the kinetics of acid dissolution and surface complexation is used to explain the trends of the experimental data on removal rates.
• Patruyo, L. G., Müller, A., & Sáez, A. (2002). Shear and extensional rheology of solutions of modified hydroxyethyl celluloses and sodium dodecyl sulfate. Polymer, 43(24), 6481-6493.
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  Abstract: This work reports on the rheology of aqueous solutions of hydroxyethyl cellulose (HEC) and three derivatives, in the presence of sodium dodecyl sulfate (SDS). The polymers employed were: a hydrophobically modified hydroxyethyl cellulose (HMHEC) containing hexadecyl grafts, a cationically modified hydroxyethyl cellulose (cat-HEC), containing glycidyl-trimethyl-ammonium grafts, and a polymer with both modifications (cat-HMHEC). Rheological measurements were performed in simple shear flow, oscillatory shear flow, opposed-jets flow and flow through porous media. The addition of surfactant increases intermolecular interactions between HMHEC molecules due to the formation of mixed micelles that bridge hydrophobic side groups from different polymer chains. These interactions lead to phase separation in an intermediate SDS concentration range and, at higher surfactant concentrations when a homogeneous phase was obtained, to higher shear and apparent extensional viscosities. Further surfactant addition eventually inhibits hydrophobe interactions due to electrostatic repulsion between micelles, leading to shear viscosities that are even lower than that of the original polymer solution. Hydrophobe interactions are inhibited by the relatively strong nature of flow in opposed-jets. The addition of cationic side groups confers the polymer a polyelectrolytic nature, which translates into higher shear and apparent extensional viscosities. Interchain interactions are strengthened by the presence of surfactant by the formation of intermolecular cross-links between polymer chains. © 2002 Published by Elsevier Science Ltd.
• Smitter, L. M., Ruiz, J. C., Torres, M. E., Müller, A., & Sáez, A. (2002). Elongational flow of solutions of poly(ethylene oxide) and sulfonated surfactants. Journal of Colloid and Interface Science, 251(2), 388-397.
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  PMID: 16290745;Abstract: In this work, the elongational flow behavior of aqueous solutions of poly(ethylene oxide) (PEO) was studied in the presence of sulfonated surfactants. The technique of opposed-jets flow was used to generate an elongational flow field in which pressure drops were measured as a function of strain rates. The surfactants used were sodium dodecyl benzene sulfonate (SDBS) and an α-olefin sulfonate (AOS). Solutions of PEO and other flexible polymers exhibit extension thickening in opposed-jets flow due to the formation of transient networks of entangled molecules. This effect is present at concentrations below the static coil overlap concentration, due to the changes in molecular conformation induced by the flow. When SDBS or AOS are added to PEO solutions at low concentrations, the extension thickening weakens due to an increase in PEO intramolecular interactions that lead to coil contraction. This occurs until the surfactant concentration is close to the critical aggregation concentration reported in the literature. Further addition of surfactant induces the formation of intermolecular interactions as the PEO molecules are expanded by the electrostatic repulsion between attached micellar aggregates, with an associated strengthening of extension thickening. Intramolecular effects were not seen beyond a specific PEO concentration. © 2002 Elsevier Science (USA).
• Torres, M. F., Müller, A., & Sáez, A. (2002). Effect of ethanol addition on the elongational flow behavior of aqueous solution of poly(ethylene oxide). Polymer Bulletin, 47(5), 475-483.
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  Abstract: In this work, we explore the effect of ethanol addition on the extension thickening behavior of aqueous solutions of poly(ethylene oxide) (PEO) in porous media and opposed-jets flow. The main aspect analyzed is the formation of transient entanglements of polymer molecules, which are responsible for the sudden increase in pressure drops and apparent extensional viscosities with strain rates observed in elongational flows of PEO solutions. The results show that changing the solvent by adding ethanol modifies the solution behavior because of two effects. First, the increase in the solvent viscosity increases the disentanglement time of the transient entanglements so that the onset of extension thickening occurs at lower strain rates in the presence of ethanol. Second, ethanol solutions are poorer solvents than water for PEO. This promotes intermolecular interactions between PEO coils when the solutions are semi-dilute. The net result is a lowering of the onset strain rate for extension thickening to values that are much smaller than those expected for the same PEO chains dissolved in a higher viscosity and poorer solvent. The results also show that coil-coil interactions in solution can be detected at lower concentrations in porous media flow than in opposed jets flow.
• Smitter, L. M., Guédez, J., Müller, A., & Sáez, A. (2001). Interactions between poly(ethylene oxide) and sodium dodecyl sulfate in elongational flows. Journal of Colloid and Interface Science, 236(2), 343-353.
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  Abstract: This work investigates the elongational flow of aqueous solutions of mixtures of a high-molecular-weight poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS). The formation of micellar aggregates of SDS along the PEO chain results in an increase in the strength of the extension thickening of the PEO solutions. This is especially pronounced under conditions in which the PEO molecules form transient entanglements in the flow field. The minimum PEO concentration required to form intermolecular entanglements is substantially reduced in the presence of micellar aggregates. This effect becomes quantitatively less important in solutions with NaCl, which suggests PEO coil contraction due to electrostatic screening of micellar aggregates. However, once extension thickening starts in the presence of NaCl, the growth of pressure drop is more abrupt than without salt, which suggests stronger interactions between PEO coils with attached aggregates. The critical aggregation concentrations of PEO/SDS and PEO/SDS/NaCl solutions agree with those reported in the literature, which were obtained by means of different experimental techniques. However, the saturation of the surfactant effect is attained at lower surfactant concentrations than the polymer saturation point previously reported. This might reflect a low sensitivity of the extension thickening effect to the amount of surfactant bound to the polymer chain as the saturation point is approached. © 2001 Academic Press.
• Smitter, L. M., Torres, M. E., Müller, A., & Sáez, A. (2001). Elongational flow of solutions containing poly(ethylene oxide)/sodium dodecyl sulfate complexes in the presence of n-alkanols. Journal of Colloid and Interface Science, 244(1), 164-172.
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  Abstract: The effect of the presence of n-alkanols on the extensional rheology of solutions containing polymer/surfactant complexes has been investigated experimentally in an opposed-jets device. Aqueous solutions of high-molecular-weight poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS) exhibit an extension thickening behavior that is stronger than that of the pure polymer solution because of the formation of micellar aggregates of SDS along the PEO chain that promote intermolecular interactions between polymer chains. The addition of a short-chain alcohol (ethanol) affects the rheology of PEO/SDS solutions by changing the solvency characteristics of both PEO and SDS. Adding ethanol to water decreases the quality of the solvent for PEO, which promotes intermolecular interactions between polymer chains and strengthens extension thickening in semi-dilute PEO/water/ethanol mixtures. On the other hand, high enough concentrations of ethanol dissolve the SDS micellar aggregates, eliminating their influence on extension thickening. Long-chain alcohols (n-octanol) substantially enhance extension thickening effects. The presence of n-octanol lowers the critical aggregation concentration for the formation of SDS micellar aggregates along the PEO chain and promotes intermolecular interactions at PEO concentrations that would not exhibit extension thickening without n-octanol. © 2001 Academic Press.
• Kabin, J. A., Withers, S. T., Grant, C. S., Carbonell, R. G., & Sáez, A. (2000). Removal of solid organic films from rotating disks using emulsion cleaners. Journal of Colloid and Interface Science, 228(2), 344-358.
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  Abstract: Measurements have been made of the rate of removal of a solid organic film (phenanthrene) from the surface of a rotating disk using emulsions containing water, the nonionic surfactant Tween 20, and d-limonene as the organic phase. The results show that phenanthrene removal initially occurs by the uptake of phenanthrene into the emulsion drops as small aggregates. Simultaneously, the organic phase penetrates into the phenanthrene film, diminishing the adhesive force between the film and the substrate. After sufficient time, the phenanthrene film detaches from the rotating disk surface as a solid. This detachment mechanism accounts for the vast majority of the phenanthrene removal (~90%). Initial solubilization rates were analyzed using two solubilization models. Both models assume that phenanthrene removal occurs via a mass transfer limited removal of phenanthrene-laden emulsion drops from the phenanthrene film surface into the bulk solution. One model treats the emulsion as homogeneous while the other accounts for the finite size of the emulsion droplets. The latter model was also used to relate the flux of organic phase impacting the phenanthrene film to the detachment times. (C) 2000 Academic Press.
• Littlejohn, F., Grant, C. S., & Sáez, A. E. (2000). Mechanisms for the removal of calcium phosphate deposits in turbulent flow. Industrial and Engineering Chemistry Research, 39(4), 933-942.
