Removal of genotoxicity in chlorinated secondary effluent of a domestic wastewater treatment plant during dechlorination

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.

Developmental programming: Preconceptional and gestational exposure of sheep to a real-life environmental chemical mixture alters maternal metabolome in a fetal sex-specific manner

BACKGROUND

Everyday, humans are exposed to a mixture of environmental chemicals some of which have endocrine and/or metabolism disrupting actions which may contribute to non-communicable diseases. The adverse health impacts of real-world chemical exposure, characterized by chronic low doses of a mixture of chemicals, are only recently emerging. Biosolids derived from human waste represent the environmental chemical mixtures humans are exposed to in real life. Prior studies in sheep have shown aberrant reproductive and metabolic phenotypes in offspring after maternal biosolids exposure.

OBJECTIVE

To determine if exposure to biosolids perturbs the maternal metabolic milieu of pregnant ewes, in a fetal sex-specific manner.

METHODS

Ewes were grazed on inorganic fertilizer (Control) or biosolids-treated pastures (BTP) from before mating and throughout gestation. Plasma from pregnant ewes (Control n = 15, BTP n = 15) obtained mid-gestation were analyzed by untargeted metabolomics. Metabolites were identified using Agilent MassHunter. Multivariate analyses were done using MetaboAnalyst 5.0 and confirmed using SIMCA.

RESULTS

Univariate and multivariate analysis of 2301 annotated metabolites identified 193 differentially abundant metabolites (DM) between control and BTP sheep. The DM primarily belonged to the super-class of lipids and organic acids. 15-HeTrE, oleamide, methionine, CAR(3:0(OH)) and pyroglutamic acid were the top DM and have been implicated in the regulation of fetal growth and development. Fetal sex further exacerbated differences in metabolite profiles in the BTP group. The organic acids class of metabolites was abundant in animals with male fetuses. Prenol lipid, sphingolipid, glycerolipid, alkaloid, polyketide and benzenoid classes showed fetal sex-specific responses to biosolids.

DISCUSSION

Our study illustrates that exposure to biosolids significantly alters the maternal metabolome in a fetal sex-specific manner. The altered metabolite profile indicates perturbations to fatty acid, arginine, branched chain amino acid and one‑carbon metabolism. These factors are consistent with, and likely contribute to, the adverse phenotypic outcomes reported in the offspring.

DBP formation and toxicity alteration during UV/chlorine treatment of wastewater and the effects of ammonia and bromide

The UV/chlorine process is efficient for the abatement of micropollutants; yet, the formation of disinfection by-products (DBPs) and the toxicity can be altered during the treatment. This study investigated effluent organic matter characterization, DBP formation and toxicity alteration after the UV/chlorine treatment of wastewater; particularly, typical water matrix components in wastewater, namely, ammonia and bromide, were studied. The raw wastewater contained low levels of ammonia (3 µM) and bromide (0.5 µM). The UV/chlorine treatment efficiently eliminated 90 - 94% of fluorescent components. Compared with chlorination alone, a 20 min UV/chlorine treatment increased the formation of trihalomethanes (THMs), haloacetic acids (HAAs), chloral hydrate (CH), haloacetonitriles (HANs), trichloronitromethane (TCNM) and haloacetamides (HAcAms) by 90 - 508%. In post-chlorination after the UV/chlorine treatment, the formation of CH, HANs, TCNM and HAcAms increased by 77 - 274%, whereas the formation of both THMs and HAAs increased slightly by 11%. Meanwhile, the calculated cytotoxicity and genotoxicity of DBPs increased considerably after the UV/chlorine treatment and in post-chlorination, primarily due to the increased formation of HAAs and nitrogenous DBPs (N-DBPs). However, the acute toxicity of the wastewater to Vibrio fischeri and genotoxicity determined by the umu test decreased by 19% and 76%, respectively, after the 20 min UV/chlorine treatment. An additional 200 µM ammonia decreased the formation of all detected DBPs during the UV/chlorine treatment and 24 h post-chlorination, except that TCNM formation increased by 11% during post-chlorination. The acute toxicity of wastewater spiked with 200 µM ammonia was 32% lower than that of raw wastewater after the UV/chlorine treatment, but the genotoxicity was 58% higher. The addition of 1 mg/L bromide to the UV/chlorine process dramatically increased the formation of brominated DBPs and the overall calculated cytotoxicity and genotoxicity of DBPs. However, the acute toxicity and genotoxicity of the wastewater decreased by 7% and 100%, respectively, when bromide was added to the UV/chlorine treatment. This study illuminated that UV/chlorine treatment can decrease acute and geno- toxicities of wastewater efficiently.

