Increase of cytotoxicity during wastewater chlorination: Impact factors and surrogates

How to achieve adequate quenching for DBP analysis in drinking water?

Quenching is an important step to terminate disinfection during preparation of disinfected water samples for the analysis of disinfection byproducts (DBPs). However, an incomplete quenching might result in continued reactions of residual chlorine, whereas an excessive quenching might decompose target DBPs. Therefore, an adequate quenching to achieve simultaneous disinfection termination and DBP preservation is of particular importance. In this study, the two-stage reaction kinetics of chlorine and three commonly used quenching agents (i.e., ascorbic acid, sodium thiosulfate, and sodium sulfite) were determined. Stopping quenching during the first stage prevented interactions of residual chlorine with natural organic matter. Complete quenching was achieved by minimizing the quenching time for ascorbic acid and sodium sulfite, while limiting the quenching time to less than 3 min for sodium thiosulfate. At the optimized quenching times, the molar ratios (MRs) of quenching agent to chlorine were 1.05, 1.10, and 0.75 for ascorbic acid, sodium sulfite, and sodium thiosulfate, respectively. The destructive effects of the three quenching agents on total organic halogen (TOX) followed the rank order of ascorbic acid (33.7-64.8 %) < sodium sulfite (41.6-72.8 %) < sodium thiosulfate (43.3-73.2 %), and the destructive effects on aliphatic DBPs also followed the rank order of ascorbic acid (29.5-44.5 %) < sodium sulfite (34.9-51.9 %) < sodium thiosulfate (46.9-53.2 %). For total organic chlorine (TOCl) and aliphatic DBPs, the quenching behavior itself had more significant destructive effect than the quenching agent type/dose and quenching time, but for total organic bromine (TOBr), the destructive effect caused by quenching agent type/dose and quenching time was more significant. High-dose, long-duration quenching enhanced the reduction of TOX, but had little effect on aliphatic DBPs. Additionally, the three quenching agents reduced the levels of halophenols (except for tribromophenol), while maintained or increased the levels of tribromophenol, halobenzoic/salicylic acids, and halobenzaldehydes/salicylaldehydes. To achieve adequate quenching for overall DBP analysis in chlorinated water samples, it is recommended to use ascorbic acid at a quenching agent-to-chlorine MR of 1.0 for a quenching time of < 0.5 h.

Phototransformation of Brominated Disinfection Byproducts and Toxicity Elimination in Sunlit-Ozonated Reclaimed Water

Ozonation is universally used during water treatment but can form hazardous brominated disinfection byproducts (Br-DBPs). While sunlight exposure is advised to reduce the risk of Br-DBPs, their phototransformation pathways remain insufficiently understood. Here, sunlight irradiation was found to reduce adsorbable organic bromine by 63%. Applying high-resolution mass spectrometry, the study investigated transformations of dissolved organic matter in sunlit-ozonated reclaimed water, revealing the number and abundance of assigned formulas decreased after irradiation. The Br-DBPs with O/C < 0.6 and MW > 400 Da were decreased or removed after irradiation, with the majority being CHOBr compounds. The peak intensity reduction ratio of CHOBr compounds correlated positively with double bound equivalent minus oxygen ratios but negatively with O/C, suggesting that photo-susceptible CHOBr compounds were highly unsaturated. Mass difference analysis revealed that the photodegradation pathways were mainly oxidation aligned with debromination. Three typical CHOBr molecular structures were resolved, and their photoproducts were proposed. Toxicity estimates indicated decreased toxicity in these photoproducts compared to their parent compounds, in line with experimentally determined values. Our proposed phototransformation pathways for Br-DBPs enhance our comprehension of their degradation and irradiation-induced toxicity reduction in reclaimed water, further illuminating their transformation under sunlight in widespread environmental scenarios.

Nontarget Insights into the Fate of Cl-/Br-Containing DOM in Leachate during Membrane Treatment

Halogenated organic compounds in wastewater are persistent and bioaccumulative contaminants of great concern, but few are known at the molecular level. Herein, we focus on nontarget screening of halogenated dissolved organic matter (DOM) in highly concentrated organic matrices of waste leachates and their concentrates. Solid-phase extraction (SPE) was optimized before capturing halogenated signatures via HaloSeeker 2.0 software on mining full-scan high-resolution mass spectrometry (HRMS) fingerprints. This study identified 438 Cl-/Br-containing DOM formulas in 21 leachates and membrane concentrates. Among them, 334 formulas were achieved via SPE with mixed-sorbent cartridges (mixed-SPE), surpassing the 164 formulas achieved through Bond Elut PPL cartridges (PPL-SPE). Herein, only four samples identified via PPL-SPE exhibited a resolution of >50% for extracted Cl-/Br-containing DOM by either SPE. The halogenated DOM constituted 6.87% of the total DOM mass features. Nevertheless, more abundant adsorbable organic halogens deciphered waste leachates and highly concentrated waste streams as reservoirs for halogenated contaminants. Remarkably, 75.7-98.1% of Cl-/Br-containing DOM in primary membrane concentrates remained stable through the secondary membrane treatment, indicating the persistence of these unknown contaminants even post-treatment.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400 °C for 2 h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00 mg L-1 by the DTCA-Na was more than 80% when the contact time was 60 min, pH was 6-10, the dosage of adsorbent was 1.00 g, and the temperature was 25 °C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

The impact of inorganic ions on the solar photolysis of chlorinated dissolved organic matter from different sources: Spectral characteristics, disinfection byproducts, and biotoxicities

Dissolved organic matter (DOM) from wastewater treatment plant (WWTP) effluent is chlorinated and then discharged into natural waters, where it is subject to solar irradiation. However, the impacts of inorganic ions in natural waters on the photochemical transformations of the chlorinated DOM (DOM-Cl) have not been studied comprehensively. In this study, variations in the spectral characteristics, disinfection byproducts (DBPs), and biotoxicities of DOM-Cl under solar irradiation at different pH values and in the presence of NO3- and HCO3- were revealed. Three sources of DOM, including DOM from a WWTP effluent, natural organic matter from the Suwannee River, and DOM from plant leaf leachate, were investigated. Solar irradiation resulted in the oxidation of the highly reactive aromatic structures and then reduced the amounts of chromophoric and fluorescent DOM, especially under alkaline conditions. Moreover, alkaline conditions significantly promoted the detected DBPs degradation and the biotoxicities attenuation, while NO3- and HCO3- generally impeded them (or did not work). Dehalogenation of the unknown halogenated DBPs and photolysis of the nonhalogenated organics were the main mechanisms for the DOM-Cl biotoxicity reductions. Hence, improving the ecological safety of WWTP effluents could be achieved through solar irradiation by removing the DBPs formed.

Occurrence of endocrine disruptors in Malaysia's water systems: A scoping review

Contamination of water systems with endocrine disrupting chemicals (EDCs) is becoming a major public health concern due to their toxicity and ubiquity. The intrusion of EDCs into water sources and drinking water has been associated with various adverse health effects on humans. However, there is no comprehensive overview of the occurrence of EDCs in Malaysia's water systems. This report aims to describe the occurrence of EDCs and their locations. Literature search was conducted electronically in two databases (PubMed and Scopus). A total of 41 peer-reviewed articles published between January 2000 and May 2021 were selected. Most of the articles dealt with pharmaceuticals (16), followed by pesticides (7), hormones (7), mixed compounds (7), and plasticisers (4). Most studies (40/41) were conducted in Peninsular Malaysia, with 60.9% in the central region and almost half (48.8%) in the Selangor State. Only one study was conducted in the northern region and East Malaysia. The Langat River, the Klang River, and the Selangor River were among the most frequently studied EDC-contaminated surface waters, while the Pahang River and the Skudai River had the highest concentrations of some of the listed compounds. Most of the risk assessments resulted in a hazard quotient (HQ) and a risk quotient (RQ) < 1, indicating negligible health risk, except for ciprofloxacin and dexamethasone, which had a potential human health risk (HQ_HH) > 1 in the Selangor River. An RQ > 1 for combined pharmaceuticals was found in Putrajaya tap water. Overall, this work provides a comprehensive overview of the occurrence of EDCs in Malaysia's water systems. The findings from this review can be used to mitigate risks and strengthen legislation and policies for safer drinking water.