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  Abstract: This work investigates the mechanisms for the removal of calcium phosphate deposits from stainless steel tubing in turbulent flows. Two types of deposits were analyzed: brushite (dicalcium phosphate dihydrate, DCPD) and a mixture of DCPD/hydroxyapatite (HAP). Cleaning studies were carried out at pHs ranging from 2.85 to 10. The data were analyzed by means of a mathematical model that incorporates the effects of interfacial dissolution and mass transfer. The results show that the HAP/DCPD cleaning rate is influenced both by the kinetics of the interfacial dissolution and by mass transfer. Within the same range of experimental conditions, the rate-limiting mechanism for DCPD removal was the abrasion of the solid by shear stresses. In this case, the interfacial dissolution process plays the role of decreasing the structural integrity of the deposit. These findings show that the removal mechanism of the HAP/DCPD mixture differs significantly from the behavior of individual components.
• Rando, M., Socías, P., Müller, A., Smitter, L. M., & Sáez, A. (2000). Flow of mixtures of poly(ethylene oxide) and hydrolyzed polyacrylamide solutions through opposed jets. Journal of Applied Polymer Science, 76(13), 1910-1919.
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  Abstract: The flow of solutions of poly(ethylene oxide) (PEO), hydrolyzed polyacrylamide (HPAA), and their blends through opposed jets is investigated. Measurements of pressure drop across the jets as a function of strain rate were used to characterize the elongational flow behavior. In deionized water, solutions of PEO/HPAA mixtures exhibit a synergistic increase in flow resistance with respect to the parent polymer solutions. The addition of amounts of HPAA as low as 2 ppm to a 500 ppm PEO solution cause sizeable increases in pressure drops. Such increases have been interpreted as arising from the formation of interpolymer transient entanglement networks that become mechanically active at time scales equivalent to the lowest strain rates available. In the case of excess salt environment, the flow resistance of the mixtures seems to be dominated by the PEO in the concentration range explored.
• Roberts, G. W., Carbonell, R. G., & Sáez, A. E. (2000). Gas-lift reactors for rapid reactions with appreciable gas consumption. Chemical Engineering and Technology, 23(1), 80-87.
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  Abstract: Gas-lift reactors offer important advantages for a number of gas/liquid and gas/liquid/solid reactions. However, the design and operation of these reactors can be complex when there is a substantial change in the molar gas flow rate along the length of the reactor, e.g., when a gaseous reactant is converted into a liquid product. In this situation, there is a strong coupling between reactor hydrodynamics and reaction kinetics, which arises from the fact that the rate of liquid circulation through the reactor and the longitudinal profile of gas holdup in the riser are mutually dependent. Several one-dimensional models have been developed to describe kinetic/hydrodynamic coupling in gas-lift reactors. These models offer useful insights into the parameters that affect reactor performance. The models can also be used to explore different approaches to scale-up.
• Colberg, M. T., Sáez, A., Grant, C. S., Hutchison, K., & Hesterberg, D. (1999). Dynamic hydration of phospholipid films in aqueous environments. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 151(3), 483-495.
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  Abstract: A dynamic study of the hydration of phospholipid films attached to solid substrates when exposed to liquid water at room temperature is presented. The phospholipids used were 1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine (DPPE), and a modification of DPPE with a fluorescent molecular probe: n-(5-fluoresceinthicarbamoyl)-1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine, triethylammonium salt (FITC-DPPE). Three different experimental techniques were used: rates of hydration were measured by depositing the phospholipid film on a quartz crystal microbalance (QCM), total internal reflection fluorescence (TIRF) studies were carried out with FITC-DPPE films deposited on the internal surface of a cylindrical quartz tube, and X-ray diffraction analysis was used to determine possible changes of the film's crystalline structure during hydration. The DPPE films exhibited different successive hydration stages: within the first 2 h, the films uniformly hydrate towards a limiting water uptake (short-time behavior); however, at one point, hydration rates suddenly increase and the hydration process continues for longer periods of time, of the order of 24 h. No evidence of change in the film crystalline structure was found when dry and hydrated DPPE films were analyzed by wide-angle X-ray diffraction. The FITC-DPPE films showed a completely different hydration pattern: water uptake reached a maximum value at short times and then decreased continuously until an asymptotic value was reached. The TIRF results on FITC-DPPE films show that the evolution of fluorescence with time closely resembles the hydration results obtained in the QCM. This is attributed to the self quenching occurring in the phospholipid films. Copyright (C) 1999 Elsevier Science B.V.
• DaRocha, C. M., Patruyo, L. G., Ramírez, N., Müller, A., & Sáez, A. (1999). Porous media flow of poly(ethylene oxide)/sodium dodecyl sulfate mixtures. Polymer Bulletin, 42(1), 109-116.
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  Abstract: In this work, the porous media flow of solutions of mixtures of Poly(ethylene oxide), PEO, and Sodium Dodecyl Sulfate, SDS, was studied. Aqueous solutions of PEO exhibited the well known critical extension thickening effect when flowing through disordered packings of glass spheres. Upon addition of SDS to a solution of fixed PEO concentration, the extension thickening of the mixture exhibits a maximum as a function of SDS concentration that mimics the shear viscosity behavior of the polymer-surfactant mixture. However, when NaCl is added to the mixture, higher extension thickening effects at relatively low SDS concentrations were detected, in spite of the fact that the shear viscosity of the mixtures was about the same as that of equivalent PEO/SDS solutions in deionized water. The results were rationalized in terms of how the formation of SDS micellar aggregates along the PEO chain can alter the ability of the polymer to form transient entanglement networks, which is the cause of the extension thickening behavior. © Springer-Verlag 1999.
• Gestoso, P., Müller, A., & Sáez, A. (1999). Two-dimcnsional flow of polymer solutions through porous media. Journal of Porous Media, 2(3), 251-262.
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  Abstract: In this work we develop a mathematical model to predict velocity and pressure profiles for two-dimensional flow of polymer solutions through porous media. The model is based on a modification of the differential form of Darcy's law in which the apparent viscosity of the polymer solution is expressed as a function of the local (pore-scale) deformation rate. The relationship between apparent viscosity and deformation rate was obtained from experimental results corresponding to one-dimensional flow. Once this relationship is available, the model is completely predictive, i.e., it has no adjustable parameters. Experiments were conducted to characterize the relationship between total pressure drop and fluid flow rate in a two-dimensional porous medium. The fluids used in the experiments were aqueous solutions of high molecular weight polymers: (1) a flexible polymer, polyfethylene oxide), which exhibits extension thickening in one-dimensional flows through porous media, and (2) a semirigid polymer, hydroxypropyl guar, whose behavior in porous media is shear thinning. For the flexible polymer, the model predicts an extension thickening behavior that is less critical in terms of deformation rate variations than what is observed experimentally. We present arguments that suggest that the absence of elasticity in the constitutive relationship used in the model formulation is the reason for this inaccuracy. This indicates that elastic behavioral the pore level plays an important role in the macroscopic pressure drops of solutions of flexible polymer in porous media flows. Copyright © 1999 by Begell House, Inc.
• Kabin, J. A., Sáez, A., Grant, C. S., & Carbonell, R. G. (1999). Removal rates of major and trace components of an organic film using aqueous nonionic surfactant solutions. Industrial and Engineering Chemistry Research, 38(3), 683-691.
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  Abstract: This work examines the cleaning of organic films composed of a primary component (abietic acid) mixed with trace amounts of a second contaminant (benzoic acid). Films were removed from a rotating disk in the presence of aqueous solutions of two poly(ethylene glycol) alkyl ether surfactants: C12E5 and C16E8. With C12E5 the abietic acid was removed from the disk in three successive cleaning stages-solubilization, shear removal, and rollup-whereas the benzoic acid was almost completely removed during the initial solubilization stage. Also, with C12E5 the results show that the micellar solubilization rate of the trace contaminant is directly proportional to its concentration in the film. The ratio of the molar removal rates of benzoic acid to abietic acid with C12E5 is an order of magnitude greater than the ratio of the mole fractions of the two components in the contaminant film. Solutions of C16E8 removed the abietic acid by only the solubilization and rollup stages. The ratio of the molar removal rates of benzoic acid to abietic acid with C16E8 was equal to the ratio of the mole fractions of the two components in the contaminant film. A mathematical model is proposed to quantify the simultaneous removal of benzoic acid and abietic acid during the micellar solubilization stage. The model takes into account the mass-transfer rate between the film and the bulk solution, as well as the micellization rates at the film/surfactant solution interface. The model adequately represents the experimental data.
• Kauser, N., Santos, L. D., Delgado, M., Müller, A., & Sáez, A. (1999). Flow of Mixtures of Poly(ethylene oxide) and Hydrolyzed Polyacrylamide Solutions Through Porous Media. Journal of Applied Polymer Science, 72(6), 783-795.
