Wendell Ela | Murdoch University (original) (raw)

Papers by Wendell Ela

Research paper thumbnail of Destruction of Gas-Phase Trichloroethylene in a Modified Fuel Cell

Environmental Science & Technology, 2006

A conventional fuel cell was used as a catalytic reactor to treat soil vapor extraction (SVE) gas... more 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.

Research paper thumbnail of Reductive Dehalogenation of Aqueous-Phase Chlorinated Hydrocarbons in an Electrochemical Reactor

Industrial & Engineering Chemistry Research, 2004

This work describes the reductive dehalogenation of carbon tetrachloride (CT) in a novel liquid-p... more 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 ...

Research paper thumbnail of Convenient New Chemical Actinometer Based on Aqueous Acetone, 2Propanol, and Carbon Tetrachloride

Environmental Science & Technology, 2005

A convenient new chemical actinometer was developed to measure the spectral output of laboratory ... more A convenient new chemical actinometer was developed to measure the spectral output of laboratory ultraviolet (UV) light sources over the wavelength range of 260-330 nm. It can also be used to measure solar UV irradiance (< or =325 nm). The actinometer is based on the photoreduction of aqueous carbon tetrachloride (CT) to chloroform (CF) in the presence of acetone (the chromophore) and 2-propanol (the reductant). In all cases, CT disappearance (and CF formation) followed zero-order kinetics over 95% of the reaction. The slope of the linear decay curve forms the basis of the new actinometer, which was calibrated using ferrioxalate actinometry. Quantum yields were measured at 10 nm intervals and were found to be uniform throughout the range of 260-300 nm. As expected, quantum yields gradually decreased to zero asthe wavelength was increased from 300 to 340 nm. The high quantum yields (approximately 150), low sensitivityto room light, and the straightforward determination of [CT] and [CF] by gas chromatography offer significant advantages over some other chemical actinometers, which might require the preparation and purification of light-sensitive compounds in a darkened environment and long exposure times.

Research paper thumbnail of NDMA Treatment by Sequential GAC Adsorption and Fenton-Driven Destruction

Environmental Engineering Science, 2003

N-nitrosodimethylamine (NDMA) is a highly toxic environmental contaminant that was first detected... more N-nitrosodimethylamine (NDMA) is a highly toxic environmental contaminant that was first detected in groundwater tainted by rocket fuel manufacturing wastes. NDMA is also a by-product of certain indus-trial processes including the chlorination of treated water and wastewater. Water ...

Research paper thumbnail of Fate of effluent organic matter during soil aquifer treatment: biodegradability, chlorine reactivity and genotoxicity

Journal of water and health, 2003

Hydrophobic acid (HPO-A) and transphilic acid (TPI-A) fractions of dissolved organic matter (DOM)... more Hydrophobic acid (HPO-A) and transphilic acid (TPI-A) fractions of dissolved organic matter (DOM) were isolated from a domestic secondary wastewater effluent that was polished via soil aquifer treatment (SAT). Fractions were isolated using XAD resin adsorption chromatography from samples obtained along the vadose zone flowpath at a full-scale basin recharge facility in Tucson, Arizona. Changes in isolate character during SAT were established via biodegradability (batch test), specific ultraviolet light absorbance (SUVA), trihalomethane formation potential (THMFP), and Ames mutagenicity assays. The dissolved organic carbon (DOC) concentration decreased by >90% during SAT. A significant fraction (up to 20%) of isolated post-SAT HPO-A was biodegradable. The (apparent) refractory nature of DOM that survives SAT may be a consequence of low DOC concentration in groundwater as well as the nature of the compounds themselves. Specific THMFP (microg THM per mg DOC) of HPO-A and TPI-A varie...