A Review of Traditional and Emerging Residual Chlorine Quenchers on Disinfection By-Products: Impact and Mechanisms

Disinfection by-products (DBPs) are the most common organic contaminants in tap water and are of wide concern because of their highly developmental toxic, cytotoxic, and carcinogenic properties. Typically, to control the proliferation of pathogenic microorganisms, a certain concentration of residual chlorine is retained in the factory water, which reacts with the natural organic matter and the disinfection by-products that have been formed, thus affecting the determination of DBPs. Therefore, to obtain an accurate concentration, residual chlorine in tap water needs to be quenched prior to treatment. Currently, the most commonly used quenching agents are ascorbic acid, sodium thiosulfate, ammonium chloride, sodium sulfite, and sodium arsenite, but these quenching agents can cause varying degrees of DBPs degradation. Therefore, in recent years, researchers have attempted to find emerging chlorine quenchers. However, no studies have been conducted to systematically review the effects of traditional quenchers and new ones on DBPs, as well as their advantages, disadvantages, and scope of application. For inorganic DBPs (bromate, chlorate, and chlorite), sodium sulfite has been proven to be the ideal chlorine quencher. For organic DBPs, although ascorbic acid caused the degradation of some DBPs, it remains the ideal quenching agent for most known DBPs. Among the studied emerging chlorine quenchers, n-acetylcysteine (NAC), glutathione (GSH), and 1,3,5-trimethoxybenzene are promising for their application as the ideal chlorine quencher of organic DBPs. The dehalogenation of trichloronitromethane, trichloroacetonitrile, trichloroacetamide, and bromochlorophenol by sodium sulfite is caused by nucleophilic substitution reaction. This paper takes the understanding of DBPs and traditional and emerging chlorine quenchers as a starting point to comprehensively summarize their effects on different types of DBPs, and to provide assistance in understanding and selecting the most suitable residual chlorine quenchers during DBPs research.

Overlooked Cytotoxicity and Genotoxicity to Mammalian Cells Caused by the Oxidant Peroxymonosulfate during Wastewater Treatment Compared with the Sulfate Radical-Based Ultraviolet/Peroxymonosulfate Process

Byproduct formation (chlorate, bromate, organic halogen, etc.) during sulfate radical (SO₄^•-)-based processes like ultraviolet/peroxymonosulfate (UV/PMS) has aroused widespread concern. However, hypohalous acid (HOCl and HOBr) can form via two-electron transfer directly from PMS, thus leading to the formation of organic halogenated byproducts as well. This study found both PMS alone and UV/PMS can increase the toxicity to mammalian cells of wastewater, while the UV/H₂O₂ decreased the toxicity. Cytotoxicity of two wastewater samples increased from 5.6-8.3 to 15.7-29.9 mg-phenol/L, and genotoxicity increased from 2.8-3.1 to 5.8-12.8 μg 4-NQO/L after PMS treatment because of organic halogen formation. Organic halogen formation from bromide rather than chloride was found to dominate the toxicity increase. The SO₄^•--based process UV/PMS led to the formation of both organic halogen and inorganic bromate and chlorate. However, because of the very low concentration (<20 μg/L) and relatively low toxicity of bromate and chlorate, contributions of inorganic byproducts to toxicity increase were negligible. PMS would not form chlorate and bromate, but it generated a higher concentration of total organic halogen, thus leading to a more toxic treated wastewater than UV/PMS. UV/PMS formed less organic halogen and toxicity because of the destruction of byproducts by UV irradiation and the removal of byproduct precursors. Currently, many studies focused on the byproducts bromate and chlorate during SO₄^•--based oxidation processes. This work revealed that the oxidant PMS even needs more attention because it caused higher toxicity due to more organic halogen formation.

Changes in toxicity and adsorbable organic bromine concentrations in ozonated reclaimed water irradiated with sunlight

Disinfecting reclaimed water for safe reuse can produce toxic disinfection by-products such as adsorbable organic bromine (AOBr). Irradiating stored reclaimed water with sunlight is a "green" and free method for eliminating some toxic disinfection by-products, but the effects of irradiation with sunlight on ozonated reclaimed water containing bromide are not well understood. In this study, AOBr was found at concentrations of 171-180 (µg Br)/L in ozonated reclaimed water containing bromide at a concentration of 2 (mg Br)/L and dissolved organic carbon at a concentration of ∼5 (mg C)/L. Irradiation with sunlight degraded 53-74% of the AOBr in two reclaimed water samples in 8 h, and the pseudo-first-order rate constants (k) were 0.09-0.17 h^-1. The concentration of tribromomethane, a typical Br-containing disinfection by-product, was decreased by >96% by irradiation for 8 h (k = 0.42-0.47 h^-1). Irradiation with sunlight decreased the toxicity of ozonated reclaimed water to Chinese hamster ovary cells. Irradiation with sunlight decreased the degree of intracellular oxidative stress and oxidative damage caused by ozonated reclaimed water. Irradiation with sunlight for 8 h decreased cytotoxicity of the ozonated reclaimed water samples by 79% and 65%. The change in AOBr concentration correlated with the change in toxicity (R²=0.69, p<0.05). The relationships between sunlight wavelength and decreases in the AOBr concentration and toxicity were assessed, and it was found that UV in sunlight was predominantly responsible for decreasing the AOBr concentration and toxicity by reclaimed water. During irradiation for 8 h, UV was responsible for 65%-66% of the decrease in the AOBr concentration and 65-79% of the decrease in reclaimed water induced cytotoxicity. Irradiation with sunlight is a promising method for degrading AOBr and detoxifying ozonated reclaimed water during storage to allow the water to be reused.

Degradation of organics and formation of DBPs in the combined LED-UV and chlorine processes: Effects of water matrix and fluorescence analysis

Combined processes of light-emitting diodes ultraviolet (LED UV) and chlorination (Cl₂) are alternative disinfection technologies in drinking water, while the formation of disinfection by-products (DBPs) needs to be evaluated. This study investigated the impacts of critical water matrix factors on the DBP formation in the combined processes. Moreover, the correlation between the degraded natural organic matter (NOM) and the formed DBP was studied. Simultaneous UV/Cl₂ outperformed single Cl₂ and sequential combined processes in degrading humic acids (HA) and resulted in the highest DBP yield. Iodide at 5-20 μg/L and bromide at 0.05-0.2 mg/L slightly affected the degradation of organics, while increased the formation of brominated DBPs up to 36.6 μg/L. pH 6 was regarded as the optimum pH, achieving high efficiency of HA degradation and a lower level of total DBP formation than pH 7 and 8 by 11 % and 24 %, respectively. Compared to HA samples (46.8-103.9 μg/L per mg/L DOC), NOM in canal water were less aromatic and yielded fewer DBPs (19.6 and 21.2 μg/L per mg/L DOC). However, the extremely high bromide in site 1 samples (18.6 mg/L) shifted the chlorinated DBPs to their brominated analogues, posting around 1 order of magnitude higher levels of toxicities than HA samples. The reduction of absorbance at 254 nm (UV₂₅₄) correlated with all DBP categories in HA samples, while the correlation coefficients were compromised when included in the canal samples. For the first time, this study found that parallel factor analysis (PARAFAC) would neglect the fluorescence change caused by iodide/bromide in UV/Cl₂, while the changes could be captured by self-organising map (SOM) trained with full fluorescence spectra. Fluorescence Ex/Em pairs were proposed to predict DBP formation, suggesting a potential method to develop an online monitoring system for DBPs.

