Degradation Of Disinfection By-products Research Articles

Gastrointestinal Degradation and Toxicity of Disinfection Byproducts in Drinking Water Using In Vitro Models and the Roles of Gut Microbiota.

Disinfection byproducts (DBPs) in drinking water are mainly exposed to the human body after oral ingestion and degradation in the gastrointestinal tract. The role of gastrointestinal degradation in the toxic effects of DBPs still needs further investigation. In this study, the degradation of five categories of DBPs (22 DBPs) in the stomach and small intestine was investigated based on a semicontinuous steady-state gastrointestinal simulation system, and 22 DBPs can be divided into three groups based on their residual proportions. The degradation of chloroacetonitrile (CAN), dibromoacetic acid (DBAA), and tetrabromopyrrole (FBPy) was further analyzed based on the Simulator of the Human Intestinal Microbial Ecosystem inoculating the gut microbiota, and approximately 60% of CAN, 45% of DBAA, and 80% of FBPy were degraded in the stomach and small intestine, followed by the complete degradation of remaining DBPs in the colon. Meanwhile, gastrointestinal degradation can reduce oxidative stress-mediated DNA damage and apoptosis induced by DBPs in DLD-1 cells, but the toxicity of DBPs did not disappear with the complete degradation of DBPs, possibly because of their interferences on gut microbiota. This study provides new insights into investigating the gastrointestinal toxic effects and mechanisms of DBPs through oral exposure.

Differences in the degradation behavior of disinfection by-products in UV/PDS and UV/H2O2 processes and the effect of their chemical properties

In this work, sixteen typical chlorinated and brominated aromatic disinfection by-products (DBPs) were selected as examples to investigate their different degradation mechanisms initiated by HO• and SO4•-. Addition reactions were the main mode of degradation of DBPs by HO•, while SO4•- dominated H-abstraction reactions and single electron transfer reactions. Chlorinated compounds had higher reactivity than brominated compounds. Furthermore, substituents with stronger electron-donating effects promoted the electrophilic reaction of DBPs with the two radicals. In addition, we developed a model based on the chemical properties LUMO, fmax−, and hardness for predicting the average reaction energy barriers for the initial reactions of DBPs with HO• and SO4•-. The model had good predictive performance for the difficulty of degradation of different DPBs by HO• and SO4•-, with R2 values of 0.85 and 0.87, respectively. Through the degradation efficiency simulation, we found that longer reaction times, higher oxidant concentrations and lower pollutant concentrations were more favorable for the removal of DBPs. The UV/PDS process showed better degradation of DBPs than the UV/H2O2 process. In addition, most degradation products of DBPs exhibited less toxicity to aquatic organisms than their parent compounds. This study provided theoretical guidance for the degradation and removal of other aromatic DBPs at the molecular level.

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.

Continuous flow operation of solar photo-Fenton fused with NaOCl as a novel tertiary treatment

A novel strategy based on solar photo-Fenton mediated by ferric nitrilotriacetate (Fe3+-NTA) combined with NaOCl in continuous flow mode for wastewater reclamation has been studied. Escherichia coli (E. coli) inactivation attained ≥ 5 log10-units, meeting the most restrictive EU 2020/741 target (10 CFU/100 mL), and 75% of organic microcontaminant total load was removed. As a remarkable finding, trihalomethanes (THMs) concentration was insignificant, complying by far with the Italian legislation limit. To attain these results, first the effect of liquid depth on E. coli inactivation and imidacloprid (IMD) removal from spiked municipal effluents was evaluated in continuous flow pilot-scale raceway pond reactors at 60-min hydraulic residence time with low reagent concentrations (0.10 mM Fe3+-NTA, 0.73 mM H2O2 and 0.13 mM NaOCl). Disinfection was due to the bactericidal effect of chlorine. In contrast, liquid depth notably influenced microcontaminant removal, highlighting that operation at 10-cm liquid depth allows achieving treatment capacities higher than at 5 cm (16.50 vs 28.20 mg IMD/m2∙day). Next, the monitoring of THMs was carried out to evaluate the generation and degradation of disinfection by-products, along with the removal of actual microcontaminants. These promising results draw attention to the treatment potential and open the way for its commercial application.