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  Abstract: In this work, the porous media flow of polymer solutions of poly(ethylene oxide) (PEO), hydrolyzed polyacrylamide (HPAA), and their blends is investigated. Aqueous solutions of PEO exhibit critical extension thickening when flowing through porous media. HPAA solutions also exhibit critical extension thickening in excess salt environments, but their behavior changes to a more gradual extension thickening when dissolved in deionized water. The mixtures of solutions of HPAA and PEO therefore vary its porous media flow behavior, depending on the ionic environment. In deionized water, a critical extension thickening similar to that obtained with PEO is still observed when HPAA is mixed in at concentrations low enough so that its apparent viscosity does not mask the influence of PEO. In the presence of salt, only a critical extension thickening is observed, which is attributed to transient network formation of both PEO and HPAA molecules. The mixtures generally exhibit a less critical behavior and display a lower than expected sensitivity of the onset Reynolds number for extension thickening with concentration. The results presented herein indicate that interspecies molecular interactions through transient network formation and the associated flow modification play a major role in determining the complex non-Newtonian flow behavior of these polymer solutions. © 1999 John Wiley & Sons, Inc.
• Márquez, M. A., Amend, R. J., Carbonell, R. G., Sáez, A. E., & Roberts, G. W. (1999). Hydrodynamics of gas-lift reactors with a fast, liquid-phase reaction. Chemical Engineering Science, 54(13-14), 2263-2271.
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  Abstract: The reactive absorption of CO2 into concentrated KOH solutions was studied in an external-loop, gas-lift reactor. Three different inlet gas compositions were used: air, 50-50 vol% air-CO2, and pure CO2. The downcomer liquid velocity and the axial profile of the cross-sectionally averaged gas holdup in the riser were measured. The reaction is so fast that the CO2 is consumed appreciably along the riser, and this causes a significant reduction in the liquid circulation relative to a system with no reaction. A one-dimensional, pseudo-steady-state model has been developed to describe the interactions of hydrodynamics, mass transfer, and chemical reaction for the bubbly flow regime in the riser. The model considers mass transfer from the gas to the liquid phase and its enhancement due to the chemical reaction, and is based on the spatially averaged equations of continuity, momentum, and macroscopic mechanical energy. The rate of liquid circulation, and the axial variation of gas holdup, gas composition, pressure, and gas and liquid velocity, are predicted. The gas/liquid mass transfer coefficient and the bubble radius at the sparger, neither of which was known a priori, were used to minimize the error of the data with respect to the model.
• Márquez, M., Sáez, A., Carbonell, R. G., & Roberts, G. W. (1999). Coupling of hydrodynamics and chemical reaction in gas-lift reactors. AIChE Journal, 45(2), 410-423.
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  Abstract: A model was developed to study the strong coupling between hydrodynamics and chemical reaction that occurs in external-loop gas-lift reactors. The model predicts the liquid circulation rate, as well as the axial profiles of gas holdup, pressure, gas and liquid velocity, and reactant conversion in the riser. The study on the first-order, irreversible, isothermal reaction in the gas phase nA k→ B with a change in the number of moles on reaction shows that for n > 1, the gas holdup decreases along the riser, the liquid circulation rate is lower than that in the absence of reaction, and liquid circulation decreases as n and k increase. The bubble radius at the sparger and the inlet gas composition can have important effects on reactor performance. Scale-up strategies that involve increasing the reactor length result in higher reactant conversion, but a lower ratio of liquid circulation rate to gas feed rate.
• See, K. H., Roberts, G. W., & Saez, A. E. (1999). Effect of drag and frictional losses on the hydrodynamics of gas-lift reactors. AIChE Journal, 45(11), 2467-2471.
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  Abstract: This work demonstrates how predictions of the hydrodynamics of gas-lift reactors can be improved by careful quantification of the mechanical-energy losses in the system. It is shown that drag and friction in all elements of the system must be taken into account in the formulation. Furthermore, it is illustrated that mechanical-energy losses in the various accessories of the system are the key elements that determine the liquid-circulation velocity for the analyzed reactor scale.
• Colberg, M. T., Carnes, K., Sáez, A., Grant, C. S., Hutchinson, K., & Hesterberg, D. (1998). Hydration and removal of supported phospholipid films in aqueous surfactant solutions. Thin Solid Films, 327-329(1-2), 247-251.
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  Abstract: Dynamic studies of the hydration and removal of phospholipid films attached to solid substrates were performed. The phospholipids used were 1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine (DPPE), and a modification of DPPE containing a fluorescent molecular probe: n-(5-fluoresceinthicarbamoyl)-1,2-dipalmitoyl-sn-glycero-3- phosphatidylethanolamine, triethylammonium salt (FITC-DPPE). The phospholipid films were exposed to water and aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS). The film mass was determined as a function of time by means of a quartz crystal microbalance (QCM). The crystalline structure of the film during the hydration process was analyzed by means of wide-angle X-ray diffraction. At low surfactant concentrations (below 20% of the critical micelle concentration (CMC)), the presence of surfactant increased the hydration rate of the film, as well as its maximum water uptake. At surfactant concentrations as low as 50% of the CMC, competitive hydration and removal of the phospholipid film were observed. X-Ray diffraction measurements show that the crystal structure of the DPPE films did not change significantly upon exposure to water and surfactant solutions. I n contrast, FITC-DPPE films exhibited changes in the long-range spacing of their crystalline structure upon hydration.
• Kabin, J. A., Tolstedt, S. L., Sáez, A. E., Grant, C. S., & Carbonell, R. G. (1998). Removal of organic films from rotating disks using aqueous solutions of nonionic surfactants: Effect of surfactant molecular structure. Journal of Colloid and Interface Science, 206(1), 102-111.
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  Abstract: In prior work, we examined the removal of abietic acid films from rotating fiberglass laminate disks by aqueous solutions of a nonionic surfactant. A three-stage cleaning mechanism was found, consisting successively of solubilization, shear-driven cleaning, and roll-up. We extend this work by exploring the influence of the surfactant molecular structure on the kinetics of the cleaning process. Five different poly(ethylene glycol) alkyl ether surfactants (C(x)E(y)) were used. Both the alkyl (x) and ethoxy (y) chain lengths were varied. Not all of the surfactants exhibited a three- stage cleaning mechanism. It was found that for surfactants with relatively high solubilization rates, the shear-driven cleaning stage did not occur. The selection of the most efficient surfactant depends on whether the surfactant concentration is below or above its critical micelle concentration (CMC). At submicellar concentrations, faster cleaning is obtained by surfactants that can induce shear-driven removal. At concentrations above the CMC, it is found that surfactant efficiency for a fixed alkyl or ethoxy chain length increases as the surfactant becomes more hydrophilic. This is attributed in part to the lower viscosity that the film achieves with the more hydrophilic surfactants due to their partitioning into the film, as well as their ability to carry water into the film.
• Littlejohn, F., Sáez, A. E., & Grant, C. S. (1998). Use of sodium polyaspartate for the removal of hydroxyapatite/ brushite deposits from stainless steel tubing. Industrial and Engineering Chemistry Research, 37(7), 2691-2700.
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  Abstract: This research investigates the use of sodium polyaspartate, a nontoxic, biodegradable polycarboxylic sequestrant, for removing calcium phosphate deposit consisting of hydroxyapatite (HAP) and brushite or dicalcium phosphate dihydrate (DCPD) from stainless steel surfaces. Cleaning studies show that the use of sodium polyaspartate under alkaline conditions significantly enhances the removal rates when compared to deionized water. In acidic solutions, sodium polyaspartate concentrations below 300 ppm inhibit removal of HAP/DCPD deposits whereas higher concentrations increase the removal rate. Comparative cleaning studies at alkaline pHs show that sodium polyaspartate cleans the surface at a rate comparable to sodium citrate but slower than in ethylenediaminetetraacetic acid. Supplementary dissolution experiments show that sodium polyaspartate enhances the HAP/DCPD dissolution rate while inhibiting the release of Ca2+. On the basis of these findings, we have concluded that sodium polyaspartate improves the HAP/DCPD dissolution and cleaning rates by Ca2+ sequestration. © 1998 American Chemical Society.
• Sáez, A. E., Márquez, M. A., Roberts, G. W., & Carbonell, R. G. (1998). Hydrodynamic model for gas-lift reactors. AIChE Journal, 44(6), 1413-1423.
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  Abstract: The hydrodynamic model of Young et al. (1991) for external-loop gas-lift reactors was modified to account for buoyancy forces in the gas phase. The revised model is based on macroscopic balances for the gas-liquid separator and external downcomer and spatially-averaged, 1-D mass and momentum balances in the riser. Using only the physical properties of the gas and liquid phases, the reactor dimensions, and the gas superfical velocity, the model predicts gas holdup profiles, gas and liquid velocity profiles, and pressure profiles in the riser for bubbly flow. Empirical correlations are used to represent frictional and drag effects, but there are no adjustable parameters in the model. The system of equations that must be solved to predict hydrodynamic behavior is simpler than that of Young et al. The sensitivity of the model to choice to drag coefficient correlation is analyzed. The model predictions match experimental data of previous works.
• Ventura-Medina, E., Pironti, F. F., & Sáez, A. (1998). Liquid phase mixing in a slurry bubble column with draft tube. Chemical Engineering Communications, 163, 219-231.