Determination of cytotoxicity following oxidative treatment of pharmaceutical residues in wastewater

Pharmaceutical residues are released in the aquatic environment due to incomplete removal from wastewater. With the presence of multiple chemicals in sewage waters, contaminants may adversely affect the effectiveness of a wastewater treatment plant (WWTP). In certain cases, discharged metabolites are transformed back into their pristine structure and become bioactive again. Other compounds are persistent and can withstand conventional wastewater treatment. When WWTP effluents are released in surface waters, pristine and persistent chemicals can affect the aquatic environment. To complement WWTPs and circumvent incomplete removal of unwanted chemicals or pharmaceuticals, on-site wastewater treatment can contribute to their removal. Advanced oxidation processes (AOPs) are very powerful techniques for the abatement of pharmaceuticals, however, under certain circumstances reactive toxic by-products can be produced. We studied the application of on-site AOPs in a laboratory setting. It is expected that treatment at the contamination source can eliminate the worst polluters. Thermal plasma and UV/H₂O₂ oxidation were applied on simulation matrices, Milli-Q and synthetic sewage water spiked with 10 different pharmaceuticals in a range of 0.1 up to 2400 μg/L. In addition, untreated end-of-pipe hospital effluent was also subjected to oxidative treatment. The matrices were activated for 180 min and added to cultured HeLa cells. The cells were 24 h and 48 h exposed at 37 °C and subsequently markers for oxidative stress and viability were measured. During the UV/H₂O₂ treatment periods no toxicity was observed. After thermal plasma activation of Milli-Q water (150 and 180 min) toxicity was observed. Direct application of thermal plasma treatment in hospital sewage water caused elimination of toxic substances. The low cytotoxicity of treated pharmaceutical residues is likely to become negligible if plasma pre-treated on-site wastewater is further diluted with other sewage water streams, before reaching the WWTP. Our study suggests that AOPs may be promising technologies to remove a substantial portion of pharmaceutical components by degradation at the source. Further studies will have to be performed to verify the feasibility of upscaling this technology from the benchtop to practice.

Photolysis of free chlorine and production of reactive radicals in the UV/chlorine system using polychromatic spectrum LEDs as UV sources

Recently, ultraviolet light-emitting diodes (UV-LEDs) and chlorine combined system has been employed as an emerging advanced oxidation process. However, UV-LEDs were commonly considered as monochromatic UV sources. In this study, the obvious quantum yields of chlorine photolysis under 265 nm and 280 nm LEDs irradiations were investigated with treating LEDs as polychromatic UV sources. Particularly, Φ_obs-poly of HOCl and OCl⁻ for 265 nm LED were found to be 1.50 and 0.70 mol E^-1, respectively, whereas Φ_obs-poly of HOCl and OCl⁻ for 280 nm LED were 1.28 and 0.64 mol E^-1, respectively. It was identified that Φ_obs-poly were 5.66-14.63 % lower than Φ_obs-mono. This suggests that obvious quantum yield using peak emission wavelength would overestimate the true quantum yield. The production of radical species in LED UV/chlorine systems were determined by the degradation of BA, and illustrated by a mathematical model. Different trends were observed for 265 nm and 280 nm LED UV/chlorine systems as pH increased from 5.0 to 10.0. As pH increased, the formation of OH continuously decreased in both 265 nm and 280 nm LED systems. The formation of Cl increased at neutral pH and more Cl and OH were formed due to the higher molar absorbance coefficient at 280 nm. The chlorine dose-dependent effects on radical productions at pH of 5.0, 7.5 and 10.0 were also assessed. At pH of 5.0, OH was the main radical product and had linear correlation with chlorine dose. At pH of 7.5, the productions of OH and Cl showed similar profiles that increased rapidly at low chlorine dosage and then slowed down.

Understanding the influence of pre-ozonation on the formation of disinfection byproducts and cytotoxicity during post-chlorination of natural organic matter: UV absorbance and electron-donating-moiety of molecular weight fractions

Pre-ozonation can reduce the formation of disinfection byproducts (DBPs) and related adverse effects during subsequent chlorination, but the change of each molecular weight (MW) fraction during each step of combined pre-ozonation and post-chlorination has not been well illustrated. In this study, it was investigated in terms of electron-donating-moieties (EDMs) and UVA₂₅₄ for a representative natural organic matter from Suwanee river (SRNOM). Pre-ozonation suppressed the post-chlorination of SRNOM through oxidation of almost all EDMs (>85%) and UVA₂₅₄ (>90%) in high MW fractions (HMW, >3.2 kDa) and moderate EDMs (43%) and UVA₂₅₄ (72%) in medium MW fractions (MMW, 1.0-3.2 kDa). Furthermore, pre-ozonation led to comparable abatements of EDMs and UVA₂₅₄ for HMW fractions, but lower abatement of EDMs than UVA₂₅₄ for MMW fractions. However, when t-BuOH was used as an ^•OH-quencher, pre-ozonation led to a few instances in which there were higher abatements of EDMs than UVA₂₅₄ for the MMW fraction. These findings suggested that the HMW fraction dominantly underwent ring-cleavage of phenols via O₃- or ^•OH-oxidation. Differently, the MMW fraction underwent ring-cleavage of phenols and quinones-formation via O₃-oxidation, but occasionally underwent hydroxylation and hydro-phenol formation via ^•OH-oxidation. Because of forehand elimination of reactive moieties (e.g. EDMs), pre-ozonation obviously inhibited the formation of representative DBPs (67%-84% inhibition), total organic chloride (51% inhibition) and cytotoxicity (31% inhibition), but may have promoted the formation of carbonyl-DBPs (trichloroacetone and chloral hydrate). When compared with UVA₂₅₄, EDMs would better for surrogate of DBPs formation. EDM abatement surrogated the formation of total organic chlorine (TOCl) and cytotoxicity following a two-stage phase, possibly because the speciation of DBPs and transformation products varied with the abatement of EDMs.

NMR spectroscopy of wastewater: A review, case study, and future potential

NMR spectroscopy is arguably the most powerful tool for the study of molecular structures and interactions, and is increasingly being applied to environmental research, such as the study of wastewater. With over 97% of the planet's water being saltwater, and two thirds of freshwater being frozen in the ice caps and glaciers, there is a significant need to maintain and reuse the remaining 1%, which is a precious resource, critical to the sustainability of most life on Earth. Sanitation and reutilization of wastewater is an important method of water conservation, especially in arid regions, making the understanding of wastewater itself, and of its treatment processes, a highly relevant area of environmental research. Here, the benefits, challenges and subtleties of using NMR spectroscopy for the analysis of wastewater are considered. First, the techniques available to overcome the specific challenges arising from the nature of wastewater (which is a complex and dilute matrix), including an examination of sample preparation and NMR techniques (such as solvent suppression), in both the solid and solution states, are discussed. Then, the arsenal of available NMR techniques for both structure elucidation (e.g., heteronuclear, multidimensional NMR, homonuclear scalar coupling-based experiments) and the study of intermolecular interactions (e.g., diffusion, nuclear Overhauser and saturation transfer-based techniques) in wastewater are examined. Examples of wastewater NMR studies from the literature are reviewed and potential areas for future research are identified. Organized by nucleus, this review includes the common heteronuclei (¹³C, ¹⁵N, ¹⁹F, ³¹P, ²⁹Si) as well as other environmentally relevant nuclei and metals such as ²⁷Al, ⁵¹V, ²⁰⁷Pb and ¹¹³Cd, among others. Further, the potential of additional NMR methods such as comprehensive multiphase NMR, NMR microscopy and hyphenated techniques (for example, LC-SPE-NMR-MS) for advancing the current understanding of wastewater are discussed. In addition, a case study that combines natural abundance (i.e. non-concentrated), targeted and non-targeted NMR to characterize wastewater, along with in vivo based NMR to understand its toxicity, is included. The study demonstrates that, when applied comprehensively, NMR can provide unique insights into not just the structure, but also potential impacts, of wastewater and wastewater treatment processes. Finally, low-field NMR, which holds considerable future potential for on-site wastewater monitoring, is briefly discussed. In summary, NMR spectroscopy is one of the most versatile tools in modern science, with abilities to study all phases (gases, liquids, gels and solids), chemical structures, interactions, interfaces, toxicity and much more. The authors hope this review will inspire more scientists to embrace NMR, given its huge potential for both wastewater analysis in particular and environmental research in general.

Nontargeted identification of chlorinated disinfection byproducts formed from natural organic matter using Orbitrap mass spectrometry and a halogen extraction code

Natural organic matter is a major source of precursors of hazardous chlorinated disinfection byproducts (Cl-DBPs) formed during water treatment, but the majority of Cl-DBPs are still unidentified. In this study, we used a self-written halogen extraction code to identify halogen isotopic patterns in combination with the R package MFAssignR, to identify Cl-DBPs from Orbitrap mass spectra. One hundred and eighty-nine Cl-DBPs were detected during chlorination of a Suwannee River natural organic matter solution, and the structures of 20 of these compounds are reported for the first time. Kendrick mass defect analysis and structural identification confirmed that chlorinated carboxylic acids are common and likely to form during chlorination. A toxicity prediction using quantitative structure-activity relationship models indicated that most of the chlorinated carboxylic acids may be highly toxic. Our analytical strategy can identify Cl-DBPs accurately from complex mixtures and may also be applicable to the identification of other halogenated disinfection byproducts formed during water treatment.

