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In academic research laboratories, well-organized group meetings are common training tools that can benefit individuals and the group as a whole. Owing to the COVID-19 pandemic, virtual meetings ha...

Ozonation is widely used in wastewater reclamation treatment trains, either for micropollutant control or as a disinfectant and preoxidant in certain reuse processes. We recently found that ozonation of secondary effluent produces nitromethane, which can be efficiently transformed to genotoxic halonitromethanes by chlorination. In this work, the fate of nitromethane through water reuse treatment trains was characterized by analyzing samples from five reuse operations employing ozone. Nitromethane was poorly (50%) rejected by reserve osmosis (RO), not removed by, and in some cases, increased by ultraviolet/advanced oxidation processes (UV/AOP). Sufficient nitromethane remained after advanced treatment that when chlorine was added to mimic secondary disinfection, halonitromethane formation was consistently observed. In contrast, biological activated carbon removed most (75%) nitromethane. Bench-scale experiments were conducted to verify low removal by RO in clean systems and with wastewater effluent and to quantify the kinetics of direct and indirect photolysis of nitromethane in UV/AOP. An explanation for increasing nitromethane concentration during AOP is proposed. These results indicate that nitromethane presents a unique hazard to direct potable reuse systems, due to its ubiquitous formation during wastewater ozonation, poor removal by RO and UV/AOP, and facile conversion into genotoxic halonitromethanes upon chlorine addition.

Water reuse is expanding due to increased water scarcity. Water reuse facilities treat wastewater effluent to a very high purity level, typically resulting in a product water that is essentially deionized water, often containing less than 100 μg/L organic carbon. However, recent research has found that low-molecular-weight aldehydes, which are toxic electrophiles, comprise a significant fraction of the final organic carbon pool in recycled wastewater in certain treatment configurations. In this manuscript, we demonstrate oxidation of trace aqueous aldehydes to their corresponding acids using a heterogeneous catalyst (5% Pt on C), with ambient dissolved oxygen serving as the terminal electron acceptor. Mass balances are essentially quantitative across a range of aldehydes, and pseudo-first-order reaction kinetics are observed in batch reactors, with

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 β-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.

Potable reuse of wastewater is expanding, and ozonation for water reuse is becoming more common, either as a preoxidant before membranes or as part of ozone/biological activated carbon (O3/BAC) sys...

Because of the difficulty of carbon–carbon bond cleavage needed to liberate the small molecule chlorine disinfection byproducts (DBPs; e.g., trihalomethanes), they typically form at

Although extensive research to date has focused on enhancing removal rates of antibiotics from municipal wastewaters, the transformation products formed by anaerobic treatment processes remain understudied. The present work aims to examine the possible roles that the different microbial communities of an anaerobic membrane bioreactor (AnMBR) play in the transformation of antibiotics during wastewater treatment. As part of this work, sulfamethoxazole, erythromycin, and ampicillin were added in separate stages to the influent of the AnMBR at incremental concentrations of 10, 50, and 250 μg/L each. Antibiotic-specific transformation products detected during each stage, as identified by high resolution LC-MS, are reported herein. Results suggest that both isoxazole (sulfamethoxazole) and β-lactam (ampicillin) ring opening could be facilitated by the AnMBR's bioprocess. Microbial community analysis results indicated that relative activity of the system's suspended biomass consistently shifted towards syntrophic groups throughout the duration of the experiment. Notable differences were also observed between the suspended biomass and the AnMBR's membrane biofilms. Membrane-attached biofilm communities showed high relative activities of several specific methanogenic (Methanothrix and Methanomethylovorans), syntrophic (Syntrophaceae), and sulfate-reducing (Desulfomonile) groups. Such groups have been previously identified as involved in the formation of the antibiotic degradation products observed in the effluent of the AnMBR. The activity of these communities within the biofilms likely confers certain advantages that aid in the biotransformation of the antibiotics tested.

Potable reuse of wastewater is expanding, and ozonation for water reuse is becoming more common, either as a preoxidant before membranes or as part of ozone/biological activated carbon (O

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, beta-diketones) and antibiotic resistance genes.

N-Nitrosodimethylamine (NDMA) is a potent carcinogen associated with chloramination of wastewater and wastewater-impacted drinking waters. Substantial effort has been expended to identify the precursors and mechanisms leading to NDMA formation. One of the major discoveries has been that molecules in the N,N-dimethyl-α-arylamine class, including the common pharmaceutical ranitidine, form NDMA in high yield during chloramination. Simultaneously, it was hypothesized that these precursors react with monochloramine, the dominant species in most chloramine mixtures, to form NDMA. This monochloramine hypothesis contradicts past mechanistic work with simple secondary amines, as well as practical experience showing that minimization of dichloramine reduces the level of NDMA formation during wastewater reuse and drinking water treatment. In this work, we address the contradiction between practical experience and model precursor studies by showing that N,N-dimethyl-α-arylamines form NDMA chiefly via reactions with d...