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  Abstract: In this work we characterize liquid phase mixing in a 150 L bubble column with a draft tube (internal airlift configuration) for a water-air-sand system at high solid concentrations. Liquid mixing is assessed by measuring the evolution of sodium chloride concentration after a pulse of concentrated NaCl solution is injected. Tracer concentrations were measured by means of electrical conductivity probes. The experimental set up consists of a 0.29 m internal diameter, 3 m length Plexiglas column with a conical bottom (cone apex angle of 60°) and a concentric draft tube with 0.14 m internal diameter and 2 m length. The gas superficial velocity based on the cross section of the column vaired from 0.057 to 0.22 m/s. Sand particles of 280 μm in average size were used, with slurry concentrations ranging from 120 to 500 kg/m3. From the tracer outputs, circulation time (time between peaks of the response curve) and mixing time (time required to achieve a 95% homogeneous solution) were determined after the pulse had been injected. The experimental data were analyzed by means of a tank in series model with recirculation. The circulation and mixing times were found to increase with solids concentration, and to decrease as the riser gas velocity was increased. The circulation times were larger in continuous operation than in semibatch mode. The results show that the system has equivalent dispersion coefficients that are one order of magnitude lower than those found in a conventional bubble column.
• Carrington, S. P., Tatham, J. P., Odell, J. A., & Sáez, A. (1997). Macromolecular dynamics in extensional flows: 1. Birefringence and viscometry. Polymer, 38(16), 4151-4164.
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  Abstract: The opposed jets apparatus is used to investigate the dynamics of the coil-stretch transition of polymer solutions in an idealized stagnation point extensional flow-field. A linear CCD detector allows optical retardation profiles to be recorded as the strain rate is varied. A numerical transformation enables true birefringence profiles to be produced, which enable the assessment of localized molecular orientation and stretching around the stagnation point. High molecular weight, closely monodisperse aPS and PEO are studied in θ and good solvents. Flow modification effects are apparent to extremely low concentration (≈c*/100). Under θ conditions, the width of the transition is consistent with the residual polydispersity. Simultaneous measurements of flow resistance enable the determination of the effective extensional viscosity. The increase in extensional viscosity due to molecular stretching is found to be of the order of the number of equivalent flexible units in the chain, after correction is made for the area of high molecular extension. © 1997 Elsevier Science Ltd.
• Carrington, S. P., Tatham, J. P., Odell, J. A., & Sáez, A. (1997). Macromolecular dynamics in extensional flows: 2. The evolution of molecular strain. Polymer, 38(18), 4595-4607.
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  Abstract: The opposed jets apparatus has been used to investigate the dynamics of the coil-stretch transition of polymer solutions in an idealized stagnation point extensional flow field. Flow simulations generated fluid strain profiles for different geometries. Assuming a molecular uncoiling model, true birefringence profiles have been converted to molecular strains for closely monodisperse, high molecular weight aPS under θ-conditions. This has enabled macromolecular deformation to be followed as a function of position and residence time. Non-linear hydrodynamic friction FENE dumb-bell simulations give qualitative agreement. Initially, molecular uncoiling is non-affine, consistent with changing hydrodynamic screening on extension. Deformation in a good solvent is more affine. Results are compared with PEO/water to investigate the effect of molecular parameters. The effective extensional viscosity has been ascertained by correction for the area of high molecular extension. The increase in extensional viscosity due to molecular stretching is substantial, of the order of the number of equivalent flexible units in the chain. © 1997 Elsevier Science Ltd.
• Muller, A. J., Patruyo, L. G., Montano, W., Roversi-M, D., Moreno, R., Ramirez, N. E., & Saez, A. E. (1997). Mechanical degradation of polymers in flows through porous media: Effect of flow path length and particle size. Applied Mechanics Reviews, 50(11 pt 2), S149-S155.
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  Abstract: In this work, we present an experimental study of flow-induced degradation of hydrolyzed polyacrylamide in aqueous solutions flowing through porous media consisting of beds packed with monodisperse spherical particles. The degradation is analyzed by passing the solution repeatedly through the porous medium at a constant flow velocity, and then characterizing the degraded solution in terms of its resistance coefficient. Repeated passes through the porous medium are equivalent to increasing the path length of the solution. When the polyacrylamide is dissolved in deionized water, it exhibits a gradual extension thickening behavior in terms of increases in flow velocity. In this case, the polymer degrades as it passes through the porous medium, even at relatively low flow rates. When the polyacrylamide is dissolved in a NaCl solution, it exhibits critical extension thickening in porous media flows, and it only degrades at Reynolds numbers that are higher than the onset of the extension thickening behavior. With repeated passes, the polymer progressively degrades until an asymptotic value of resistance coefficient is reached. The results show that the effect of particle size on degradation rates depends on the basis used for comparison between experiments carried out in beds with different particle sizes. However, the degree of degradation achieved after long path lengths is always higher for the largest particle size employed under equivalent comparison parameters.
• Siquier, S., Ronchett, A., Calderón, M., Llaguno, P., & Sáez, A. (1997). Spatial distribution of gas and solid phases in conical slurry bubble columns. Chemical Engineering Communications, 159, 173-190.
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  Abstract: In this work we perform an experimental study of the spatial distribution of phases in slurry bubble columns with conical distributors that have a volume comparable to that of the cylindrical section. Three different distributors were used whose apex angles were 13°, 22° and 34°. In gas-liquid operation, the gas holdups are axially uniform in the cylindrical section and decrease towards the wall, whereas in the conical section they increase towards the inlet. These trends are observed in the three cones for all the operating conditions explored. The solids distributions in the conical sections are qualitatively different depending on whether the operation is semibatch or continuous with respect to the flow of solid liquid suspension: in semibatch operation, the concentration monotonically increases towards the bottom of the cone and exhibits a slight increase as the wall is approached; in continuous operation, an absolute maximum in solids concentration is obtained at a point located on the wall of the cone and intermediate height. The location of this maximum moves upwards as the total solids content in the column increases and as the apex angle decreases. The maximum in solids concentration signals the most probable site for the onset of solids sedimentation and the presence of low mixing levels and reduced mass transfer rates in a slurry reactor. In the range of conditions explored in the present work, the lowest apex angle (13°) yields a more uniform solids distribution throughout the system.
• Yan, J., Sáez, A. E., & Grant, C. S. (1997). Removal of Oil Films from Stainless Steel Tubes. AIChE Journal, 43(1), 251-259.
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  Abstract: The removal of oil films from the inner surface of a stainless steel tube cell using aqueous cleaning solutions was studied. The two oils used in the cleaning experiments, Sunquench 1042 and heavy mineral oil, contained P32 labeled tributyl phosphate (TBP) as a radioactive tracer. The β- particles emitted from the radioactive TBP were detected by a CaF2 scintillator and used as a measure of the amount of oil remaining in the tube cell. Cleaning experiments performed at different flow rates, surface treatment, and surfactant concentrations indicated that initially the oil films were removed rapidly. At the end of the experiments, the oil removal rate reduced significantly, eventually becoming negligible. The stainless steel morphology affected oil removal significantly, and the rougher tube tended to retard the oil removal. The rate and extent of the decontamination were significantly increased in the presence of sodium dodecyl sulfate, a nonionic surfactant. Experimental data were compared to a hydrodynamic model based on the removal of a liquid contaminant from a solid surface by an immiscible fluid. The model deviated from the experimental data due to the presence of instabilities at the oil-water interface.
• Alarcón, Z., Parra, E., Gómez, M., Siquier, S., & Sáez, A. (1996). Phase distributions in semibatch slurry bubble columns with guar gum solutions. Chemical Engineering Science, 51(12), 3367-3371.
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  Abstract: An experimental study was conducted of the hydrodynamics of slurry bubble columns in which the liquid phase is a solution of guar gum. The main emphasis is to analyze how the presence of intermolecular cross links affects hydrodynamic parameters such as gas holdup and solids distribution in the bubble column.
• Bello, J. B., Müller, A., & Sáez, A. (1996). Effect of intermolecular cross links on drag reduction by polymer solutions. Polymer Bulletin, 36(1), 111-118.
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  Abstract: In this work we explore the effect of a cross-linking agent on the drag reduction capability of hydroxypropyl guar and guar gum solutions in turbulent flow through horizontal pipes. The results show that the addition of a cross-linking agent (borax) to solutions with concentrations below those required for gel formation enhances drag reduction due to the increased dimensions of the macromolecules in the presence of intermolecular cross links. The flow-induced degradation of the polymers is not appreciably affected by the addition of cross-linking agent.
• Dyakonova, N. E., Odell, J. A., Brestkin, Y., Lyulin, A. V., & Saez, A. E. (1996). Macromolecular strain in periodic models of porous media flows. Journal of Non-Newtonian Fluid Mechanics, 67(1-3), 285-310.
