Bill Mitch received a B.A. in Anthropology (Archaeology) from Harvard University in 1993. During his studies, he excavated at Mayan sites in Belize and surveyed sites dating from 2,000 B.C. in Louisiana. He switched fields by receiving a M.S. degree in Civil and Environmental Engineering at UC Berkeley. He worked for 3 years in environmental consulting, receiving his P.E. license in Civil Engineering in California. Returning to UC Berkeley in 2000, he received his PhD in Civil and Environmental Engineering in 2003. He moved to Yale as an assistant professor after graduation. His dissertation received the AEESP Outstanding Doctoral Dissertation Award in 2004. At Yale, he serves as the faculty advisor for the Yale Student Chapter of Engineers without Borders. In 2007, he won a NSF CAREER Award. He moved to Stanford University as an associate professor in 2013.

Employing a fundamental understanding of organic chemical reaction pathways, his research explores links between public health, engineering and sustainability. Topics of current interest include:

Public Health and Emerging Carcinogens: Recent changes to the disinfection processes fundamental to drinking and recreational water safety are creating a host of highly toxic byproducts linked to bladder cancer. We seek to understand how these compounds form so we can adjust the disinfection process to prevent their formation.

Global Warming and Oceanography: Oceanic dissolved organic matter is an important global carbon component, and has important impacts on the net flux of CO2 between the ocean and atmosphere. We seek to understand some of the important abiotic chemical reaction pathways responsible for carbon turnover.

Sustainability and Persistent Organic Pollutants (POPs): While PCBs have been banned in the US, we continue to produce a host of structurally similar chemicals. We seem to understand important chemical pathways responsible for POP destruction in the environment, so we can design less persistent and problematic chemicals in the future.

Engineering for Sustainable Wastewater Recycling: The shortage of clean water represents a critical challenge for the next century, and has necessitated the recycling of wastewater. We seek to understand ways of engineer this process in ways to minimize harmful byproduct formation.

Carbon Sequestration: We are evaluating the formation of nitrosamine and nitraminecarcinogens from amine-based carbon capture, as well as techniques to destroy any of these byproducts that form.

Academic Appointments

Honors & Awards

  • Excellence in Review Award, Environmental Science and Technology (2013)
  • Elected Vice-Chair of the 4th Disinfection Byproducts Gordon Conference in 2015, Disinfection Byproducts Gordon Conference (2015)
  • Invited speaker for the 3rd Disinfection Byproducts Gordon Conference, Mt. Holyoke College, Disinfection Byproducts Gordon Conference (2012)
  • Environmental Science and Technology Editors Choice Award Best Paper 3rd runner up, Environmental Science and Technology (2010)
  • Top 10 most-accessed articles, 2nd Quarter, Environmental Science and Technology (2010)
  • Invited speaker, Environmental Sciences Water Gordon Conference (2010)
  • Member, US EPA Scientific Advisory Board Drinking Water Committee (2010)
  • Invited speaker, Disinfection Byproducts Gordon Conference, Mt. Holyoke College (2009)
  • CAREER Award, NSF (2007)
  • Advisor of recipient, ACS Environmental Chemistry Graduate Student Award (2007)
  • Invited speaker, Disinfection Byproducts Gordon Conference, Mt. Holyoke College (2006)
  • Certificate of Merit, 230th ACS National Meeting (2005)
  • Arthur Greer Memorial Prize for teaching and research excellence by a junior faculty member, Yale University (2005)
  • Outstanding Doctoral Dissertation Award, Association of Environmental Engineering and Science Professors and Parsons Engineering (2004)
  • Graduated Summa Cum Laude and elected into the Phi Beta Kappa Academic Honor Society, Harvard University (1993)

Professional Education

  • B.A., Harvard University (Summa Cum Laude), Anthropology (Archaeology) (1993)
  • M.S., University of California, Berkeley, Civil and Environmental Engineering (1996)
  • Ph.D., University of California, Berkeley, Civil and Environmental Engineering (2003)

2023-24 Courses

Stanford Advisees

All Publications

  • Tap water and bladder cancer in China NATURE SUSTAINABILITY Mitch, W. A. 2022
  • Recovery of Clean Water and Ammonia from Domestic Wastewater: Impacts on Embodied Energy and Greenhouse Gas Emissions. Environmental science & technology Shin, C., Szczuka, A., Liu, M. J., Mendoza, L., Jiang, R., Tilmans, S. H., Tarpeh, W. A., Mitch, W. A., Criddle, C. S. 2022


    Treatment of domestic wastewater can recover valuable resources, including clean water, energy, and ammonia. Important metrics for these systems are greenhouse gas (GHG) emissions and embodied energy, both of which are location- and technology-dependent. Here, we determine the embodied energy and GHG emissions resulting from a conventional process train, and we compare them to a nonconventional process train. The conventional train assumes freshwater conveyance from a pristine source that requires energy for pumping (US average of 0.29 kWh/m3), aerobic secondary treatment with N removal as N2, and Haber-Bosch synthesis of ammonia. Overall, we find that this process train has an embodied energy of 1.02 kWh/m3 and a GHG emission of 0.77 kg-CO2eq/m3. We compare these metrics to those of a nonconventional process train that features anaerobic secondary treatment technology followed by further purification of the effluent by reverse osmosis and air stripping for ammonia recovery. This "short-cut" process train reduces embodied energy to 0.88 kWh/m3 and GHG emissions to 0.42 kg-CO2eq/m3, while offsetting demand for ammonia from the Haber-Bosch process and decreasing reliance upon water transported over long distances. Finally, to assess the potential impacts of nonconventional nitrogen removal technology, we compared the embodied energy and GHG emissions resulting from partial nitritation/anammox coupled to anaerobic secondary treatment. The resulting process train enabled a lower embodied energy but increased GHG emissions, largely due to emissions of N2O, a potent greenhouse gas.

    View details for DOI 10.1021/acs.est.1c07992

    View details for PubMedID 35656915

  • Effects of Intrusion on Disinfection Byproduct Formation in Intermittent Distribution Systems ACS ES&T WATER Furst, K. E., Smith, D. W., Bhatta, L. R., Islam, M., Sultana, S., Rahman, M., Davis, J., Mitch, W. A. 2022; 2 (5): 807-816
  • Conversion of oxybenzone sunscreen to phototoxic glucoside conjugates by sea anemones and corals. Science (New York, N.Y.) Vuckovic, D., Tinoco, A. I., Ling, L., Renicke, C., Pringle, J. R., Mitch, W. A. 2022; 376 (6593): 644-648


    The reported toxicity of oxybenzone-based sunscreens to corals has raised concerns about the impacts of ecotourist-shed sunscreens on corals already weakened by global stressors. However, oxybenzone's toxicity mechanism(s) are not understood, hampering development of safer sunscreens. We found that oxybenzone caused high mortality of a sea anemone under simulated sunlight including ultraviolet (UV) radiation (290 to 370 nanometers). Although oxybenzone itself protected against UV-induced photo-oxidation, both the anemone and a mushroom coral formed oxybenzone-glucoside conjugates that were strong photo-oxidants. Algal symbionts sequestered these conjugates, and mortality correlated with conjugate concentrations in animal cytoplasm. Higher mortality in anemones that lacked symbionts suggests an enhanced risk from oxybenzone to corals bleached by rising temperatures. Because many commercial sunscreens contain structurally related chemicals, understanding metabolite phototoxicity should facilitate the development of coral-safe products.

    View details for DOI 10.1126/science.abn2600

    View details for PubMedID 35511969

  • Disinfection byproducts formed during drinking water treatment reveal an export control point for dissolved organic matter in a subalpine headwater stream. Water research X Leonard, L. T., Vanzin, G. F., Garayburu-Caruso, V. A., Lau, S. S., Beutler, C. A., Newman, A. W., Mitch, W. A., Stegen, J. C., Williams, K. H., Sharp, J. O. 2022; 15: 100144


    Changes in climate, season, and vegetation can alter organic export from watersheds. While an accepted tradeoff to protect public health, disinfection processes during drinking water treatment can adversely react with organic compounds to form disinfection byproducts (DBPs). By extension, DBP monitoring can yield insights into hydrobiogeochemical dynamics within watersheds and their implications for water resource management. In this study, we analyzed temporal trends from a water treatment facility that sources water from Coal Creek in Crested Butte, Colorado. These trends revealed a long-term increase in haloacetic acid and trihalomethane formation over the period of 2005-2020. Disproportionate export of dissolved organic carbon and formation of DBPs that exceeded maximum contaminant levels were consistently recorded in association with late spring freshet. Synoptic sampling of the creek in 2020 and 2021 identified a biogeochemical hotspot for organic carbon export in the upper domain of the watershed that contained a prominent fulvic acid-like fluorescent signature. DBP formation potential analyses from this domain yielded similar ratios of regulated DBP classes to those formed at the drinking water facility. Spectrometric qualitative analyses of pre and post-reacted waters with hypochlorite indicated lignin-like and condensed hydrocarbon-like molecules were the major reactive chemical classes during chlorine-based disinfection. This study demonstrates how drinking water quality archives combined with synoptic sampling and targeted analyses can be used to identify and understand export control points for dissolved organic matter. This approach could be applied to identify and characterize analogous watersheds where seasonal or climate-associated organic matter export challenge water treatment disinfection and by extension inform watershed management and drinking water treatment.

    View details for DOI 10.1016/j.wroa.2022.100144

    View details for PubMedID 35542761

  • Bridging boundaries: On the contributions of Dr. Michael Plewa to the disinfection byproduct field. Journal of environmental sciences (China) Mitch, W. A. 2022; 117: 3-5

    View details for DOI 10.1016/j.jes.2022.03.001

    View details for PubMedID 35725083

  • Formation of Oleic Acid Chlorohydrins in Vegetables during Postharvest Chlorine Disinfection. Environmental science & technology Simpson, A. M., Suh, M., Plewa, M. J., Mitch, W. A. 1800


    High chlorine doses (50-200 mg/L) are used in postharvest washing facilities to control foodborne pathogen outbreaks. However, chlorine can react with biopolymers (e.g., lipids) within the produce to form chlorinated byproducts that remain in the food. During chlorination of micelles of oleic acid, an 18-carbon alkene fatty acid, chlorine added rapidly across the double bond to form the two 9,10-chlorohydrin isomers at a 100% yield. The molar conversion of lipid-bound oleic acid to 9,10-chlorohydrins in chlorine-treated glyceryl trioleate and produce was much lower, reflecting the restricted access of chlorine to lipids. Yields from spinach treated with 100 mg/L chlorine at 7.5 °C for 2 min increased from 0.05% (0.9 nmol/g-spinach) for whole leaf spinach to 0.11% (2 nmol/g) when shredding increased chlorine access. Increasing temperature (21 °C) and chlorine contact time (15 min) increased yields from shredded spinach to 0.83% (22 nmol/g) at 100 mg/L chlorine and to 1.8% (53 nmol/g) for 200 mg/L chlorine. Oleic acid 9,10-chlorohydrin concentrations were 2.4-2.7 nmol/g for chlorine-treated (100 mg/L chlorine at 7.5 °C for 2 min) broccoli, carrots, and butterhead lettuce, but 0.5-1 nmol/g for cabbage, kale, and red leaf lettuce. Protein-bound chlorotyrosine formation was higher in the same vegetables (5-32 nmol/g). The Chinese hamster ovary cell chronic cytotoxicity LC50 value for oleic acid 9,10-chlorohydrins was 0.106 mM. The cytotoxicity associated with the chlorohydrins and chlorotyrosines in low masses (9-52 g) of chlorine-washed vegetables would be comparable to that associated with trihalomethanes and haloacetic acids at levels of regulatory concern in drinking water.

    View details for DOI 10.1021/acs.est.1c04362

    View details for PubMedID 34941240

  • Corrigendum to Pilot-scale evaluation of oxidant speciation, 1,4-dioxane degradation and disinfection byproduct formation during UV/hydrogen peroxide, UV/free chlorine and UV/chloramines advanced oxidation process treatment for potable reuse'[Water Research, Volume 164,1 November 2019, 114939]. Water research Zhang, Z., Chuang, Y., Szczuka, A., Ishida, K. P., Roback, S., Plumlee, M. H., Mitch, W. A. 2021; 208: 117868

    View details for DOI 10.1016/j.watres.2021.117868

    View details for PubMedID 34823085

  • Chlorine taste can increase simulated exposure to both fecal contamination and disinfection byproducts in water supplies. Water research Smith, D. W., Islam, M., Furst, K. E., Mustaree, S., Crider, Y. S., Akter, N., Islam, S. A., Sultana, S., Mahmud, Z. H., Rahman, M., Mitch, W. A., Davis, J. 2021; 207: 117806


    Expanding drinking water chlorination could substantially reduce the burden of disease in low- and middle-income countries, but the taste of chlorinated water often impedes adoption. We developed a Monte Carlo simulation to estimate the effect of people's choice to accept or reject drinking water based on chlorine taste and their subsequent exposure to E. coli and trihalomethanes, a class of disinfection byproduct (DBP). The simulation used empirical data from Dhaka, Bangladesh, a megacity with endemic waterborne disease. We drew on published taste acceptability thresholds from Dhaka residents, measured residual chlorine and thermotolerant E. coli inactivation following the addition of six chlorine doses (0.25-3.0mg/L as Cl2) to untreated piped water samples from 100 locations, and analyzed trihalomethane formation in 54 samples. A dose of 0.5mg/L, 75% lower than the 2mg/L dose typically recommended for household chlorination of low-turbidity waters, minimized overall exposure to E. coli. Doses of 1-2mg/L maximized overall exposure to trihalomethanes. Accounting for chlorine taste aversion indicates that microbiological exposure increases and DBP exposure decreases above certain doses as a higher proportion of people reject chlorinated water in favor of untreated water. Taken together with findings from other modeling analyses, empirical studies, and field trials, our results suggest that taste acceptability should be a critical consideration in establishing chlorination dosing guidelines. Particularly when chlorination is first implemented in water supplies with low chlorine demand, lower doses than those generally recommended for household water treatment can help avoid taste-related objections while still meaningfully reducing contaminant exposure.

    View details for DOI 10.1016/j.watres.2021.117806

    View details for PubMedID 34768105

  • Sunlight-Driven Chlorate Formation during Produce Irrigation with Chlorine- or Chloramine-Disinfected Water. Environmental science & technology Suh, M., Mitch, W. A. 2021


    The increasing use of chlorine- or chloramine-containing irrigation waters to minimize foodborne pathogens is raising concerns about the formation and uptake of disinfection byproducts into irrigated produce. Chlorate has received particular attention in the European Union. While previous research demonstrated the formation of chlorate from dark disproportionation reactions of free chlorine and uptake of chlorate into produce from roots, this study evaluated chlorate formation from solar irradiation of chlorine- and chloramine-containing irrigation droplets and uptake through produce surfaces. Sunlight photolysis of 50 muM (3.6 mg/L as Cl2) chlorine significantly enhanced the formation of chlorate, with a 7.2% molar yield relative to chlorine. Chlorate formation was much less significant in sunlit chloramine solutions. In chlorinated solutions containing 270 mug/L bromide, sunlight also induced the conversion of bromide to 280 mug/L bromate. Droplet evaporation and the resulting increase in chlorine concentrations approximately doubled sunlight-induced chlorate formation relative to that in the bulk solutions in which evaporation is negligible. When vegetables (broccoli, cabbage, chicory, lettuce, and spinach) were sprayed with chlorine-containing irrigation water in a sunlit field, sunlight promoted chlorate formation and uptake through vegetable surfaces to concentrations above maximum residue levels in the European Union. Spraying with chloramine-containing waters in the dark minimized chlorate formation and uptake into the vegetables.

    View details for DOI 10.1021/acs.est.1c04994

    View details for PubMedID 34652150

  • Disinfection Byproduct Recovery during Extraction and Concentration in Preparation for Chemical Analyses or Toxicity Assays. Environmental science & technology Lau, S. S., Forster, A. L., Richardson, S. D., Mitch, W. A. 2021


    Over 700 disinfection byproducts (DBPs) have been identified, but they account for only 30% of total organic halogen (TOX). Extracting disinfected water is necessary to assess the overall toxicity of both known and unknown DBPs. Commonly used DBP extraction methods include liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which may use either XAD resins or other polymeric sorbents. With few exceptions, DBP recoveries have not been quantified. We compared recoveries by LLE, XAD resins, and a mixture of Phenomenex Sepra SPE sorbents (hereafter SPE) for (semi-)volatile DBPs and nonvolatile model compounds at the 1-L scale. We scaled up the three methods to extract DBPs in 10 L of chlorinated creek waters. For (semi-)volatile DBPs, XAD resulted in lower recoveries than LLE and SPE at both 1- and 10-L scales. At the 10-L scale, recovery of certain trihalomethanes and trihalogenated haloacetic acids by XAD was negligible, while recovery of other (semi-)volatile DBPs extracted by XAD (<30%) was lower than by SPE or LLE (30-60%). TOX recovery at the 10-L scale was generally similar by the three extraction methods. The low TOX recovery (<30%) indicates that the toxicity assessed by bioassays predominantly reflects the contribution of the nonvolatile, hydrophobic fraction of DBPs.

    View details for DOI 10.1021/acs.est.1c04323

    View details for PubMedID 34618438

  • Use of trihalomethanes as a surrogate for haloacetonitrile exposure introduces misclassification bias. Water research X Furst, K. E., Bolorinos, J., Mitch, W. A. 2021; 11: 100089


    Epidemiologists have used trihalomethanes (THMs) as a surrogate for overall disinfection byproduct (DBP) exposure based on the assumption that THM concentrations are proportional to concentrations of other DBP classes. Toxicological evidence indicates THMs are less potent toxins than unregulated classes like haloacetonitriles (HANs). If THMs are not proportional to the DBPs driving toxicity, the use of THMs to measure exposure may introduce non-trivial exposure misclassification bias in epidemiologic studies. This study developed statistical models to evaluate the covariance and proportionality of HAN and THM concentrations in a dataset featuring over 9500 measurements from 248 public water systems. THMs only explain 30% of the variance in HANs, whether the data is pooled in a classic linear regression or hierarchically grouped by water system in a multilevel linear regression. The 95% prediction interval on HANs for the median THM concentration exceeds the interquartile range of HANs. Mean HAN:THM ratios range from 2.4% to 80% across water systems, and varied with source water category, season, disinfectant sequence and distribution system location. The HAN:THM ratio was 265% higher in groundwater systems than in surface water systems and declined by 40% between finished effluent and maximum residence times in surface water systems with chlorine-chlorine disinfection. A maximum likelihood approach was used to estimate the misclassification bias that may result from using THMs to construct risk-ratios, assuming that HANs represent the "true" DBP exposure risk. The results indicate an odds ratio of 2 estimated with THM concentrations could correspond to a true odds ratio of 4-5. These findings demonstrate the need for epidemiologic studies to evaluate exposure by measuring DBPs that are likely to drive toxicity.