Species and formation characteristics of halogenated DBPs in chloramination of tannic acid after biodegradation

Tannic acid is widely found in source water and wastewater, and it is also a typical degradation precursor of natural organic matter. In this study, focused on chloramination, the formation characteristics of halogenated DBPs from tannic acid biodegradation products were examined. Fifty-nine polar emerging DBPs (including four nitrogenous DBPs) were detected and forty of them were identified for the first time; meanwhile, their formation pathways were tentatively proposed. In general, much more polar emerging DBPs were formed at the early biodegradation stage than those at the later stage, while commonly observed aliphatic DBPs presented an exactly inverse trend, because initially-formed emerging DBPs can be transformed to those aliphatic DBPs by residual chloramine. Interestingly, while the relative formation level of brominated species in overall halogenated polar emerging DBPs maintained at high level at the later biodegradation stage during chlorination, it decreased significantly later during chloramination. The discrepancy may be due to that hydrolysis effects became dominant at this period in chloramination, whereas DBP formation from the reactions between slow reactive sites and hypohalous acids prevailed in chlorination. In addition, the calculated toxicity drivers among the 21 aliphatic DBPs were found to be haloacetonitriles, although they contribute mildly to the total concentration.

Formation of nitro(so) and chlorinated products and toxicity alteration during the UV/monochloramine treatment of phenol

The UV/monochloramine (UV/NH₂Cl) process is an emerging advanced oxidation process (AOP) to remove organic contaminants in water treatment with radicals including hydroxyl radicals (HO^•), reactive chlorine species (RCS) and reactive nitrogen species (RNS). This study investigated the formation of nitro(so) and chlorinated products and toxicity alteration during the UV/NH₂Cl treatment of phenol. RNS and/or RCS induced the formation of nitro(so), chlorinated and polymeric compounds during phenol transformation by UV/NH₂Cl. These compounds dramatically increased the cytotoxicity to Chinese hamster ovary cells after 20 min UV/NH₂Cl treatment, which was 10 times higher than that after 24 h chloramination. The increase of cytotoxicity in UV/NH₂Cl was primarily attributable to 4-nitrosophenol, and the cytotoxicity followed the order of 4-nitrosophenol >> 4-nitrophenol > 2,4,6-trichlorophenol > 2,4-dichlorophenol > phenol. 4-Nitrosophenol was significantly generated by the combination of ^•NO and phenoxy radical, where the maximum conversion rates of phenol to 4-nitrosophenol increased from 4.9% to 62.4% when pH increased from 5 to 10. The highest conversion rate was at pH 10 because the ^•NO concentration increased with increasing pH from 5 to 10 in UV/NH₂Cl, as verified by the electron paramagnetic resonance (EPR) analysis. Nitrophenols were also detected at much lower concentrations than 4-nitrosophenol, which were mainly formed by the oxidation of 4-nitrosophenol and the combination of ^•NO₂ with phenoxy radicals. RCS was responsible for the formation of chlorinated products mainly through Cl^• addition and the reactions of Cl^•/Cl₂^•- with phenoxy radicals. Also, RCS and RNS significantly enhanced the formation of carbonaceous (i.e., chloroform and chloral hydrate) and nitrogenous disinfection byproducts (i.e., chloropicrin and dichloroacetonitrile) in UV/NH₂Cl. This study indicates that the UV/NH₂Cl treatment significantly increased toxicity and validates the roles of RNS and RCS in producing toxic nitro(so) and chlorinated products.

Kinetic removal of acetaminophen and phenacetin during LED-UV365 photolysis of persulfate system: Reactive oxygen species generation

Acetaminophen (ACT) and phenacetin (PNT) removal during light-emitting diode (LED)-UV photolysis of persulfate (PS) was evaluated with a typical wavelength of 365 nm. Decay of PNT and ACT in pH ranges of 5.5-8.5 followed pseudo-first order kinetics. Maximum pseudo-first order rate constants (k_obs) of ACT and PNT decomposition of 1.8 × 10^-1 and 1.2 × 10^-1 min^-1, respectively, were obtained at pH 8.5. Hydroxyl radicals (·OH), sulfate radicals (SO₄·^-), superoxide radicals (O₂^-·), and singlet oxygen (¹O₂) were determined in-situ electron paramagnetic resonance (EPR) and alcohol scavenging tests. The average contributions of ·OH and SO₄·^- were 23.5% and 53.0% for PNT removal, and 15.9% and 53.0% for ACT removal at pH ranges of 5.5-8.5. In samples subjected to chlorination after LED-UV₃₆₅/PS pre-oxidation, a relatively small total concentration of five halogenated disinfection by-products (DBPs) was obtained of 90.9 μg L^-1 (pH 5.5) and 126.7 μg L^-1 (pH 7.0), which is 58.5% and 30.2% lower than that in system without LED-UV₃₆₅/PS pre-oxidation. Meanwhile, a higher maximum value of total DBP concentration was obtained at pH 8.5 (445.6 μg L^-1) following LED-UV₃₆₅/PS pre-oxidation. The results of economy evaluation showed that UV₃₆₅ was more cost-effective in application for organic contaminant removal compared with UV₂₅₄.

Combination of high resolution mass spectrometry and a halogen extraction code to identify chlorinated disinfection byproducts formed from aromatic amino acids

Chlorination can lead to the formation of hazardous chlorinated disinfection byproducts (Cl-DBPs). We identified tyrosine (Tyr) and tryptophan (Trp) as precursors of toxic Cl-DBPs and developed a halogen extraction code to complement ultra performance liquid chromatography in tandem with high resolution mass spectrometry (UPLC-HRMS) in detecting and identifying Cl-DBPs. We detected 20 and 11 Cl-DBPs formed from chlorination of Tyr and Trp, respectively, and identified the structures of 15 Cl-DBPs. Fourteen structures were previously unreported. We also proposed the tentative formation pathways of these newly identified Cl-DBPs. Their incidence in real water sources demonstrated that these Cl-DBPs are likely to form during chlorination of reclaimed water. We computationally predicted the toxicity of these Cl-DBPs, which was relatively high, indicating that these Cl-DBPs could be hazardous and were of valid concern. Combining analytical data with the halogen extraction code can identify Cl-DBPs accurately from complex compounds. This analytical method can be used to identify Cl-DBPs of water treatment procedures in further studies.

Tracing nitrogenous byproducts during ozonation in the presence of bromide and ammonia using stable isotope labeling and high resolution mass spectrometry

Ammonia has been widely used to inhibit bromate formation during ozonation. However, our recent study found that during ozonation in the presence of bromide and ammonia, toxicity increased under certain conditions that might be attributed to the formation of nitrogenous byproducts. Herein, a typical structural moiety of natural organic matter (NOM), hydroquinone, was evaluated for its potential to form nitrogenous byproducts. During ozonation of the hydroquinone solution containing bromide and ammonia, toxicity of organic byproducts increased significantly. As organic bromine was hardly detected, organic nitrogen was responsible for the increased toxicity. An effective method combining ultra-performance liquid chromatography in tandem with high resolution mass spectrometry (UPLC-HRMS) with an isotope labeling strategy was used to trace nitrogenous byproducts. Four newly formed nitrogenous byproducts were detected, two of which were also detected in Suwannee River natural organic matter (SRNOM) solution treated under the same ozonation condition. Furthermore, the molecular structures and formation pathways of these nitrogenous byproducts were proposed. This study highlights that, despite the widespread use, adding ammonia to inhibit bromate formation during ozonation might increase the toxicity posed by nitrogenous byproducts. During ozonation in the presence of bromide and ammonia, particular attention should be paid to nitrogenous byproducts.