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  Abstract: This paper is concerned with the deformation of macromolecules in flows which model porous media and its influence on macrorheological parameters. Two flow cells ("oscillatory convergent-divergent" and "cylinder array") have been constructed. Adding an extra cylinder to the symmetry axis of the cylinder array cell creates a stagnation point. These cells simulate important extensional components of the flows occurring in porous media, yet they possess well-defined geometries and better characterised flow fields. A numerical simulation of viscous flow in the cylinder array cell applicable to the flow regimes used in experiments has been performed. Solutions of high molecular weight polystyrene (with concentrations well below the conventional critical concentration) were used in the experiments. Birefringence measurements revealed that molecules can achieve large strains, even in extensional flows with short residence times. This observation is discussed using a dumb-bell model with conformation dependent elastic and friction coefficients. Simultaneous pressure drop measurements showed the onset of viscoelasticity coupled with an increase in birefringence intensity. Concentration effects, the influence of the stagnation point on the observed onset of viscoelasticity and a possible mechanism of thickening are discussed.
• Grosser, K., Carbonell, R. G., Cavero, A., & Sáez, A. (1996). Lateral Thermal Dispersion in Gas-Liquid Cocurrent Downflow Through Packed Beds. AIChE Journal, 42(10), 2977-2983.
• Gómez, M., Alarcón, Z., Parra, E., Siquier, S., Pironti, F., & Sáez, A. (1996). Hydrodynamics of semibatch slurry bubble columns with polymer solutions. Chemical Engineering Science, 51(11), 2739-2744.
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  Abstract: In this work we perform an experimental study of the hydrodynamics of semibatch slurry bubble columns in which the liquid phase is a solution of a high molecular weight hydrolyzed polyacrylamide. Experiments were conducted in bubble columns with two different diameters (10 and 29 cm.) In gas-liquid operation, the gas holdup decreases as the polymer concentration increases due to the formation of large stable bubbles. In the presence of high solids concentration, this trend is reversed in the larger column due to an increase in the number of small bubbles and an appreciable increase in the residence times of the large bubbles brought about by an increase in slurry circulation. The distribution of solid phase becomes more uniform as the polymer concentration increases. This trend is quantified by means of the application of a modified form of the sedimentation-dispersion model. The macromolecular conformation of the polymer in solution is altered by adding NaCl, whose positive ions screen negative charges in the polymer molecule producing a contraction of the coil. At the concentration levels used in this work, the addition of salt decreases the ability of the polymer to produce a more uniform solids distribution.
• Kabin, J. A., Sáez, A., Grant, C. S., & Carbonell, R. G. (1996). Removal of Organic Films from Rotating Disks Using Aqueous Solutions of Nonionic Surfactants: Film Morphology and Cleaning Mechanisms. Industrial and Engineering Chemistry Research, 35(12), 4494-4506.
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  Abstract: In this work, we consider the cleaning of an organic liquid film, consisting initially of a concentrated solution of abietic acid in isopropyl alcohol, from the surface of a rotating disk by using aqueous solutions of a nonionic surfactant, pentaethylene glycol mono-n-dodecyl ether. The results show that the removal process takes place in three consecutive stages. The first stage is controlled by the solubilization of the abietic acid by surfactant penetration and subsequent mass transfer from the interface to the bulk of the aqueous solution. During the first stage, the film absorbs water from the aqueous solution and breaks up into drops that leave portions of the surface exposed. The absorption of surfactant and water reduces the organicphase viscosity, until the drops start to move on the disk surface under the action of shear forces. These drops aggregate into spiral-shaped continuous rivulets through which the organic phase flows until it comes off the disk edge. Such behavior occurs during the second stage of cleaning, which has a rate of removal appreciably faster than the first stage. The rivulets are shown to be tangent to the stress exerted by the aqueous solution on the surface of the organic phase. The rivulets eventually break, leading to a third stage with lower removal rates, in which the removal mechanism is apparently the roll up of organic-phase drops under the action of shear forces. In this work, we present experimental evidence that supports the described mechanism, based on photographs showing the morphology of the film structure in the different cleaning stages. A model is derived that relates the empirical observations of cleaning rates to physical parameters describing the solubilizing film hydrodynamics.
• Moreno, R. A., Müller, A., & Sáez, A. (1996). Flow-induced degradation of hydrolyzed polyacrylamide in porous media. Polymer Bulletin, 37(5), 663-670.
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  Abstract: In this work we present an experimental study of flow-induced degradation of hydrolyzed polyacrylamide in aqueous solutions flowing through porous media. The degradation is analyzed by passing the solution repeatedly through the medium at a constant flow velocity and the degraded solution is then characterized by porous media and opposed jets flows. When the polyacrylamide is dissolved in deionized water, it exhibits a gradual extension thickening in the flow through porous media and opposed jets. In this case, the polymer degrades as it passes through the porous medium even at relatively low flow rates. When the polyacrylamide is dissolved in an NaCl solution, it exhibits critical extension thickening in porous media flows, and it only degrades at Reynolds numbers that are higher than the onset of the extension thickening behavior. Chain degradation is therefore only encountered when extension thickening is produced. The results also show that the extent of degradation decreases as the pore size decreases.
• Müller, A., Sáez, A., & Odell, J. A. (1995). Turbulence suppression by polymer solutions in opposed jets flow. AIChE Journal, 41(5), 1333-1336.
• Pino, L. R., & Sáez, A. (1995). Thermal dispersion in vertical gas-liquid flows with foaming and non-foaming liquids. International Communications in Heat and Mass Transfer, 22(3), 391-400.
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  Abstract: Heat transfer experiments have been performed in gas-liquid upwards flow in a vertical column with non-foaming (water) and foaming (kerosene) liquids. The main purpose of the experiments has been to characterize the degree of thermal mixing in the system. For the range of conditions employed, the non-foaming liquid exhibits complete mixing at low liquid superficial velocities. An increase in liquid velocity leads to incomplete mixing. In the latter case, the thermal dispersion coefficient at low gas superficial velocities is larger than what correlations in the literature predict. For the foaming liquid, when foaming and bubbling regions coexist in the bubble column, each region behaves as a completely-mixed subsystem. © 1995.
• Pironti, F. F., Medina, V. R., Calvo, R., & Sáez, A. (1995). Effect of draft tube position on the hydrodynamics of a draft tube slurry bubble column. The Chemical Engineering Journal and The Biochemical Engineering Journal, 60(1-3), 155-160.
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  Abstract: Two- and three-phase hydrodynamic studies were conducted in an air lift bubble column with an internal loop. The bubble column had a conical distributor at the bottom, through which the gas was sparged, creating a liquid or slurry circulation from the draft tube to be annular region. The axial position of the draft tube was varied with respect to the conical section. The experiments were performed with the air-water system at ambient conditions, using siliceous sand as the solid phase. When the bottom of the draft tube was located precisely at the transition between the conical and cylindrical regions, no liquid circulation was observed. When the draft tube was located in a lower position, liquid circulation started and its magnitude increased as the draft tube was further lowered inside the conical region. The results presented indicate that the hydrodynammic behaviour of these systems can be effectively controlled by varying the axial position of the draft tube. © 1995.
• Silva, F. D., Pironti, F. F., & Saez, A. E. (1995). The sedimentation-dispersion model for slurry bubble columns with a conical distributor. Chemical Engineering Communications, 138, 157-170.
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  Abstract: A mathematical model is presented to simulate the distribution of solid phase in slurry bubble columns with a conical entrance section. The model is based on the sedimentation-dispersion model that is commonly used to simulate solids distribution in cylindrical columns. The model equations are obtained from a mass balance of solids expressed in terms of a cross-sectional average of the solids concentration. The resulting differential equations are integrated numerically. The model was used to analyze the effect of the taper angle of a conical distributor on the suspension of solids in a cylindrical spouted bed with pilot scale dimensions. The effects of gas and slurry flow rates, and average feed solids concentrations are also studied. The results show that there is a range of operating conditions for which the solids concentration profile exhibits a maximum within the conical region. (from Authors)
• Tatham, J. P., Carrington, S., Odell, J. A., Gamboa, A. C., MÜller, A., & Sáez, A. (1995). Extensional behavior of hydroxypropyl guar solutions: Optical rheometry in opposed jets and flow through porous media. Journal of Rheology, 39(5), 961-986.
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  Abstract: In this work we perform an experimental characterization of the rheology of hydroxypropyl guar (HPG) solutions. The flow situations investigated are shear rheometry, elongational flow in opposed jets, and flow through porousm edia.T he resultso f the experimentss how that hydroxypropyl guar behaves as a semiflexible molecule in aqueous solutions under elongational flow situations. In shear flows and under semidilute conditions, the HPG solutions have a shear-thinning behavior, whereas in opposed-jets flow they exhibit extension thickening. In porous media flows, semidilute solutions behave as shear thinning, but there is evidence that extension thickening is present. We have developed a technique in which a linear charged-coupled device (CCD) array is used as a retardation detector to measure birefringence profiles in opposed-jets flow. This technique has shown that HPG molecules are stretched in the flow field, which confirms that the HPG molecules are semiflexible. The addition of a cross-linking agent to HPG solutions was found to have a pronounced effect on their flow behavior in extensional flows. Filtered dilute solutions exhibit intramolecular cross links that reduce the apparent viscosity of the solution in both opposed jets and porous media flows. On the other hand, semidilute solutions (as well as filtered solutions of low concentrations) exhibit intermolecular cross links that, in porous media flows, result in a sizable increase in pressure drops.Copyright © 1995 Society of Rheology.