    View details for DOI 10.1016/j.wroa.2021.100089

    View details for PubMedID 33554102

  • Control of sulfides and coliphage MS2 using hydrogen peroxide and UV disinfection for non-potable reuse of pilot-scale anaerobic membrane bioreactor effluent. Water research X Szczuka, A., Berglund-Brown, J. P., MacDonald, J. A., Mitch, W. A. 2021; 11: 100097


    Anaerobic membrane bioreactors reduce the energy cost of wastewater treatment and meet filtration requirements for non-potable reuse. However, sulfides (H2S/HS-) formed during anaerobic treatment exert a high chlorine demand and inhibit UV disinfection by photon shielding at 254nm. This study evaluated the feasibility of hydrogen peroxide (H2O2) for sulfide oxidation, UV disinfection for inactivation of MS2 bacteriophage, and chlorine to provide a residual for distribution. H2O2 treatment at pH ≥ 8 favored sulfide oxidation to sulfate in 30min at a 4:1 H2O2:sulfide stoichiometry. Compared to a 6:1 H2O2:sulfide molar ratio, treatment of anaerobic effluent with 0.5mM sulfides with a 4:1 H2O2:sulfide molar ratio would increase the applied UV fluence needed for 5-log MS2 inactivation from 180 mJ cm-2 to 225 mJ cm-2. However, the lower H2O2 dose reduced the dose of chlorine needed to quench residual H2O2 and provide a residual for distribution. Treatment at the 4:1 H2O2:sulfide molar ratio was favored, because the cost savings in H2O2 and chlorine reagents outweighed the energy savings associated with UV treatment. However, H2O2/UV/chlorine treatment of anaerobic effluent was cost-competitive with conventional treatment of aerobic effluent for non-potable reuse only for < 285M sulfides.

    View details for DOI 10.1016/j.wroa.2021.100097

    View details for PubMedID 33817615

  • Optimization of reverse osmosis operational conditions to maximize ammonia removal from the effluent of an anaerobic membrane bioreactor ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY Shin, C., Szczuka, A., Jiang, R., Mitch, W. A., Criddle, C. S. 2021; 7 (4): 739–47

    View details for DOI 10.1039/d0ew01112f

    View details for Web of Science ID 000637878900005

  • Production of N-Nitrosodimethylamine Precursors by Biofilters Is Highly Dynamic and Affected by Filter Media Type and Backwashing Conditions ACS ENVIRONMENTAL SCIENCE AND TECHNOLOGY WATER Hozalski, R. M., Ma, B., Evans, A. N., Page, S. E., Zhang, Z., Mitch, W. A., Russell, C., Peldszus, S., Van Dyke, M., Huck, P. M. 2021; 1 (3): 661-671
  • Organic wastewater treatment by a single-atom catalyst and electrolytically produced H2O2. Nature sustainability Xu, J., Zheng, X., Feng, Z., Lu, Z., Zhang, Z., Huang, W., Li, Y., Vuckovic, D., Li, Y., Dai, S., Chen, G., Wang, K., Wang, H., Chen, J. K., Mitch, W., Cui, Y. 2021; 4: 233-241


    The presence of organic contaminants in wastewater poses considerable risks to the health of both humans and ecosystems. Although advanced oxidation processes that rely on highly reactive radicals to destroy organic contaminants are appealing treatment options, substantial energy and chemical inputs limit their practical applications. Here we demonstrate that Cu single atoms incorporated in graphitic carbon nitride can catalytically activate H2O2 to generate hydroxyl radicals at pH 7.0 without energy input, and show robust stability within a filtration device. We further design an electrolysis reactor for the on-site generation of H2O2 from air, water and renewable energy. Coupling the single-atom catalytic filter and the H2O2 electrolytic generator in tandem delivers a wastewater treatment system. These findings provide a promising path toward reducing the energy and chemical demands of advanced oxidation processes, as well as enabling their implementation in remote areas and isolated communities.

    View details for DOI 10.1038/s41893-020-00635-w

    View details for PubMedID 34355066

    View details for PubMedCentralID PMC8330436

  • Pilot UV-AOP Comparison of UV/Hydrogen Peroxide, UV/Free Chlorine, and UV/Monochloramine for the Removal of N-Nitrosodimethylamine (NDMA) and NDMA Precursors ACS ENVIRONMENTAL SCIENCE AND TECHNOLOGY WATER Roback, S. L., Ishida, K. P., Chuang, Y., Zhang, Z., Mitch, W. A., Plumlee, M. H. 2021; 1 (2): 396-406
  • Evaluation of Histidine Reactivity and Byproduct Formation during Peptide Chlorination. Environmental science & technology Choe, J. K., Hua, L., Komaki, Y., Simpson, A. M., McCurry, D. L., Mitch, W. A. 2021


    The covalent modifications resulting from chlorine reactions with peptide-bound amino acids contribute to pathogen inactivation and disinfection byproduct (DBP) formation. Previous research suggested that histidine is the third most reactive of the seven chlorine-reactive amino acids, leading to the formation of 2-chlorohistidine, 2-oxohistidine, or low-molecular-weight byproducts such as trihalomethanes. This study demonstrates that histidine is less reactive toward formation of chlorine transformation products (transformation time scale of hours to days) than five of the seven chlorine-reactive amino acids, including tyrosine (transformation time scale of minutes). Chlorine targeted tyrosine in preference to histidine within peptides, indicating that chlorine reactions with tyrosine and other more reactive amino acids could contribute more to the structural modifications to proteins over the short time scales relevant to pathogen inactivation. Over the longer time scales relevant to disinfection byproduct formation in treatment plants or distribution systems, this study identified beta-cyanoalanine as the dominant transformation product of chlorine reactions with peptide-bound histidine, with molar yields of 50% after 1 day. While a chlorinated histidine intermediate was observed at lower yields (maximum 5%), the cumulative concentration of the conventional low-molecular-weight DBPs (e.g., trihalomethanes) was ≤7%. These findings support the need to identify the high-yield initial transformation products of chlorine reactions with important precursor structures to facilitate the identification of unknown DBPs.

    View details for DOI 10.1021/acs.est.0c07408

    View details for PubMedID 33492937

  • Removal of Pathogens and Chemicals of Emerging Concern by Pilot-Scale FO-RO Hybrid Units Treating RO Concentrate, Graywater, and Sewage for Centralized and Decentralized Potable Reuse ACS ENVIRONMENTAL SCIENCE AND TECHNOLOGY WATER Szczuka, A., Chuang, Y., Chen, F. C., Zhang, Z., Desormeaux, E., Flynn, M., Parodi, J., Mitch, W. A. 2021; 1 (1): 89-100
  • Chlorine and ozone disinfection and disinfection byproducts in postharvest food processing facilities: A review CRITICAL REVIEWS IN ENVIRONMENTAL SCIENCE AND TECHNOLOGY Simpson, A., Mitch, W. A. 2020
  • Transformation of Trace Organic Contaminants from Reverse Osmosis Concentrate by Open-Water Unit-Process Wetlands with and without Ozone Pretreatment. Environmental science & technology Scholes, R. C., King, J. F., Mitch, W. A., Sedlak, D. L. 2020


    Reverse osmosis (RO) treatment of municipal wastewater effluent is becoming more common as water reuse is implemented in water-stressed regions. Where RO concentrate is discharged with limited dilution, concentrations of trace organic contaminants could pose risks to aquatic ecosystems. To provide a low-cost option for removing trace organic compounds from RO concentrate, a pilot-scale treatment system comprising open-water unit-process wetlands with and without ozone pretreatment was studied over a 2-year period. A suite of ecotoxicologically relevant organic contaminants was partially removed via photo- and bio-transformations, including beta-adrenergic blockers, antivirals, antibiotics, and pesticides. Biotransformation rates were as fast as or up to approximately 50% faster than model predictions based upon data from open-water wetlands that treated municipal wastewater effluent. Phototransformation rates were comparable to or as much as 60% slower than those predicted by models that accounted for light penetration and scavenging of reactive oxygen species. Several compounds were transformed during ozone pretreatment that were poorly removed in the open-water wetland. The combined treatment system resulted in a decrease in the risk quotients of trace organic contaminants in the RO concentrate, but still dilution may be required to protect sensitive species from urban-use pesticides with low environmental effect concentrations.

    View details for DOI 10.1021/acs.est.0c04406

    View details for PubMedID 33269915

  • Designing a Nanoscale Three-phase Electrochemical Pathway to Promote Pt-catalyzed Formaldehyde Oxidation. Nano letters Xu, J., Xiao, X., Zhang, Z., Wu, Y., Boyle, D. T., Lee, H. K., Huang, W., Li, Y., Wang, H., Li, J., Zhu, Y., Chen, B., Mitch, W., Cui, Y. 2020


    Gas-phase heterogeneous catalysis is a process spatially constrained on the two-dimensional surface of a solid catalyst. Here, we introduce a new toolkit to open up the third dimension. We discovered that the activity of a solid catalyst can be dramatically promoted by covering its surface with a nanoscale-thin layer of liquid electrolyte while maintaining efficient delivery of gas reactants, a strategy we call three-phase catalysis. Introducing the liquid electrolyte converts the original surface catalytic reaction into an electrochemical pathway with mass transfer facilitated by free ions in a three-dimensional space. We chose the oxidation of formaldehyde as a model reaction and observed a 25000-times enhancement in the turnover frequency of Pt in three-phase catalysis as compared to conventional heterogeneous catalysis. We envision three-phase catalysis as a new dimension for catalyst design and anticipate its applications in more chemical reactions from pollution control to the petrochemical industry.

    View details for DOI 10.1021/acs.nanolett.0c03560

    View details for PubMedID 33201720

  • N-Nitrosodimethylamine Formation during UV/Hydrogen Peroxide and UV/Chlorine Advanced Oxidation Process Treatment Following Reverse Osmosis for Potable Reuse. Environmental science & technology Szczuka, A., Huang, N., MacDonald, J. A., Nayak, A., Zhang, Z., Mitch, W. A. 2020


    Chloramines applied to control microfiltration and reverse osmosis (RO) membrane biofouling in potable reuse trains form the potent carcinogen, N-nitrosodimethylamine (NDMA). In addition to degrading other contaminants, UV-based advanced oxidation processes (AOPs) strive to degrade NDMA by direct photolysis. The UV/chlorine AOP is gaining attention because of its potential to degrade other contaminants at lower UV fluence than the UV/hydrogen peroxide AOP, although previous pilot studies have observed that the UV/chlorine AOP was less effective for NDMA control. Using dimethylamine (DMA) as a model precursor and secondary municipal wastewater effluent, this study evaluated NDMA formation during the AOP treatment via two pathways. First, NDMA formation by UV treatment of monochloramine (NH2Cl) and chlorinated DMA (Cl-DMA) passing through RO membranes was maximized at 350 mJ/cm2 UV fluence, declining at higher fluence, where NDMA photolysis outweighed NDMA formation. Second, this study demonstrated that chlorine addition to the chloramine-containing RO permeate during the UV/chlorine AOP treatment initiated rapid NDMA formation by dark breakpoint reactions associated with reactive intermediates from the hydrolysis of dichloramine. At pH 5.7, this formation was maximized at a chlorine/ammonia molar ratio of 3 (out of 0-10), conditions typical for UV/chlorine AOPs. At 700 mJ/cm2 UV fluence, which is applicable to current practice, NDMA photolysis degraded a portion of the NDMA formed by breakpoint reactions. Lowering UV fluence to 350 mJ/cm2 when switching to the UV/chlorine AOP exacerbates effluent NDMA concentrations because of concurrent NDMA formation via the UV/NH2Cl/Cl-DMA and breakpoint chlorination pathways. Fluence >700 mJ/cm2 or chlorine doses greater than the 3:1 chlorine/ammonia molar ratios under consideration for the UV/HOCl AOP treatment are needed to achieve NDMA control.

    View details for DOI 10.1021/acs.est.0c05704

    View details for PubMedID 33185421

  • Organic wastewater treatment by a single-atom catalyst and electrolytically produced H2O2 NATURE SUSTAINABILITY Xu, J., Zheng, X., Feng, Z., Lu, Z., Zhang, Z., Huang, W., Li, Y., Vuckovic, D., Li, Y., Dai, S., Chen, G., Wang, K., Wang, H., Chen, J. K., Mitch, W., Cui, Y. 2020
  • Sulfide-induced reduction of nitrobenzene mediated by different size fractions of rice straw-derived black carbon: A key role played by reactive polysulfide species. The Science of the total environment Wei, C., Yin, S., Fu, H., Qu, X., Mitch, W. A., Zhu, D. 2020; 748: 141365


    Here we investigated the mediation efficiency of different size fractions of rice straw-derived black carbon (BC) using sulfide-induced nitrobenzene reduction as a model system. The bulk BC was divided into three size fractions: dissolved BC (size <0.45 mum), colloidal BC (0.45 mum < size < 1 mum), and particulate BC (size > 1 mum). With the presence of BC fractions (250 mg/L) nitrobenzene reduction by Na2S was significantly facilitated, wherein the mediation efficiency was positively correlated with the BC fraction's oxygen group content in an order of particulate BC < colloidal BC ≪ dissolved BC. Consistently, the oxidation treatment of particulate BC with O3 or HNO3 improved the mediation efficiency, whereas the reduction treatment with NaBH4 reduced the mediation efficiency. The supernatant collected with dialysis or filtration of suspension of BC materials pre-reacted with Na2S could effectively reduce nitrobenzene, suggesting that reactive reducing sulfur species were produced in aqueous solutions by reacting sulfide only with BC materials. This was evidenced by the fact that polysulfides and polysulfide radicals were both detected in the supernatant. As demonstrated by electron paramagnetic resonance analysis, the quinone moieties at the surface of BC materials accepted electrons from sulfide and turned into semiquinone free radicals, consequently leading to formation of reactive reducing sulfur species and thus enhanced nitrobenzene reduction. The strong mediation efficiency on redox reactions observed for colloidal BC and dissolved BC combined with their significant mobility in subsurface environments indicate that these carbonaceous materials may play an important role in the fate process of organic contaminants as both carriers and catalysts. CAPSULE: The surface quinone moieties of BC induce the formation of reactive reducing sulfur species by acting as one-electron acceptors and facilitate nitrobenzene reduction by sulfide.

    View details for DOI 10.1016/j.scitotenv.2020.141365

    View details for PubMedID 32810807

  • Pilot-scale ozone/biological activated carbon treatment of reverse osmosis concentrate: potential for synergism between nitrate and contaminant removal and potable reuse ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY Zhang, Z., King, J. F., Szczuka, A., Chuang, Y., Mitch, W. A. 2020; 6 (5): 1421–31

    View details for DOI 10.1039/d0ew00013b

    View details for Web of Science ID 000534237200018

  • Efficacy of ozone for removal of pesticides, metals and indicator virus from reverse osmosis concentrates generated during potable reuse of municipal wastewaters. Water research King, J. F., Szczuka, A., Zhang, Z., Mitch, W. A. 2020; 176: 115744


    This study evaluated ozone treatment to address concerns regarding the discharge to marine waters of chemical contaminants and pathogens in reverse osmosis (RO) concentrates generated during the potable reuse of municipal wastewaters. Previous studies indicated that contaminants can be sorted into five groups based on their reaction rate constants with ozone and hydroxyl radical to predict degradation of chemical contaminants during ozonation of municipal effluents. Spiking representatives of each group into five RO concentrate samples, this study demonstrated that the same contaminant grouping scheme could be used to predict contaminant degradation during ozonation of RO concentrates, despite the higher concentrations of ozone and hydroxyl radical scavengers. The predictive capability of the contaminant grouping scheme was further validated for four contaminants of concern in RO concentrates, including the pesticides fipronil and imidacloprid, and the metal chelates Ni-EDTA and Cu-EDTA. After measuring their ozone and hydroxyl radical reaction rate constants, these compounds were assigned to contaminant groups, and their degradation during ozonation matched predictions. Addition of 300mg/L CaO at pH 11 achieved partial removal of the native nickel and copper by precipitation. Ozone pretreatment further enhanced precipitation of nickel, but not copper. Ozonation achieved 5-log inactivation of MS2 in all five concentrate samples at 1.18mg O3/mg DOC. Ozonation at 0.9mg O3/mg DOC formed 139-451mug/L bromate. Pretreatment of RO concentrates with chlorine and ammonia reduced bromate formation by a maximum of 48% but increased total halogenated DBP concentrations from 20mug/L to 36mug/L. Regardless, neither bromate nor trihalomethane concentrations exceeded threshold concentrations of concern for discharge to marine waters.

    View details for DOI 10.1016/j.watres.2020.115744

    View details for PubMedID 32251944

  • Novel Chlorination Byproducts of Tryptophan: Initial High-Yield Transformation Products versus Small Molecule Disinfection Byproducts ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS Hua, L., Kim, E., McCurry, D. L., Huang, C., Mitch, W. A. 2020; 7 (3): 149–55
  • Reductive Electrochemical Activation of Hydrogen Peroxide as an Advanced Oxidation Process for Treatment of Reverse Osmosis Permeate during Potable Reuse. Environmental science & technology Weng, C. n., Chuang, Y. H., Davey, B. n., Mitch, W. A. 2020


    The UV/hydrogen peroxide (H2O2) advanced oxidation process (AOP) frequently employed to generate hydroxyl radical (•OH) to treat reverse osmosis permeate (ROP) in potable reuse treatment trains is inefficient, using only 10% of the H2O2. This study evaluated ·OH generation by electron transfer from a low-cost stainless steel cathode. In deionized water, the electrochemical system achieved 0.5 log removal of 1,4-dioxane, a benchmark for AOP validation for potable reuse, within 4 min using only 1.25 mg/L H2O2. Hydrogen peroxide and 1,4-dioxane degradations were maximized near -0.18 and + 0.02 V versus standard hydrogen electrode, respectively. Degradations of positively and negatively charged compounds were comparable to neutral 1,4-dioxane, indicating that degradation occurs by ·OH generation from neutral H2O2 and that electrostatic repulsion of contaminants from the electrode is not problematic. For ROP without chloramines, 0.5 log 1,4-dioxane removal was achieved in 6.7 min with 7 mM salts for ionic strength and 2.5 mg/L H2O2. For ROP with 1.4 mg/L as Cl2 chloramines, 0.5 log 1,4-dioxane removal was achieved in 13.2 min with 7 mM salts and 4.5 mg/L total H2O2 dosed in three separate injections in 5 min intervals. Initial estimates based on lab-scale electrochemical AOP treatment indicated that, except for the cost of salts, the electrochemical AOP featured lower reagent costs than the UV/H2O2 AOP but higher electricity costs that could be reduced by optimization of the electrochemical design.

    View details for DOI 10.1021/acs.est.0c02144

    View details for PubMedID 32822532

  • Assessing Additivity of Cytotoxicity Associated with Disinfection Byproducts in Potable Reuse and Conventional Drinking Waters. Environmental science & technology Lau, S. S., Wei, X. n., Bokenkamp, K. n., Wagner, E. D., Plewa, M. J., Mitch, W. A. 2020


    Recent studies used the sum of the measured concentrations of individual disinfection byproducts (DBPs) weighted by their Chinese hamster ovary (CHO) cell cytotoxicity LC50 values to estimate the DBP-associated cytotoxicity of disinfected waters. This approach assumed that cytotoxicity was additive rather than synergistic or antagonistic. In this study, we evaluated whether this assumption was valid for mixtures containing DBPs at the concentration ratios measured in authentic disinfected waters. We examined the CHO cell cytotoxicity of defined DBP mixtures based on the concentrations of 43 regulated and unregulated DBPs measured in eight drinking and potable reuse waters. The hypothesis for additivity was supported using three experimental approaches. First, we demonstrated that the calculated additive toxicity (CAT) and bioassay-based calculated additive toxicity (BCAT) of the DBP mixtures agree within 12% on a median basis. We also found an additive toxicity response (CAT ≈ BCAT) between the regulated and unregulated DBP classes. Finally, the empirical biological cytotoxicity of the DBP subset mixtures, independent of the calculated toxicity, was additive. These results support the validity of using the sum of cytotoxic potency-weighted DBP concentrations as an estimate of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters.