Research paper thumbnail of Laboratory dust generation and size-dependent characterization of metal and metalloid-contaminated mine tailings deposits

Journal of Hazardous Materials, 2014

The particle size distribution of mine tailings material has a major impact on the atmospheric tr... more The particle size distribution of mine tailings material has a major impact on the atmospheric transport of metal and metalloid contaminants by dust. Implications to human health should be assessed through a holistic size-resolved characterization involving multidisciplinary research, which requires large uniform samples of dust that are difficult to collect using conventional atmospheric sampling instruments. To address this limitation, we designed a laboratory dust generation and fractionation system capable of producing several grams of dust from bulk materials. The equipment was utilized in the characterization of tailings deposits from the arsenic and lead-contaminated Iron King Superfund site in Dewey-Humboldt, Arizona. Results show that metal and metalloid contaminants are more concentrated in particles of < 10 μm aerodynamic diameter, which are likely to affect surrounding communities and ecosystems. In addition, we traced the transport of contaminated particles from the tailings to surrounding soils by identifying Pb and Sr isotopic signatures in soil samples. The equipment and methods developed for this assessment ensure uniform samples for further multidisciplinary studies, thus providing a tool for comprehensive representation of emission sources and associated risks of exposure.

Research paper thumbnail of Repeated Reductive and Oxidative Treatments of Granular Activated Carbon

Journal of Environmental Engineering-asce, 2005

Repeated Reductive and Oxidative Treatments of Granular Activated Carbon. [Journal of Environment... more Repeated Reductive and Oxidative Treatments of Granular Activated Carbon. [Journal of Environmental Engineering 131, 287 (2005)]. Scott G. Huling, Patrick K. Jones, Wendell P. Ela, M.ASCE, Robert G. Arnold, M.ASCE. Abstract. ...

Research paper thumbnail of Fenton-driven chemical regeneration of MTBE-spent GAC

Water Research, 2005

Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was chemically regenerated u... more Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was chemically regenerated utilizing the Fenton mechanism. Two successive GAC regeneration cycles were performed involving iterative adsorption and oxidation processes: MTBE was adsorbed to the GAC, oxidized, re-adsorbed, oxidized, and finally re-adsorbed. Oxidant solutions comprised of hydrogen peroxide (H 2 O 2 ) (1.7-2.0%) and FeSO 4 Á 7H 2 O (3 g/L) (pH 2.5), were recirculated through the GAC column (30% bed expansion). The regeneration efficiency after two full cycles of treatment was calculated to be 91%. The cost of H 2 O 2 was 0.59/kgGAC(0.59/kg GAC (0.59/kgGAC(0.27/lb) per regeneration cycle. There was no loss of sorptive capacity. Small reductions in carbon surface area and pore volume were measured. The lack of carbon deterioration under aggressive oxidative conditions was attributed to the oxidation of the target contaminants relative to the oxidation of carbon surfaces. The reaction byproducts from MTBE oxidation, tertiary butanol and acetone, were also degraded and did not accumulate significantly on the GAC. Excessive accumulation of Fe on the GAC and consequent interference with MTBE sorption and carbon regeneration was controlled by monitoring and adjusting Fe in the oxidative solution. Published by Elsevier Ltd.

Research paper thumbnail of Changes in estrogen/anti-estrogen activities in ponded secondary effluent

Science of The Total Environment, 2007

Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decre... more Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decreased from 60 pM (equivalent 17alpha-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.

Research paper thumbnail of Nitrogen Transformations during Soil–Aquifer Treatment of Wastewater Effluent—Oxygen Effects in Field Studies

Journal of Environmental Engineering, 2006

ABSTRACT

Research paper thumbnail of Removal of Aqueous Phase Trichloroethylene Using Membrane Air Stripping Contactors

Journal of Environmental Engineering, 2004

... Jiahan He, Robert G. Arnold, A. Eduardo Sáez, Eric A. Betterton, Wendell P. Ela. Abstract. ..... more ... Jiahan He, Robert G. Arnold, A. Eduardo Sáez, Eric A. Betterton, Wendell P. Ela. Abstract. ... The diffusivity of TCE, , in water was estimated using the Wilke–Chang equation () which iswhere molal volume of ; viscosity of water ; and in Kelvin. Materials and Methods. Fig. ...

Research paper thumbnail of Destruction of Aqueous-Phase Carbon Tetrachloride in an Electrochemical Reactor with a Porous Cathode

Industrial & Engineering Chemistry Research, 2004

In this work we investigate the use of a continuous-flow, laboratory-scale electrochemical reacto... more 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.

