The occurrence, formation and transformation of disinfection byproducts in the water distribution system: A review

Unexpected weakened formation of disinfection byproducts and enhanced production of halates by cupric oxide during chlorination of peptide-bound aspartic acid

Under the condition that the residual chlorine is guaranteed, the biofilm still thrives in drinking water distribution systems through secreting a large number of extracellular polymeric substances (EPS), in which protein components are the primary precursor of disinfection byproducts (DBPs), mostly in the form of combined amino acids. The aim of this study is to investigate the action of CuO on the formation of halates (XO3-, ClO3- and BrO3-) and DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as protein surrogate. The presence of CuO promoted the self-decay rather than TAsp-induced decay of oxidants, resulting in an increase in XO3- yield and a decrease in DBPs yield. It was CuO-induced weaker production of cyanoacetic acid and 3-oxopropanoic acid that induced the decreased yields of HANs and THMs, respectively. The FTIR and Raman spectra indicate a weak complexation between CuO and TAsp. Given this, the CuO-HOX/OX- complexes were inferred to be reactive to HOX/OX- but less reactive to TAsp. The study helps to better understand the formation of XO3- and DBPs during the chlorination of EPS, and propose precise control strategies when biofilm boosts in water pipes.

Occurrence, bioaccumulation, fate, and risk assessment of emerging pollutants in aquatic environments: A review

Significant concerns on a global scale have been raised in response to the potential adverse impacts of emerging pollutants (EPs) on aquatic creatures. We have carefully reviewed relevant research over the past 10 years. The study focuses on five typical EPs: pharmaceuticals and personal care products (PPCPs), per- and polyfluoroalkyl substances (PFASs), drinking water disinfection byproducts (DBPs), brominated flame retardants (BFRs), and microplastics (MPs). The presence of EPs in the global aquatic environment is source-dependent, with wastewater treatment plants being the main source of EPs. Multiple studies have consistently shown that the final destination of most EPs in the water environment is sludge and sediment. Simultaneously, a number of EPs, such as PFASs, MPs, and BFRs, have long-term environmental transport potential. Some EPs exhibit notable tendencies towards bioaccumulation and biomagnification, while others pose challenges in terms of their degradation within both biological and abiotic treatment processes. The results showed that, in most cases, the ecological risk of EPs in aquatic environments was low, possibly due to potential dilution and degradation. Future research topics should include adding EPs detection items for the aquatic environment, combining pollution, and updating prediction models.

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br-) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br-. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br-. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br-: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br- were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

Exposure to haloacetic acid disinfection by-products and male steroid hormones: An epidemiological and in vitro study

Haloacetic acids (HAAs) are ubiquitous in drinking water and have been associated with impaired male reproductive health. However, epidemiological evidence exploring the associations between HAA exposure and reproductive hormones among males is scarce. In the current study, the urinary concentrations of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the internal exposure markers of HAAs, as well as sex hormones (testosterone [T], progesterone [P], and estradiol [E2]) were measured among 449 Chinese men. Moreover, in vitro experiments, designed to simulate the real-world scenarios of human exposure, were conducted to assess testosterone synthesis in the Leydig cell line MLTC-1 and testosterone metabolism in the hepatic cell line HepG2 in response to low-dose HAA exposure. The DCAA and TCAA urinary concentrations were found to be positively associated with urinary T, P, and E2 levels (all p < 0.001), but negatively associated with the ratio of urinary T to E2 (p < 0.05). Combined with in vitro experiments, the results suggest that environmentally-relevant doses of HAA stimulate sex hormone synthesis and steroidogenesis pathway gene expression in MLTC-1 cells. In addition, the inhibition of the key gene CYP3A4 involved in the testosterone phase Ⅰ catabolism, and induction of the gene UGT2B15 involved in testosterone phase Ⅱ glucuronide conjugation metabolism along with the ATP-binding cassette (ABC) transport genes (ABCC4 and ABCG2) in HepG2 cells could play a role in elevation of urinary hormone excretion upon low-dose exposure to HAAs. Our novel findings highlight that exposure to HAAs at environmentally-relevant concentrations is associated with increased synthesis and excretion of sex hormones in males, which potentially provides an alternative approach involving urinary hormones for the noninvasive evaluation of male reproductive health following exposure to DBPs.