    View details for DOI 10.1021/acs.est.0c00958

    View details for PubMedID 32275830

  • Co-occurrence of geogenic and anthropogenic contaminants in groundwater from Rajasthan, India. The Science of the total environment Coyte, R. M., Singh, A., Furst, K. E., Mitch, W. A., Vengosh, A. 2019; 688: 1216-1227


    Northwest India suffers from severe water scarcity issues due to a combination of over-exploitation and climate effects. Along with concerns over water availability, endemic water quality issues are critical and affect the usability of available water and potential human health risks. Here we present data from 243 groundwater wells, representing nine aquifer lithologies in 4 climate regions that were collected from the Northwestern Indian state of Rajasthan. Rajasthan is India's largest state by area, and has a significant groundwater reliant population due to a general lack of surface water accessibility. We show that the groundwater, including water that is used for drinking without any treatment, contains multiple inorganic contaminants in levels that exceed both Indian and World Health Organization (WHO) drinking water guidelines. The most egregious of these violations were for fluoride, nitrate, and uranium; 76% of all water samples in this study had contaminants levels that exceed the WHO guidelines for at least one of these species. In addition, we show that much of the groundwater contains high concentrations of dissolved organic carbon (DOC) and halides, both of which are risk factors for the formation of disinfectant byproducts in waters that are treated with chemical disinfectants such as chlorine. By using geochemical and isotopic (oxygen, hydrogen, carbon, strontium, and boron isotopes) data, we show that the water quality issues derive from both geogenic (evapotranspiration, water-rock interactions) and anthropogenic (agriculture, domestic sewage) sources, though in some cases anthropogenic activities, such as infiltration of organic- and nitrate-rich water, may contribute to the persistence and enhanced mobilization of geogenic contaminants. The processes affecting Rajasthan's groundwater quality are common in many other worldwide arid areas, and the lessons learned from evaluation of the mechanisms that affect the groundwater quality are universal and should be applied for other parts of the world.

    View details for DOI 10.1016/j.scitotenv.2019.06.334

    View details for PubMedID 31726552

  • Co-occurrence of geogenic and anthropogenic contaminants in groundwater from Rajasthan, India SCIENCE OF THE TOTAL ENVIRONMENT Coyte, R. M., Singh, A., Furst, K. E., Mitch, W. A., Vengosh, A. 2019; 688: 1216–27
  • Is it time to move beyond the trihalomethane paradigm in developing countries? Lessons learned from wastewater-impacted drinking waters in South Asia Furst, K., Coyte, R., Smith, D., Davis, J., Vengosh, A., Mitch, W. AMER CHEMICAL SOC. 2019
  • Energy efficient potable reuse: Lowering organic RO membrane fouling and DBP formation when treating anaerobic secondary effluent Szczuka, A., Mitch, W. AMER CHEMICAL SOC. 2019
  • Evaluation of contaminant of emerging concern removal in wastewater by a hybrid forward osmosis-reverse osmosis system Szczuka, A., Mitch, W. AMER CHEMICAL SOC. 2019
  • Pilot-scale evaluation of oxidant speciation, 1,4-dioxane degradation and disinfection byproduct formation during UV/hydrogen peroxide, UV/free chlorine and UV/chloramines advanced oxidation process treatment for potable reuse. Water research Zhang, Z., Chuang, Y., Szczuka, A., Ishida, K. P., Roback, S., Plumlee, M. H., Mitch, W. A. 2019; 164: 114939


    Advanced oxidation using UV/free chlorine and UV/chloramines are being considered as alternatives to UV/H2O2 for treatment of reverse osmosis (RO) permeate in treatment trains for the potable reuse of municipal wastewater. This pilot-scale comparison of the three advanced oxidation processes (AOPs) evaluated three factors important for selecting among these alternatives. First, the study characterized the speciation of oxidants serving as the source of radicals within the AOPs to facilitate process modeling. Kinetic modeling that included consideration of the chloramines occurring in RO permeate accurately predicted oxidant speciation. Modeling of the UV/free chlorine AOP indicated that free chlorine is scavenged by reactions with ammonia and monochloramine in RO permeate, such that oxidant speciation can shift in favor of dichloramine over the short (30 s) timescale of AOP treatment. Second, the order of efficacy for degrading the target contaminant, 1,4-dioxane, in terms of minimizing UV fluence was UV/free chlorine > UV/H2O2 ≫ UV/chloramines. However, estimates indicated that the UV/chloramines and UV/H2O2 AOPs could be similar on a cost-effectiveness basis due to savings in reagent costs by the UV/chloramines AOP, provided the RO permeate featured >3 mg/L as Cl2 chloramines. Third, the study evaluated whether the use of chlorine-based oxidants within the UV/free chlorine and UV/chloramines AOPs enhanced disinfection byproduct (DBP) formation. Even after AOP treatment and chloramination, total halogenated DBP formation remained low at <15 mug/L for all three AOPs. DBP formation was similar between the AOPs, except that the UV/free chlorine AOP promoted haloacetaldehyde formation, while the UV/H2O2 and UV/chloramines AOPs followed by chloramination increased chloropicrin formation. However, total DBP formation on a toxic potency-weighted basis was similar among the AOPs, since haloacetonitriles and haloacetamides were the dominant contributors and did not differ significantly among the AOPs.

    View details for DOI 10.1016/j.watres.2019.114939

    View details for PubMedID 31408756

  • Predicting the Contribution of Chloramines to Contaminant Decay during Ultraviolet/Hydrogen Peroxide Advanced Oxidation Process Treatment for Potable Reuse ENVIRONMENTAL SCIENCE & TECHNOLOGY Zhang, Z., Chuang, Y., Huang, N., Mitch, W. A. 2019; 53 (8): 4416–25
  • Comparison of Toxicity-Weighted Disinfection Byproduct Concentrations in Potable Reuse Waters and Conventional Drinking Waters as a New Approach to Assessing the Quality of Advanced Treatment Train Waters ENVIRONMENTAL SCIENCE & TECHNOLOGY Chuang, Y., Szczuka, A., Mitch, W. A. 2019; 53 (7): 3729–38
  • Pilot-scale comparison of microfiltration/reverse osmosis and ozone/biological activated carbon with UV/hydrogen peroxide or UV/free chlorine AOP treatment for controlling disinfection byproducts during wastewater reuse WATER RESEARCH Chuang, Y., Szczuka, A., Shabani, F., Munoz, J., Aflaki, R., Hammond, S. D., Mitch, W. A. 2019; 152: 215–25
  • Comparing industrial and domestic discharges as sources of N-nitrosamines and their chloramine or ozone-reactive precursors ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY Chuang, Y., Shabani, F., Munoz, J., Aflaki, R., Hammond, S. D., Mitch, W. A. 2019; 5 (4): 726–36

    View details for DOI 10.1039/c8ew00942b

    View details for Web of Science ID 000462942400009

  • Formation of N-nitrosamines during the analysis of municipal secondary biological nutrient removal process effluents by US EPA method 521 CHEMOSPHERE Chuang, Y., Shabani, F., Munoz, J., Aflaki, R., Hammond, S. D., Mitch, W. A. 2019; 221: 597–605
  • Comparing the quality of water produced by O3/BAC vs. MF/RO for potable reuse of municipal wastewater Mitch, W., Chuang, Y. AMER CHEMICAL SOC. 2019
  • Evaluation of a Pilot Anaerobic Secondary Effluent for Potable Reuse: Impact of Different Disinfection Schemes on Organic Fouling of RO Membranes and DBP Formation ENVIRONMENTAL SCIENCE & TECHNOLOGY Szczuka, A., Berglund-Brown, J. P., Chen, H. K., Quay, A. N., Mitch, W. A. 2019; 53 (6): 3166–76
  • Comparison of Toxicity-Weighted Disinfection Byproduct Concentrations in Potable Reuse Waters and Conventional Drinking Waters as a New Approach to Assessing the Quality of Advanced Treatment Train Waters. Environmental science & technology Chuang, Y., Szczuka, A., Mitch, W. A. 2019


    Advanced treatment trains based on oxidation, biofiltration, and/or granular activated carbon (Ox/BAF/GAC) are an attractive alternative to those based on microfiltration, reverse osmosis, and advanced oxidation (MF/RO/AOP) for the potable reuse of municipal wastewater effluents, but their effluent quality is difficult to validate with respect to chemical contaminants. This study evaluated the sum of the concentrations of 46 disinfection byproducts (DBPs) after treatment by chlorine or chloramines weighted by metrics of toxic potency in 10 full- or pilot-scale reuse trains to estimate the DBP-associated toxicity of their effluents. These total toxicity-weighted DBP concentrations were compared to those measured in their local, conventional drinking waters as a benchmark for water quality receiving regulatory and widespread public acceptance. The results indicated that while the DBP-associated quality of MF/RO/AOP-based reuse waters can readily exceed that of drinking waters, that of Ox/BAF/GAC-based reuse waters can approach or exceed that of drinking waters, particularly when they are chloraminated. Unregulated, halogenated DBPs were the dominant contributors to the estimated DBP-associated toxicity. While RO/AOP treatment preferentially reduced the concentrations of the more toxic brominated DBP species, BAC and GAC treatment favored brominated DBP species by removing DOC but not bromide. Comparing the total toxicity-weighted DBP concentration between reuse and drinking waters provides drinking water as a rational benchmark for water quality comparison, explicitly recognizes that contaminants occur as mixtures, provides utilities flexibility in selecting the most efficient treatment trains to reduce estimated toxicity, and can be expanded to encompass new contaminants as toxic potency data become available.

    View details for PubMedID 30811182

  • A Tale of Two Treatments: The Multiple Barrier Approach to Removing Chemical Contaminants During Potable Water Reuse ACCOUNTS OF CHEMICAL RESEARCH Marron, E. L., Mitch, W. A., von Gunten, U., Sedlak, D. L. 2019; 52 (3): 615–22


    In response to water scarcity and an increased recognition of the risks associated with the presence of chemical contaminants, environmental engineers have developed advanced water treatment systems that are capable of converting municipal wastewater effluent into drinking water. This practice, which is referred to as potable water reuse, typically relies upon reverse osmosis (RO) treatment followed by exposure to ultraviolet (UV) light and addition of hydrogen peroxide (H2O2). These two treatment processes individually are capable of controlling many of the chemical and microbial contaminants in wastewater; however, a few chemicals may still be present after treatment at concentrations that affect water quality. Low-molecular weight (<200 Da), uncharged compounds represent the greatest challenge for RO treatment. For potable water reuse systems, compounds of greatest concern include oxidation products formed during treatment (e.g., N-nitrosodimethylamine, halogenated disinfection byproducts) and compounds present in wastewater effluent (e.g., odorous compounds, organic solvents). Although the concentrations of most of these compounds decrease to levels where they no longer compromise water quality after they encounter the second treatment barrier (i.e., UV/H2O2), low-molecular weight compounds that are resistant to direct photolysis and exhibit low reactivity with hydroxyl radical (·OH) may persist. While attempts to identify the compounds that pass through both barriers have accounted for approximately half of the dissolved organic carbon remaining after treatment, it is unlikely that a significant fraction of the remaining unknowns will ever be identified with current analytical techniques. Nonetheless, the toxicity-weighted concentration of certain known compounds (e.g., disinfection byproducts) is typically lower in RO-UV/H2O2 treated water than conventional drinking water. To avoid the expense associated with managing the concentrate produced by RO, environmental engineers have begun to employ alternative treatment barriers. The use of alternatives such as nanofiltration, ozonation followed by biological filtration, or activated carbon filtration avoids the problems associated with the production and disposal of RO concentrate, but they may allow a larger number of chemical contaminants to pass through the treatment process. In addition to the transformation products and solvents that pose risks in the RO-UV/H2O2 system, these alternative barriers are challenged by larger, polar compounds that are not amenable to oxidation, such as perfluoroalkyl acids and phosphate-containing flame retardants. To fully protect consumers who rely upon potable water reuse systems, new policies are needed to prevent chemicals that are difficult to remove during advanced treatment from entering the sewer system. By using knowledge about the composition of municipal wastewater and the mechanisms through which contaminants are removed during treatment, it should be possible to safely reuse municipal wastewater effluent as a drinking water source.

    View details for DOI 10.1021/acs.accounts.8b00612

    View details for Web of Science ID 000462098100011

    View details for PubMedID 30821146

  • Evaluation of a Pilot Anaerobic Secondary Effluent for Potable Reuse: Impact of Different Disinfection Schemes on Organic Fouling of RO Membranes and DBP Formation. Environmental science & technology Szczuka, A., Berglund-Brown, J. P., Chen, H. K., Quay, A. N., Mitch, W. A. 2019


    Anaerobic biological secondary treatment has the potential to substantially reduce the energy cost and footprint of wastewater treatment. However, for utilities seeking to meet future water demand through potable reuse, the compatibility of anaerobically treated secondary effluent with potable reuse trains has not been evaluated. This study characterized the effects of different combinations of chloramines, ozone, and biological activated carbon (BAC), applied as pretreatments to mitigate organic chemical fouling of reverse osmosis (RO) membranes, and the production of 43 disinfection byproducts (DBPs). The study employed effluent from a pilot-scale anaerobic reactor and soluble microbial products (SMPs) generated from a synthetic wastewater. Ozonation alone minimized RO flux decline by rendering the dissolved organic carbon (DOC) more hydrophilic. When combined with chloramination, ozone addition after chloramines maintained a higher RO flux. BAC treatment was ineffective for reducing the pressure and energy requirements for a set permeate flux. Regardless of pretreatment method prior to RO, the total DBP concentrations were <14 mug/L upstream of RO. After treatment by RO, the UV/hydrogen peroxide advanced oxidation process, and chloramination, the total DBP concentrations were ≤5 mug/L. When DBP concentrations were weighted by metrics of toxic potency, the total DBP calculated toxicity was 4-fold lower than observed previously in full-scale potable reuse facilities receiving aerobically treated secondary effluent. The RO fouling and DBP formation behavior of anaerobic SMPs were similar to that of the pilot-scale anaerobic effluent. The results of this study are promising, but more research is needed to evaluate whether anaerobic effluent is suitable as an influent to potable reuse trains.

    View details for PubMedID 30763514

  • Evaluation of Enhanced Ozone-Biologically Active Filtration Treatment for the Removal of 1,4-Dioxane and Disinfection Byproduct Precursors from Wastewater Effluent. Environmental science & technology Vatankhah, H., Szczuka, A., Mitch, W. A., Almaraz, N., Brannum, J., Bellona, C. 2019


    Ozonation followed by biologically active filtration (BAF) (O3-BAF) treatment has become an alternative to reverse osmosis in potable wastewater reuse applications because of the ability to produce a high-quality effluent while reducing brine production and disposal. In this study, effluent from a sequencing batch membrane bioreactor (SBMBR) was treated by O3-BAF at three specific ozone doses (0.5, 0.7, and 1.0 mg O3/mg DOC) and different empty bed contact times (EBCTs; 15-45 min). The reaction of O3 with granular activated carbon (GAC) (O3/GAC) to promote the formation of hydroxyl radicals (·OH) was evaluated at 1.0 mg O3/mg DOC followed by BAF at 15-45 min EBCT. The efficacy of these techniques was compared for the removal of O3 refractory 1,4-dioxane and the reduction in the formation of bromate, 35 regulated and unregulated halogenated disinfection byproducts (DBPs), and 8 N-nitrosamines after chloramination. Conventional ozonation (without the presence of GAC during ozonation) removed 6-11% of 1,4-dioxane, while BAF increased the removal to 25%. O3/GAC improved the removal of 1,4-dioxane to 40%, while BAF increased the removal to 50%. No bromate was detected during conventional ozonation. Although O3/GAC formed 12.5 mug/L bromate, this concentration was reduced during BAF treatment to <6.8 mug/L. Even though conventional ozonation was more effective than O3/GAC for the reduction in chloramine-reactive N-nitrosodimethylamine (NDMA) precursors, BAF treatment after either conventional or enhanced ozonation reduced NDMA formation during chloramination to <10 ng/L. O3/GAC was more effective at reducing halogenated DBP formation during postchloramination. Regardless, the reduction in halogenated DBP formation during postchloramination achieved by BAF treatment was 90% relative to the formation in the SBMBR effluent after either conventional or enhanced ozonation. The reduction of haloacetic acid (HAA) formation improved moderately with increasing BAF EBCT. Both O3-BAF and (O3/GAC)-BAF met regulatory levels for trihalomethanes, HAAs, NDMA, and bromate.

    View details for PubMedID 30698962

  • Enhanced Phototransformation of Tetracycline at Smectite Clay Surfaces under Simulated Sunlight via a Lewis-Base Catalyzed Alkalization Mechanism ENVIRONMENTAL SCIENCE & TECHNOLOGY Xu, L., Li, H., Mitch, W. A., Tao, S., Zhu, D. 2019; 53 (2): 710–18


    As an important class of soil minerals and a key constituent of colloidal particles in surface aquifers, smectite clays can strongly retain tetracyclines due to their large surface areas and high cation exchange capacities. However, the research on phototransformation of tetracyclines at smectite clay surfaces is rarely studied. Here, the phototransformation kinetics of tetracycline pre-adsorbed on two model smectite clays (hectorite and montmorillonite) exchanged with Na+, K+, or Ca2+ suspended in aqueous solution under simulated sunlight was compared with that of tetracycline dissolved in water using batch experiments. Adsorption on clays accelerated tetracycline phototransformation (half-lives shortened by 1.1-5.3 times), with the most significant effects observed for Na+-exchanged clays. Regardless of the presence or absence of clay, the phototransformation of tetracycline was facilitated by increasing pH from 4 to 7. Inhibition or enhancement of photolysis-induced reactive species combined with their measurement using scavenger/probe chemicals indicate that the facilitated production of self-photosensitized singlet oxygen (1O2) was the key factor contributing to the clay-enhanced phototransformation of tetracycline. As evidenced by the red shifts and the increased molar absorptivity in the UV-vis absorption spectra, the complexation of tetracycline with the negatively charged (Lewis base) sites on clay siloxane surfaces led to formation of the alkalized form, which has larger light absorption rate and is more readily to be oxidized compared to tetracycline in aqueous solution at equivalent pH. Our findings indicate a previously unrecognized, important phototransformation mechanism of tetracyclines catalyzed by smectite clays.