Convenient recycling and efficient photocatalytic degradation of disinfection by-products by in-situ growth MOF on PET

Drinking water disinfection processes have made remarkable contributions to keeping drinking water safe. However, these processes can lead to the formation of numerous harmful disinfection by-products (DBPs). Therefore, it is crucial to implement effective measures to minimize the production of DBPs. Herein, PET@PDA@NH2-MIL-53(Fe) (PNM) composite was successfully prepared via surface etching and solvothermal method. The material exhibited excellent photocatalytic activity for DBPs and their precursors at the photo-Fenton system formed by PNM and trace H2O2, which system achieved 99% degradation of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) in 30 min, and more than 98% and 95% degradation of phenol and bisphenol A (BPA) in 60 min. The PNM shows more than 90% degradation of DBPs even in real water. Based on free radical trapping experiments, a possible catalytic mechanism was proposed. ·OH and holes were the main active species in the catalytic process. Meanwhile, using UPLC-QTOF and GC–MS to identify intermediate degradation products and Toxtree software to assess toxicity. The PNM maintained a degradation rate over 95% after 5 cycles which demonstrates a remarkable recyclability. This study achieves the reuse of waste PET and opens a new way in exploring the development of eco-friendly photocatalytic materials.

Evaluation of N-acetylcysteine and glutathione as quenching agents for the analysis of halogenated disinfection by-products

Disinfection by-products (DBPs), formed from the reactions of disinfectants with natural organic matter and halides in drinking water, were considered to be cytotoxic and genotoxic, and might trigger various cancers. The relatively low concentration of DBPs in finished water (low µg/L or even ng/L levels) and the interference from water matrix inhibited in situ determination of DBPs. Moreover, the further formation and degradation of DBPs by disinfectants during the holding time (several hours to several days) from sample collection to analysis could adversely affect the determination of DBPs. To obtain accurate, precise and reliable data of DBP occurrence and formation, robust and reliable sample preservation is indispensable. However, the commonly used quenching agents (e.g., sodium sulfite, sodium thiosulfate, and ascorbic acid) for sample preservation can decompose reactive DBPs by reductive dehalogenation. This study evaluated the performance of N-acetylcysteine (NAC) and glutathione (GSH) as quenching agents for the analysis of halogenated DBPs by investigating the stoichiometry of the disinfectant-quenching agent reaction, the formation of DBPs during chlor(am)ination of NAC or GSH, and the effects of NAC or GSH on the stability of 18 individual DBPs and total organic halogen (TOX). Based on the results of this study, NAC and GSH were considered to be ideal quenching agents for the analysis of most DBPs and TOX, except halonitromethanes.

Insight into efficient degradation of 3,5-dichlorosalicylic acid by Fe-Si-B amorphous ribbon under neutral condition

Water disinfection would result in unintended formation of halogenated disinfection by-products (DBPs) which pose potential harm to human health. In present work, Fe78Si9B13 amorphous ribbons (Fe-Si-BAR) showed excellent catalytic degradation performance towards an aromatic DBP, 3,5-dichlorosalicylic acid (3,5-DiClSA) by Fenton-like reaction. The catalytic degradation performances of Fe-Si-BAR, Fe78Si9B13 crystalline ribbons (Fe-Si-BCR) and iron powders towards 3,5-DiClSA were compared, and Fe-Si-BAR (0.0166 min−1) showed the fastest degradation rate. The faster surface mobility of Fe-Si-BAR, which made it easy for Fe2+ to be oxidized by H2O2, facilitated the degradation process. High-valent iron of FeIV could be generated which accounted for degradation of 3,5-DiClSA. The Fe-Si-BAR also showed better and better catalytic performance in 10 reuse cycles. Besides, the cytotoxicity tests indicated that the overall toxicity level of 3,5-DiClSA was declined by 88.1 % after degradation by Fe-Si-BAR. Our results showed that Fe-Si-BAR is a promising catalyst for the degradation of aromatic DBPs.