CdS-Based Hydrothermal Photocatalysts for Complete Reductive Dehalogenation of a Chlorinated Propionic Acid in Water by Visible Light

Cadmium sulfide (CdS)-based photocatalysts are prepared following a hydrothermal procedure (with CdCl2 and thiourea as precursors). The HydroThermal material annealed (CdS-HTa) is crystalline with a band gap of 2.31 eV. Photoelectrochemical investigation indicates a very reducing photo-potential of -0.9 V, which is very similar to that of commercial CdS. CdS-HTa, albeit having similar reducing properties, is more active than commercial CdS in the reductive dehalogenation of 2,2-dichloropropionic acid (dalapon) to propionic acid. Spectroscopic, electro-, and photoelectrochemical investigation show that photocatalytic properties of CdS are correlated to its electronic structure. The reductive dehalogenation of dalapon has a double significance: on one hand, it represents a demanding reductive process for a photocatalyst, and on the other hand, it has a peculiar interest in water treatment because dalapon can be considered a representative molecule of persistent organic pollutants and is one of the most important disinfection by products, whose removal from the water is the final obstacle to its complete reuse. HPLC-MS investigation points out that complete disappearance of dalapon passes through 2-monochloropropionic acid and leads to propionic acid as the final product. CdS-HTa requires very mild working conditions (room temperature, atmospheric pressure, natural pH), and it is stable and recyclable without significant loss of activity.

Formation of halonitromethanes from benzylamine during UV/chlorination: Impact factors, toxicity alteration, and pathways

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br-) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br- concentration raised from 2 to 6 µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Impact of boiling on chemical and physical processes for reduction of halomethanes, haloacetonitriles, and haloacetic acids in drinking water

Tap water is boiled by families across the globe in their daily life for cooking food and beverages, as well as for controlling some chlorine-resistant organisms to improve the water quality. However, the effects of boiling methods (heating temperature, heating modes, open or closed containers) on water quality, in particular the reduction of disinfection byproducts (DBPs), are unclear. This comprehensive research demonstrates that during the heating process, trihalomethanes (THMs) were markedly decreased, haloacetonitriles (HANs) were drastically reduced and sometimes completely removed, while haloacetic acids (HAAs) were reduced the least. Heating to boiling in open containers reduced DBPs concentrations more than heating in the closed containers. Residual chlorine from 0.1 to 5.0 mg/L did not affect the removal of HANs, but could increase concentrations of HAAs likely due to reaction of organic matter with chlorine at elevated temperatures. THMs demonstrated good removal at 0.1-1 mg/L residual chlorine, but less removal at 5 mg/L residual chlorine. Sodium chloride (salt), often added as seasoning agent in the process of family cooking, was found to have little effect on the removal of DBPs during cooking and boiling. Compared with the toxicity of DBPs in tap water, boiling could greatly reduce both the cytotoxicity and carcinogenicity through removal of DBPs. Consequently, boiling of tap water had a significant effect on reducing human exposure to DBPs and their associated toxicities.

Phytotoxicity of trihalomethanes and trichloroacetic acid on Vigna radiata and Allium cepa plant models

Disinfection by-products (DBPs) are a concern due to their presence in chlorinated wastewater, sewage treatment plant discharge, and surface water, and their potential for environmental toxicity. Despite some attention to their ecotoxicity, little is known about the phytotoxicity of DBPs. This study aimed to evaluate the individual and combined phytotoxicity of four trihalomethanes (THMs: trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM) and their mixture (THM4)), and trichloroacetic acid (TCAA) using genotoxic and cytotoxic assays. The analysis included seed germination tests using Vigna radiata and root growth tests, mitosis studies, oxidative stress response, chromosomal aberrations (CA), and DNA laddering using Allium cepa. The results showed a progressive increase in root growth inhibition for both plant species as the concentration of DBPs increased. High concentrations of mixtures of four THMs resulted in significant (p < 0.05) antagonistic interactions. The effective concentration (EC50) value for V. radiata was 5655, 3145, 2690, 1465, 3570, and 725 mg/L for TCM, BDCM, DBCM, TBM, THM4, and TCAA, respectively. For A. cepa, the EC50 for the same contaminants was 700, 400, 350, 250, 450, and 105 mg/L, respectively. DBP cytotoxicity was observed through CAs, including C-metaphase, unseparated anaphase, lagging chromosome, sticky metaphase, and bridging. Mitotic depression (MD) increased with dose, reaching up to 54.4% for TCAA (50-500 mg/L). The electrophoresis assay showed DNA fragmentation and shearing, suggesting genotoxicity for some DBPs. The order of phytotoxicity for the tested DBPs was TCAA > TBM > DBCM > BDCM > THM4 > TCM. These findings underscore the need for further research on the phytotoxicity of DBPs, especially given their common use in agricultural practices such as irrigation and the use of sludge as manure.