    View details for PubMedID 30561992

  • Pilot-scale comparison of microfiltration/reverse osmosis and ozone/biological activated carbon with UV/hydrogen peroxide or UV/free chlorine AOP treatment for controlling disinfection byproducts during wastewater reuse. Water research Chuang, Y., Szczuka, A., Shabani, F., Munoz, J., Aflaki, R., Hammond, S. D., Mitch, W. A. 2019; 152: 215–25


    Ozone and biological activated carbon (O3/BAC) is being considered as an alternative advanced treatment process to microfiltration and reverse osmosis (MF/RO) for the potable reuse of municipal wastewater. Similarly, the UV/free chlorine (UV/HOCl) advanced oxidation process (AOP) is being considered as an alternative to the UV/hydrogen peroxide (UV/H2O2) AOP. This study compared the performance of these alternative treatment processes for controlling N-nitrosamines and chloramine-reactive N-nitrosamine and halogenated disinfection byproduct (DBP) precursors during parallel, pilot-scale treatment of tertiary municipal wastewater effluent. O3/BAC outperformed MF/RO for controlling N-nitrosodimethylamine (NDMA), while MF/RO was more effective for controlling N-nitrosomorpholine (NMOR) and chloramine-reactive NDMA precursors. The UV/H2O2 and UV/HOCl AOPs were equally effective for controlling N-nitrosamines in O3/BAC effluent, but UV/HOCl was less effective for controlling NDMA in MF/RO effluent, likely due to the promotion of dichloramine under these conditions. MF/RO was more effective than O3/BAC for controlling chloramine-reactive halogenated DBP precursors on both a mass and toxicity-weighted basis. UV/H2O2 AOP treatment was more effective at controlling the toxicity-weighted chloramine-reactive DBP precursors for most halogenated DBP classes by preferentially degrading the more toxic brominated species. However, the total toxicity-weighted DBP precursor concentrations were similar for treatment by either AOP because UV/H2O2 AOP treatment promoted the formation of iodoacetic acid, which exhibits a very high toxic potency. The combined O3/BAC/MF/RO train was the most effective for controlling N-nitrosamines and the total toxicity-weighted DBP precursor concentrations with or without treatment by either AOP.

    View details for PubMedID 30677632

  • Role of absorber and desorber units and operational conditions for N-nitrosamine formation during amine-based carbon capture. Water research Wang, Z. n., Zhang, Z. n., Mitch, W. A. 2019; 170: 115299


    The formation of carcinogenic N-nitrosamines from reactions between solvent amines and flue gas NOx is an important concern for the application of amine-based processes to capture CO2 post-combustion. Using an advanced test rig with interconnected absorber and desorber units, we evaluated the importance for N-nitrosamine formation of the desorber relative to the absorber, and any synergism between the two units. Variations in desorber temperature and in flue gas composition indicated that N-nitrosamine formation from fresh monoethanolamine (MEA) occurred predominantly in the absorber. N-nitrosamine formation was driven by high NO2 and O2 flue gas concentrations, although NO also contributed. In contrast, N-nitrosamine formation from piperazine (PZ) was driven by reactions with nitrite in the heated desorber, and accelerated concurrent with nitrite accumulation. A complementary experiment simulating aged MEA solvent (high nitrite, 1.5% sarcosine as a proxy of secondary amine degradation products) suggested the desorber becomes an order of magnitude more important than the absorber for N-nitrosamine formation. For fresh MEA solvent, increasing the desorber temperature from 110 °C to 130 °C promoted thermal decomposition of N-nitrosamines, reducing N-nitrosamine accumulation rates two-fold. Compared to the test rig, the prevailing practice of using separate absorber columns and autoclave-like treatments to mimic desorber units predicted the direction, but underestimated the magnitude of N-nitrosamine formation. Because N-nitrosamine accumulation rates are the net result of competing formation and thermal decomposition processes, use of continuously cycling test rigs may be necessary to understand the impacts of different operating conditions.

    View details for DOI 10.1016/j.watres.2019.115299

    View details for PubMedID 31760360

  • Disinfection Byproducts in Rajasthan, India: Are Trihalomethanes a Sufficient Indicator of Disinfection Byproduct Exposure in Low-Income Countries? Environmental science & technology Furst, K. E., Coyte, R. M., Wood, M. n., Vengosh, A. n., Mitch, W. A. 2019


    The implementation of chlorine disinfection in low-income countries reduces the risk of waterborne illness but initiates exposure to disinfection byproducts (DBPs). Like high-income countries, low-income countries typically are adopting regulations focusing on trihalomethanes (THM4) as an indicator of overall DBP exposure. However, the use of impaired water sources can decouple the formation of THM4 from other DBP classes that are more potent toxins. The documentation of DBP species other than THM4 is rare in low-income countries, where water sources may be degraded by inadequate sanitation infrastructure and other uncontrolled wastewater discharges. We measured THM4 and 21 unregulated DBPs in tap waters and laboratory-treated source waters from two cities in northwestern India. The contribution of each DBP class to the cumulative toxicity was estimated by weighting each species by metrics of toxic potency; haloacetonitriles typically were the dominant contributor, while the contribution of THM4 was negligible. THM4 concentrations did not correlate with the total toxic potency-weighted DBP concentrations. Although THM4 rarely exceeded international guidelines, DBPs of greater toxicological concern were observed in high concentrations. The total toxic potency-weighted DBP concentrations in some waters were elevated compared to conventional drinking waters in high-income countries and more closely resembled chlorine-disinfected wastewater effluents. Artificial sweeteners confirmed widespread contamination of both surface and groundwaters by domestic sewage. The results suggest that THM4 may not be an adequate indicator of overall DBP exposure in impaired water supplies prevalent in some low-income nations.

    View details for DOI 10.1021/acs.est.9b03484

    View details for PubMedID 31549828

  • Bench-scale column evaluation of factors associated with changes in N-nitrosodimethylamine (NDMA) precursor concentrations during drinking water biofiltration. Water research Zhang, Z. n., Ma, B. n., Hozalski, R. M., Russell, C. G., Evans, A. N., Led, K. O., Van Dyke, M. n., Peldszus, S. n., Huck, P. M., Szczuka, A. n., Mitch, W. A. 2019; 167: 115103


    Biofiltration has been observed to increase or decrease the concentrations of N-nitrosodimethylamine (NDMA) precursors in the effluents of full-scale drinking water facilities, but these changes have been inconsistent over time. Bench-scale tests comparing biofiltration columns side-by-side exposed to different conditions were employed to characterize factors associated with changes in NDMA precursor concentrations, as measured by application of chloramines under uniform formation conditions (UFC). Side-by-side comparisons of biofiltration media from different facilities fed with water from each of these facilities demonstrated that differences in source water quality were far more important than any original differences in the microbial communities on the biofiltration media for determining whether NDMA precursor concentrations increased, decreased or remained constant across biofilters. Additional tests involving spiking of specific constituents hypothesized to promote increases in NDMA precursor concentrations demonstrated that inorganic nitrogen species associated with nitrification, including ammonia, hydroxylamine and chloramines, and biotransformation of known precursors (i.e., municipal wastewater and the cationic polymer, polyDADMAC) to more potent forms were not important. Biotransformation of uncharacterized components of source waters determined whether NDMA precursor concentrations increased or decreased across biofilters. These uncharacterized source water component concentrations varied temporally and across locations. Where biotransformation of source water precursors increased NDMA precursor concentrations, ∼30-60% of the levels observed in column effluents fed with biofiltration influent water remained associated with the media and could be rinsed therefrom in either the dissolved or particulate form. Ozone pre-treatment significantly reduced NDMA precursor concentrations at one facility, suggesting that pre-oxidation could be an effective technique to mitigate the increase in NDMA precursor concentrations during biofiltration. Biofiltration decreased the concentrations of halogenated disinfection byproduct precursors.

    View details for DOI 10.1016/j.watres.2019.115103

    View details for PubMedID 31581035

  • Serum electrolytes can promote hydroxyl radical-initiated biomolecular damage from inflammation. Free radical biology & medicine Komaki, Y. n., Simpson, A. M., Choe, J. K., Pinney, M. M., Herschlag, D. n., Chuang, Y. H., Mitch, W. A. 2019; 141: 475–82


    Chronic inflammatory disorders are associated with biomolecular damage attributed partly to reactions with Reactive Oxygen Species (ROS), particularly hydroxyl radicals (•OH). However, the impacts of serum electrolytes on ROS-associated damage has received little attention. We demonstrate that the conversion of •OH to carbonate and halogen radicals via reactions with serum-relevant carbonate and halide concentrations fundamentally alters the targeting of amino acids and loss of enzymatic activity in catalase, albumin and carbonic anhydrase, three important blood proteins. Chemical kinetic modeling indicated that carbonate and halogen radical concentrations should exceed •OH concentrations by 6 and 2 orders of magnitude, respectively. Steady-state γ-radiolysis experiments demonstrated that serum-level carbonates and halides increased tyrosine, tryptophan and enzymatic activity losses in catalase up to 6-fold. These outcomes were specific to carbonates and halides, not general ionic strength effects. Serum carbonates and halides increased the degradation of tyrosines and methionines in albumin, and increased the degradation of histidines while decreasing enzymatic activity loss in carbonic anhydrase. Serum electrolytes increased the degradation of tyrosines, tryptophans and enzymatic activity in the model enzyme, ketosteroid isomerase, predominantly due to carbonate radical reactions. Treatment of a mutant ketosteroid isomerase indicated that preferential targeting of the active site tyrosine accounted for half of the total tyrosine loss. The results suggest that carbonate and halogen radicals may be more significant than •OH as drivers for protein degradation in serum. Accounting for the selective targeting of biomolecules by these daughter radicals is important for developing a mechanistic understanding of the consequences of oxidative stress.

    View details for DOI 10.1016/j.freeradbiomed.2019.07.023

    View details for PubMedID 31349038

  • Exposure to disinfection by-products in swimming pools and biomarkers of genotoxicity and respiratory damage - The PISCINA2 Study. Environment international Font-Ribera, L. n., Marco, E. n., Grimalt, J. O., Pastor, S. n., Marcos, R. n., Abramsson-Zetterberg, L. n., Pedersen, M. n., Grummt, T. n., Junek, R. n., Barreiro, E. n., Heederik, D. n., Spithoven, J. n., Critelli, R. n., Naccarati, A. n., Schmalz, C. n., Zwiener, C. n., Liu, J. n., Zhang, X. n., Mitch, W. n., Gracia-Lavedan, E. n., Arjona, L. n., de Bont, J. n., Tarès, L. n., Vineis, P. n., Kogevinas, M. n., Villanueva, C. M. 2019; 131: 104988


    Swimming in pools is a healthy activity that entails exposure to disinfection by-products (DBPs), some of which are irritant and genotoxic.We evaluated exposure to DBPs during swimming in a chlorinated pool and the association with short-term changes in genotoxicity and lung epithelium permeability biomarkers.Non-smoker adults (N = 116) swimming 40 min in an indoor pool were included. We measured a range of biomarkers before and at different times after swimming: trihalomethanes (THMs) in exhaled breath (5 min), trichloroacetic acid (TCAA) in urine (30 min), micronuclei in lymphocytes (1 h), serum club cell protein (CC16) (1 h), urine mutagenicity (2 h) and micronuclei in reticulocytes (4 days in a subset, N = 19). Several DBPs in water and trichloramine in air were measured, and physical activity was extensively assessed. We estimated interactions with polymorphisms in genes related to DBP metabolism.Median level of chloroform, brominated and total THMs in water was 37.3, 9.5 and 48.5, μg/L, respectively, and trichloramine in air was 472.6 μg/m3. Median exhaled chloroform, brominated and total THMs increased after swimming by 10.9, 2.6 and 13.4, μg/m3, respectively. Creatinine-adjusted urinary TCAA increased by 3.1 μmol/mol. Micronuclei in lymphocytes and reticulocytes, urine mutagenicity and serum CC16 levels remained unchanged after swimming. Spearman correlation coefficients showed no association between DBP exposure and micronuclei in lymphocytes, urine mutagenicity and CC16. Moderate associations were observed for micronuclei in reticulocytes and DBP exposure.The unchanged levels of the short-term effect biomarkers after swimming and null associations with personal estimates of exposure to DBPs suggest no measurable effect on genotoxicity in lymphocytes, urine mutagenicity and lung epithelium permeability at the observed exposure levels. The moderate associations with micronuclei in reticulocytes require cautious interpretation given the reduced sample size.

    View details for DOI 10.1016/j.envint.2019.104988

    View details for PubMedID 31323486

  • Behavior of NDMA precursors at 21 full-scale water treatment facilities ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY Krasner, S. W., Westerhoff, P., Mitch, W. A., Hanigan, D., McCurry, D. L., von Gunten, U. 2018; 4 (12): 1966–78

    View details for DOI 10.1039/c8ew00442k

    View details for Web of Science ID 000451072500007

  • Impact of Combined Chlorination and Chloramination Conditions on N-Nitrosodimethylamine Formation JOURNAL AMERICAN WATER WORKS ASSOCIATION Krasner, S. W., Lee, C., Mitch, W. A., von Gunten, U. 2018; 110 (12): 11–24

    View details for DOI 10.1002/awwa.1128

    View details for Web of Science ID 000451576800004

  • Chlorotyrosines versus Volatile Byproducts from Chlorine Disinfection during Washing of Spinach and Lettuce ENVIRONMENTAL SCIENCE & TECHNOLOGY Komaki, Y., Simpson, A., Choe, J., Plewa, M. J., Mitch, W. A. 2018; 52 (16): 9361–69


    Following the Food Safety Modernization Act of 2011 in the U.S., guidelines for disinfection washes in food packaging facilities are under consideration to control pathogen risks. However, disinfectant exposures may need optimization because the high concentrations of chlorine disinfectant promote the formation of high levels of disinfection byproducts (DBPs). When chlorine doses up through the 200 mg/L as Cl2 range relevant to the current practice were applied to spinach and lettuce, significant DBP formation was observed, even within 5 min at 7 °C. Concentrations of volatile chlorinated DBPs in washwater were far higher than typically observed in disinfected drinking water (e.g., 350 μg/L 1,1-dichloropropanone). However, these DBPs partitioned to the aqueous phase and so represent a greater concern for the disposal or reuse of washwater than for consumer exposure via food. The volatile DBPs represent the low-yield, final products of chlorination reactions with multiple biomolecular precursors. The initial, high-yield transformation products of such reactions may represent a greater concern for consumer exposure because they remain bound within the biopolymers in food and would be liberated during digestion. Using protein-bound tyrosine as an example precursor, the concentrations of the initial 3-chlorotyrosine and 3,5-dichlorotyrosine transformation products from this one precursor in the leaf phase were comparable to, and, in the case of some lettuces, exceeded, the aggregate aqueous concentration of volatile DBPs formed from multiple precursors. Chlorotyrosine formation increased when spinach was shredded due to the greater accessibility of chlorine to proteins in the leaf interiors. The cytotoxicity of chlorotyrosines to Chinese hamster ovary cells was higher than any of the trihalomethanes regulated in drinking water.

    View details for PubMedID 30040386

  • N-nitrosamine, halogenated disinfection byproduct, and byproduct precursor control in UV/free chlorine and UV/H2O2 treatment trains: A parallel comparison in a pilot plant Chuang, Y., Szczuka, A., Mitch, W. AMER CHEMICAL SOC. 2018
  • Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS Nelson, K. L., Boehm, A. B., Davies-Colley, R. J., Dodd, M. C., Kohn, T., Linden, K. G., Liu, Y., Maraccini, P. A., McNeill, K., Mitch, W. A., Nguyen, T. H., Parker, K. M., Rodriguez, R. A., Sassoubre, L. M., Silverman, A. I., Wigginton, K. R., Zepp, R. G. 2018; 20 (8): 1089–1122


    Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

    View details for DOI 10.1039/c8em00047f

    View details for Web of Science ID 000441765000001

    View details for PubMedID 30047962

  • Distributed Chlorine Injection To Minimize NDMA Formation during Chloramination of Wastewater ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS Furst, K. E., Pecson, B. M., Webber, B. D., Mitch, W. A. 2018; 5 (7): 462–66
  • Tradeoffs between pathogen inactivation and disinfection byproduct formation during sequential chlorine and chloramine disinfection for wastewater reuse. Water research Furst, K. E., Pecson, B. M., Webber, B. D., Mitch, W. A. 2018; 143: 579–88


    Treatment of fully nitrified municipal wastewater effluents with chlorine followed by chloramines (i.e., sequential chlorine disinfection) upstream of advanced treatment trains can contribute pathogen inactivation credits for potable reuse while leaving a chloramine residual to control biofouling on membrane units in the advanced treatment train. However, free chlorine exposures must be optimized to maximize pathogen inactivation while minimizing the formation of disinfection byproducts (DBPs) that are challenging to remove in the advanced treatment train. Using a pilot-scale disinfection contactor receiving fully-nitrified, tertiary municipal wastewater effluent, this study found that a 3 mg * min/L free chlorine CT (i.e., the product of the chlorine residual "C" and the contact time "T") followed by a 140 mg * min/L chloramine CT could reliably achieve 5-log inactivation of MS2 bacteriophage and reduce median total coliform concentrations below 2.2 MPN/100 mL. Free chlorine disinfection was equally effective when chlorine was dosed to exceed the breakpoint for 1 mg/L of ammonia as N. At this free chlorine exposure, regulated trihalomethane (THM) and haloacetic acid (HAA) formation remained below their Maximum Contaminant Levels (MCLs), but NDMA concentrations of 30 ng/L were above the 10 ng/L California Notification Level. Increasing the free chlorine exposure to 30 mg * min/L increased THM and HAA formation, with regulated THMs approaching or exceeding the MCL. Although this free chlorine exposure prevented NDMA formation during chloramination, the 10 ng/L background NDMA formation in the tertiary effluent remained. Increasing the free chlorine exposure also increased the formation of unregulated halogenated DBP classes that may be significant contributors to the DBP-associated toxicity of the disinfected wastewater. The results indicate that sequential chlorination can be used to optimize the benefits of free chlorine (virus and NDMA control) and chloramine disinfection (THM, HAA, and coliform control).

    View details for PubMedID 30015098

  • Chlorotyrosines versus volatile byproducts from disinfection during washing of lettuce and spinach Mitch, W., Komaki, Y., Simpson, A. AMER CHEMICAL SOC. 2018
  • When ROS are not ROS: The effect of salts on the degradation of protein Mitch, W., Komaki, Y., Choe, J. AMER CHEMICAL SOC. 2018
  • Halogen radicals promote the photodegradation of microcystins in estuarine systems Mitch, W., Parker, K., Ghadouani, A., Reichwaldt, E. AMER CHEMICAL SOC. 2018
  • Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities ENVIRONMENTAL SCIENCE & TECHNOLOGY Li, X., Mitch, W. A. 2018; 52 (4): 1681–89


    While drinking water disinfection has effectively prevented waterborne diseases, an unintended consequence is the generation of disinfection byproducts (DBPs). Epidemiological studies have consistently observed an association between consumption of chlorinated drinking water with an increased risk of bladder cancer. Out of the >600 DBPs identified, regulations focus on a few classes, such as trihalomethanes (THMs), whose concentrations were hypothesized to correlate with the DBPs driving the toxicity of disinfected waters. However, the DBPs responsible for the bladder cancer association remain unclear. Utilities are switching away from a reliance on chlorination of pristine drinking water supplies to the application of new disinfectant combinations to waters impaired by wastewater effluents and algal blooms. In light of these changes in disinfection practice, this article discusses new approaches being taken by analytical chemists, engineers, toxicologists and epidemiologists to characterize the DBP classes driving disinfected water toxicity, and suggests that DBP exposure should be measured using other DBP classes in addition to THMs.