Research paper thumbnail of Estrogenic Activity and Volume Fraction of Waste Water Origin in Monitoring Wells Along the Santa Cruz River, Arizona

Ground Water Monitoring & Remediation, 2004

Research paper thumbnail of Microscale Speciation of Arsenic and Iron in Ferric-Based Sorbents Subjected to Simulated Landfill Conditions

Environmental Science & Technology, 2013

During treatment for potable use, water utilities generate arsenic-bearing ferric wastes that are... more During treatment for potable use, water utilities generate arsenic-bearing ferric wastes that are subsequently dispatched to landfills. The biogeochemical weathering of these residuals in mature landfills affects the potential mobilization of sorbed arsenic species via desorption from solids subjected to phase transformations driven by abundant organic matter and bacterial activity. Such processes are not simulated with the toxicity characteristic leaching procedure (TCLP) currently used to characterize hazard. To examine the effect of sulfate on As retention in landfill leachate, columns of As(V) loaded amorphous ferric hydroxide were reacted biotically at two leachate sulfate concentrations (0.064 mM and 2.1 mM). After 300 days, ferric sorbents were reductively dissolved. Arsenic released to porewaters was partially coprecipitated in mixed-valent secondary iron phases whose speciation was dependent on sulfate concentration. As and Fe XAS showed that, in the low sulfate column, 75−81% of As(V) was reduced to As(III), and 53−68% of the Fe(III) sorbent was transformed, dominantly to siderite and green rust. In the high sulfate column, Fe(III) solids were reduced principally to FeS (am) , whereas As(V) was reduced to a polymeric sulfide with local atomic structure of realgar. Multienergy micro-X-ray fluorescence (ME-μXRF) imaging at Fe and As K-edges showed that As formed surface complexes with ferrihydrite > siderite > green rust in the low sulfate column; while discrete realgar-like phases formed in the high sulfate systems. Results indicate that landfill sulfur chemistry exerts strong control over the potential mobilization of As from ferric sorbent residuals by controlling secondary As and Fe sulfide coprecipitate formation.

Research paper thumbnail of Fate of Wastewater Effluent hER-Agonists and hER-Antagonists during Soil Aquifer Treatment

Environmental Science & Technology, 2005

Research paper thumbnail of Fate of Polybrominated Diphenyl Ethers during Wastewater Treatment/Polishing and Sludge Stabilization/Disposal

Annals of the New York Academy of Sciences, 2008

Large quantities of polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in ... more 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.

Research paper thumbnail of Effect of silicic acid on arsenate and arsenite retention mechanisms on 6-L ferrihydrite: A spectroscopic and batch adsorption approach

Applied Geochemistry, 2013

The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water i... more The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water interface was investigated over a wide pH range using batch sorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) modeling. Batch sorption results indicate that the adsorption of arsenate and arsenite on the 6-L ferrihydrite surface exhibits a strong pH-dependence, and the effect of pH on arsenic sorption differs between arsenate and arsenite. Arsenate adsorption decreases consistently with increasing pH; whereas arsenite adsorption initially increases with pH to a sorption maximum at pH 7-9, where after sorption decreases with further increases in pH. Results indicate that competitive adsorption between silicic acid and arsenate is negligible under the experimental conditions; whereas strong competitive adsorption was observed between silicic acid and arsenite, particularly at low and high pH. In-situ, flow-through ATR-FTIR data reveal that in the absence of silicic acid, arsenate forms inner-sphere, binuclear bidentate, complexes at the ferrihydrite surface across the entire pH range. Silicic acid also forms inner-sphere complexes at ferrihydrite surfaces throughout the entire pH range probed by this study (pH 2.8 - 9.0). The ATR-FTIR data also reveal that silicic acid undergoes polymerization at the ferrihydrite surface under the environmentally-relevant concentrations studied (e.g., 1.0 mM). According to ATR-FTIR data, arsenate complexation mode was not affected by the presence of silicic acid. EXAFS analyses and DFT modeling confirmed that arsenate tetrahedra were bonded to Fe metal centers via binuclear bidentate complexation with average As(V)-Fe bond distance of 3.27 Å. The EXAFS data indicate that arsenite forms both mononuclear bidentate and binuclear bidentate complexes with 6-L ferrihydrite as indicated by two As(III)-Fe bond distances of ~2.92-2.94 and 3.41-3.44 Å, respectively. The As-Fe bond distances in both arsenate and arsenite EXAFS spectra remained unchanged in the presence of Si, suggesting that whereas Si diminishes arsenite adsorption preferentially, it has a negligible effect on As-Fe bonding mechanisms.