Pressure-driven membrane filtration technology for terminal control of organic DBPs: A review

Disinfection by-products (DBPs), a series of undesired secondary contaminants formed during the disinfection processes, deteriorate water quality, threaten human health and endanger ecological safety. Membrane-filtration technologies are commonly used in the advanced water treatment and have shown a promising performance for removing trace contaminants. In order to gain a clearer understanding of the behavior of DBPs in membrane-filtration processes, this work dedicated to: (1) comprehensively reviewed the retention efficiency of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) for DBPs. (2) summarized the mechanisms involved size exclusion, electrostatic repulsion and adsorption in the membrane retention of DBPs. (3) In conjunction with principal component analysis, discussed the influence of various factors (such as the characteristics of membrane and DBPs, feed solution composition and operating conditions) on the removal efficiency. In general, the characteristics of the membranes (salt rejection, molecular weight cut-off, zeta potential, etc.) and DBPs (molecular size, electrical property, hydrophobicity, polarity, etc.) fundamentally determine the membrane-filtration performance on retaining DBPs, and the actual operating environmental factors (such as solute concentration, coexisting ions/NOMs, pH and transmembrane pressure) exert a positive/negative impact on performance to some extent. Current researches indicate that NF and RO can be effective in removing DBPs, and looking forward, we recommend that multiple factors should be taken into account that optimize the existed membrane-filtration technologies, rationalize the selection of membrane products, and develop novel membrane materials targeting the removal of DBPs.

Chlorine-mediated electrochemical advanced oxidation process for ammonia removal: Mechanisms, characteristics and expectation

Chlorine-Mediated Electrochemical Advanced Oxidation (Cl-EAO) technology is a promising approach for ammonia removal from wastewater due to its numerous advantages, including small infrastructure, short processing time, easy operation, high security, and high nitrogen selectivity. This paper provides a review of the ammonia oxidation mechanisms, characteristics, and anticipated applications of Cl-EAO technology. The mechanisms of ammonia oxidation encompass breakpoint chlorination and chlorine radical oxidation, although the contributions of active chlorine, Cl, and ClO remain uncertain. This study critically examines the limitations of existing research and suggests that a combination of determining free radical concentration and simulating a kinetic model would help elucidate the contributions of active chlorine, Cl, and ClO to ammonia oxidation. Furthermore, this review comprehensively summarizes the characteristics of ammonia oxidation, including kinetic properties, influencing factors, products, and electrodes. The amalgamation of Cl-EAO technology with photocatalytic and concentration technologies has the potential to enhance ammonia oxidation efficiency. Future research should concentrate on clarifying the contributions of active chlorine, Cl, and ClO to ammonia oxidation, the production of chloramines and other byproducts, and the development of more efficient anodes for the Cl-EAO process. The main objective of this review is to enhance the understanding of the Cl-EAO process. The findings presented herein contribute to the advancement of Cl-EAO technology and provide a foundation for future studies in this field.

Potential and mechanism of disinfection by-products removal in drinking water by bubbling corona discharge

Disinfection by-products (DBPs) with significant teratogenic and carcinogenic properties have become a growing concern among the public. As an efficient and environmentally friendly technology, non-thermal plasma offers potential for removing emerging micro-pollutants. In this study, the degradation performance of bubbling corona discharge was evaluated on 24 halogenated alicyclic and aliphatic DBPs present in drinking water at concentrations ranging from ng/L to μg/L. The degradation of DBPs followed pseudo-first-order kinetics with rate constants (kobs) in the descending order of halonitromethanes (HNMs), halogenated benzoquinones (HBQs), haloacetonitriles, trihalomethanes (THMs), haloketones, halogenated aldehydes, and haloacetic acids (HAAs). THMs, HNMs, and HBQs were effectively removed within 5 min under a discharge power of 28 W. Degradation rates achieved by plasma treatment surpass those of other conventional treatment technologies. The required energy consumption was in the range of 5-30 kW·h/m3/order. Furthermore, the study investigated the effects of discharge power, initial concentration, and economic analysis on the degradation of four selected DBPs as representatives of mono-, di- and multi-carbon-containing DBPs, namely chloroform (TCM) and bromoform (TBM), tribromoacetic acid (TBAA), and 2,3,5,6-tetrachloro-1,4-benzoquinone (TetraC-BQ). Reactive radicals in the plasma system were investigated using electron paramagnetic resonance, optical emission spectroscopy, fluorimetry, and radical scavengers. Hydrated electrons and hydroxyl radicals played an important role in the removal of DBPs. The intermediates generated during the degradation of TCM, TBM, TBAA, and TetraC-BQ were identified, and the possible degradation pathways for mono- and binary C-DBPs and HBQs were deduced. The breakdown of HBQs did not produce secondary contamination with aliphatic DBPs. The carbon in DBPs was primarily converted to formic acid, acetic acid, and oxalic acid, and the halogens were mainly converted to halogen ions. Additionally, luminescent bacteria toxicity testing confirmed that plasma treatment could reduce the acute toxicity of water samples. These findings demonstrate the potential of plasma treatment as a post-treatment device at the household level.