A source-to-tap evaluation of the origin and fate of chloramination N-nitrosodimethylamine (NDMA) precursors at 21 full-scale drinking water plants was conducted. Upstream wastewater discharges accounted for (on a median basis) ∼16 ng L−1 NDMA formation potential (FP). A correlation between concentrations of the artificial sweetener sucralose (wastewater tracer) and NDMA FP was found within certain watersheds, with increased river flow decreasing sucralose and NDMA FP concentrations by diluting the wastewater discharges. The polymers polydiallyldimethylammonium chloride (polyDADMAC) and polyamine contributed (median) 6 and 14 ng L−1 of NDMA FP to coagulated water (which was pre-chloraminated in two cases), respectively. Biofiltration increased NDMA FP by (median) 6 ng L−1; biofiltration tended to increase precursor loading rather than reduce it. Although wastewater and polymers are known sources of precursors, biofilters as a source of precursors was an important finding. Ozonation of raw or settled water was effective at destroying NDMA precursors (median 34%). As free chlorine exposure increased (from ≤3 min to >1 h), NDMA formation in the chloraminated distribution system decreased (from median removal of 21% to 90% of the NDMA FP sampled prior to chlorination). For either oxidant, precursor abatement was typically higher at pH ∼8–9 than at 7. Riverbank filtration, and powdered and granular activated carbon removed (median) 64, 47, and 64% of watershed-derived NDMA precursors, respectively. Each was able to remove NDMA FP better than that of the bulk total organic carbon. Granular activated carbon did not appear to be effective at removing polyDADMAC-derived precursors added during coagulation. The contribution of different watershed or in-plant sources to NDMA precursors varies by plant and over time and, depending upon precursor sources, different in-plant treatment strategies can effectively control NDMA formation.

The cyto- and genotoxic potencies of disinfection by-products (DBPs) have been evaluated in published literature by measuring the response of exposed Chinese hamster ovary cells. In recent publications, DBP concentrations divided by their individual toxicity indices are summed to predict the relative toxicity of a water sample. We hypothesized that the omission or inclusion of certain DBPs over others is equivalent to statistical sampling bias and may result in biased conclusions. To test this hypothesis, we removed or added actual or simulated DBP measurements to that of published studies which evaluated granular activated carbon as a treatment to reduce the relative toxicity of the effluent. In several examples, it was possible to overturn the conclusions (i.e., activated carbon is detrimental or beneficial in reducing toxicity) by preferentially including specific DBPs. In one example, removing measured haloacetaldehydes caused the predicted cytotoxicity of a treated sample to decrease by up to 47%, reversing the initial conclusion that activated carbon increased the toxicity of the water. We also discuss measurements of statistical error, which are rarely included in publications related to predicted toxicity, but strongly influence the outcomes. Finally, we discuss future research needs in the light of these and other concerns.

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.

Water utilities practicing chlorination of poorly nitrified wastewater effluents for non-potable reuse, or of ammonia-containing, wastewater-impacted source waters during de facto reuse may form N-nitrosodimethylamine (NDMA) by reactions between wastewater-derived NDMA precursors and inorganic chloramines formed in situ when chlorine reacts with ammonia. Treatment with moderate doses (186 mJ cm−2 germicidal fluence) of UV from medium pressure mercury lamps (MPUV) upstream of chloramination minimized NDMA formation by destroying ambient NDMA (i.e., the NDMA occurring in wastewater) by >70% and deactivating chloramine-reactive NDMA precursors by 46%. UV from low pressure mercury lamps (LPUV) was less effective for NDMA precursor deactivation. Ozonation does not destroy ambient NDMA and formed significant levels of NDMA from ozone-reactive precursors. For waters with low ammonia concentrations, breakpoint chlorination deactivated NDMA precursors, but does not destroy ambient NDMA, and formed an array of regulated and unregulated halogenated byproducts. Even over a 3 d contact time, application of preformed monochloramine reduced NDMA formation by 39% by minimizing the exposure to inorganic dichloramine, the inorganic chloramine precursor to NDMA. However, the benefit of preformed monochloramine was restricted to waters with low to moderate ammonia concentrations (