Comparison of ozonation and UV based oxidation as pre-treatment process for ultrafiltration in wastewater reuse: Simultaneous water risks reduction and membrane fouling mitigation

Wastewater reuse risk and membrane fouling are two concerns in ultrafiltration (UF) of secondary effluent (SE) for wastewater reuse. In this work, several wastewater reuse risk issues, such as dissolved effluent organic matters (dEfOM), organic micro-pollutants (OMPs) and bio-toxicity of SE, as well as membrane fouling were comprehensively investigated when ozonation, UV/H₂O₂ and UV/persulfate (UV/PS) were used as the pre-treatments for UF process. To be specific, individual UF could remove DOC and UV₂₅₄ by only 7.5% and 19.8%, respectively, however, humics were largely degraded during the pre-oxidation processes revealed by molecular weight and fluorescence analysis. UF and ozonation showed limited removal of OMPs, however, UV/H₂O₂ and UV/PS dramatically degraded all the OMPs by more than 80%. Genotoxicity were not detected after the oxidation treatment. Membrane fouling may result from the collaborative effect of organic components, such as humic and protein like substances. Fourier transform infrared spectra of the fouled membranes showed that aromatic CC group and polysaccharides group in dEfOM were largely reduced after the oxidation pre-treatments, resulting in the improved membrane flux sustaining. Increased roughness of the membranes in the combined process supported that the less organics content after the oxidation pre-treatment contributed to improve the performance of the UF process. For the excellent organics degradation in UV/PS pre-treatment process, membrane fouling of subsequent UF process showed maximum mitigation.

Investigation on degradation behavior of dissolved effluent organic matter, organic micro-pollutants and bio-toxicity reduction from secondary effluent treated by ozonation

The environmental risk of secondary effluent has caused increasing attention in recent years, the negative effect of dissolved effluent organic matters (dEfOM) and organic micro-pollutants (OMPs) was a hot research point. In this research, the degradation behavior of dEfOM and fourteen OMPs in the ozonation was revealed using spectroscopic and chromatographic tools. Ozonation was effective for reducing UV₂₅₄, but had limited effect in dissolved organic carbon reduction. The dEfOM with shorter absorption wavelength was preferentially removed in the ozonation (230 nm  >  240 nm > 254 nm) and high molecular weight humics was largely reduced by the ozonation. Soluble microbial by-products were more reactive with ozone than humic acid as reflected by the fluorescence. Degradation behavior of the OMPs was identified based on their elimination kinetics and molecular structures and a simplified classification method was proposed. The group I OMPs (logk_O3>5) showed high removal efficiency with 1 mg/L of ozone, while the removal of group II OMPs (1< logk_O3<5) was largely dependent on the ozone dose. The CC bond, deprotonated amidogen, phenolic, aniline and anisole groups in these OMPs structures were the main reaction sites with ozone. The group III OMPs without active groups in the molecules showed slight removal in the ozonation. Moreover, genotoxicity and estrogenic activity were simultaneously analyzed for further evaluation on the risk of the effluent. The genotoxicity and estrogenic activity of the secondary effluent were 73.46 μg 4-NQO/L and 519.86 ng E2/L, respectively and an ozone dose of 10 mg/L could reduce the bio-toxicity to the detection limit.

Advanced Approaches to Model Xenobiotic Metabolism in Bacterial Genotoxicology In Vitro

During the past 30 years there has been considerable progress in the development of bacterial test systems for use in genotoxicity testing by the stable introduction of expression vectors (cDNAs) coding for xenobiotic-metabolizing enzymes into bacterial cells. The development not only provides insights into the mechanisms of bioactivation of xenobiotic compounds but also evaluates the roles of enzymes involved in metabolic activation or inactivation in chemical carcinogenesis. This review describes recent advances in bacterial genotoxicity assays and their future prospects, with a focus on the development and application of genetically engineering bacterial cells to incorporate some of the enzymatic activities involved in the bio-activation process of xenobiotics. Various genes have been introduced into bacterial umu tester strains encoding enzymes for genotoxic bioactivation, including bacterial nitroreductase and O-acetyltransferase, human cytochrome P450 monooxygenases, rat glutathione S-transferases, and human N-acetyltransferases and sulfotransferases. Their application has provided new tools for genotoxicity assays and for studying the role of biotransformation in chemical carcinogenesis in humans.

Increase of cytotoxicity during wastewater chlorination: Impact factors and surrogates

Toxic and harmful disinfection byproducts (DBPs) were formed during wastewater chlorination. It was recently suggested that cytotoxicity to mammalian cells reflects risks posed by chlorinated wastewater. Here, ATP assays were performed to evaluate the cytotoxicity to mammalian cells. Chlorination significantly increased cytotoxicity of treated wastewater. Factors affecting cytotoxicity formation during wastewater chlorination were investigated. Quenching with sodium thiosulfate and ascorbic acid decreased the formed cytotoxicity, while ammonium kept the cytotoxicity stable. The chlorine dose required for the maximum cytotoxicity increase was dramatically affected by DOC and ammonia concentrations. The maximum cytotoxicity increase, defined as the cytotoxicity formation potential (CtFP), occurred when wastewater was treated for 48h with a chlorine dose of 2·DOC+11·NH₃N+10 (mg-Cl₂/L). During chlorination, the amounts of AOX formation was found to be significantly correlated with cytotoxicity formation when no DBPs were destroyed. AOX formation could be used as a surrogate to estimate cytotoxicity increase during wastewater chlorination. Besides, the CtFP of 14 treated wastewater samples was assessed ranged from 5.4-20.4mg-phenol/L. The CtFP could be estimated from UV₂₅₄ of treated wastewater because CtFP and UV₂₅₄ were strongly correlated.