Research paper thumbnail of Destruction of Gas-Phase Trichloroethylene in a Modified Fuel Cell

Environmental Science & Technology, 2006

A conventional fuel cell was used as a catalytic reactor to treat soil vapor extraction (SVE) gas... more 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.

Research paper thumbnail of Reductive Dehalogenation of Aqueous-Phase Chlorinated Hydrocarbons in an Electrochemical Reactor

Industrial & Engineering Chemistry Research, 2004

This work describes the reductive dehalogenation of carbon tetrachloride (CT) in a novel liquid-p... more 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 ...

Research paper thumbnail of Convenient New Chemical Actinometer Based on Aqueous Acetone, 2Propanol, and Carbon Tetrachloride

Environmental Science & Technology, 2005

A convenient new chemical actinometer was developed to measure the spectral output of laboratory ... more A convenient new chemical actinometer was developed to measure the spectral output of laboratory ultraviolet (UV) light sources over the wavelength range of 260-330 nm. It can also be used to measure solar UV irradiance (< or =325 nm). The actinometer is based on the photoreduction of aqueous carbon tetrachloride (CT) to chloroform (CF) in the presence of acetone (the chromophore) and 2-propanol (the reductant). In all cases, CT disappearance (and CF formation) followed zero-order kinetics over 95% of the reaction. The slope of the linear decay curve forms the basis of the new actinometer, which was calibrated using ferrioxalate actinometry. Quantum yields were measured at 10 nm intervals and were found to be uniform throughout the range of 260-300 nm. As expected, quantum yields gradually decreased to zero asthe wavelength was increased from 300 to 340 nm. The high quantum yields (approximately 150), low sensitivityto room light, and the straightforward determination of [CT] and [CF] by gas chromatography offer significant advantages over some other chemical actinometers, which might require the preparation and purification of light-sensitive compounds in a darkened environment and long exposure times.

Research paper thumbnail of NDMA Treatment by Sequential GAC Adsorption and Fenton-Driven Destruction

Environmental Engineering Science, 2003

N-nitrosodimethylamine (NDMA) is a highly toxic environmental contaminant that was first detected... more N-nitrosodimethylamine (NDMA) is a highly toxic environmental contaminant that was first detected in groundwater tainted by rocket fuel manufacturing wastes. NDMA is also a by-product of certain indus-trial processes including the chlorination of treated water and wastewater. Water ...

Research paper thumbnail of Fate of effluent organic matter during soil aquifer treatment: biodegradability, chlorine reactivity and genotoxicity

Journal of water and health, 2003

Hydrophobic acid (HPO-A) and transphilic acid (TPI-A) fractions of dissolved organic matter (DOM)... more Hydrophobic acid (HPO-A) and transphilic acid (TPI-A) fractions of dissolved organic matter (DOM) were isolated from a domestic secondary wastewater effluent that was polished via soil aquifer treatment (SAT). Fractions were isolated using XAD resin adsorption chromatography from samples obtained along the vadose zone flowpath at a full-scale basin recharge facility in Tucson, Arizona. Changes in isolate character during SAT were established via biodegradability (batch test), specific ultraviolet light absorbance (SUVA), trihalomethane formation potential (THMFP), and Ames mutagenicity assays. The dissolved organic carbon (DOC) concentration decreased by >90% during SAT. A significant fraction (up to 20%) of isolated post-SAT HPO-A was biodegradable. The (apparent) refractory nature of DOM that survives SAT may be a consequence of low DOC concentration in groundwater as well as the nature of the compounds themselves. Specific THMFP (microg THM per mg DOC) of HPO-A and TPI-A varie...