• Gamboa, A. C., Sáez, A., & Müller, A. (1994). Flow of solutions of hydroxypropyl guar-poly(ethylene oxide) mixtures through a porous medium. Polymer Bulletin, 33(6), 717-724.
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  Abstract: In flow through porous media, solutions of poly(ethylene oxide) (PEO) exhibit extension thickening, whereas hydroxypropyl guar (HPG) solutions are shear-thinning at high concentrations. The results show that the extension-thickening exhibited by PEO solutions becomes less critical with increasing flow rate as the concentration of HPG in the solution is increased. At high concentrations of HPG, the presence of PEO inhibits the shear-thinning behaviour, without increasing the apparent viscosity of the solution. The presence of HPG reduces the rate and extent of degradation of PEO in the flowing solution. © 1994 Springer-Verlag.
• Muller, A. J., Balsamo, V., Silva, F. D., Rosales, C. M., & Saez, A. E. (1994). Shear and elongational behavior of linear low-density and low-density polyethylene blends from capillary rheometry. Polymer Engineering and Science, 34(19), 1455-1463.
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  Abstract: In this work we present an experimental study of shear and apparent elongational behavior of linear low-density (LLDPE) and low-density (LDPE) polyethylene blends by means of capillary rheometry. The characterization of these rheological properties is crucial in the design of a blend that combines the ease of processing of LDPE with the mechanical advantages of the LLDPE. Two different low-density polyethylenes and one common linear low-density polyethylene were used to prepare the blends. The results obtained indicate a strong sensitivity of the rheology of the blend to changes in the molecular weight of the LDPE employed. For the higher molecular weight LDPE, the shear viscosity of the blend was essentially equal to that of the LDPE homopolymer up to a concentration of 25% of LLDPE, whereas the apparent extensional viscosity was appreciably lower. For the lower molecular weight LDPE, the same trend was obtained regarding the shear viscosity, but in this case the apparent extensional viscosity of the blend was somewhat higher than that of the LDPE homopolymer.
• Sáez, A., Müller, A., & Odell, J. A. (1994). Flow of monodisperse polystyrene solutions through porous media. Colloid & Polymer Science, 272(10), 1224-1233.
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  Abstract: In this work, we study the origin of the extension thickening commonly observed when solutions of flexible polymers flow through porous media and ideal elongational flows. We have used randomly packed beds of glass beads as porous media. We have performed experiments with closely monodisperse atactic polystyrene of different molecular weights dissolved in organic solvents. The use of a closely monodisperse polymer allowed us to make a more meaningful comparison between the results obtained using opposed jets and porous media flow, as compared to previous works on polydisperse polymers. The results indicate that the coil-stretch transition of isolated polymer molecules in solution cannot be the only mechanism responsible for the extension thickening. It is clear that part of the observed effect is due to the extension of isolated molecules, but the main factor causing a great increase in the elongation viscosity beyond a critical strain rate is the formation of transient entanglement networks. © 1994 Steinkopff-Verlag.
• Arguelles, C., Yepez, M. M., & Saez, A. E. (1993). Hydrodynamics of bubble columns with two immiscible liquid phases. Chemical Engineering Communications, 122, 201-212.
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  Abstract: An experimental study of hydrodynamic parameters of bubble columns with the presence of two immiscible liquid phases, water and kerosene, was performed. The solid used consisted of glass beads with a narrow size distribution. The analysis was based on the determination of global gas holdups and phases distribution along the length of the column in the semibatch mode of operation. The results show that the presence of two immiscible liquid phases significantly reduces the gas holdup in the bubble column as compared to the results obtained with pure aqueous and organic liquid phases. The distribution of solid phase in a slurry bubble column is drastically affected by the presence of immiscible liquid phases, and exhibits a qualitatively different behavior when compared to systems with one liquid phase. The addition of small amounts of aqueous phase to a slurry bubble column in which the liquid phase is kerosene results in the sedimentation of the solid. As the amount of aqueous phase added is increased, the solid fluidizes yielding almost flat concentration profiles.
• Rodriguez, S., Romero, C., Sargenti, M. L., Müller, A., Sáez, A., & Odell, J. A. (1993). Flow of polymer solutions through porous media. Journal of Non-Newtonian Fluid Mechanics, 49(1), 63-85.
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  Abstract: The molecular mechanism for viscosity enhancement during the flow of poly(ethylene oxide) solutions through porous media has been investigated. Random packed beds of uniform-size spheres have been used as porous media. Experiments were conducted for one-dimensional (uniform) flow, as well as for a particular three-dimensional (nonuniform) flow situation. A substantial increase in flow resistance with respect to that exhibited by Newtonian fluids has been observed in both cases. The results obtained suggest that, under the conditions employed in the present work, the mechanism that causes the increased flow resistance is related to the formation of transient networks of polymer molecules in the flow field. The nonuniform flow results indicate that the presence of the polymer induces a change in the macroscopic flow distribution within the porous medium. © 1993.
• Pino, L. Z., Solari, R. B., Siquier, S., Estevez, L., Yepez, M. M., & Saez, A. E. (1992). Effect of operating conditions on gas holdup in slurry bubble columns with a foaming liquid. Chemical Engineering Communications, 117, 367-382.
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  Abstract: This work presents experimental data on gas holdup in slurry bubble columns with a foaming liquid. The effects of solids concentration, solid particle size, superficial phase velocities and column dimensions on the gas holdup are analyzed. At low superficial gas velocities (less than 4 cm/s), for which the liquid does not foam, the presence of solids with small particle size does not affect the gas holdup whereas solids with large particle size induce foam formation and thus their presence increases the gas holdup. In the foaming regime, an increase of solids concentration decreases the gas holdup. The operating mode has a strong effect on the gas holdup: the semi-batch operating mode (stagnant liquid-solid suspension) increases the ability of the liquid to foam with respect to the continuous mode. Regarding the effect of column dimensions, the results presented show that the height of the bubble column does not affect at an appreciable extent the gas holdup in the range 6 < L/D < 12. At high gas velocities (greater than 6 cm/s) the gas holdups obtained in a 30 cm-internal diameter column are the same as those measured in a 10 cm-internal diameter column.
• Saez, A. E., Yepez, M. M., Cabrera, C., & Soria, E. M. (1991). Static liquid holdup in packed beds of spherical particles. AIChE Journal, 37(11), 1733-1736.
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  Abstract: The authors use dimensional analysis to establish the independent parameters that affect the static liquid holdup. They also present experimental data to explore the dependence of the static holdup on the Eotvos number; through comparison with previous theoretical works, they analyze the mechanisms resppnsible for the effect of Eotvos number on the static liquid holdup.
• Siquier, S., Yepez, M. M., & Saez, A. E. (1991). Solid distribution in a slurry bubble column with two immiscible liquid phases. AIChE Journal, 37(3), 466-469.
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  Abstract: In this work we will explore the distribution of a monodisperse solid in a semibatch bubble column with two immiscible liquid phases. The results obtained in the present work show that small amounts of water in slurry bubble columns with organic liquids can have a strong effect over the solids distribution. This should be taken into account when working with two immiscible liquids in a slurry bubble column or when working with an organic liquid with the possible existence of small quantities of a dispersed aqueous phase.
• Sáez, A., Perfetti, J. C., & Rusinek, I. (1991). Prediction of effective diffusivities in porous media using spatially periodic models. Transport in Porous Media, 6(2), 143-157.
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  Abstract: Calculations of effective diffusivities in three-dimensional, spatially periodic porous media are performed. For isotropic systems, it is found that, for a given porosity, the predicted value of the effective diffusivity matches experimental results for randomly-packed beds of spheres. Furthermore, the three-dimensional geometry yields approximately the same results as previous calculations employing two-dimensional representations, indicating a relative insensitivity of the effective diffusivity to local geometry. Regarding anisotropic systems, for which two-dimensional modes fail, it is found that there is a significant improvement in the prediction of the effective diffusivity perpendicular to the bedding plane when the three-dimensional model is employed using one adjustable parameter. However, the three-dimensional model overestimates the effective diffusivity parallel to the bedding plane. © 1991 Kluwer Academic Publishers.
• Otero, C., Saez, A. E., & Rusinek, I. (1990). Effective permeabilities for model heterogeneous porous media. In Situ, 14(3), 229-244.