Organic micropollutants and disinfection byproducts removal from drinking water using concurrent anion exchange and chlorination process

Many traditional drinking water treatment processes have limited removal efficiencies on natural organic matter (NOM) and organic micropollutants (OMPs), and thus may lead to the production of harmful disinfection byproducts (DBPs). We examined four kinds of anion exchange resins (D205, D213, NDMP-3, and M80) in conjunction with chlorination in the treatment of drinking water. Five categories including 40 OMPs at environmentally relevant concentrations were analyzed. M80 showed the best performance to remove OMPs in water. However, it was vulnerable to the presence of humic acid (HA), indicating its limitation on removing OMPs and NOM at the same time. In contrast, D205, D213, NDMP-3 resins were less affected by HA. Besides, D205, D213 and NDMP-3 provided higher efficiencies on the reduction of DBPs than M80. The amount of trihalomethanes (THMs) lowered by 42.7%, 37.6%, 32.1%, and 0%, whereas haloacetic acids (HAAs) were decreased by 34.0%, 31.2%, 23.0%, and 17.9% by D205, D312, NDMP-3, and M80. Notably, D205 showed the highest removal effects on the bromide ion, brominated THMs, and HAAs, supporting that D205 can be a selective resin for the treatment of drinking water in high bromide-containing areas.

New progress of ammonia recovery during ammonia nitrogen removal from various wastewaters

The recovery of ammonia-nitrogen during wastewater treatment and water purification is increasingly critical in energy and economic development. The concentration of ammonia-nitrogen in wastewater is different depending on the type of wastewater, making it challenging to select ammonia-nitrogen recovery technology. Meanwhile, the conventional nitrogen removal method wastes ammonia-nitrogen resources. Based on the circular economy, this review comprehensively introduces the characteristics of several main ammonia-nitrogen source wastewater plants and their respective challenges in treatment, including municipal wastewater, industrial wastewater, livestock and poultry wastewater and landfill leachate. Furthermore, we introduce the main methods currently adopted in the ammonia-nitrogen removal process of wastewater from physical (air stripping, ion exchange and adsorption, membrane and capacitive deionization), chemical (chlorination, struvite precipitation, electrochemical oxidation and photocatalysis) and biological (classical and typical activated sludge, novel methods based on activated sludge, microalgae and photosynthetic bacteria) classification based on the ammonia recovery concept. We discuss the applicable methods of recovering ammonia nitrogen in several main wastewater plants. Finally, we prospect the research direction of ammonia removal and recovery in wastewater based on sustainable development.

Ammonia-Mediated Bromate Inhibition during Ozonation Promotes the Toxicity Due to Organic Byproduct Transformation

Ammonia (NH₄⁺) and hydrogen peroxide (H₂O₂) have been widely used to inhibit bromate formation during ozonation. However, organic byproducts can also pose a risk under these conditions. During bromate inhibition, the influence of NH₄⁺ and H₂O₂ on organic byproducts and their toxicity should be elucidated. Our study found that NH₄⁺ suppressed organic bromine, but might result in increased toxicity. Adding 0.5 mg/L of NH₄⁺-N substantially increased both the formation of cytotoxicity and genotoxicity (DNA double-strand breaks) of organic byproducts from 0.6 to 1.6 mg-phenol/L, and from 0.3 to 0.8 μg-4-NQO/L (0.5 mg/L Br^-, 5 mg/L O₃). NH₄⁺ decreased bromate, but increased the overall toxicity of the integrated byproducts (organic byproducts and bromate). Organic nitrogen measurements and ¹⁵N isotope analysis showed enhanced incorporation of nitrogen into organic matter when NH₄⁺ and Br^- coexisted during ozonation. NH₄⁺ decreased the formation of brominated acetonitriles, but enhanced the formation of brominated nitromethanes and brominated acetamides. These brominated nitrogenous byproducts were partially responsible for this increase in toxicity. Different from ammonia, H₂O₂ could reduce both bromate and the toxicity of organic byproducts. In the presence of 0.5 mg/L Br^- and 10 mg/L O₃, adding H₂O₂ (0.5 mM) substantially suppressed bromate, cytotoxicity formation and genotoxicity formation by 88%, 63% and 67%. This study highlights that focusing on bromate control with NH₄⁺ addition might result in higher toxicity. Efforts are needed to effectively control the toxicities of bromate and organic byproducts simultaneously.

Elimination of isothiazolinone biocides in reverse osmosis concentrate by ozonation: A two-phase kinetics and a non-linear surrogate model

Elimination of commercial Kathon biocide (methyl-isothiazolinone (MIT) and chloro-methyl-isothiazolinone (CMIT) mixture) by ozonation was investigated in real RO influent and concentrate. MIT and CMIT had different reactivities (second-order-rate-constants) with molecular ozone and OH. Ozonation of biocides followed an instantaneous phase (16.6 %-36.9 % contributions) and then a gradual phase (33.6 %-78.8 % contributions). Newly developed kinetics including both phases demonstrated that O₃ oxidation contributed 25.6 %-39.8 % and <10 % of MIT and CMIT eliminations, respectively, and OH oxidation contributed 60.2 %-74.4 % and >90 % of MIT and CMIT eliminations, respectively. OH oxidation at the instantaneous phase accounted 15.7 %-37.9 % of total OH oxidation. Mass ratios of O₃/DOC of 0.24 and 0.32 were needed for ∼80 % eliminations of MIT and CMIT in RO concentrate, respectively. The kinetics including both phases allowed a para-chlorobenzoic acid indicator model to predict MIT and CMIT elimination better than that including gradual ozonation only, with 58.9 %-96.0 % lower relative error. The attenuations of electron-donating-moiety indicated that O₃ may preferentially react with chromophores through aromatic cleavage and electrophilic extraction, while ^•OH may non-selectively react with chromophores through predominant electrophilic addition. A surrogate model for biocide elimination by UVA₂₅₄ loss was proposed to be nonlinear rather than linear, which reduced 31.8 %-71.3 % surrogating error.

The growth suppression effects of UV-C irradiation on Microcystis aeruginosa and Chlorella vulgaris under solo-culture and co-culture conditions in reclaimed water

Harmful algal blooms (HABs) are serious problems in landscape waters sourced from reclaimed water. In this study, the suppression effects of UV-C irradiation on microalgal growth were researched to find a possible preventive approach. Microcystis aeruginosa and Chlorella vulgaris were exposed to UV-C irradiation and then cultured in real reclaimed water for 7-18 d. UV-C irradiation at 50-200 mJ cm^-2 could inhibit the growth of M. aeruginosa, C. vulgaris, and both microalgae in co-culture for 3-14, 1-3, and 1-5 d respectively. In addition, UV-C irradiation could cause damage to the cell integrity. At 100-200 mJ cm^-2 UV-C, the proportion of microalgal membrane damage (P_md) in M. aeruginosa cells increased rapidly to 56%-76% from day 3, whereas that in C. vulgaris cells increased to 23%-62% within 3 d. The photochemical efficiency (represented by Y value) of the irradiated groups was negatively affected immediately after UV-C irradiation and recovered gradually during the incubation. The Y value of M. aeruginosa cells began to recover from days 3 to 14, whereas that of C. vulgaris recovered much more quickly, from days 0.1 to 1. Overall, the irradiation-induced suppressive effects on algal growth correlated positively with the UV-C doses. Because M. aeruginosa was more sensitive to UV-C irradiation, UV-C irradiation not only controlled the total biomass of the mixed algae but also selectively reestablished the dominance of the nontoxic C. vulgaris.

Methyl chloride produced during UV254 irradiation of saline water

Ultraviolet (UV) irradiation is widely used for water treatment due to its effectiveness against a wide range of waterborne pathogens with minimal production of regulated disinfection byproducts. However, in this study, the formation of methyl chloride (CH₃Cl) from guaiacol and chloride was observed during UV₂₅₄ irradiation. The results indicated that direct photolysis of guaiacol produced an arenium ion, and the reactive methoxy group was further transformed to CH₃Cl in the presence of chloride. O-quinone was detected as the primary product of the degradation of guaiacol resulting from UV₂₅₄ irradiation. Other organic compounds containing methoxy, ethoxy, or methylamino groups with structures that are similar to guaiacol were also demonstrated to generate halocarbons in aqueous chloride or bromide solution under UV₂₅₄ irradiation. Scavenging experiments and removal of oxygen demonstrated that neither oxygen nor chlorine radicals were involved in CH₃Cl formation. In seawater samples, CH₃Cl was also detected in the presence or absence of added organic matter. These results demonstrate that CH₃Cl can be formed during UV₂₅₄ irradiation in saline water and that attention should be paid to this compound and structurally-related compounds in the application of UV₂₅₄ processes.