    View details for PubMedID 29283253

  • Capture and Reductive Transformation of Halogenated Pesticides by an Activated Carbon-Based Electrolysis System for Treatment of Runoff ENVIRONMENTAL SCIENCE & TECHNOLOGY Li, Y., Mitch, W. A. 2018; 52 (3): 1435–43


    This study evaluates an electrochemical system to treat the halogenated pesticides, fipronil, permethrin, and bifenthrin, in urban runoff. Compared to the poor sorption capacity of metal-based electrodes, granular activated carbon (GAC)-based electrodes could sorb halogenated pesticides, permitting electrochemical degradation to occur over longer timescales than reactor hydraulic residence times. In a dual-cell configuration, a cathode constructed of loose GAC containing sorbed pesticides was separated from the anode by an ion-exchange membrane to prevent chloride transport and oxidation to chlorine at the anode. When -1 V was applied to the cathode, fipronil concentrations declined by 92% over 15 h, releasing molar equivalents of chloride (2) and fluoride (6), suggesting complete dehalogenation of fipronil. An electrode constructed of crushed GAC particles attached to a carbon cloth current distributor achieved >90% degradation of fipronil, permethrin, and bifenthrin within 2 h under the same conditions. To evaluate a simpler single-cell configuration suitable for scale-up, two of the carbon cloth-based electrodes were placed in parallel without an ion-exchange membrane. For -1 V applied to the cathode, fipronil degradation was >95% over 2 h, and energy consumption declined with closer electrode spacing. However, chloride oxidation at the anode produced chlorine, and the anode degraded. Application of an alternating potential (-1 to +1 V at 0.0125 Hz) to the parallel-plate electrodes achieved >90% degradation of fipronil, bifenthrin, and permethrin over 4 h, releasing chloride at 50-70% of that expected for complete dechlorination. No loss of performance or formation of chlorine or halogenated byproducts was observed over 5 cycles of treating fipronil-spiked surface water.

    View details for PubMedID 29281267

  • Comparing the UV/Monochloramine and UV/Free Chlorine Advanced Oxidation Processes (AOPs) to the UV/Hydrogen Peroxide AOP Under Scenarios Relevant to Potable Reuse ENVIRONMENTAL SCIENCE & TECHNOLOGY Chuang, Y., Chen, S., Chinn, C. J., Mitch, W. A. 2017; 51 (23): 13859–68
  • Comparing the UV/Monochloramine and UV/Free Chlorine Advanced Oxidation Processes (AOPs) to the UV/Hydrogen Peroxide AOP Under Scenarios Relevant to Potable Reuse. Environmental science & technology Chuang, Y. H., Chen, S., Chinn, C. J., Mitch, W. A. 2017; 51 (23): 13859-13868


    Utilities incorporating the potable reuse of municipal wastewater are interested in converting from the UV/H2O2 to the UV/free chlorine advanced oxidation process (AOP). The AOP treatment of reverse osmosis (RO) permeate often includes the de facto UV/chloramine AOP because chloramines applied upstream permeate RO membranes. Models are needed that accurately predict oxidant photolysis and subsequent radical reactions. By combining radical scavengers and kinetic modeling, we have derived quantum yields for radical generation by the UV photolysis of HOCl, OCl-, and NH2Cl of 0.62, 0.55, and 0.20, respectively, far below previous estimates that incorporated subsequent free chlorine or chloramine scavenging by the •Cl and •OH daughter radicals. The observed quantum yield for free chlorine loss actually decreased with increasing free chlorine concentration, suggesting scavenging of radicals participating in free chlorine chain decomposition and even free chlorine reformation. Consideration of reactions of •ClO and its daughter products (e.g., ClO2-), not included in previous models, were critical for modeling free chlorine loss. Radical reactions (indirect photolysis) accounted for ∼50% of chloramine decay and ∼80% of free chlorine loss or reformation. The performance of the UV/chloramine AOP was comparable to the UV/H2O2 AOP for degradation of 1,4-dioxane, benzoate and carbamazepine across pH 5.5-8.3. The UV/free chlorine AOP was more efficient at pH 5.5, but only by 30% for 1,4-dioxane. At pH 7.0-8.3, the UV/free chlorine AOP was less efficient. •Cl converts to •OH. The modeled •Cl:•OH ratio was ∼20% for the UV/free chlorine AOP and ∼35% for the UV/chloramine AOP such that •OH was generally more important for contaminant degradation.

    View details for DOI 10.1021/acs.est.7b03570

    View details for PubMedID 29121472

  • New Takes on Emerging Contaminants: Preface JOURNAL OF ENVIRONMENTAL SCIENCES Mitch, W. A. 2017; 62: 1–2

    View details for PubMedID 29289280

  • Nitrosamines and Nitramines in Amine-Based Carbon Dioxide Capture Systems: Fundamentals, Engineering Implications, and Knowledge Gaps ENVIRONMENTAL SCIENCE & TECHNOLOGY Yu, K., Mitch, W. A., Dai, N. 2017; 51 (20): 11522–36


    Amine-based absorption is the primary contender for postcombustion CO2 capture from fossil fuel-fired power plants. However, significant concerns have arisen regarding the formation and emission of toxic nitrosamine and nitramine byproducts from amine-based systems. This paper reviews the current knowledge regarding these byproducts in CO2 capture systems. In the absorber, flue gas NOx drives nitrosamine and nitramine formation after its dissolution into the amine solvent. The reaction mechanisms are reviewed based on CO2 capture literature as well as biological and atmospheric chemistry studies. In the desorber, nitrosamines are formed under high temperatures by amines reacting with nitrite (a hydrolysis product of NOx), but they can also thermally decompose following pseudo-first order kinetics. The effects of amine structure, primarily amine order, on nitrosamine formation and the corresponding mechanisms are discussed. Washwater units, although intended to control emissions from the absorber, can contribute to additional nitrosamine formation when accumulated amines react with residual NOx. Nitramines are much less studied than nitrosamines in CO2 capture systems. Mitigation strategies based on the reaction mechanisms in each unit of the CO2 capture systems are reviewed. Lastly, we highlight research needs in clarifying reaction mechanisms, developing analytical methods for both liquid and gas phases, and integrating different units to quantitatively predict the accumulation and emission of nitrosamines and nitramines.

    View details for PubMedID 28946738

  • Regulated and unregulated halogenated disinfection byproduct formation from chlorination of saline groundwater WATER RESEARCH Szczuka, A., Parker, K. M., Harvey, C., Hayes, E., Vengosh, A., Mitch, W. A. 2017; 122: 633–44


    Coastal utilities exploiting mildly saline groundwater (<150 mg/L chloride) may be challenged by disinfection byproduct (DBP) formation, a concern likely to increase with sea-level rise. Groundwater from North Carolina coastal aquifers is characterized by large variations in concentrations of halides (bromide up to 10,600 μg/L) and dissolved organic carbon (up to 5.7 mg-C/L). Formation of 33 regulated and unregulated halogenated DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles, haloacetamides, and haloacetaldehydes, was measured after simulated chlorination of 24 coastal North Carolina groundwater samples under typical chlorination conditions. Results of chlorination simulation show that THM levels exceeded the Primary Maximum Contaminant Levels in half of the chlorinated samples. Addition of halides to a low salinity groundwater (110 mg/L chloride) indicated that elevated bromide triggered DBP formation, but chloride was not a critical factor for their formation. DBP speciation, but not overall molar formation, was strongly correlated with bromide variations in the groundwater. THMs and HAAs dominated the measured halogenated DBPs on a mass concentration basis. When measured concentrations were weighted by metrics of toxic potency, haloacetonitriles, and to a lesser degree, haloacetaldehydes and HAAs, were the predominant contributors to calculated DBP-associated toxicity. For some samples exhibiting elevated ammonia concentrations, the addition of chlorine to form chloramines in situ significantly reduced halogenated DBP concentrations and calculated toxicity. HAAs dominated the calculated toxicity of chloraminated waters. Reverse osmosis treatment of saline groundwater (chloride >250 mg/L) can reduce DBP formation by removing halides and organic precursors. However, we show that in a case where reverse osmosis permeate is blended with a separate raw groundwater, the residual bromide level in the permeate could still exceed that in the raw groundwater, and thereby induce DBP formation in the blend. DBP-associated calculated toxicity increased for certain blends in this system due to the DBPs resulting from the combination of the elevated bromide concentration in the permeate and the organic precursors from the raw coastal groundwater.

    View details for PubMedID 28646800

  • Environmental and Human Impacts of Unconventional Energy Development. Environmental science & technology Vengosh, A., Mitch, W. A., McKenzie, L. M. 2017; 51 (18): 10271-10273

    View details for DOI 10.1021/acs.est.7b04336

    View details for PubMedID 28922918

  • Activity and Reactivity of Pyrogenic Carbonaceous Matter toward Organic Compounds. Environmental science & technology Pignatello, J. J., Mitch, W. A., Xu, W. 2017; 51 (16): 8893-8908


    Pyrogenic carbonaceous matter (PCM) includes environmental black carbon (fossil fuel soot, biomass char), engineered carbons (biochar, activated carbon), and related materials like graphene and nanotubes. These materials contact organic pollutants due to their widespread presence in the environment or through their use in various engineering applications. This review covers recent advances in our understanding of adsorption and chemical reactions mediated by PCM and the links between these processes. It also covers adsorptive processes previously receiving little attention and ignored in models such as steric constraints, physicochemical effects of confinement in nanopores, π interactions of aromatic compounds with polyaromatic surfaces, and very strong hydrogen bonding of ionizable compounds with surface functional groups. Although previous research has regarded carbons merely as passive sorbents, recent studies show that PCM can promote chemical reactions of sorbed contaminants at ordinary temperature, including long-range electron conduction between molecules and between microbes and molecules, local redox reactions between molecules, and hydrolysis. PCM may itself contain redox-active functional groups that are capable of oxidizing or reducing organic compounds and of generating reactive oxygen species (ROS) from oxygen, peroxides, or ozone. Amorphous carbons contain persistent free radicals that may play a role in observed redox reactions and ROS generation. Reactions mediated by PCM can impact the biogeochemical fate of pollutants and lead to useful strategies for remediation.

    View details for DOI 10.1021/acs.est.7b01088

    View details for PubMedID 28753285

  • Reverse Osmosis Shifts Chloramine Speciation Causing Re-Formation of NDMA during Potable Reuse of Wastewater ENVIRONMENTAL SCIENCE & TECHNOLOGY McCurry, D. L., Ishida, K. P., Oelker, G. L., Mitch, W. A. 2017; 51 (15): 8589–96


    UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4+ promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H+ ↔ NHCl2 + NH4+. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.

    View details for PubMedID 28671841

  • Effect of Ozonation and Biological Activated Carbon Treatment of Wastewater Effluents on Formation of N-nitrosamines and Halogenated Disinfection Byproducts. Environmental science & technology Chuang, Y., Mitch, W. A. 2017; 51 (4): 2329-2338


    Ozonation followed by biological activated carbon (O3/BAC) is being considered as a key component of reverse osmosis-free advanced treatment trains for potable wastewater reuse. Using a laboratory-scale O3/BAC system treating two nitrified wastewater effluents, this study characterized the effect of different ozone dosages (0-1.0 mg O3/mg dissolved organic carbon) and BAC empty bed contact times (EBCT; 15-60 min) on the formation after chlorination or chloramination of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), 8 N-nitrosamines, and bromate. DBP concentrations were remarkably similar between the two wastewaters across O3/BAC conditions. Ozonation increased bromate, TCNM, and N-nitrosodimethylamine, but ozonation was less significant for other DBPs. DBP formation generally decreased significantly with BAC treatment at 15 min EBCT, but little further reduction was observed at higher EBCT where low dissolved oxygen concentrations may have limited biological activity. The O3/BAC-treated wastewaters met regulatory levels for trihalomethanes (THMs), haloacetic acids (HAAs), and bromate, although N-nitrosodimethylamine exceeded the California Notification Level in one case. Regulated THMs and HAAs dominated by mass. When DBP concentrations were weighted by measures of their toxic potencies, unregulated haloacetonitriles, haloacetaldehydes, and haloacetamides dominated. Assuming toxicity is additive, the calculated DBP-associated toxicity of the O3/BAC-treated chloraminated effluents were comparable or slightly higher than those calculated in a recent evaluation of Full Advanced Treatment trains incorporating reverse osmosis.

    View details for DOI 10.1021/acs.est.6b04693

    View details for PubMedID 28092936

  • Relative Importance of Different Water Categories as Sources of N-Nitrosamine Precursors ENVIRONMENTAL SCIENCE & TECHNOLOGY Zeng, T., Glover, C. M., Marti, E. J., Woods-Chabane, G. C., Karanfil, T., Mitch, W. A., Dickenson, E. R. 2016; 50 (24): 13239-13248


    A comparison of loadings of N-nitrosamines and their precursors from different source water categories is needed to design effective source water blending strategies. Previous research using Formation Potential (FP) chloramination protocols (high dose and prolonged contact times) raised concerns about precursor loadings from various source water categories, but differences in the protocols employed rendered comparisons difficult. In this study, we applied Uniform Formation Condition (UFC) chloramination and ozonation protocols mimicking typical disinfection practice to compare loadings of ambient specific and total N-nitrosamines as well as chloramine-reactive and ozone-reactive precursors in 47 samples, including 6 pristine headwaters, 16 eutrophic waters, 4 agricultural runoff samples, 9 stormwater runoff samples, and 12 municipal wastewater effluents. N-Nitrosodimethylamine (NDMA) formation from UFC and FP chloramination protocols did not correlate, with NDMA FP often being significant in samples where no NDMA formed under UFC conditions. N-Nitrosamines and their precursors were negligible in pristine headwaters. Conventional, and to a lesser degree, nutrient removal wastewater effluents were the dominant source of NDMA and its chloramine- and ozone-reactive precursors. While wastewater effluents were dominant sources of TONO and their precursors, algal blooms, and to a lesser degree agricultural or stormwater runoff, could be important where they affect a major fraction of the water supply.

    View details for DOI 10.1021/acs.est.6b04650

    View details for Web of Science ID 000390620900009

    View details for PubMedID 27993049

  • Development of an Activated Carbon-Based Electrode for the Capture and Rapid Electrolytic Reductive Debromination of Methyl Bromide from Postharvest Fumigations. Environmental science & technology Li, Y., Liu, C., Cui, Y., Walse, S. S., Olver, R., Zilberman, D., Mitch, W. A. 2016; 50 (20): 11200-11208


    Due to concerns surrounding its ozone depletion potential, there is a need for technologies to capture and destroy methyl bromide (CH3Br) emissions from postharvest fumigations applied to control agricultural pests. Previously, we described a system in which CH3Br fumes vented from fumigation chambers could be captured by granular activated carbon (GAC). The GAC was converted to a cathode by submergence in a high ionic strength solution and connection to the electrical grid, resulting in reductive debromination of the sorbed CH3Br. The GAC bed was drained and dried for reuse to capture and destroy CH3Br fumes from the next fumigation. However, the loose GAC particles and slow kinetics of this primitive electrode necessitated improvements. Here, we report the development of a cathode containing a thin layer of small GAC particles coating carbon cloth as a current distributor. Combining the high sorption potential of GAC for CH3Br with the conductivity of the carbon cloth current distributor, the cathode significantly lowered the total cell resistance and achieved 96% reductive debromination of CH3Br sorbed at 30% by weight to the GAC within 15 h at -1 V applied potential vs standard hydrogen electrode, a time scale and efficiency suitable for postharvest fumigations. The cathode exhibited stable performance over 50 CH3Br capture and destruction cycles. Initial cost estimates indicate that this technique could treat CH3Br fumes at ∼$5/kg, roughly one-third of the cost of current alternatives.

    View details for PubMedID 27611209

  • Development of Predictive Models for the Degradation of Halogenated Disinfection Byproducts during the UV/H2O2 Advanced Oxidation Process ENVIRONMENTAL SCIENCE & TECHNOLOGY Chuang, Y., Parker, K. M., Mitch, W. A. 2016; 50 (20): 11209-11217
  • N-Nitrosamines and halogenated disinfection byproducts in U.S. Full Advanced Treatment trains for potable reuse. Water research Zeng, T., Plewa, M. J., Mitch, W. A. 2016; 101: 176-186


    Water utilities are increasingly considering indirect and direct potable reuse of municipal wastewater effluents. Disinfection byproducts (DBPs), particularly N-nitrosamines, are key contaminants of potential health concern for potable reuse. This study quantified the concentrations of N-nitrosamines and a suite of regulated and unregulated halogenated DBPs across five U.S. potable reuse Full Advanced Treatment trains incorporating microfiltration, reverse osmosis, and UV-based advanced oxidation. Low μg/L concentrations of trihalomethanes, haloacetic acids, dichloroacetonitrile, and dichloroacetamide were detected in the secondary or tertiary wastewater effluents serving as influents to potable reuse treatment trains, while the concentrations of N-nitrosamines were more variable (e.g., <2-320 ng/L for N-nitrosodimethylamine). Ozonation promoted the formation of N-nitrosamines, haloacetaldehydes, and haloacetamides, but biological activated carbon effectively reduced concentrations of these DBPs. Application of chloramines upstream of microfiltration for biofouling control increased DBP concentrations to their highest levels observed along the treatment trains. Reverse osmosis rejected DBPs to varying degrees, ranging from low for some (e.g., N-nitrosamines, trihalomethanes, and haloacetonitriles) to high for other DBPs. UV-based advanced oxidation eliminated N-nitrosamines, but only partially removed halogenated DBPs. Chloramination of the treatment train product waters under simulated distribution system conditions formed additional DBPs, with concentrations often equaling or exceeding those in the treatment train influents. Overall, the concentration profiles of DBPs were fairly consistent within individual treatment trains for sampling campaigns separated by months and across different treatment trains for the same sampling time window. Weighting DBP concentrations by their toxic potencies highlighted the potential significance of haloacetonitriles, which were not effectively removed by reverse osmosis and advanced oxidation, to the DBP-associated toxicity in potable reuse waters.

    View details for DOI 10.1016/j.watres.2016.03.062

    View details for PubMedID 27262122

  • Halogen Radicals Promote the Photodegradation of Microcystins in Estuarine Systems. Environmental science & technology Parker, K. M., Reichwaldt, E. S., Ghadouani, A., Mitch, W. A. 2016; 50 (16): 8505-8513


    The transport of microcystin, a hepatotoxin produced by cyanobacteria (e.g., Microcystis aeruginosa), to estuaries can adversely affect estuarine and coastal ecosystems. We evaluated whether halogen radicals (i.e., reactive halogen species (RHS)) could significantly contribute to microcystin photodegradation during transport within estuaries. Experiments in synthetic and natural water samples demonstrated that the presence of seawater halides increased quantum yields for microcystin indirect photodegradation by factors of 3-6. Additional experiments indicated that photoproduced RHS were responsible for this effect. Despite the fact that dissolved organic matter (DOM) concentrations decreased in more saline waters, the calculated photochemical half-life of microcystin decreased 6-fold with increasing salinity along a freshwater-estuarine transect due to the halide-associated increase in quantum yield. Modeling of microcystin photodegradation along this transect indicated that the time scale for RHS-mediated microcystin photodegradation is comparable to the time scale of transport. Microcystin concentrations decline by ∼98% along the transect when considering photodegradation by RHS, but only by ∼54% if this pathway were ignored. These results suggest the importance of considering RHS-mediated photodegradation in future models of microcystin fate in freshwater-estuarine systems.