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  Abstract: This paper presents a rigorous technique to evaluate effective absolute permeabilities for heterogeneous porous media. The technique is based on a perturbation analysis of the equations of motion of a slightly compressible fluid in a homogeneous porous medium at low Reynolds numbers. The effective permeabilities can be calculated once the local geometry of the heterogeneous medium is specified. The technique is used to evaluate two- and three-dimensional effective vertical permeabilities in porous media with shale intercalations. including the case in which the porous matrix is anisotropic. The results indicate that the use of two-dimensional models is not adequate when describing such systems, since three-dimensional calculations differ substantially from two-dimensional ones Effective permeabilities are also reported for the standard 'sugar cubes' model for fractured porous media. In this case, the differences between two- and three-dimensional models are quantitatively insignificant.
• Pino, L. R., Yepez, M. M., & Saez, A. E. (1990). Hydrodynamics of a semibatch slurry bubble column with a foaming liquid. AIChE Journal, 36(11), 1758-1762.
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  Abstract: In this work we present an experiment study of solids distribution in a semi-batch slurry bubble column in the presence of foam formation. The solids concentration profiles are analyzed by means of a modification of the sedimentation-dispersion model. The effect of the presence of solids on the gas holdup is given. At the lowest gas velocity, the solids content does not affect appreciably the gas holdup in the range of concentrations considered. At intermediate and high gas velocities, an increase in solids concentration results in a decrease in gas holdup. The decrease of gas holdup with solids concentration is consistent with the trend observed in nonfoaming systems and the particle size range considered in this work.
• Ramírez, N., & Sáez, A. (1990). The effect of variable viscosity on boundary-layer heat transfer in a porous medium. International Communications in Heat and Mass Transfer, 17(4), 477-488.
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  Abstract: In this work we present a theoretical analysis of forced-convection heat transfer over a flat surface imbedded in a saturated porous medium, considering that the viscosity of the fluid varies with temperature. The velocity and temperature profiles are described by means of a similarity solution. The effect of viscosity variations is quantified for the case of a fluid whose dependence of viscosity on temperature is linear. Illustrative results indicate that, for liquids, this effect should be taken into account, even for relatively low temperature gradients. This confirms experimental observations made in previous works. © 1990.
• Rodriguez-Prada, H., Pironti, F. F., & Saez, A. E. (1990). Fundamental solutions of the streamfunction-vorticity formulation of the Navier-Stokes equations. International Journal for Numerical Methods in Fluids, 10(1), 1-12.
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  Abstract: A new boundary element procedure is developed for the solution of the streamfunction-vorticity formulation of the Navier-Stokes equations in two dimensions. The differential equations are stated in their transient version and then discretized via finite differences with respect to time. In this discretization, the non-linear inertial terms are evaluated in a previous time step, thus making the scheme explicit with respect to them. In the resulting discretized equations, fundamental solutions that take into account the coupling between the equations are developed by treating the non-linear terms as inhomogeneities. The resulting boundary integral equations are solved by the regular boundary element method, in which the singular points are placed outside the solution domain.
• Sáez, A., & Carbonell, R. (1990). The equilibrium and stability of menisci between touching spheres under the effect of gravity. Journal of Colloid And Interface Science, 140(2), 408-418.
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  Abstract: The equilibrium shapes and stability of menisci formed at the contact point between two vertically aligned spheres were theoretically studied. The equilibrium configurations were determined as solutions of the equation of Young-LaPlace. The stability of the equilibrium shapes was determined by means of a perturbation analysis of the three-dimensional form of the equation of Young-LaPlace. It was found that there is a maximum amount of liquid that can be retained at the contact point, which is determined by geometrical considerations when gravitational effects are important, and by the onset of instability when gravitational effects are negligible. The maximum amount of liquid diminishes as the gravitational forces become stronger with respect to surface tension forces. In the case of small contact angles, an increase in the contact angle results in an increase in the maximum liquid retention, whereas, when the contact angle is large, this trend is reversed. © 1990.
• Sáez, A., Otero, C. J., & Rusinek, I. (1989). The effective homogeneous behavior of heterogeneous porous media. Transport in Porous Media, 4(3), 213-238.
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  Abstract: The macroscopic equations that govern the processes of one- and two-phase flow through heterogeneous porous media are derived by using the method of multiple scales. The resulting equations are mathematically similar to the point equations, with the fundamental difference that the local permeabilities are replaced by effective parameters. The method allows the determination of these parameters from a knowledge of the geometrical structure of the medium and its heterogeneities. The technique is applied to determine the effective parameters for one- and two-phase flows through heterogeneous porous media made up of two homogeneous porous media. © 1989 Kluwer Academic Publishers.
• Estevez, L., Saez, A., Pachano, J., & Cavicchioli, I. (1988). Effect of surfactants on gas holdup of two-phase bubble columns. American Institute of Chemical Engineers, National Meeting, 9G 29p.
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  Abstract: Two-phase experiments have been carried out using organic liquids with a surfactant and air in a bubble column 30 [cm] inside diameter and 3 [m] tall. Under the presence of the surfactant, two distinct regions are observed: a bubbling region in the lower part, and a froth zone in the upper part of the column. Intrinsic gas holdup were measured in each region. Results showed that intrinsic gas holdup did not vary significantly with surfactant concentration. However, the position of the limiting surface separating the two regions varied considerably with surfactant concentration, thus affecting strongly the overall gas holdup. Based on these facts, correlations for intrinsic and overall gas holdup have been proposed.
• Rodriguez-Prada, H., & Saez, A. E. (1987). A boundary element solution of the stream function vorticity formulation of the Navier-Stokes equations.. Array.
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  Abstract: The Boundary Element Method is applied to solve the stream function vorticity formulation of the steady state Navier Stokes equations. The procedure developed relies on the use of fundamental solutions that take into account the coupling between the differential equations through the vorticity term in the stream function equation. The nonlinear terms are considered as inhomogeneities in the development of the boundary integral equations and treated by means of direct iteration. The method allows the handling of no slip boundary conditions in a direct manner, avoiding iteration to find the vorticity values on no slip boundaries. The discretization of the resulting boundary integral equations is performed by placing the singular points outside the solution domain, as it is done in the Regular Boundary Element Method.
• Saez, A. E., & Carbonell, R. G. (1987). EQUILIBRIUM SHAPE AND STABILITY OF MENISCI FORMED BETWEEN TWO TOUCHING CYLINDERS.. Journal of Fluid Mechanics, 176, 357-378.
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  Abstract: The equilibrium shape and stability of menisci formed at the contact line between two vertically aligned cylinders were investigated by developing a general bifurcation analysis from the classic equation of Young-Laplace. It was found that the maximum amount of liquid that can be held at the contact line is determined by the existence of a bifurcation of the equilibrium solutions. The onset of instability is characterized by a translationally symmetric bifurcation that always precedes the instability to asymmetric perturbations. The maximum stable liquid retention is a strong function of the ratio of gravitational to surface-tension forces, indicating that gravity acts as a destabilizing force. The effect of contact angle on the maximum liquid retention is more complex: when the gravitational effects are small, an increase in contact angle results in a decrease in liquid retention; on the other hand, when the gravitational effects are appreciable, a maximum value of the liquid retention is obtained for intermediate values of the contact angle.
• Levec, J., Saez, A. E., & Carbonell, R. G. (1986). HYDRODYNAMICS OF TRICKLING FLOW IN PACKED BEDS. PART II: EXPERIMENTAL OBSERVATIONS.. AIChE Journal, 32(3), 369-380.
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  Abstract: The liquid holdup and the pressure drop for two-phase trickling flow in a packed bed were measured experimentally. Different values of those parameters were obtained as the liquid flow rate was increased and then decreased, indicating a multiplicity in hydrodynamic states. This behavior was observed even when the gas flow rate was zero in the bed. It was determined that the hysteresis exhibited by the process is due to imperfect wetting of the packing and to the difference between advancing and receding contact angles at the gas-liquid-solid contact lines. A new correlation for predicting liquid holdups and pressure drops for trickling flow in packed beds is proposed for the decreasing liquid flow rate operating mode.
• Saez, A. E., Carbonell, R. G., & Levec, J. (1986). HYDRODYNAMICS OF TRICKLING FLOW IN PACKED BEDS. PART 1: CONDUIT MODELS.. AIChE Journal, 32(3), 353-368.
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  Abstract: The hydrodynamics of trickling flow in packed beds is modeled by representing the porous medium as an array of parallel conduits of circular cross section. First, a straight tube model is developed and analytical solutions are obtained for the relative permeabilities of the gas and liquid phases. Then a periodically constricted tube model is proposed and the equations of motion are solved numerically to determine the effect that surface tension forces have on the relative permeabilities. The constricted tube model predicts that the relative permeabilities of the phases are appreciably sensitive to surface tension forces, a prediction that seems at odds with experimental observations.
• Saez, A. E., & Carbonell, R. G. (1985). HYDRODYNAMIC PARAMETERS FOR GAS-LIQUID COCURRENT FLOW IN PACKED BEDS.. AIChE Journal, 31(1), 52-62.