Developing an equivalent toxicity area approach to comparing toxicity of urban road deposited sediments

Urban road stormwater has been seen as an alternative water resource for mitigating water scarcity. Road deposited sediments (RDS) is the primary source of road stormwater pollution since many toxic pollutants are attached to RDS and eventually enter stormwater runoff when rainfall events occur. This could threaten road stormwater reuse safety. This study developed an innovative equivalent toxicity area (ETA) approach to comparing overall toxicity of RDS among different road sites. In the ETA approach, the road surface area was used to represent how toxic the RDS generated from the area was. This ETA approach overcomes the difficulty to compare RDS toxicity among road sites due to variability of sampling volumes, which constrains the effective application of conventional toxicity comparison method of using pollutant amounts (loads/concentrations). Twelve road sites in Shenzhen, China were selected as a case study, where the ETA approach developed was used to compare their RDS toxicity using Chinese Hamster Ovary cells. Additionally, the key factors influencing RDS toxicity were identified by using a forward stepwise regression method. These outcomes provide a useful approach to comparing overall toxicity where various pollutant types with different amounts (loads/concentrations) and toxicity levels are present. Additionally, the results can also contribute to ensuring safety of RDS polluted stormwater reuse.

Surrogates for the removal by ozonation of the cytotoxicity and DNA double-strand break effects of wastewater on mammalian cells

Effluents from wastewater treatment plants (WWTPs) may contain various pollutants with potential toxic effects. Ozonation is widely applied to purify wastewater, which may influence the toxicity and water quality indices simultaneously. The main goal of this study was to reveal influence of ozonation on toxicity of WWTP effluents and to find the surrogates for toxicity changes. Cytotoxicity and DNA double-strand break (DSB) effect of WWTP effluents were measured based on Chinese hamster ovary (CHO) cells. Changes of water quality parameters and molecular weight distribution of WWTP effluents were also measured. The organic extracts in WWTP effluents were shown to decrease the cell viability. Besides, an increased level of DNA DSBs was found in cells when exposed to the organic extracts. Ozonation significantly eliminated cytotoxicity and DNA DSB-based genotoxicity of WWTP effluents, with removal rates of 53-66% and 51-76% for cytotoxicity and genotoxicity, respectively, with 10 mg/L ozone dose. Although the DOC contents in WWTP effluents were hardly removed by ozonation, the chromophores and fluorophores were significantly eliminated. Organic matter in WWTP effluents mainly consists of fractions with molecular weight (MW) < 500 Da. Ozonation generally decreased the fluorescence intensity and UV₂₅₄ values of all the MW fractions, but increased the DOC contents of the 100-500 Da fraction. During ozonation, the removal rates of UV₂₅₄ and SUVA₂₅₄ were significantly correlated to the removal rates of both cytotoxicity and genotoxicity. UV₂₅₄ might be an ideal surrogate for cytotoxicity and genotoxicity reduction during wastewater ozonation.

Chlorinated effluent organic matter causes higher toxicity than chlorinated natural organic matter by inducing more intracellular reactive oxygen species

During unplanned indirect potable reuse, treated wastewater that contains effluent organic matter (EOM) enters the drinking water source, resulting in different toxicity from natural organic matter (NOM) in surface water during chlorination. This study found that, during chlorination, EOM formed more total organic halogen (TOX) and highly toxic nitrogenous disinfection byproducts (DBPs) like dichloroacetonitrile and trichloronitromethane than NOM did. Oxidative stress including both reactive oxygen species (ROS) and reactive nitrogen species (RNS) in Chinese hamster ovary (CHO) cells substantially increased when exposed to chlorinated EOM and chlorinated NOM. The excessive ROS damaged biological macromolecules including DNA, RNA to form 8-hydroxy-(deoxy)guanosine and proteins to form protein carbonyls. Impaired macromolecule further triggered cell cycle arrest at the S and G₂ phases, led to cell apoptosis and eventual necrosis. Cytotoxicity and genotoxicity of chlorinated EOM were both higher than those of chlorinated NOM. Adding the blocker L-buthionine-sulfoximine of intracellular antioxidant glutathione demonstrating that oxidative stress might be responsible for toxicity. ROS was further identified to be the main cause of toxicity induction. These findings highlight the risk from chlorinated EOM in the case of unplanned indirect potable reuse, because it showed higher level of cytotoxicity and genotoxicity than chlorinated NOM via inducing more ROS in mammalian cells.

Influence of UV irradiation on the toxicity of chlorinated water to mammalian cells: Toxicity drivers, toxicity changes and toxicity surrogates

UV irradiation was reported to be able to degrade some kinds of DBPs, yet its influence on the toxicity of chlorinated water to mammalian cells remains unknown. This study systematically investigated the influence of low-pressure UV irradiation on the DBPs and toxicity of chlorinated drinking water (DW) and reclaimed water (RW). The apparent first-order rate constant (k_obs) of degradation kinetics of known DBPs increased with the increased Br substitutions. Haloacetonitriles were identified as toxicity drivers among the detected DBPs, which even contributed more to the toxicity after UV irradiation, mainly due to the refractory bromochloroacetonitrile (BCAN) and dichloroacetonitrile (dCAN). Both total organic halogen, cytotoxicity and genotoxicity were significantly removed under UV irradiation, with the removal rate of 22.9%-41.7% for cytotoxicity and a higher rate of 33.1%-55.5% for genotoxicity under 2400 mJ/cm² irradiation. UV irradiation significantly decreased the UV₂₅₄, SUVA₂₅₄ and fluorescence intensity (FLU) of chlorinated water. Results from high performance size exclusion chromatography revealed that chlorinated DW mainly contained high molecular weight (MW) compounds (>1000 Da) while chlorinated RW mainly contained lower MW compounds (100-500 Da). Chromophores and fluorophores in compounds of 100-500 Da increased in chlorinated DW while decreased in chlorinated RW under UV irradiation. Both the removal of UV₂₅₄, SUVA₂₅₄, FLU, MW-based UV₂₅₄ (>1000 Da) and MW-based FLU (each fractions) were significantly correlated (p < 0.05) with the removal of toxicity under UV irradiation. The UV₂₅₄ of chlorinated water was recommended as the optimal surrogate for toxicity removal.

Underestimated risk from ozonation of wastewater containing bromide: Both organic byproducts and bromate contributed to the toxicity increase

Ozonation is widely used in wastewater treatment but the associated byproduct formation is a concern. When ozonation is used in the presence of bromide, bromate is generally considered as a major byproduct, and few studies have examined the toxicity of organic byproducts. This study was designed to investigate the cytotoxicity, genotoxicity and DNA/RNA oxidative damage to Chinese hamster ovary (CHO) cells of organic extracts from ozonated wastewater in the absence or presence of bromide. Ozonation effectively detoxified secondary effluents containing no bromide. However, ozonation significantly increased the cytotoxicity and genotoxicity of the effluents spiked with a bromide concentration as low as 100 μg/L, compared with the bromide-free effluent. When the bromide concentration in the effluent was increased to 2000 μg/L, ozonation resulted in 1.4-1.5 times the cytotoxicity and 1.5-5.0 times the genotoxicity of the non-ozonated secondary effluent. Besides, the oxidative stress (including reactive oxygen species and reactive nitrogen species) and DNA/RNA oxidative damage also became more severe and a high level of 8-hydroxy-(deoxy)guanosine was detected in the CHO cell nucleus in the presence of bromide. Cytotoxicity and genotoxicity were found to increase with the formation of total organic bromine (TOBr). When the CHO cells were exposed to both the organic byproducts and bromate formed from wastewater containing 500 and 2000 μg/L bromide, bromate significantly increased oxidative stress and DNA/RNA oxidative damage at relatively high concentration factors, suggesting both organic byproduct and bromate can contribute to toxicity increase. During ozonation of the effluent containing bromide, particular attention should be paid to the organic byproducts such as TOBr.