    View details for DOI 10.1021/acs.est.6b01801

    View details for PubMedID 27447196

  • Environmental and personal determinants of the uptake of disinfection by-products during swimming ENVIRONMENTAL RESEARCH Font-Ribera, L., Kogevinas, M., Schmalz, C., Zwiener, C., Marco, E., Grimalt, J. O., Liu, J., Zhang, X., Mitch, W., Critelli, R., Naccarati, A., Heederik, D., Spithoven, J., Arjona, L., de Bont, J., Gracia-Lavedan, E., Villanueva, C. M. 2016; 149: 206-215


    Trihalomethanes (THMs) in exhaled breath and trichloroacetic acid (TCAA) in urine are internal dose biomarkers of exposure to disinfection by-products (DBPs) in swimming pools.We assessed how these biomarkers reflect the levels of a battery of DBPs in pool water and trichloramine in air, and evaluated personal determinants.A total of 116 adults swam during 40min in a chlorinated indoor pool. We measured chloroform, bromodichloromethane, dibromochloromethane and bromoform in exhaled breath and TCAA in urine before and after swimming, trichloramine in air and several DBPs in water. Personal determinants included sex, age, body mass index (BMI), distance swum, energy expenditure, heart rate and 12 polymorphisms in GSTT1, GSTZ1 and CYP2E1 genes.Median level of exhaled total THMs and creatinine adjusted urine TCAA increased from 0.5 to 14.4µg/m(3) and from 2.5 to 5.8µmol/mol after swimming, respectively. The increase in exhaled brominated THMs was correlated with brominated THMs, haloacetic acids, haloacetonitriles, haloketones, chloramines, total organic carbon and total organic halogen in water and trichloramine in air. Such correlations were not detected for exhaled chloroform, total THMs or urine TCAA. Exhaled THM increased more in men, urine TCAA increased more in women, and both were affected by exercise intensity. Genetic variants were associated with differential increases in exposure biomarkers.Our findings suggest that, although affected by sex, physical activity and polymorphisms in key metabolizing enzymes, brominated THMs in exhaled breath could be used as a non-invasive DBP exposure biomarker in swimming pools with bromide-containing source waters. This warrants confirmation with new studies.

    View details for DOI 10.1016/j.envres.2016.05.013

    View details for Web of Science ID 000378366000023

    View details for PubMedID 27214136

  • Reductive dehalogenation of disinfection byproducts by an activated carbon-based electrode system WATER RESEARCH Li, Y., Kemper, J. M., Datuin, G., Akey, A., Mitch, W. A., Luthy, R. G. 2016; 98: 354-362


    Low molecular weight, uncharged, halogenated disinfection byproducts (DBPs) are poorly removed by the reverse osmosis and advanced oxidation process treatment units often applied for further treatment of municipal wastewater for potable reuse. Granular activated carbon (GAC) treatment effectively sorbed 22 halogenated DBPs. Conversion of the GAC to a cathode within an electrolysis cell resulted in significant degradation of the 22 halogenated DBPs by reductive electrolysis at -1 V vs. Standard Hydrogen Electrode (SHE). The lowest removal efficiency over 6 h electrolysis was for trichloromethane (chloroform; 47%) but removal efficiencies were >90% for 13 of the 22 DBPs. In all cases, DBP degradation was higher than in electrolysis-free controls, and degradation was verified by the production of halides as reduction products. Activated carbons and charcoal were more effective than graphite for electrolysis, with graphite featuring poor sorption for the DBPs. A subset of halogenated DBPs (e.g., haloacetonitriles, chloropicrin) were degraded upon sorption to the GAC, even without electrolysis. Using chloropicrin as a model, experiments indicated that this loss was attributable to the partial reduction of sorbed chloropicrin from reducing equivalents in the GAC. Reducing equivalents depleted by these reactions could be restored when the GAC was treated by reductive electrolysis. GAC treatment of an advanced treatment train effluent for potable reuse effectively reduced the concentrations of chloroform, bromodichloromethane and dichloroacetonitrile measured in the column influent to below the method detection limits. Treatment of the GAC by reductive electrolysis at -1 V vs. SHE over 12 h resulted in significant degradation of the chloroform (63%), bromodichloromethane (96%) and dichloroacetonitrile (99%) accumulated on the GAC. The results suggest that DBPs in advanced treatment train effluents could be captured and degraded continuously by reductive electrolysis using a GAC-based cathode.

    View details for DOI 10.1016/j.watres.2016.04.019

    View details for Web of Science ID 000376805500039

    View details for PubMedID 27124125

  • Oral intake of ranitidine increases urinary excretion of N-nitrosodimethylamine CARCINOGENESIS Zeng, T., Mitch, W. A. 2016; 37 (6): 625-634


    The H2-receptor antagonist, ranitidine, is among the most widely used pharmaceuticals to treat gastroesophageal reflux disease and peptic ulcers. While previous studies have demonstrated that amines can form N-nitrosamines when exposed to nitrite at stomach-relevant pH, N-nitrosamine formation from ranitidine, an amine-based pharmaceutical, has not been demonstrated under these conditions. In this work, we confirmed the production of N-nitrosodimethylamine (NDMA), a potent carcinogen, by nitrosation of ranitidine under stomach-relevant pH conditions in vitro We also evaluated the urinary NDMA excretion attributable to ingestion of clinically used ranitidine doses. Urine samples collected from five female and five male, healthy adult volunteers over 24-h periods before and after consumption of 150mg ranitidine were analyzed for residual ranitidine, ranitidine metabolites, NDMA, total N-nitrosamines and dimethylamine. Following ranitidine intake, the urinary NDMA excreted over 24h increased 400-folds from 110 to 47 600ng, while total N-nitrosamines increased 5-folds. NDMA excretion rates after ranitidine intake equaled or exceeded those observed previously in patients with schistosomiasis, a disease wherein N-nitrosamines are implicated as the etiological agents for bladder cancer. Due to metabolism within the body, urinary NDMA measurements represent a lower-bound estimate of systemic NDMA exposure. Our results suggest a need to evaluate the risks attributable to NDMA associated with chronic consumption of ranitidine, and to identify alternative treatments that minimize exposure to N-nitrosamines.

    View details for DOI 10.1093/carcin/bgw034

    View details for Web of Science ID 000377915800012

    View details for PubMedID 26992900

  • Halogen radicals contribute to photooxidation in coastal and estuarine waters PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Parker, K. M., Mitch, W. A. 2016; 113 (21): 5868-5873


    Although halogen radicals are recognized to form as products of hydroxyl radical ((•)OH) scavenging by halides, their contribution to the phototransformation of marine organic compounds has received little attention. We demonstrate that, relative to freshwater conditions, seawater halides can increase photodegradation rates of domoic acid, a marine algal toxin, and dimethyl sulfide, a volatile precursor to cloud condensation nuclei, up to fivefold. Using synthetic seawater solutions, we show that the increased photodegradation is specific to dissolved organic matter (DOM) and halides, rather than other seawater salt constituents (e.g., carbonates) or photoactive species (e.g., iron and nitrate). Experiments in synthetic and natural coastal and estuarine water samples demonstrate that the halide-specific increase in photodegradation could be attributed to photochemically generated halogen radicals rather than other photoproduced reactive intermediates [e.g., excited-state triplet DOM ((3)DOM*), reactive oxygen species]. Computational kinetic modeling indicates that seawater halogen radical concentrations are two to three orders of magnitude greater than freshwater (•)OH concentrations and sufficient to account for the observed halide-specific increase in photodegradation. Dark (•)OH generation by gamma radiolysis demonstrates that halogen radical production via (•)OH scavenging by halides is insufficient to explain the observed effect. Using sensitizer models for DOM chromophores, we show that halogen radicals are formed predominantly by direct oxidation of Cl(-) and Br(-) by (3)DOM*, an (•)OH-independent pathway. Our results indicate that halogen radicals significantly contribute to the phototransformation of algal products in coastal or estuarine surface waters.

    View details for DOI 10.1073/pnas.1602595113

    View details for Web of Science ID 000376779900046

    View details for PubMedID 27162335

    View details for PubMedCentralID PMC4889391

  • Structural Modifications to Quaternary Ammonium Polymer Coagulants to Inhibit N-Nitrosamine Formation ENVIRONMENTAL SCIENCE & TECHNOLOGY Zeng, T., Li, R. J., Mitch, W. A. 2016; 50 (9): 4778-4787


    Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) and epichlorohydrin-dimethylamine (Epi-DMA), are commonly used by water utilities to enhance removal of particles and dissolved organic matter (DOM) from raw waters. Unfortunately, chloramination of waters treated with quaternary ammonium polymers leads to the formation of carcinogenic N-nitrosodimethylamine (NDMA). In this study, two approaches were developed to modify polyDADMAC and Epi-DMA to inhibit N-nitrosamine formation. The first approach involved treatment of polymers with methyl iodide (MeI), an alkylating agent, to convert polymer-bound tertiary amine groups to less chloramine-reactive quaternary ammonium groups. The second approach involved synthesis of polymers bearing less chloramine-reactive quaternary ammonium groups with dipropylamino (DPA) substituents. Treatment with MeI reduced NDMA formation from polymers by ∼75%, while synthesis of DPA-based polymers eliminated NDMA formation and formed N-nitrosodipropylamine, which is 10-fold less carcinogenic than NDMA, at 20-fold lower yields. Bench-scale jar tests demonstrated that both MeI-treated and DPA-based polymers achieved similar removal of particles and DOM as the original polyDADMAC and Epi-DMA at both low and high doses, but formed significantly less N-nitrosamines. This work demonstrates two approaches for modifying quaternary ammonium cationic polymers, which may enable water utilities to meet potential future regulations on N-nitrosamines while maintaining polymer usage to meet existing regulations.

    View details for DOI 10.1021/acs.est.6b00602

    View details for Web of Science ID 000375521400022

    View details for PubMedID 27096602

  • Impact of Nitrification on the Formation of N-Nitrosamines and Halogenated Disinfection Byproducts within Distribution System Storage Facilities ENVIRONMENTAL SCIENCE & TECHNOLOGY Zeng, T., Mitch, W. A. 2016; 50 (6): 2964-2973
  • Impact of Nitrification on the Formation of N-Nitrosamines and Halogenated Disinfection Byproducts within Distribution System Storage Facilities. Environmental science & technology Zeng, T., Mitch, W. A. 2016; 50 (6): 2964-2973


    Distribution system storage facilities are a critical, yet often overlooked, component of the urban water infrastructure. This study showed elevated concentrations of N-nitrosodimethylamine (NDMA), total N-nitrosamines (TONO), regulated trihalomethanes (THMs) and haloacetic acids (HAAs), 1,1-dichloropropanone (1,1-DCP), trichloroacetaldehyde (TCAL), haloacetonitriles (HANs), and haloacetamides (HAMs) in waters with ongoing nitrification as compared to non-nitrifying waters in storage facilities within five different chloraminated drinking water distribution systems. The concentrations of NDMA, TONO, HANs, and HAMs in the nitrifying waters further increased upon application of simulated distribution system chloramination. The addition of a nitrifying biofilm sample collected from a nitrifying facility to its non-nitrifying influent water led to increases in N-nitrosamine and halogenated DBP formation, suggesting the release of precursors from nitrifying biofilms. Periodic treatment of two nitrifying facilities with breakpoint chlorination (BPC) temporarily suppressed nitrification and reduced precursor levels for N-nitrosamines, HANs, and HAMs, as reflected by lower concentrations of these DBPs measured after re-establishment of a chloramine residual within the facilities than prior to the BPC treatment. However, BPC promoted the formation of halogenated DBPs while a free chlorine residual was maintained. Strategies that minimize application of free chlorine while preventing nitrification are needed to control DBP precursor release in storage facilities.

    View details for DOI 10.1021/acs.est.5b05668

    View details for PubMedID 26859842

  • Ozone Promotes Chloropicrin Formation by Oxidizing Amines to Nitro Compounds. Environmental science & technology McCurry, D. L., Quay, A. N., Mitch, W. A. 2016; 50 (3): 1209-1217


    Chloropicrin formation has been associated with ozonation followed by chlorination, but the reaction pathway and precursors have been poorly characterized. Experiments with methylamine demonstrated that ozonation converts methylamine to nitromethane at ∼100% yield. Subsequent chlorination converts nitromethane to chloropicrin at ∼50% yield under the conditions evaluated. Similarly high yields from other primary amines were limited to those with functional groups on the β-carbon (e.g., the carboxylic acid in glycine) that facilitate carbon-carbon bond cleavage to release nitromethyl anion. Secondary amines featuring these reactive primary amines as functional groups (e.g., secondary N-methylamines) formed chloropicrin at high yields, likely by facile dealkylation to release the primary nitro compound. Chloropicrin yields from tertiary amines were low. Natural water experiments, including derivatization to transform primary and secondary amines to less reactive carbamate functional groups, indicated that primary and secondary amines were the dominant chloropicrin precursors during ozonation/chlorination. Ozonation followed by chlorination of the primary amine side chain of lysine demonstrated low yields (∼0.2%) of chloropicrin, but high yields (∼17%) of dichloronitrolysine, a halonitroalkane structural analogue to chloropicrin. However, chloropicrin yields increased and dichloronitrolysine yields decreased in the absence of hydroxyl radical scavengers, suggesting that future research should characterize the potential occurrence of such halonitroalkane analogues relative to natural radical scavenger (e.g., carbonate) concentrations.

    View details for DOI 10.1021/acs.est.5b04282

    View details for PubMedID 26752338

  • Effect of matrix components on UV/H2O2 and UV/S2O8(2-) advanced oxidation processes for trace organic degradation in reverse osmosis brines from municipal wastewater reuse facilities. Water research Yang, Y., Pignatello, J. J., Ma, J., Mitch, W. A. 2016; 89: 192-200


    When reverse osmosis brines from potable wastewater reuse plants are discharged to poorly-flushed estuaries, the concentrated organic contaminants are a concern for receiving water ecosystems. UV/hydrogen peroxide (UV/H2O2) and UV/persulfate (UV/S2O8(2-)) advanced oxidation processes (AOPs) may reduce contaminant burdens prior to discharge, but the effects of the high levels of halide, carbonate and effluent organic matter (EfOM) normally present in these brines are unclear. On the one hand, these substances may reduce process efficiency by scavenging reactive oxygen species (ROS), hydroxyl (OH) and sulfate (SO4(-) radicals. On the other, the daughter radicals generated by halide and carbonate scavenging may themselves degrade organics, offsetting the effect of ROS scavenging. UV/H2O2 and UV/S2O8(2-) AOPs were compared for degradation of five pharmaceuticals spiked into brines obtained from two reuse facilities and the RO influent from one of them. For UV/H2O2, EfOM scavenged ∼75% of the OH, reducing the degradation efficiency of the target contaminants to a similar extent; halide and carbonate scavenging and the reactivities of associated daughter radicals were less important. For UV/S2O8(2-), anions (mostly Cl(-)) scavenged ∼93% of the SO4(-). Because daughter radicals of Cl(-) contributed to contaminant degradation, the reduction in contaminant degradation efficiency was only ∼75-80%, with the reduction driven by daughter radical scavenging by EfOM. Conversion of SO4(-) to more selective halogen and carbonate radicals resulted in a wider range of degradation efficiencies among the contaminants. For both AOPs, 250 mJ/cm(2) average fluence achieved significant removal of four pharmaceuticals, with significantly better performance by UV/S2O8(2-) treatment for some constituents. Accounting for the lower brine flowrates, the energy output to achieve this fluence in brines is comparable to that often applied to RO permeates. However, much higher fluence was required for the least reactive pharmaceutical. Comparing AOP application to the RO influent or brine, equal or greater removal was achieved for brine treatment for comparable energy input. AOP treatment of brines could be applied to reduce, but not eliminate, contaminant burdens prior to discharge.

    View details for DOI 10.1016/j.watres.2015.11.049

    View details for PubMedID 26657355

  • Influence of Bi-doping on Mn1-xBixFe2O4 catalytic ozonation of di-n-butyl phthalate CHEMICAL ENGINEERING JOURNAL Ren, Y., Chen, Y., Zeng, T., Feng, J., Ma, J., Mitch, W. A. 2016; 283: 622-630
  • Control of nitrosamines during non-potable and de facto wastewater reuse with medium pressure ultraviolet light and preformed monochloramine ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY McCurry, D. L., Krasner, S. W., Mitch, W. A. 2016; 2 (3): 502-510

    View details for DOI 10.1039/c6ew00044d

    View details for Web of Science ID 000376360300008

  • Formation Pathways and Trade-Offs between Haloacetamides and Haloacetaldehydes during Combined Chlorination and Chloramination of Lignin Phenols and Natural Waters ENVIRONMENTAL SCIENCE & TECHNOLOGY Chuang, Y., McCurry, D. L., Tung, H., Mitch, W. A. 2015; 49 (24): 14432-14440

    View details for DOI 10.1021/acs.est.5b04783

    View details for Web of Science ID 000366872300064

    View details for PubMedID 26571080

  • Degradation of Amino Acids and Structure in Model Proteins and Bacteriophage MS2 by Chlorine, Bromine, and Ozone. Environmental science & technology Choe, J. K., Richards, D. H., Wilson, C. J., Mitch, W. A. 2015; 49 (22): 13331-13339

    View details for DOI 10.1021/acs.est.5b03813

    View details for PubMedID 26488608

  • Contribution of N-Nitrosamines and Their Precursors to Domestic Sewage by Greywaters and Blackwaters. Environmental science & technology Zeng, T., Mitch, W. A. 2015; 49 (22): 13158-13167

    View details for DOI 10.1021/acs.est.5b04254

    View details for PubMedID 26496512

  • Determinants of disinfectant pretreatment efficacy for nitrosamine control in chloraminated drinking water. Water research McCurry, D. L., Krasner, S. W., von Gunten, U., Mitch, W. A. 2015; 84: 161-170


    Utilities using chloramines need strategies to mitigate nitrosamine formation to meet potential future nitrosamine regulations. The ability to reduce NDMA formation under typical post-chloramination conditions of pretreatment with ultraviolet light from a low pressure mercury lamp (LPUV), free chlorine (HOCl), ozone (O3), and UV light from a medium pressure mercury lamp (MPUV) were compared at exposures relevant to drinking water treatment. The order of efficacy after application to waters impacted by upstream wastewater discharges was O3 > HOCl ≈ MPUV > LPUV. NDMA precursor abatement generally did not correlate well between oxidants, and waters exhibited different behaviors with respect to pH and temperature, suggesting a variety of source-dependent NDMA precursors. For wastewater-impacted waters, the observed pH dependence for precursor abatement suggested the important role of secondary or tertiary amine precursors. Although hydroxyl radicals did not appear to be important for NDMA precursor abatement during O3 or MPUV pretreatment, the efficacy of MPUV correlated strongly with dissolved organic carbon concentration (p = 0.01), suggesting alternative indirect photochemical pathways. The temperature dependences during pre- and post-disinfection indicated that NDMA formation is likely to increase during warm seasons for O3 pretreatment, decrease for HOCl pretreatment, and remain unchanged for MPUV treatment, although seasonal changes in source water quality may counteract the temperature effects. For two waters impacted by relatively high polyDADMAC coagulant doses, pretreatment with HOCl, O3, and MPUV increased NDMA formation during post-chloramination. For O3 pretreatment, hydroxyl radicals likely led to precursor formation from the polymer in the latter tests. MPUV treatment of polymer-impacted water increased subsequent NDMA formation through an indirect photochemical process. Many factors may mitigate the importance of this increased NDMA formation, including the low polyDADMAC doses typically applied, and simultaneous degradation of watershed-associated precursors.