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  Abstract: The hydrodynamics of cocurrent gas-liquid flow in packed beds is analyzed by extending the concept of relative permeability to the inertial regime. The relative permeabilities of the gas and liquid phases are functions of the saturation of the liquid phase. These functions are found from an analysis of experimental data. The relations obtained are used to develop empirical correlations for predicting liquid holdup and pressure drop in gas-liquid cocurrent downflow in packed beds over a wide range of operating conditions. The correlations proposed give very good results when compared to experimental data yielding, in general, mean relative deviations lower than existing correlations. A new equation is proposed for predicting static holdup in packed beds, based on a more physically realistic characteristic length than that used in previous studies.
• Saez, A. E., & Carbonell, R. G. (1985). ON THE PERFORMANCE OF QUADRILATERAL FINITE ELEMENTS IN THE SOLUTION TO THE STOKES EQUATIONS IN PERIODIC STRUCTURES.. International Journal for Numerical Methods in Fluids, 5(7), 601-614.
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  Abstract: The use of the finite element method in solving the problem of flow of a Newtonian fluid in periodically constricted tubes is explored. The performance of eight node serendipity and nine node Lagrangian elements is compared. It was found that the Lagrangian element results in unstable velocity fields when stagnant or recirculation regions are present. This is characteristic of tubes with large expansion zones. The eight node element does not exhibit instabilities. Both elements give accurate pressure fields. This behavior is contrary to traditional results obtained for flow problems with similar geometrical characteristics. This suggests that the periodicity of the boundary conditions might be the cause of the instabilities in the numerical solution.
• Levec, J., Saez, A. E., & Carbonell, R. G. (1984). HOLDUP AND PRESSURE DROP IN TRICKLE BED REACTORS.. Institution of Chemical Engineers Symposium Series, 185-194.
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  Abstract: The concept of relative permeabilities for the gas and liquid phases is used to unify a large number of existing data for liquid holdup and gas phase pressure drops in trickle bed reactors. At relatively high gas flow rates, the liquid and gas phase relative permeabilities are a function of saturation only, and this function is insensitive to the shape of the packing. New data taken at relatively low gas velocities show that the relative permeability can be a function of the gas phase Reynolds number as well as saturation. The nature of this dependence is analyzed using a simple capillary tube model for the concurrent gas-liquid flow in the trickle bed.
• Saez, A. E., & McCoy, B. J. (1984). Response to Dr. D. Fitzgerald's comments. Solar Energy, 32(2), 313-.
• Saez, A. E., & McCoy, B. J. (1984). Response to comments by Drs. D. E. Beasley and J. A. Clark. Solar Energy, 32(2), 314-.
• Saez, A. E., & McCoy, B. J. (1983). Transient analysis of packed-bed thermal storage systems. International Journal of Heat and Mass Transfer, 26(1), 49-54.
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  Abstract: A model, including longitudinal thermal dispersion and intraparticle conduction, is developed to describe the transient response of a packed column with a time-varying inlet temperature. The model can be applied to a diabatic column with uniform and constant ambient temperature, or to a perfectly insulated system. The expression for the temperature response within the column as a function of time and axial position is obtained by expanding the solution to an impulse of heat at the inlet in terms of either Hermite or Laguerre polynomials. The response to an arbitrary inlet temperature transient, found via a convolution integral, is expressed as a single quadrature. The response to a step input is an algebraic expression. © 1983 Pergamon Press Ltd.
• Saez, A. E., & McCoy, B. J. (1982). Dynamic response of a packed bed thermal storage system-a model for solar air heating. Solar Energy, 29(3), 201-206.
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  Abstract: A mathematical model for simulating the dynamic temperature response of a packed column to an arbitrary time-dependent inlet air temperature is developed. The model includes axial thermal dispersion as well as intra-particle conduction, features that have usually been neglected but can be important in solar energy applications. Solutions, presented in terms of moments of the temperature response to an impulse of heat at the inlet, can be evaluated by simple numerical quadrature. Results of the model compare favorably with experimental data found in the literature. The model is used to optimize heat storage in a rock bin system subject to a realistic transient inlet temperature. © 1982.
• Saez, A. E., & McCoy, B. J. (1982). TRANSIENT ANALYSIS OF PACKED COLUMN THERMAL STORAGE SYSTEMS.. Annual Meeting - American Institute of Chemical Engineers.
• Solari, R. B., Saez, A. E., & Castillo, C. A. (1982). DISTILLATION COLUMNS OPTIMIZATION BY A FASTER CONVERGENCE PROCEDURE.. Revista Tecnica INTEVEP, 2(2), 121-129.
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  Abstract: A fast method to optimize distillation column design is presented. Optimum column design and operating conditions can be obtained with a few iterations through a procedure of successive linear approximations to the optimum. The procedure can be applied to the design and rating of complex distillation columns to minimize overdesign. The method shows a high convergence rate and requires less computer time than other rigorous distillation optimization schemes.
• Solari, R. B., Saez, E., D'Apollo, I., & Bellet, A. (1982). VELOCITY DISTRIBUTION AND LIQUID FLOW PATTERNS ON INDUSTRIAL SIEVE TRAYS.. Chemical Engineering Communications, 13(4-6), 369-384.
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  Abstract: The objective of this work is to measure the flow parameters which define the non-uniform flow patterns used in the theoretical models to predict tray efficiency. Stagnant zone areas and flow recirculation parameters have been correlated to dimensionless variables which are representative of tray design and flow conditions. Experiments were performed in a 1. 25 m air/water simulator to measure velocity distributions in sieve trays with 5% downcomer area, as a function of hole area, weir height and liquid and vapor rates. This work is pertinent to the design of distillation and absorption trays.
• Solari, R. B., Saez, E., D'Apollo, I., & Bellet, A. (1982). Velocity distribution and liquid flow patterns on industrial sieve trays.. CHEM. ENGNG. COMMUN., 13(4-6 , 1982, 369-384.).
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  Abstract: The objective of this work was to measure the flow parameters which define the non uniform flow patterns used in theoretical models to predict tray efficiency. Stagnant zone areas and flow recirculation parameters were correlated to dimensionless variables which are representative of tray design and flow conditions. Experiments were performed in a 1.25 m air/water simulator to measure velocity distributions in sieve trays with 5% downcomer area, as a function of hole area, weir height and liquid and vapour rates. (from paper)

Presentations

• Saez, A. E. (2021, August). Scale-up of Gap Membrane Distillation Systems Using Bench-scale Direct Contact Membrane Distillation Data. North American Membrane Society 30th Annual Meeting. Estes Park, Colorado.
• Saez, A. E., Field, J. P., Rasmussen, C., Rathke, S., & Blankinship, J. (2021). Deadly dust on Arizona highways: Developing an improved dust risk index based on soil stabilization mechanisms and Ecological Site Descriptions. National Cooperative Soil Survey National Conference.
• Tfaily, M., Rasmussen, C., Saez, A. E., Field, J., Barberan, A., Gornish, E., Babst-Kostecka, A., Rathke, S., & Blankinship, J. (2021). Mitigating dust pollution for climate-resilience development in arid regions. Arizona Institutes for Resilience.
• Tfaily, M., Rasmussen, C., Saez, A. E., Field, J., Barberan, A., Gornish, E., Babst-Kostecka, A., Rathke, S., & Blankinship, J. (2021). Mitigating dust pollution for climate-resilient development in arid regions. Symposium on Resilience Research for Global Development ChallengesArizona Institutes for Environment.
• Saez, A. E., Arnold, R. G., Quanrud, D. M., Rojas, N., Martinez, V., Barnett, B., Vo, H., & Marquez, I. (2019, April). Photo-transformation of Trace Organic Compounds by Singlet Oxygen. Kinetics and Mechanism. 2019 American Chemical Society National Annual Meeting. Orlando, FL: American Chemical Society.
• Hao, V., Saez, A. E., Quanrud, D. M., & Arnold, R. G. (2017, April). Kinetic modeling of sunlight-assisted degradation of trace organic substances. 253rd ACS National Meeting. San Francisco, California: American Chemical Society.

Poster Presentations

• Saez, A. E. (2023).

  Evaluation of photochemical properties of dissolved organic matter in constructed treatment wetlands

  . AZ Water.
• Saez, A. E. (2023). Water Pollution in El Salvador: Preliminary Assessment of Trace Organic Compounds in the Lempa River and Drinking Water Sources. ACS Spring Meeting 2023.
• Barnett, B., Weiler, C., Lee, D., Rojas, N., Castella, K., Martinez, V., Arnold, R. G., Saez, A. E., & Quanrud, D. M. (2020, January). Degradation of trace organic compounds in wastewater effleunt via indirect photolysis. UA Student Showcase 2020. University of Arizona: Graduate and Professional Student Council.
• Manjon, I., Betterton, E. A., Saez, A. E., & Ramirez, M. D. (2017, March). Assessing the Capability of Plants as In-Situ Air Pollution Monitors: A Pilot Study Conducted in Arizona.. University of Arizona SWESxUniversity of Arizona SWESx.