Comparative toxicity of organic mixture attached to road deposited sediments: Inadequacy of conventionally using individual pollutants to assess comprehensive hazard effects

Organic pollutants attached on road deposited sediments (RDS) during dry days can be washed-off into stormwater runoff during rainfall events, undermining stormwater reuse safety. Previous research studies commonly utilized individual pollutant groups and their quantity to evaluate the hazard effect of pollutants attached to RDS in terms of stormwater reuse. Since many types of organic pollutants are present together rather than individually, conventional approaches might not permit a comprehensive understanding of how appropriately the RDS polluted stormwater can be reused. This study undertook a toxicity test of organic pollutants attached to RDS using Chinese hamster ovary cells (CHO), testing a hypothesis that solely focusing on individual pollutant groups are not adequate to represent hazard effects of resulting stormwater and hence their adequacy for reuse. It is noted that comparative toxicity of RDS is not strongly related to total solids (commonly seen as the key carrier of pollutants) and chemical oxygen demand (COD, representing organic matters). Additionally, the comparison results of spatial distributions of toxicity (in this study) and individual pollutants in previous studies did not show a similar trend. These results imply that toxicity should be also used to indicate how stormwater can be safely reused while solely investigating individual pollutants can not adequately show a comprehensive hazard effect in terms of ensuring stormwater reuse safety. Based on study outcomes, a new assessment approach considering both pollutant and toxicity were proposed. This will assist on effective stormwater reuse and ensuring their reuse safety.

Research progress of disinfection and disinfection by-products in China

Disinfection is an indispensable water treatment process for killing harmful pathogens and protecting human health. However, the disinfection has caused significant public concern due to the formation of toxic disinfection by-products (DBPs). Lots of studies on disinfection and DBPs have been performed in the world since 1974. Although related studies in China started in 1980s, a great progress has been achieved during the last three decades. Therefore, this review summarized the main achievements on disinfection and DPBs studies in China, which included: (1) the occurrence of DBPs in water of China, (2) the identification and detection methods of DBPs, (3) the formation mechanisms of DBPs during disinfection process, (4) the toxicological effects and epidemiological surveys of DBPs, (5) the control and management countermeasures of DBPs in water disinfection, and (6) the challenges and chances of DBPs studies in future. It is expected that this review would provide useful information and reference for optimizing disinfection process, reducing DBPs formation and protecting human health.

Occurrence and ecological risk assessment of disinfection byproducts from chlorination of wastewater effluents in East China

Effluents containing disinfection byproducts (DBPs) from wastewater treatment plants (WWTPs) may be discharged to the receiving water bodies or reused for irrigation, landscaping, and environmental supplies as well as a source to replenish groundwater. Thus the formation and risk of the DBPs in disinfected wastewater effluents should be concerned. In this study, the occurrence of 44 DBPs including 6 trihalomethanes (THMs), 9 haloaceticacids (HAAs), 2 haloketones (HKs), 9 halonitromethanes (HNMs), 9 haloacetonitriles (HANs) and 9 nitrosamines (NAs) was investigated in 12 chlorinated WWTP effluents from five cities of East China. The contribution of each class of DBPs to the total DBPs concentration and additive toxicity was calculated. The average concentrations of the 6 classes of DBPs were ranked as follows: HAAs (47.0 μg/L) > THMs (28.0 μg/L) > HANs (9.9 μg/L) > HNMs (2.9 μg/L) > HKs (0.79 μg/L) > NAs (0.69 μg/L). The significant positive correlations were observed between the formation of THMs and HAAs, THMs and HANs, as well as HAAs and HANs. The results showed that HAAs and THMs were the dominant DBPs on a mass concentration basis and accounted for 54% and 29%, respectively in the total measured DBPs, but they made a minor contribution to the calculated DBP-associated cytotoxicity. HANs and NAs dominated the DBP-associated cytotoxicity, accounting for 50% and 34% on an additive toxicity basis despite the minor contributions to the mass concentration with 10% and 1%, respectively. The risk quotients for three taxonomic groups (fish, daphnid, and green algae) were calculated to assess the ecological risk of DBPs, and the results demonstrated that both HAAs and HANs had high ecological risk for green algae in chlorinated wastewater effluents.

Metabolomic responses to pre-chlorinated and final effluent wastewater with the addition of a sub-lethal persistent contaminant in Daphnia magna

Consumer products such as perfluorooctanesulfonic acid (PFOS) and pharmaceuticals (PCPPs) enter aquatic ecosystems through inefficient removal during wastewater treatment. Often, the sterilization process of wastewater includes the addition of sodium hypochlorite that can react with PCPPs and other organic matter (i.e., dissolve organic matter) to generate disinfection by-products and can cause the final effluent to be more harmful to aquatic organisms. Here, we exposed Daphnia magna to two stages of wastewater, the pre-chlorinated wastewater (PreCl) and the final effluent. In addition, we exposed D. magna, to the final effluent with a concentration gradient of added PFOS, to investigate if this persistent contaminant altered the toxicity of the final effluent. After 48 h of contaminant exposure, we measured the daphnids metabolic responses to the different stages of wastewater treatment, and with the addition of PFOS, utilizing proton nuclear magnetic resonance spectroscopy and liquid chromatography tandem mass spectrometry. We found few significant changes to the metabolic profile of animals exposed to the PreCl wastewater; however, animals exposed to the final effluent displayed increases in many amino acids and decreases in some sugar metabolites. With the addition of PFOS to the final effluent, the metabolic profile shifted from increased amino acids and decreased sugar metabolites and energy molecules especially at the low and high concentrations of PFOS. Overall, our results demonstrate the metabolome is sensitive to changes in the final effluent that are caused by sterilization, and with the addition of a persistent contaminant, the metabolic profile is further altered.

Electron donating capacity reduction of dissolved organic matter by solar irradiation reduces the cytotoxicity formation potential during wastewater chlorination

After treated wastewater is discharged into surface water for unplanned indirect potable reuse, solar irradiation transforms the dissolved organic matter (DOM), which would alter the formation of disinfection byproducts (DBPs) and change the cytotoxicity formation potential (CtFP) during post-chlorination in drinking water treatment plants. This study investigated the effects of solar irradiation on the CtFP and total organic halogen formation potential (TOXFP) of wastewater during post-chlorination. Exposure to natural sunlight decreased the formation potential of cytotoxicity to Chinese Hamster Ovary cells. Under 24 h simulated solar irradiation, CtFP and TOXFP decreased by more than 40%. X-ray photoelectron spectra and Fourier transformation infrared spectra suggested solar irradiation destroyed the key DBP precursors containing phenolic hydroxyl moieties (Ph-OH). The destruction of Ph-OH under solar irradiation was reflected by a decrease in the electron donating capacity (EDC) of DOM and the post-chlorination decreased the EDC further. Increasing the irradiation-consumed EDC abated the chlorine-consumed EDC, while the chlorine-consumed EDC was positively correlated to the CtFP and TOXFP by means of the electrophilic substitution-aromatic ring cleavage. Solar irradiation thus reduced the CtFP and TOXFP in wastewater during post-chlorination. This study revealed that solar irradiation decreased the risks of treated wastewater for unplanned indirect potable reuse and provided a strategy of controlling CtFP and TOXFP via reducing EDC of DOM in pretreatments.

Exposure to solar light reduces cytotoxicity of sewage effluents to mammalian cells: Roles of reactive oxygen and nitrogen species

Sewage effluents can contain hundreds of toxic pollutants, making them a risk to humans when involved in drinking water. It is therefore important to evaluate the cytotoxicity of sewage effluents to mammalian cells. Solar light might influence the water quality of sewage effluents after their discharge into lakes or rivers, altering their cytotoxicity. In this study, natural solar light was found to lower the cytotoxicity of sewage effluents to Chinese hamster ovary (CHO) cells. Cytotoxicity of different samples decreased by 31%-65% after 12 h of simulated irradiation. Ultraviolet in sunlight was the major contributor to the cytotoxicity reduction. Aquatic reactive oxygen species (ROS), including singlet oxygen, superoxide anions, hydrogen peroxide, and hydroxyl radicals, were generated in the effluents under irradiation and they contributed to part of cytotoxicity reduction. Pollutants in sewage effluents induced cytotoxicity by simultaneously elevating the levels of intracellular ROS and intracellular reactive nitrogen species (RNS) in CHO cells. Solar light and the aquatic ROS formed under irradiation reduced the cytotoxicity because the transformed pollutants in sewage effluents increased lower intracellular ROS and RNS levels. These results help reveal the detoxification mechanism of sewage effluents in natural environment.