    View details for DOI 10.1016/j.watres.2015.07.024

    View details for PubMedID 26232674

  • Influence of Dissolved Metals on N-Nitrosamine Formation under Amine-based CO2 Capture Conditions ENVIRONMENTAL SCIENCE & TECHNOLOGY Wang, Z., Mitch, W. A. 2015; 49 (19): 11974-11981


    As the prime contender for postcombustion CO2 capture technology, amine-based scrubbing has to address the concerns over the formation of potentially carcinogenic N-nitrosamine byproducts from reactions between flue gas NOx and amine solvents. This bench-scale study evaluated the influence of dissolved metals on the potential to form total N-nitrosamines in the solvent within the absorber unit and upon a pressure-cooker treatment that mimics desorber conditions. Among six transition metals tested for the benchmark solvent monoethanolamine (MEA), dissolved Cu promoted total N-nitrosamine formation in the absorber unit at concentrations permitted in drinking water, but not the desorber unit. The Cu effect increased with oxygen concentration. Variation of the amine structural characteristics (amine order, steric hindrance, -OH group substitution and alkyl chain length) indicated that Cu promotes N-nitrosamine formation from primary amines with hydroxyl or carboxyl groups (amino acids), but not from secondary amines, tertiary amines, sterically hindered primary amines, or amines without oxygenated groups. Ethylenediaminetetraacetate (EDTA) suppressed the Cu effect. The results suggested that the catalytic effect of Cu may be associated with the oxidative degradation of primary amines in the absorber unit, a process known to produce a wide spectrum of secondary amine products that are more readily nitrosatable than the pristine primary amines, and that can form stable N-nitrosamines. This study highlighted an intriguing linkage between amine degradation (operational cost) and N-nitrosamine formation (health hazards), all of which are challenges for commercial-scale CO2 capture technology.

    View details for DOI 10.1021/acs.est.5b03085

    View details for Web of Science ID 000362629100083

    View details for PubMedID 26335609

  • Leveraging the Mechanism of Oxidative Decay for Adenylate Kinase to Design Structural and Functional Resistances ACS CHEMICAL BIOLOGY Howell, S. C., Richards, D. H., Mitch, W. A., Wilson, C. J. 2015; 10 (10): 2393-2404

    View details for DOI 10.1021/acschembio.5b00431

    View details for Web of Science ID 000363225100024

    View details for PubMedID 26266833

  • Controlling Nitrosamines, Nitramines, and Amines in Amine-Based CO2 Capture Systems with Continuous Ultraviolet and Ozone Treatment of Washwater ENVIRONMENTAL SCIENCE & TECHNOLOGY Dai, N., Mitch, W. A. 2015; 49 (14): 8878-8886


    Formation of nitrosamines and nitramines from reactions between flue gas NOx and the amines used in CO2 capture units has arisen as a significant concern. Washwater scrubbers can capture nitrosamines and nitramines. They can also capture amines, preventing formation of nitrosamines and nitramines downwind by amine reactions with ambient NOx. The continuous application of UV alone, or a combination of UV and ozone to the return line of a washwater treatment unit was evaluated to control the accumulation of nitrosamines, nitramines and amines in a laboratory-scale washwater unit. With model secondary amine solvents ranging from nonvolatile diethanolamine to volatile morpholine, application of 272-537 mJ/cm(2) UV incident fluence alone reduced the accumulation of nitrosamines and nitramines by approximately an order of magnitude. Modeling indicated that the gains achieved by UV treatment should increase over time, because UV treatment converts the time dependence of nitrosamine accumulation from a quadratic to a linear function. Ozone (21 mg/L) maintained low steady-state concentrations of amines in the washwater. While modeling indicated that more than 80% of nitrosamine accumulation in the washwater was associated with reaction of washwater amines with residual NOx, a reduction in nitrosamine accumulation rates due to ozone oxidation of amines was not fully realized because the ozonation products of amines reduced nitrosamine photolysis rates by competing for photons.

    View details for DOI 10.1021/acs.est.5b01365

    View details for Web of Science ID 000358557900070

  • Controlling Nitrosamines, Nitramines, and Amines in Amine-Based CO2 Capture Systems with Continuous Ultraviolet and Ozone Treatment of Washwater. Environmental science & technology Dai, N., Mitch, W. A. 2015; 49 (14): 8878-86


    Formation of nitrosamines and nitramines from reactions between flue gas NOx and the amines used in CO2 capture units has arisen as a significant concern. Washwater scrubbers can capture nitrosamines and nitramines. They can also capture amines, preventing formation of nitrosamines and nitramines downwind by amine reactions with ambient NOx. The continuous application of UV alone, or a combination of UV and ozone to the return line of a washwater treatment unit was evaluated to control the accumulation of nitrosamines, nitramines and amines in a laboratory-scale washwater unit. With model secondary amine solvents ranging from nonvolatile diethanolamine to volatile morpholine, application of 272-537 mJ/cm(2) UV incident fluence alone reduced the accumulation of nitrosamines and nitramines by approximately an order of magnitude. Modeling indicated that the gains achieved by UV treatment should increase over time, because UV treatment converts the time dependence of nitrosamine accumulation from a quadratic to a linear function. Ozone (21 mg/L) maintained low steady-state concentrations of amines in the washwater. While modeling indicated that more than 80% of nitrosamine accumulation in the washwater was associated with reaction of washwater amines with residual NOx, a reduction in nitrosamine accumulation rates due to ozone oxidation of amines was not fully realized because the ozonation products of amines reduced nitrosamine photolysis rates by competing for photons.

    View details for DOI 10.1021/acs.est.5b01365

    View details for PubMedID 26087660

  • Destruction of methyl bromide sorbed to activated carbon by thiosulfate or electrolysis. Environmental science & technology Yang, Y., Li, Y., Walse, S. S., Mitch, W. A. 2015; 49 (7): 4515-4521


    Methyl bromide (CH3Br) is widely used as a fumigant for postharvest and quarantine applications for agricultural products at port facilities due to the short treatment period required, but it is vented from fumigation chambers to the atmosphere after its use. Due to the potential contributions of CH3Br to stratospheric ozone depletion, technologies for the capture and degradation of the CH3Br are needed to enable its continued use. Although granular activated carbon (GAC) has been used for CH3Br capture and thiosulfate has been used for destruction of CH3Br in aqueous solution, this research explored techniques for direct destruction of CH3Br sorbed to GAC. Submerging the GAC in an aqueous thiosulfate solution achieved debromination of CH3Br while sorbed to the GAC, but it required molar concentrations of thiosulfate because of the high CH3Br loading and produced substantial concentrations of methyl thiosulfate. Submergence of the GAC in water and use of the GAC as the cathode of an electrolysis unit also debrominated sorbed CH3Br. The reaction appeared to involve a one-electron transfer, producing methyl radicals that incorporated into the GAC. Destruction rates increased with decreasing applied voltage down to ∼-1.2 V vs the standard hydrogen electrode. Cycling experiments conducted at -0.77 V indicated that >80% debromination of CH3Br was achieved over ∼30 h with ∼100% Coulombic efficiency. Sorptive capacity and degradation efficiency were maintained over at least 3 cycles. Capture of CH3Br fumes from fumigation chambers onto GAC, and electrolytic destruction of the sorbed CH3Br could mitigate the negative impacts of CH3Br usage pending the development of suitable replacement fumigants.

    View details for DOI 10.1021/es505709c

    View details for PubMedID 25789797

  • Reduction of Nitroaromatics Sorbed to Black Carbon by Direct Reaction with Sorbed Sulfides ENVIRONMENTAL SCIENCE & TECHNOLOGY Xu, W., Pignatello, J. J., Mitch, W. A. 2015; 49 (6): 3419-3426


    Sorption to black carbons is an important sink for organic contaminants in sediments. Previous research has suggested that black carbons (graphite, activated carbon, and biochar) mediate the degradation of nitrated compounds by sulfides by at least two different pathways: reduction involving electron transfer from sulfides through conductive carbon regions to the target contaminant (nitroglycerin) and degradation by sulfur-based intermediates formed by sulfide oxidation (RDX). In this study, we evaluated the applicability of black carbon-mediated reactions to a wider variety of contaminant structures, including nitrated and halogenated aromatic compounds, halogenated heterocyclic aromatic compounds, and halogenated alkanes. Among these compounds, black carbon-mediated transformation by sulfides over a 3-day time scale was limited to nitroaromatic compounds. The reaction for a series of substituted nitroaromatics proceeded by reduction, as indicated by formation of 3-bromoaniline from 3-bromonitrobenzene, and inverse correlation of log kobs with energy of the lowest unoccupied molecular orbital (ELUMO). The log kobs was correlated with sorbed sulfide concentration, but no reduction of 3-bromonitrobenzene was observed in the presence of graphite and sulfite, thiosulfate, or polysulfides. Whereas nitroglycerin reduction occurred in an electrochemical cell containing sheet graphite electrodes in which the reagents were placed in separate compartments, nitroaromatic reduction only occurred when sulfides were present in the same compartment. The results suggest that black carbon-mediated reduction of sorbed nitroaromatics by sulfides involves electron transfer directly from sorbed sulfides rather than transfer of electrons through conductive carbon regions. The existence of three different reaction pathways suggests a complexity to the sulfide-carbon system compared to the iron-carbon system, where contaminants are reduced by electron transfer through conductive carbon regions.

    View details for DOI 10.1021/es5045198

    View details for Web of Science ID 000351324400019

    View details for PubMedID 25671390

  • Predicting N-Nitrosamines: N-Nitrosodiethanolamine as a Significant Component of Total N-Nitrosamines in Recycled Wastewater ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS Dai, N., Zeng, T., Mitch, W. A. 2015; 2 (3): 54-58
  • Iodide, Bromide, and Ammonium in Hydraulic Fracturing and Oil and Gas Wastewaters: Environmental Implications ENVIRONMENTAL SCIENCE & TECHNOLOGY Harkness, J. S., Dwyer, G. S., Warner, N. R., Parker, K. M., Mitch, W. A., Vengosh, A. 2015; 49 (3): 1955-1963


    The expansion of unconventional shale gas and hydraulic fracturing has increased the volume of the oil and gas wastewater (OGW) generated in the U.S. Here we demonstrate that OGW from Marcellus and Fayetteville hydraulic fracturing flowback fluids and Appalachian conventional produced waters is characterized by high chloride, bromide, iodide (up to 56 mg/L), and ammonium (up to 420 mg/L). Br/Cl ratios were consistent for all Appalachian brines, which reflect an origin from a common parent brine, while the I/Cl and NH4/Cl ratios varied among brines from different geological formations, reflecting geogenic processes. There were no differences in halides and ammonium concentrations between OGW originating from hydraulic fracturing and conventional oil and gas operations. Analysis of discharged effluents from three brine treatment sites in Pennsylvania and a spill site in West Virginia show elevated levels of halides (iodide up to 28 mg/L) and ammonium (12 to 106 mg/L) that mimic the composition of OGW and mix conservatively in downstream surface waters. Bromide, iodide, and ammonium in surface waters can impact stream ecosystems and promote the formation of toxic brominated-, iodinated-, and nitrogen disinfection byproducts during chlorination at downstream drinking water treatment plants. Our findings indicate that discharge and accidental spills of OGW to waterways pose risks to both human health and the environment.

    View details for DOI 10.1021/es504654n

    View details for Web of Science ID 000349060300086

    View details for PubMedID 25587644

  • Synthesis and Application of a Quaternary Phosphonium Polymer Coagulant To Avoid N-Nitrosamine Formation ENVIRONMENTAL SCIENCE & TECHNOLOGY Zeng, T., Pignatello, J. J., Li, R. J., Mitch, W. A. 2014; 48 (22): 13392-13401

    View details for DOI 10.1021/es504091s

    View details for Web of Science ID 000345262900045

  • Synthesis and application of a quaternary phosphonium polymer coagulant to avoid N-nitrosamine formation. Environmental science & technology Zeng, T., Pignatello, J. J., Li, R. J., Mitch, W. A. 2014; 48 (22): 13392-13401


    Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) are widely used for coagulating and removing negatively charged particles and dissolved organic matter (DOM) from drinking water. Their use, however, has been linked to the formation of carcinogenic N-nitrosamines as byproducts during chloramine-based drinking water disinfection. In this study, a novel quaternary phosphonium cationic polymer, poly(diallyldiethylphosphonium chloride) (polyDADEPC), was synthesized such that the quaternary nitrogen atom of polyDADMAC was substituted with a phosphorus atom. Formation potential tests revealed that even under strong nitrosation conditions, polyDADEPC and related lower-order P-based compounds formed oxygenated and not nitrosated products. Bench-scale jar tests using three different source waters further demonstrated that polyDADEPC achieved coagulation performance comparable to commercial polyDADMACs for particle and DOM removals within the typical dose range used for drinking water treatment. This work highlights the potential use of a phosphonium coagulant polymer, polyDADEPC, as a viable alternative to polyDADMAC to avoid nitrosated byproduct formation during chloramination.

    View details for DOI 10.1021/es504091s

    View details for PubMedID 25322258

  • Superior Removal of Disinfection Byproduct Precursors and Pharmaceuticals from Wastewater in a Staged Anaerobic Fluidized Membrane Bioreactor Compared to Activated Sludge ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS McCurry, D. L., Bear, S. E., Bae, J., Sedlak, D. L., McCarty, P. L., Mitch, W. A. 2014; 1 (11): 459-464

    View details for DOI 10.1021/ez500279a

    View details for Web of Science ID 000350831700005

  • Impact of UV/H2O2 Pre-Oxidation on the Formation of Haloacetamides and Other Nitrogenous Disinfection Byproducts during Chlorination ENVIRONMENTAL SCIENCE & TECHNOLOGY Chu, W., Gao, N., Yin, D., Krasner, S. W., Mitch, W. A. 2014; 48 (20): 12190-12198

    View details for DOI 10.1021/es502115x

    View details for Web of Science ID 000343640900054

  • Enhanced Formation of Disinfection Byproducts in Shale Gas Wastewater-Impacted Drinking Water Supplies ENVIRONMENTAL SCIENCE & TECHNOLOGY Parker, K. M., Zeng, T., Harkness, J., Vengosh, A., Mitch, W. A. 2014; 48 (19): 11161-11169

    View details for DOI 10.1021/es5028184

    View details for Web of Science ID 000343016600020

  • Enhanced formation of disinfection byproducts in shale gas wastewater-impacted drinking water supplies. Environmental science & technology Parker, K. M., Zeng, T., Harkness, J., Vengosh, A., Mitch, W. A. 2014; 48 (19): 11161-11169


    The disposal and leaks of hydraulic fracturing wastewater (HFW) to the environment pose human health risks. Since HFW is typically characterized by elevated salinity, concerns have been raised whether the high bromide and iodide in HFW may promote the formation of disinfection byproducts (DBPs) and alter their speciation to more toxic brominated and iodinated analogues. This study evaluated the minimum volume percentage of two Marcellus Shale and one Fayetteville Shale HFWs diluted by fresh water collected from the Ohio and Allegheny Rivers that would generate and/or alter the formation and speciation of DBPs following chlorination, chloramination, and ozonation treatments of the blended solutions. During chlorination, dilutions as low as 0.01% HFW altered the speciation toward formation of brominated and iodinated trihalomethanes (THMs) and brominated haloacetonitriles (HANs), and dilutions as low as 0.03% increased the overall formation of both compound classes. The increase in bromide concentration associated with 0.01-0.03% contribution of Marcellus HFW (a range of 70-200 μg/L for HFW with bromide = 600 mg/L) mimics the increased bromide levels observed in western Pennsylvanian surface waters following the Marcellus Shale gas production boom. Chloramination reduced HAN and regulated THM formation; however, iodinated trihalomethane formation was observed at lower pH. For municipal wastewater-impacted river water, the presence of 0.1% HFW increased the formation of N-nitrosodimethylamine (NDMA) during chloramination, particularly for the high iodide (54 ppm) Fayetteville Shale HFW. Finally, ozonation of 0.01-0.03% HFW-impacted river water resulted in significant increases in bromate formation. The results suggest that total elimination of HFW discharge and/or installation of halide-specific removal techniques in centralized brine treatment facilities may be a better strategy to mitigate impacts on downstream drinking water treatment plants than altering disinfection strategies. The potential formation of multiple DBPs in drinking water utilities in areas of shale gas development requires comprehensive monitoring plans beyond the common regulated DBPs.

    View details for DOI 10.1021/es5028184

    View details for PubMedID 25203743

  • Comparative in Vitro Toxicity of Nitrosamines and Nitramines Associated with Amine-based Carbon Capture and Storage ENVIRONMENTAL SCIENCE & TECHNOLOGY Wagner, E. D., Osiol, J., Mitch, W. A., Plewa, M. J. 2014; 48 (14): 8203-8211


    Amine-based CO2 capture is a prime contender for the first full-scale implementation of CO2 capture at fossil fuel-fired power plants postcombustion. However, the formation of potentially carcinogenic N-nitrosamines and N-nitramines from reactions of flue gas NOx with the amines presents a potential risk for contaminating airsheds and drinking water supplies. Setting regulatory emission limits is hampered by the dearth of toxicity information for the N-nitramines. This study employed quantitative in vitro bioassays for mutagenicity in Salmonella typhimurium, and chronic cytotoxicity and acute genotoxicity in Chinese hamster ovary (CHO) cells to compare the toxicity of analogous N-nitrosamines and N-nitramines relevant to CO2 capture. Although the rank order was similar for genotoxicity in CHO cells and mutagenicity in S. typhimurium, the Salmonella assay was far more sensitive. In general, mutagenicity was higher with S9 hepatic microsomal activation. The rank order of mutagenicity was N-nitrosodimethylamine (NDMA)>N-nitrosomorpholine>N-nitrodimethylamine>1,4-dinitrosopiperazine>N-nitromorpholine>1,4-dinitropiperazine>N-nitromonoethanolamine>N-nitrosodiethanolamine>N-nitrodiethanolamine. 1-Nitrosopiperazine and 1-nitropiperazine were not mutagenic. Overall, N-nitrosamines were ∼15-fold more mutagenic than their N-nitramine analogues.

    View details for DOI 10.1021/es5018009

    View details for Web of Science ID 000339227500065

    View details for PubMedID 24940705

  • Effects of Flue Gas Compositions on Nitrosamine and Nitramine Formation in Postcombustion CO2 Capture Systems ENVIRONMENTAL SCIENCE & TECHNOLOGY Dai, N., Mitch, W. A. 2014; 48 (13): 7519-7526

    View details for DOI 10.1021/es501864a

    View details for Web of Science ID 000338488700041

  • Sunlight-Driven Photochemical Halogenation of Dissolved Organic Matter in Seawater: A Natural Abiotic Source of Organobromine and Organoiodine ENVIRONMENTAL SCIENCE & TECHNOLOGY Diego Mendez-Diaz, J., Shimabuku, K. K., Ma, J., Enumah, Z. O., Pignatello, J. J., Mitch, W. A., Dodd, M. C. 2014; 48 (13): 7418-7427


    Reactions of dissolved organic matter (DOM) with photochemically generated reactive halogen species (RHS) may represent an important natural source of organohalogens within surface seawaters. However, investigation of such processes has been limited by difficulties in quantifying low dissolved organohalogen concentrations in the presence of background inorganic halides. In this work, sequential solid phase extraction (SPE) and silver-form cation exchange filtration were utilized to desalt and preconcentrate seawater DOM prior to nonspecific organohalogen analysis by ICP-MS. Using this approach, native organobromine and organoiodine contents were found to range from 3.2-6.4 × 10(-4) mol Br/mol C and 1.1-3.8 × 10(-4) mol I/mol C (or 19-160 nmol Br L(-1) and 6-36 nmol I L(-1)) within a wide variety of natural seawater samples, compared with 0.6-1.2 × 10(-4) mol Br/mol C and 0.6-1.1 × 10(-5) mol I/mol C in terrestrial natural organic matter (NOM) isolates. Together with a chemical probe method specific for RHS, the SPE+ICP-MS approach was also employed to demonstrate formation of nanomolar levels of organobromine and organoiodine during simulated and natural solar irradiation of DOM in artificial and natural seawaters. In a typical experiment, the organobromine content of 2.1 × 10(-4) mol C L(-1) (2.5 mg C L(-1)) of Suwannee River NOM in artificial seawater increased by 69% (from 5.9 × 10(-5) to 1.0 × 10(-4) mol Br/mol C) during exposure to 24 h of simulated sunlight. Increasing I(-) concentrations (up to 2.0 × 10(-7) mol L(-1)) promoted increases of up to 460% in organoiodine content (from 8.5 × 10(-6) to 4.8 × 10(-5) mol I/mol C) at the expense of organobromine formation under the same conditions. The results reported herein suggest that sunlight-driven reactions of RHS with DOM may play a significant role in marine bromine and iodine cycling.