Research paper thumbnail of Laboratory dust generation and size-dependent characterization of metal and metalloid-contaminated mine tailings deposits

Journal of Hazardous Materials, 2014

The particle size distribution of mine tailings material has a major impact on the atmospheric tr... more The particle size distribution of mine tailings material has a major impact on the atmospheric transport of metal and metalloid contaminants by dust. Implications to human health should be assessed through a holistic size-resolved characterization involving multidisciplinary research, which requires large uniform samples of dust that are difficult to collect using conventional atmospheric sampling instruments. To address this limitation, we designed a laboratory dust generation and fractionation system capable of producing several grams of dust from bulk materials. The equipment was utilized in the characterization of tailings deposits from the arsenic and lead-contaminated Iron King Superfund site in Dewey-Humboldt, Arizona. Results show that metal and metalloid contaminants are more concentrated in particles of < 10 μm aerodynamic diameter, which are likely to affect surrounding communities and ecosystems. In addition, we traced the transport of contaminated particles from the tailings to surrounding soils by identifying Pb and Sr isotopic signatures in soil samples. The equipment and methods developed for this assessment ensure uniform samples for further multidisciplinary studies, thus providing a tool for comprehensive representation of emission sources and associated risks of exposure.

Research paper thumbnail of Repeated Reductive and Oxidative Treatments of Granular Activated Carbon

Journal of Environmental Engineering-asce, 2005

Repeated Reductive and Oxidative Treatments of Granular Activated Carbon. [Journal of Environment... more Repeated Reductive and Oxidative Treatments of Granular Activated Carbon. [Journal of Environmental Engineering 131, 287 (2005)]. Scott G. Huling, Patrick K. Jones, Wendell P. Ela, M.ASCE, Robert G. Arnold, M.ASCE. Abstract. ...

Research paper thumbnail of Fenton-driven chemical regeneration of MTBE-spent GAC

Water Research, 2005

Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was chemically regenerated u... more Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was chemically regenerated utilizing the Fenton mechanism. Two successive GAC regeneration cycles were performed involving iterative adsorption and oxidation processes: MTBE was adsorbed to the GAC, oxidized, re-adsorbed, oxidized, and finally re-adsorbed. Oxidant solutions comprised of hydrogen peroxide (H 2 O 2 ) (1.7-2.0%) and FeSO 4 Á 7H 2 O (3 g/L) (pH 2.5), were recirculated through the GAC column (30% bed expansion). The regeneration efficiency after two full cycles of treatment was calculated to be 91%. The cost of H 2 O 2 was 0.59/kgGAC(0.59/kg GAC (0.59/kgGAC(0.27/lb) per regeneration cycle. There was no loss of sorptive capacity. Small reductions in carbon surface area and pore volume were measured. The lack of carbon deterioration under aggressive oxidative conditions was attributed to the oxidation of the target contaminants relative to the oxidation of carbon surfaces. The reaction byproducts from MTBE oxidation, tertiary butanol and acetone, were also degraded and did not accumulate significantly on the GAC. Excessive accumulation of Fe on the GAC and consequent interference with MTBE sorption and carbon regeneration was controlled by monitoring and adjusting Fe in the oxidative solution. Published by Elsevier Ltd.

Research paper thumbnail of Changes in estrogen/anti-estrogen activities in ponded secondary effluent

Science of The Total Environment, 2007

Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decre... more Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decreased from 60 pM (equivalent 17alpha-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.

Research paper thumbnail of Nitrogen Transformations during Soil–Aquifer Treatment of Wastewater Effluent—Oxygen Effects in Field Studies

Journal of Environmental Engineering, 2006

ABSTRACT

Research paper thumbnail of Removal of Aqueous Phase Trichloroethylene Using Membrane Air Stripping Contactors

Journal of Environmental Engineering, 2004

... Jiahan He, Robert G. Arnold, A. Eduardo Sáez, Eric A. Betterton, Wendell P. Ela. Abstract. ..... more ... Jiahan He, Robert G. Arnold, A. Eduardo Sáez, Eric A. Betterton, Wendell P. Ela. Abstract. ... The diffusivity of TCE, , in water was estimated using the Wilke–Chang equation () which iswhere molal volume of ; viscosity of water ; and in Kelvin. Materials and Methods. Fig. ...

Research paper thumbnail of Destruction of Aqueous-Phase Carbon Tetrachloride in an Electrochemical Reactor with a Porous Cathode

Industrial & Engineering Chemistry Research, 2004

In this work we investigate the use of a continuous-flow, laboratory-scale electrochemical reacto... more 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.