Enhancement of H2O2 Decomposition by the Co-catalytic Effect of WS2 on the Fenton Reaction for the Synchronous Reduction of Cr(VI) and Remediation of Phenol

The greatest problem in the Fe(II)/H₂O₂ Fenton reaction is the low production of ·OH owing to the inefficient Fe(III)/Fe(II) cycle and the low decomposition efficiency of H₂O₂ (<30%). Herein, we report a new discovery regarding the significant co-catalytic effect of WS₂ on the decomposition of H₂O₂ in a photoassisted Fe(II)/H₂O₂ Fenton system. With the help of WS₂ co-catalytic effect, the H₂O₂ decomposition efficiency can be increased from 22.9% to 60.1%, such that minimal concentrations of H₂O₂ (0.4 mmol/L) and Fe²⁺ (0.14 mmol/L) are necessary for the standard Fenton reaction. Interestingly, the co-catalytic Fenton strategy can be applied to the simultaneous oxidation of phenol (10 mg/L) and reduction of Cr(VI) (40 mg/L), and the corresponding degradation and reduction rates can reach up to 80.9% and 90.9%, respectively, which are much higher than the conventional Fenton reaction (52.0% and 31.0%). We found that the expose reductive W⁴⁺ active sites on the surface of WS₂ can greatly accelerate the rate-limiting step of Fe³⁺/Fe²⁺ conversion, which plays the key role in the decomposition of H₂O₂ and the reduction of Cr(VI). Our discovery represents a breakthrough in the field of inorganic catalyzing AOPs and greatly advances the practical utility of this method for environmental applications.

Water Quality and Brain Function

In the United States, regulations are in place to ensure the quality of drinking water. Such precautions are intended to safeguard the health of the population. However, regulatory guidelines may at times fail to achieve their purpose. This may be due to lack of sufficient data regarding the health hazards of chronic low dose exposure to contaminants or the introduction of new substances that pose a health hazard risk that has yet to be identified. In this review, examples of different sources of contaminants in drinking water will be discussed, followed by an evaluation of some select individual toxicants with known adverse neurological impact. The ability of mixtures to potentially cause additive, synergistic, or antagonistic neurotoxic responses will be briefly addressed. The last section of the review will provide examples of select mechanisms by which different classes of contaminants may lead to neurological impairments. The main objective of this review is to bring to light the importance of considering trace amounts of chemicals in the drinking water and potential brain abnormalities. There is continued need for toxicology studies to better understand negative consequences of trace amounts of toxins and although it is beyond the scope of this brief overview it is hoped that the review will underscore the paucity of studies focused on determining how long-term exposure to minute levels of contaminants in drinking water may pose a significant health hazard.

Solar light irradiation significantly reduced cytotoxicity and disinfection byproducts in chlorinated reclaimed water

Chlorinated reclaimed water is widely used for landscaping and recreational purposes, resulting in human exposure to toxic disinfection byproducts. Although the quality of chlorinated reclaimed water might be affected by sunlight during storage, the effects of solar light irradiation on the toxicity remain unknown. This study investigated the changes in cytotoxicity and total organic halogen (TOX) of chlorinated reclaimed water exposed to solar light. Irradiation with solar light for 12 h was found to significantly reduce the cytotoxicity of chlorinated reclaimed water by about 75%, with ultraviolet light being responsible for the majority of this reduction. Chlorine residual in reclaimed water tended to increase the cytotoxicity, and the synergy between solar light and free chlorine could not enhance the reduction of cytotoxicity. Adding hydroxyl radical scavengers revealed that the contribution of hydroxyl radical to cytotoxicity reduction was limited. Solar light irradiation concurrently reduced TOX. The low molecular weight (<1 kDa) fraction was the major contributor of cytotoxicity and TOX in chlorinated reclaimed water. Detoxification of the low molecular weight fraction by light irradiation was mainly a result of TOX dehalogenation, while detoxification of the high molecular weight (>1 kDa) fraction was probably caused by photoconversion from high toxic TOX to low toxic TOX.

Transformation of DON in reclaimed water under solar light irradiation leads to decreased haloacetamide formation potential during chloramination

Reclaimed water is usually stored in rivers or lakes before subsequent use. In storage ecosystems, the natural process of solar light irradiation plays a key role in water quality, altering disinfection byproduct formation potential in later use. This study investigated changes in haloacetamide formation potential (HAcAm FP) during subsequent chloramination when reclaimed water was exposed to solar light irradiation. Significant decreases in HAcAm FP were observed for the solar light irradiated reclaimed water, with reductions of 27%-69% for different haloacetamides. Moreover, transformation of dissolved organic nitrogen (DON) to inorganic nitrogen occurred during irradiation. The application of ¹⁵N- labeled monochloramine indicated that the nitrogen source of the decreased HAcAms mainly originated from DON, rather than chloramine. Chloramination of the model compound l-asparagine after irradiation demonstrated that the decreased HAcAms could be attributed to the decrease in DON. After solar light irradiation, the brominated HAcAm FP in the presence of bromide was also reduced, while the bromine incorporation factor remained steady. Overall, this study revealed the contribution of natural processes in controlling HAcAm FP during subsequent chloramination, suggesting solar light irradiation is important to water purification during reclaimed water storage.

Formation and control of disinfection byproducts and toxicity during reclaimed water chlorination: A review

Chlorination is essential to the safety of reclaimed water; however, this process leads to concern regarding the formation of disinfection byproducts (DBPs) and toxicity. This study reviewed the formation and control strategies for DBPs and toxicity in reclaimed water during chlorination. Both regulated and emerging DBPs have been frequently detected in reclaimed water during chlorination at a higher level than those in drinking water, indicating they pose a greater risk to humans. Luminescent bacteria and Daphnia magna acute toxicity, anti-estrogenic activity and cytotoxicity generally increased after chlorination because of the formation of DBPs. Genotoxicity by umu-test and estrogenic activity were decreased after chlorination because of destruction of toxic chemicals. During chlorination, water quality significantly impacted changes in toxicity. Ammonium tended to attenuate toxicity changes by reacting with chlorine to form chloramine, while bromide tended to aggravate toxicity changes by forming hypobromous acid. During pretreatment by ozonation and coagulation, disinfection byproduct formation potential (DBPFP) and toxicity formation potential (TFP) occasionally increase, which is accompanied by DOC removal; thus, the decrease of DOC was limited to indicate the decrease of DBPFP and TFP. It is more important to eliminate the key fraction of precursors such as hydrophobic acid and hydrophilic neutrals. During chlorination, toxicities can increase with the increasing chlorine dose and contact time. To control the excessive toxicity formation, a relatively low chlorine dose and short contact time were required. Quenching chlorine residual with reductive reagents also effectively abated the formation of toxic compounds.

Three-step effluent chlorination increases disinfection efficiency and reduces DBP formation and toxicity

Chlorination is extensively applied for disinfecting sewage effluents, but it unintentionally generates disinfection byproducts (DBPs). Using seawater for toilet flushing introduces a high level of bromide into domestic sewage. Chlorination of sewage effluent rich in bromide causes the formation of brominated DBPs. The objectives of achieving a disinfection goal, reducing disinfectant consumption and operational costs, as well as diminishing adverse effects to aquatic organisms in receiving water body remain a challenge in sewage treatment. In this study, we have demonstrated that, with the same total chlorine dosage, a three-step chlorination (dosing chlorine by splitting it into three equal portions with a 5-min time interval for each portion) was significantly more efficient in disinfecting a primary saline sewage effluent than a one-step chlorination (dosing chlorine at one time). Compared to one-step chlorination, three-step chlorination enhanced the disinfection efficiency by up to 0.73-log reduction of Escherichia coli. The overall DBP formation resulting from one-step and three-step chlorination was quantified by total organic halogen measurement. Compared to one-step chlorination, the DBP formation in three-step chlorination was decreased by up to 23.4%. The comparative toxicity of one-step and three-step chlorination was evaluated in terms of the development of embryo-larva of a marine polychaete Platynereis dumerilii. The results revealed that the primary sewage effluent with three-step chlorination was less toxic than that with one-step chlorination, indicating that three-step chlorination could reduce the potential adverse effects of disinfected sewage effluents to aquatic organisms in the receiving marine water.