In vitro bioassays have indicated that haloacetamides and haloacetaldehydes exhibit the highest cytotoxicity among DBP classes. Previous research has focused on their potential formation from the chlorination or chloramination of aliphatic compounds, particularly nonaromatic amino acids, and acetaldehyde. The present work found that acetaldehyde served as a relatively poor precursor for trichloroacetaldehyde and dichloroacetamide, generally the most prevalent of the haloacetaldehydes and haloacetamides, during chlorination or chlorination/chloramination. Using phenolic model compounds, particularly 4-hydroxybenzoic acid, as models for structures in humic substances, we found significantly higher formation of trichloroacetaldehyde and dichloroacetamide from prechlorination followed by chloramination. Evaluation of the stoichiometry of chlorine reactions with 4-hydroxybenzoic acid and several intermediates indicated that seven successive Cl[+1] transfers, faster with chlorination than chloramination, can form 2,3,5,5,6-pentachloro-6-hydroxy-cyclohexa-2-ene-1,4-dione via chlorophenol and chlorobenzoquinone intermediates. Formation of 2,3,5,5,6-pentachloro-6-hydroxy-cyclohexa-2-ene-1,4-dione may serve as a key branching point, with chloramines promoting the formation of dichloroacetamide and chlorination promoting the formation of trichloroacetaldehyde. The behavior of 4-hydroxybenzoic acid with respect to yields of dichloroacetamide and trichloroacetaldehyde during chlorination followed by chloramination was similar to the behavior observed for model humic acids and several surface waters, suggesting that phenolic structures in natural waters may serve as the predominant, and common pool of precursors for haloacetamides and haloacetaldehydes. Experiments with natural waters indicated that the branching point is reached over prechlorine exposures (100-500 mg-min/L) relevant to drinking water utilities using chlorine as a primary disinfectant and chloramines for maintenance of a distribution system residual.

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 (O-3), 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 O-3 > HOCl approximate to 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 O-3 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 O-3 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, O-3, and MPUV increased NDMA formation during post-chloramination. For O-3 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. (C) 2015 Elsevier Ltd. All rights reserved.

A recently developed, staged anaerobic fluidized membrane bioreactor (SAF-MBR) system has demonstrated performance comparable to that of conventional activated sludge systems at similar hydraulic residence times. The low biosolid generation rate, small footprint, and energy-positive potential (from captured methane) suggest the possible advantages of using the SAF-MBR upstream of advanced treatment for decentralized water reuse. Previous research conducted on laboratory-scale systems indicated that the SAF-MBR system is capable of removing pharmaceutical compounds. The purpose of this study was to compare the removals of disinfection byproduct precursors as well as pharmaceuticals by parallel pilot-scale SAF-MBR and full-scale aerobic systems treating municipal wastewater. Significantly better removals of antivirals (acyclovir and lamivudine), β-blockers (atenolol, metoprolol, and propranolol), a β-blocker aerobic biotransformation product (metoprolol acid), an anticonvulsant (carbamazepine), antibiotics ...

Although protein degradation by neutrophil-derived hypochlorous acid (HOCl) and eosinophil-derived hypobromous acid (HOBr) can contribute to the inactivation of pathogens, collateral damage to host proteins can also occur and has been associated with inflammatory diseases ranging from arthritis to atherosclerosis. Though previous research suggested halotyrosines as biomarkers of protein damage and lysine as a mediator of the transfer of a halogen to tyrosine, these reactions within whole proteins are poorly understood. Herein, reactions of HOCl and HOBr with three well-characterized proteins [adenylate kinase (ADK), ribose binding protein, and bovine serum albumin] were characterized. Three assessments of oxidative modifications were evaluated for each of the proteins: (1) covalent modification of electron-rich amino acids (assessed via liquid chromatography and tandem mass spectrometry), (2) attenuation of secondary structure (via circular dichroism), and (3) fragmentation of protein backbones (via sodium dodecyl sulfate-polyacrylamide gel electrophoresis). In addition to forming halotyrosines, HOCl and HOBr converted lysine into lysine nitrile (2-amino-5-cyanopentanoic acid), a relatively stable and largely overlooked product, in yields of up to 80%. At uniform oxidant levels, fragmentation and loss of secondary structure correlated with protein size. To further examine the role of lysine, a lysine-free ADK variant was rationally designed. The absence of lysine increased yields of chlorinated tyrosines and decreased yields of brominated tyrosines following treatments with HOCl and HOBr, respectively, without influencing the susceptibility of ADK to HOX-mediated losses of secondary structure. These findings suggest that lysine serves predominantly as a sacrificial antioxidant (via formation of lysine nitrile) toward HOCl and as a halogen-transfer mediator [via reactions involving ε-N-(di)haloamines] with HOBr.