    View details for DOI 10.1021/es5016668

    View details for Web of Science ID 000338488700029

  • Effect of Chemical Oxidation on the Sorption Tendency of Dissolved Organic Matter to a Model Hydrophobic Surface ENVIRONMENTAL SCIENCE & TECHNOLOGY Zeng, T., Wilson, C. J., Mitch, W. A. 2014; 48 (9): 5118-5126


    The application of chemical oxidants may alter the sorption properties of dissolved organic matter (DOM), such as humic and fulvic acids, proteins, polysaccharides, and lipids, affecting their fate in water treatment processes, including attachment to other organic components, activated carbon, and membranes (e.g., organic fouling). Similar reactions with chlorine (HOCl) and bromine (HOBr) produced at inflammatory sites in vivo affect the fate of biomolecules (e.g., protein aggregation). In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to evaluate changes in the noncovalent interactions of proteins, polysaccharides, fatty acids, and humic and fulvic acids with a model hydrophobic surface as a function of increasing doses of HOCl, HOBr, and ozone (O3). All three oxidants enhanced the sorption tendency of proteins to the hydrophobic surface at low doses but reduced their sorption tendency at high doses. All three oxidants reduced the sorption tendency of polysaccharides and fatty acids to the hydrophobic surface. HOCl and HOBr increased the sorption tendency of humic and fulvic acids to the hydrophobic surface with maxima at moderate doses, while O3 decreased their sorption tendency. The behavior observed with two water samples was similar to that observed with humic and fulvic acids, pointing to the importance of these constituents. For chlorination, the highest sorption tendency to the hydrophobic surface was observed within the range of doses typically applied during water treatment. These results suggest that ozone pretreatment would minimize membrane fouling by DOM, while chlorine pretreatment would promote DOM removal by activated carbon.

    View details for DOI 10.1021/es405257b

    View details for Web of Science ID 000335720100058

    View details for PubMedID 24697505

  • Comparison of Halide Impacts on the Efficiency of Contaminant Degradation by Sulfate and Hydroxyl Radical-Based Advanced Oxidation Processes (AOPs) ENVIRONMENTAL SCIENCE & TECHNOLOGY Yang, Y., Pignatello, J. J., Ma, J., Mitch, W. A. 2014; 48 (4): 2344-2351


    The effect of halides on organic contaminant destruction efficiency was compared for UV/H2O2 and UV/S2O8(2-) AOP treatments of saline waters; benzoic acid, 3-cyclohexene-1-carboxylic acid, and cyclohexanecarboxylic acid were used as models for aromatic, alkene, and alkane constituents of naphthenic acids in oil-field waters. In model freshwater, contaminant degradation was higher by UV/S2O8(2-) because of the higher quantum efficiency for S2O8(2-) than H2O2 photolysis. The conversion of (•)OH and SO4(•-) radicals to less reactive halogen radicals in the presence of seawater halides reduced the degradation efficiency of benzoic acid and cyclohexanecarboxylic acid. The UV/S2O8(2-) AOP was more affected by Cl(-) than the UV/H2O2 AOP because oxidation of Cl(-) is more favorable by SO4(•-) than (•)OH at pH 7. Degradation of 3-cyclohexene-1-carboxylic acid, was not affected by halides, likely because of the high reactivity of halogen radicals with alkenes. Despite its relatively low concentration in saline waters compared to Cl(-), Br(-) was particularly important. Br(-) promoted halogen radical formation for both AOPs resulting in ClBr(•-), Br2(•-), and CO3(•-) concentrations orders of magnitude higher than (•)OH and SO4(•-) concentrations and reducing differences in halide impacts between the two AOPs. Kinetic modeling of the UV/H2O2 AOP indicated a synergism between Br(-) and Cl(-), with Br(-) scavenging of (•)OH leading to BrOH(•-), and further reactions of Cl(-) with this and other brominated radicals promoting halogen radical concentrations. In contaminant mixtures, the conversion of (•)OH and SO4(•-) radicals to more selective CO3(•-) and halogen radicals favored attack on highly reactive reaction centers represented by the alkene group of 3-cyclohexene-1-carboxylic acid and the aromatic group of the model compound, 2,4-dihydroxybenzoic acid, at the expense of less reactive reaction centers such as aromatic rings and alkane groups represented in benzoic acid and cyclohexanecarboxylic acid. This effect was more pronounced for the UV/S2O8(2-) AOP.

    View details for DOI 10.1021/es404118q

    View details for Web of Science ID 000331774100031

    View details for PubMedID 24479380

  • Influence of Amine Structural Characteristics on N-Nitrosamine Formation Potential Relevant to Postcombustion CO2 Capture Systems ENVIRONMENTAL SCIENCE & TECHNOLOGY Dai, N., Mitch, W. A. 2013; 47 (22): 13175-13183


    Concerns have arisen for the possible contamination of air or drinking water supplies downwind of amine-based CO2 capture facilities by potentially carcinogenic N-nitrosamines formed from reactions between flue gas NOx and amine solvents. This study evaluated the influence of amine structure on the potential to form total N-nitrosamines within the absorber and washwater units of a laboratory-scale CO2 capture reactor, and in the solvent after a pressure-cooker treatment as a mimic of desorber conditions. Among 16 amines representing 3 amine classes (alkanolamines, straight-chain and cyclic diamines, and amino acids), the order of the amine was the primary determinant of total N-nitrosamine formation in the absorber unit, with total N-nitrosamine formation in the order: secondary amines ≈ tertiary amines ≫ primary amines. Similar results were observed upon pressure-cooker treatment, due to reactions between nitrite and amines at high temperature. For secondary and tertiary amines, total N-nitrosamine formation under these desorber-like conditions appeared to be more important than in the absorber, but for primary amines, significant formation of total N-nitrosamines was only observed in the absorber. For diamines and amino acids, total N-nitrosamine accumulation rates in washwaters were lowest for primary amines. For alkanolamines, however, total N-nitrosamine accumulation in the washwater was similar regardless of alkanolamine order, due to the combined effects of amine reactivity toward nitrosation and amine volatility. While total N-nitrosamine accumulation rates in washwaters were generally 1-2 orders of magnitude lower than in the absorber, they were comparable to absorber rates for several primary amines. Decarboxylation of the amino acid sarcosine resulted in the accumulation of significant concentrations of N-nitrosodimethylamine and N-nitrodimethylamine in the washwater.

    View details for DOI 10.1021/es4035396

    View details for Web of Science ID 000327360600069

    View details for PubMedID 24138561

  • Influence of ionic strength on triplet-state natural organic matter loss by energy transfer and electron transfer pathways. Environmental science & technology Parker, K. M., Pignatello, J. J., Mitch, W. A. 2013; 47 (19): 10987-10994


    Triplet state excited natural organic matter chromophores ((3)NOM*) are important reactive intermediates in indirect photochemical processes, yet the impact of salt concentrations relevant to estuarine and marine environments on (3)NOM* is poorly understood. The formation rates, pseudo-first-order loss rate constants, and steady-state concentration of (3)NOM* were monitored using the sorbate probe method in synthetic matrices with increasing ionic strength (IS) to seawater values using seawater halides or other salts. The steady-state concentration of (3)NOM* approximately doubled at seawater IS, regardless of the salt used, due to a decrease in the (3)NOM* decay rate constant. The electron transfer-mediated degradation of 2,4,6-trimethylphenol (TMP) by (3)NOM* was significantly slowed at higher IS. A model is proposed wherein high IS slows intra-organic matter electron transfer pathways, an important (3)NOM* loss pathway, leading to longer (3)NOM* lifetimes. Although IS did not appear to impact energy transfer pathways directly, the higher (3)NOM* steady-state concentrations promote energy transfer interactions. The observed decrease in decay rate constant, increase in steady-state concentration of (3)NOM* at high IS, and the inhibition of electron transfer pathways should be considered when determining the fate of organic pollutants in estuarine and marine environments.

    View details for DOI 10.1021/es401900j

    View details for PubMedID 23952218

  • Dual role for lysine during protein modification by HOCl and HOBr: lysine nitrile as a putative biomarker for oxidative stress. Biochemistry Sivey, J., D., Howell, S., C., Bean, D., J., McCurry, D., L., Mitch, W., A., Wilson, C., J. 2013; 52: 1260-1271
  • Influence of amine structural characteristics of N-nitrosamine formation potential relevant to postcombustion CO2 capture systems. Environ. Sci. Technol. Dai, N., Mitch, W., A. 2013; 47: 13175-13183
  • Application of ultraviolet, ozone, and advanced oxidation treatments to washwaters to destroy nitrosamines, nitramines, amines, and aldehydes formed during amine-based carbon capture. Environ. Sci. Technol. Shah, A., D., Dai, N., Mitch, W., A. 2013; 47: 2799-2808
  • Formation, precursors, control, and occurrence of nitrosamines in drinking water: areview. Wat. Res. Krasner, S., W., Mitch, W., A., McCurry, D., L., Hanigan, D., Westerhoff, P. 2013; 47: 4433-4450
  • The role of black carbon electrical conductivity in mediating hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) transformation on carbon surfaces by sulfides. Environ. Sci. Technol. Xu, W., Pignatello, J., J., Mitch, W., A. 2013; 47: 7129-7136
  • Relative importance of N-nitrosodimethylamine compared to total N-nitrosamines in drinking waters. Environ. Sci. Technol. Dai, N., Mitch, W., A. 2013; 47: 3648-3656
  • Formation and control of emerging C- and N-DBPs in drinking water. Journal AWWA Krasner, S., W., Mitch, W., A., Westerhoff, P., Dotson, A., D. 2012; 104: E582-E595
  • Dichloroacetonitrile and dichloroacetamidecan form independently during chlorination and chloramination of drinking waters, model organic matters and wastewater effluents. Environ. Sci. Technol. Huang, H., Wu, Q.-Y., Hu, H.-Y., Mitch, W., A. 2012; 46: 10624-10631
  • Measurement of nitrosamine and nitramine formation from NOx reactions with amines during amine-based carbon dioxide capture for post-combustion carbon sequestration. Environ. Sci. Technol. Dai, N., Shah, A., D., Hu, L., Plewa, M., J., McKague, B., Mitch, W., A. 2012; 46: 9793-9801
  • Impact of halide ions on natural organic matter-sensitized photolysis of 17β-Estradiol in saline waters. Environ. Sci. Technol. Grebel, J., E., Pignatello, J., J., Mitch, W., A. 2012; 46: 7128-7134
  • Halonitroalkanes, halonitriles, haloamides and N-nitrosamines: A critical review of nitrogenous disinfection byproduct (N-DBP) formation pathways. Environ. Sci. Technol. Shah, A., D., Mitch, W., A. 2012; 46: 119-131
  • Comparative genotoxicity of nitrosamine drinking water disinfection byproducts in Salmonella and mammalian cells. Mutation Research Wagner, E., D., Hsu, K.-M., Lagunas, A., Mitch, W., A., Plewa, M., J. 2012; 741: 109-115
  • Tradeoffs in disinfection byproduct formation associated with precursor pre-oxidation for control of nitrosamine formation. Environ. Sci. Technol. Shah, A., D., Krasner, S., W., Chen, T., C.-F., Gunten, U., von, Mitch, W., A. 2012; 46: 4809-4818
  • Comparative mammalian cell cytotoxicity of water concentrates from disinfected recreational pools. Environ. Sci. Technol. Plewa, M., J., Wagner, E., D., Mitch, W., A. 2011; 45: 4159-4165
  • Sorbic acid as a quantitative probe for the formation, scavenging and steady-state concentrations of the triplet-excited state of organic compounds. Wat. Res. Grebel, J., E., Pignatello, J., J., Mitch, W., A. 2011; 45: 6535-6544
  • Impact of UV disinfection combined with chlorination/chloramination on the formation of halonitromethanes and haloacetonitriles in drinking water. Environ. Sci. Technol. Shah, A., D., Dotson, A., D., Linden, K., G., Mitch, W., A. 2011; 45: 3657-3664
  • Effect of halide ions on organic contaminant degradation by hydroxyl radical-based advanced oxidation processes. Environ. Sci. Technol. Grebel, J., E., Pignatello, J., J., Mitch, W., A. 2010; 44: 6822-6828
  • Chapter 7 Micropollutants in water recycling: A case study of N-nitrosodimethylamine (NDMA) exposure from water versus food. Sustainability Science and Engineering Schafer, A., I., Mitch, W., A., Walewijk, S., Munoz, A., Teuten, E. 2010; 2: 203-228
  • Quaternary amines as NDMA precursors: a role for consumer products? Environ. Sci. Technol. Kemper, J., M., Walse, S., S., Mitch, W., A. 2010; 4 (44): 1224-1231
  • Influence of the method of reagent addition on dichloroacetonitrile formation during chloramination. Environ. Sci. Technol. Hayes-Larson, E., L., Mitch, W., A. 2010; 2 (44): 700-706
  • Genotoxicity of water concentrates from recreational pools after various disinfection methods. Environ. Sci. Technol. Liviac, D., Wagner, E., D., Mitch, W., A., Altonji, M., J., Plewa, M., J. 2010; 44: 3537-3332
  • Fecal coliform accumulation within a river subject to seasonally-disinfected wastewater discharges. Wat. Res. Mitch, A., A., Gasner, K., C., Mitch, W., A. 2010; 16 (44): 4776-4782
  • Comparison of byproduct formation in waters treated with chlorine and iodine: relevance to point-of-use treatment Environ. Sci. Technol. Smith, E., M., Plewa, M., J., Lindell, C., L., Richardson, S., D., Mitch, W., A. 2010; 44: 8446-8552
  • Black-carbon mediated destruction of nitroglycerin and RDX by hydrogen sulfide: relevance to in-situ remediation. Environ. Sci. Technol. Xu, W., Dana, K., E., Mitch, W., A. 2010; 44: 6409-6415
  • Application of an optimized total N-nitrosamine (TONO) assay to pools: placing N-nitrosodimethylamine (NDMA) determinations into perspective. Environ. Sci. Technol. Kulshrestha, P., McKinstry, K., C., Fernandez, B., O., Feelisch, M., Mitch, W., A. 2010; 44: 3369-3375
  • Exploring amino acid side chain decomposition using enzymatic digestion and HPLC-MS: combined lysine transformations in chlorinated waters. Anal. Chem. Walse, S., S., Plewa, M., J., Mitch, W., A. 2009; 18 (81): 7650-7659
  • Occurrence and fate of nitrosamines and their precursors in municipal sludge and anaerobic digestion systems. Environ. Sci. Technol. Padhye, L., Tezel, U., Mitch, W., A., Pavlostathis, S., G., Huang, C.-H. 2009; 9 (43): 3087-3093
  • Nitrosamine, dimethylnitramine and chloropicrin formation during strong base anion exchange treatment. Environ. Sci. Technol. Kemper, J., M., Westerhoff, P., Dotson, A., D., Mitch, W., A. 2009; 2 (43): 466-472
  • Impact of halides on the photobleaching of dissolved organic matter. Marine Chem. Grebel, J., E., Pignatello, J., J., Song, W., Cooper, W., J., Mitch, W., A. 2009; 115: 134-144
  • Nitrosamine carcinogens also swim in pools. Environ. Sci. Technol. Walse, S., S., Mitch, W., A. 2008; 4 (42): 1032-1037
  • Degradation of tertiary alkylamines during chlorination/chloramination: implications for formation of aldehydes, nitriles, halonitroalkanes, and nitrosamines. Environ. Sci. Technol. Mitch, W., A., Schreiber, I., M. 2008; 13 (42): 4811 - 4817
  • Abiotic degradation of RDX in the presence of hydrogen sulfide and black carbon. Environ. Sci. Technol. Kemper, J., M., Ammar, E., Mitch, W., A. 2008; 6 (42): 2118-2123
  • Enhanced nitrogenous disinfection byproduct formation near the breakpoint: implications for nitrification control. Environ. Sci. Technol. Schreiber, I., M., Mitch, W., A. 2007; 20 (41): 7039-7046
  • Nitrile, aldehyde and halonitroalkane formation during chlorination/chloramination of primary amines. Environ. Sci. Technol. Joo, S.-H., Mitch, W., A. 2007; 4 (41): 1288-1296
  • Nitrosamine formation pathway revisited: the importance of dichloramine and dissolved oxygen. Environ. Sci. Technol. Schreiber, I., M., Mitch, W., A. 2006; 19 (40): 6007-6014
  • Occurrence and fate of nitrosamines and nitrosamine precursors in wastewater-impacted surface waters using boron as a conservative tracer. Environ. Sci. Technol. Schreiber, I., M., Mitch, W., A. 2006; 10 (40): 3203-3210
  • Minimization of NDMA formation during chlorine disinfection of municipal wastewater by application of pre-formed chloramines. Environ. Eng. Sci. Mitch, W., A., Oelker, G., L., Hawley, E., L., Deeb, R., A., Sedlak, D., L. 2005; 6 (22): 882-890
  • The influence of the order of reagent addition on N-nitrosodimethylamine formation. Environ. Sci. Technol. Schreiber, I., M., Mitch, W., A. 2005; 10 (39): 3811-3818
  • Sources and fate of nitrosodimethylamine and its precursors in municipal wastewater treatment plants. Wat. Environ. Res. Sedlak, D., L., Deeb, R., Hawley, E., Mitch, W., Durbin, T., Mowbray, S. 2005; 1 (77): 32-39
  • Characterization and fate of N-nitrosodimethylamine (NDMA) precursors during municipal wastewater treatment Environ. Sci. Technol. Mitch, W., A., Sedlak, D., L. 2004; 5 (38): 1445-1454
  • A N-nitrosodimethylamine (NDMA) precursor analysis for chlorination of water and wastewater. Wat. Res. Mitch, W., A., Gerecke, A., Sedlak, D., L. 2003; 15 (37): 3733-3741
  • N-nitrosodimethylamine (NDMA) as a drinking water contaminant: a review. Environ. Eng. Sci. Mitch, W., A., Sharp, J., O., Trussell, R., R., Valentine, R., L., Alvarez-Cohen, L., Sedlak, D., L. 2003; 5 (20): 389-404
  • Factors controlling nitrosamine formation during wastewater chlorination. Water Sci Technol. Mitch, W., A., Sedlak, D., L. 2002; 3 (2): 191-198
  • Formation of N-nitrosodimethylamine (NDMA) from dimethylamine during chlorination. Environ. Sci. Technol. Mitch, W., A., Sedlak, D., L. 2002; 36: 588-595