Research paper thumbnail of Estrogenic Activity and Volume Fraction of Waste Water Origin in Monitoring Wells Along the Santa Cruz River, Arizona

Ground Water Monitoring & Remediation, 2004

Research paper thumbnail of Microscale Speciation of Arsenic and Iron in Ferric-Based Sorbents Subjected to Simulated Landfill Conditions

Environmental Science & Technology, 2013

During treatment for potable use, water utilities generate arsenic-bearing ferric wastes that are... more During treatment for potable use, water utilities generate arsenic-bearing ferric wastes that are subsequently dispatched to landfills. The biogeochemical weathering of these residuals in mature landfills affects the potential mobilization of sorbed arsenic species via desorption from solids subjected to phase transformations driven by abundant organic matter and bacterial activity. Such processes are not simulated with the toxicity characteristic leaching procedure (TCLP) currently used to characterize hazard. To examine the effect of sulfate on As retention in landfill leachate, columns of As(V) loaded amorphous ferric hydroxide were reacted biotically at two leachate sulfate concentrations (0.064 mM and 2.1 mM). After 300 days, ferric sorbents were reductively dissolved. Arsenic released to porewaters was partially coprecipitated in mixed-valent secondary iron phases whose speciation was dependent on sulfate concentration. As and Fe XAS showed that, in the low sulfate column, 75−81% of As(V) was reduced to As(III), and 53−68% of the Fe(III) sorbent was transformed, dominantly to siderite and green rust. In the high sulfate column, Fe(III) solids were reduced principally to FeS (am) , whereas As(V) was reduced to a polymeric sulfide with local atomic structure of realgar. Multienergy micro-X-ray fluorescence (ME-μXRF) imaging at Fe and As K-edges showed that As formed surface complexes with ferrihydrite > siderite > green rust in the low sulfate column; while discrete realgar-like phases formed in the high sulfate systems. Results indicate that landfill sulfur chemistry exerts strong control over the potential mobilization of As from ferric sorbent residuals by controlling secondary As and Fe sulfide coprecipitate formation.

Research paper thumbnail of Fate of Wastewater Effluent hER-Agonists and hER-Antagonists during Soil Aquifer Treatment

Environmental Science & Technology, 2005

Research paper thumbnail of Fate of Polybrominated Diphenyl Ethers during Wastewater Treatment/Polishing and Sludge Stabilization/Disposal

Annals of the New York Academy of Sciences, 2008

Large quantities of polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in ... more 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.

Research paper thumbnail of Effect of silicic acid on arsenate and arsenite retention mechanisms on 6-L ferrihydrite: A spectroscopic and batch adsorption approach

Applied Geochemistry, 2013

The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water i... more The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water interface was investigated over a wide pH range using batch sorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) modeling. Batch sorption results indicate that the adsorption of arsenate and arsenite on the 6-L ferrihydrite surface exhibits a strong pH-dependence, and the effect of pH on arsenic sorption differs between arsenate and arsenite. Arsenate adsorption decreases consistently with increasing pH; whereas arsenite adsorption initially increases with pH to a sorption maximum at pH 7-9, where after sorption decreases with further increases in pH. Results indicate that competitive adsorption between silicic acid and arsenate is negligible under the experimental conditions; whereas strong competitive adsorption was observed between silicic acid and arsenite, particularly at low and high pH. In-situ, flow-through ATR-FTIR data reveal that in the absence of silicic acid, arsenate forms inner-sphere, binuclear bidentate, complexes at the ferrihydrite surface across the entire pH range. Silicic acid also forms inner-sphere complexes at ferrihydrite surfaces throughout the entire pH range probed by this study (pH 2.8 - 9.0). The ATR-FTIR data also reveal that silicic acid undergoes polymerization at the ferrihydrite surface under the environmentally-relevant concentrations studied (e.g., 1.0 mM). According to ATR-FTIR data, arsenate complexation mode was not affected by the presence of silicic acid. EXAFS analyses and DFT modeling confirmed that arsenate tetrahedra were bonded to Fe metal centers via binuclear bidentate complexation with average As(V)-Fe bond distance of 3.27 Å. The EXAFS data indicate that arsenite forms both mononuclear bidentate and binuclear bidentate complexes with 6-L ferrihydrite as indicated by two As(III)-Fe bond distances of ~2.92-2.94 and 3.41-3.44 Å, respectively. The As-Fe bond distances in both arsenate and arsenite EXAFS spectra remained unchanged in the presence of Si, suggesting that whereas Si diminishes arsenite adsorption preferentially, it has a negligible effect on As-Fe bonding mechanisms.