A fingerprint analysis method for characterization of dissolved organic matter in secondary effluents of municipal wastewater treatment plant

Dissolved organic matter (DOM) in wastewater and reclaimed water is related to water quality, safety, and treatability. In this study, DOM was characterized through a fingerprint analysis method for DOM characterization using resin fractionation followed by size exclusion chromatography (SEC). Resin fractionation was used in the first step to divide the DOM in water samples into six resin fractions, namely, hydrophobic acids (HOA), hydrophobic bases (HOB), hydrophobic neutrals (HON), hydrophilic acids (HIA), hydrophilic bases (HIB), and hydrophilic neutrals (HIN). SEC analysis was then performed to separate each resin fraction into several (n) subfractions with different molecular weights (MW). Thus, the total DOM in the water sample was fractionated into 6n subfractions. After quantification of each subfraction by dissolved organic carbon (DOC), a fingerprint graph was constructed to express the distribution of DOM in the subfractions. The fingerprint analysis method was applied to a secondary effluent sample during ozonation. Ozonation (dose of 10 mg L(-1)) removed the DOC only by 8 % and reduced UV254 of the sample by 36 %. Fingerprint graphs also revealed that the resin fractions changed quite limitedly but transformation of subfractions occurred notably.

Anti-estrogenic activity formation potential assessment and precursor analysis in reclaimed water during chlorination

Chlorination was reported to increase the anti-estrogenic activity in reclaimed water from domestic wastewater treatment plants, which may add to the risk of reclaimed water reuse. In order to assess the anti-estrogenic disinfection by-product (DBP) precursors, the anti-estrogenic activity formation potential (AEAFP) during chlorination was studied. Firstly, the conditions for the experimental measurement of AEAFP were determined. A 24-h chlorination experiment was applied for AEAFP measurement. After chlorination, dechlorination using reductive reagents led to significant loss of anti-estrogenic activity formation. In addition, as the presence of ammonia nitrogen and other major chlorine consumers would result in lower anti-estrogenic activity formation, a basic chlorine dose of 3× DOC (mg-Cl2 L(-1)) was adequate for completely transforming the anti-estrogenic DBP precursors while an extra chlorine dose of 8× ammonia-nitrogen + 5× nitrite-nitrogen (mg-Cl2 L(-1)) should be added when there was a high level of ammonia nitrogen and nitrite nitrogen in the reclaimed water. Therefore, 24-h chlorination without dechlorination or using only non-reductive quenching reagents (e.g. ammonium) for dechlorination and a total chlorine dose of 3× DOC + 8× ammonia nitrogen + 5× nitrite nitrogen (mg-Cl2 L(-1)) should be fulfilled for the AEAFP measurement. Moreover, the AEAFP (0.2-2.1 mg-TAM L(-1)) of the reclaimed water samples (n = 20) were further analyzed. The AEAFP was highly correlated to UV254 and the fluorescence volume in excitation emission matrix fluorescence spectrum which can be used as surrogates to indicate the level of the AEAFP and assess the precursors in reclaimed water.

Simultaneous adsorption and degradation of Zn(2+) and Cu (2+) from wastewaters using nanoscale zero-valent iron impregnated with clays

Clays such as kaolin, bentonite and zeolite were evaluated as support material for nanoscale zero-valent iron (nZVI) to simultaneously remove Cu(2+) and Zn(2+) from aqueous solution. Of the three supported nZVIs, bentonite-supported nZVI (B-nZVI) was most effective in the simultaneous removal of Cu(2+) and Zn(2+) from a aqueous solution containing a 100 mg/l of Cu(2+) and Zn(2+), where 92.9 % Cu(2+) and 58.3 % Zn(2+) were removed. Scanning electronic microscope (SEM) revealed that the aggregation of nZVI decreased as the proportion of bentonite increased due to the good dispersion of nZVI, while energy dispersive spectroscopy (EDS) demonstrated the deposition of copper and zinc on B-nZVI after B-nZVI reacted with Cu(2+) and Zn(2+). A kinetics study indicated that removing Cu(2+) and Zn(2+) with B-nZVI accorded with the pseudo first-order model. These suggest that simultaneous adsorption of Cu(2+)and Zn(2+) on bentonite and the degradation of Cu(2+)and Zn(2+) by nZVI on the bentonite. However, Cu(2+) removal by B-nZVI was reduced rather than adsorption, while Zn(2+) removal was main adsorption. Finally, Cu(2+), Zn(2+), Ni(2+), Pb(2+) and total Cr from various wastewaters were removed by B-nZVI, and reusability of B-nZVI with different treatment was tested, which demonstrates that B-nZVI is a potential material for the removal of heavy metals from wastewaters.