Drinking water treatment research can be complicated by difficulties in shipping large water quantities and changing natural organic matter (NOM) characteristics over time. To overcome these issues, it is advantageous to have a reliable method for concentrating NOM with minimal loss and maximum shelf-life. NOM concentration and preservation by lyophilization (freeze-drying) has been practiced for many years; however, little information for lyophilizing and reconstituting NOM exists in the literature. The purpose of this research was to both evaluate and improve the lyophilization process of a concentrated NOM solution and to determine the appropriate conditions (pH, mixing time, and concentration factor) under which to reconstitute lyophilized NOM for maximum total organic carbon (TOC) and ultraviolet absorbance at 254-nm (UV254 ) recovery. To achieve this, a new lyophilization method was developed, in which NOM concentrate is supercooled below its freezing point and heat transfer is carefully reg...

BaCO3 dispersed PVC composites were prepared through a polymer re-precipitation method. The composites were tested for sulfate removal using rapid small scale column test (RSSCT) and found to significantly reduce sulfate concentration. The method was extended to synthesize barium carbonate-loaded silica aero-gels-polyvinyl chloride (PVC) polymer composites. The PVC composites were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray mapping, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and inductively coupled plasma mass spectrometry (ICP-MS) analysis. The method has advantages over conventional sulfate precipitation (sulfate removal process) using BaCO3 wherein clogging of the filter can be avoided. The method is environmentally friendly and does not interfere with natural organic matter as the conventional resin does. Some of the composites were thermally more stable as compared with the pure PVC discussed in the literature.

This review summarizes major findings over the last decade related to nitrosamines in drinking water, with a particular focus on N-nitrosodimethylamine (NDMA), because it is among the most widely detected nitrosamines in drinking waters. The reaction of inorganic dichloramine with amine precursors is likely the dominant mechanism responsible for NDMA formation in drinking waters. Even when occurrence surveys found NDMA formation in chlorinated drinking waters, it is unclear whether chloramination resulted from ammonia in the source waters. NDMA formation has been associated with the use of quaternary amine-based coagulants and anion exchange resins, and wastewater-impaired source waters. Specific NDMA precursors in wastewater-impacted source waters may include tertiary amine-containing pharmaceuticals or other quaternary amine-containing constituents of personal care products. Options for nitrosamine control include physical removal of precursors by activated carbon or precursor deactivation by application of oxidants, particularly ozone or chlorine, upstream of chloramination. Although NDMA has been the most prevalent nitrosamine detected in worldwide occurrence surveys, it may account for only ≈ 5% of all nitrosamines in chloraminated drinking waters. Other significant contributors to total nitrosamines are poorly characterized. However, high levels of certain low molecular weight nitrosamines have been detected in certain Chinese waters suspected to be impaired by industrial effluents. The review concludes by identifying research needs that should be addressed over the next decade.

Drinking water treatment and disinfection byproduct (DBP) research can be complicated by natural organic matter (NOM) temporal variability. NOM preservation by lyophilization (freeze-drying) has been long practiced to address this issue; however, its applicability for drinking water research has been limited because the selected NOM sources are atypical of most drinking water sources. The purpose of this research was to demonstrate that reconstituted NOM from a lyophilized reverse-osmosis (RO) concentrate of a typical drinking water source closely represents DBP formation in the original NOM. A preliminary experiment assessed DBP formation kinetics and yields in concentrated NOM, which demonstrated that chlorine decays faster in concentrate, in some cases leading to altered DBP speciation. Potential changes in NOM reactivity caused by lyophilization were evaluated by chlorination of lyophilized and reconstituted NOM, its parent RO concentrate, and the source water. Bromide lost during RO concentration was replaced by adding potassium bromide prior to chlorination. Although total measured DBP formation tended to decrease slightly and unidentified halogenated organic formation tended to increase slightly as a result of RO concentration, the changes associated with lyophilization were minor. In lyophilized NOM reconstituted back to source water TOC levels and then chlorinated, the concentrations of 19 of 21 measured DBPs, constituting 96% of the total identified DBP mass, were statistically indistinguishable from those in the chlorinated source water. Furthermore, the concentrations of 16 of 21 DBPs in lyophilized NOM reconstituted back to the RO concentrate TOC levels, constituting 86% DBP mass, were statistically indistinguishable from those in the RO concentrate. This study suggests that lyophilization can be used to preserve concentrated NOM without substantially altering the precursors to DBP formation.