Effect of visible light on the removal of trichloromethane by graphene oxide

In this experimental study, the degradation of disinfection by-products using graphene oxide was studied. Degradation of chloroform, which is the most common type of trihalomethanes in water, was investigated. Graphene oxide (GO) was synthesized by the Modified Hummers' Method. TEM images showed that the synthesized graphene oxide was exfoliated layer by layer and was very stable according to the zeta potential result. In the degradation studies; the effect of time, chloroform concentration and graphene oxide concentration were investigated both under visible light and under darkness. According to the experimental results, studies containing 100 μg/L trichloromethane and 250 mg/L GO were stabilized after 30 min and the removal of 70.6% for darkness increased to 98% under visible light. When the graphene oxide concentration is increased, it is seen that the positive effect of visible light increases from 22% to 30%. According to the isotherm and kinetic model research, it was found that the studies conducted in both conditions were appropriate to Freundlich isotherm and Pseudo second-order kinetic model. The maximum adsorption capacities based on Pseudo second-order kinetic modeling was obtained as 350 and 450 μg/g for darkness and visible light, respectively.

Kinetics of the formation and degradation of carbonaceous and nitrogenous disinfection by-products in Bangkok and Songkhla source waters

The kinetics of the formation and degradation of disinfection by-products (DBPs) in the treated water from the Bangkhen and Hatyai water treatment plants in Thailand were investigated. The DBPs studied included trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and trichloronitromethane (TCNM). When the chlorination time was increased, the levels of TCM, BDCM, DBCM, and TCNM increased, while the levels of TCAN, DCAN, and BCAN decreased. The kinetic rates of DBPs’ formation were assessed based on the formation and degradation rates, which were best described by first-order kinetics. TCM had the highest formation rate with a range of rate constants from 5.5 × 10−3 to 7.3 × 10−3 h−1. TCAN had the lowest degradation rate with a range of rate constants from 0.6 × 10−3 to 2.9 × 10−3 h−1. Good correlations were observed between chlorination time and DBPs’ formation normalized by LC50, lowest cytotoxicity, and lowest genotoxicity. A high formation rate of TCM and a low degradation rate of TCAN normalized by their toxicity were observed. The optimal retention time providing low DBPs’ formation together with high DBPs’ degradation was determined. The retention time of three days decreased the sum of the DBPs/LC50, DBPs/lowest cytotoxicity, and DBPs/lowest genotoxicity from a retention time of one day by 40–60%, 45–65%, and 25–36%, respectively.

Short-term spatial and temporal variability of disinfection by-product occurrence in small drinking water systems

Disinfection by-products (DBPs) constitute a large family of compounds. Trihalomethanes and haloacetic acids are regulated in various countries, but most DBPs are not. Monitoring DBPs can be delicate, especially for small systems, because various factors influence their formation and speciation. Short-term variations of DBPs can be important and particularly difficult for small systems to handle because they require robust treatment and operation processes. According to our knowledge, for the first time, our study covers the short-term variability of regulated and non-regulated DBP occurrence in small systems in the summer. An intensive sampling program was carried out in six small systems in Canada. Systems in the provinces of Newfoundland and Labrador and Quebec were sampled daily at the water treatment plant and at six different locations along the distribution system. Five DBP families were studied: trihalomethanes, haloacetic acids, haloacetonitriles, halonitromethanes and haloketones. Results show that there were considerable variations in DBP levels from week to week during the month of study and even from day to day within the week. On a daily basis, DBP levels can fluctuate by 22% to 96%. Likewise, the large number of sampling locations served to observe DBP variations along the distribution system. Observations revealed some degradation and decomposition of non-regulated DBPs never before studied in small systems that are associated with the difficulty these systems experience in maintaining adequate levels of residual disinfectant. Finally, this study reveals that the short term temporal variability of DBPs is also influenced by spatial location along the distribution system. In the short term, DBP levels can fluctuate by 23% at the beginning of the system, compared to 40% at the end. Thus, spatial and temporal variations of DBPs in the short term may make it difficult to select representative locations and periods for DBP monitoring purposes in small systems.

Chemical Degradation of Drinking Water Disinfection Byproducts by Millimeter-Sized Particles of Iron−Silicon and Magnesium−Aluminum Alloys

The candidature of Fe-Si and Mg-Al alloys at millimeter-scale particle sizes for chemical degradation of disinfection byproducts (DBPs) in drinking water systems was substantiated by their enhanced corrosion resistance and catalytic effect on the degradation. The Mg-Al particles supplied electrons for reductive degradation, and the Fe-Si particles acted as a catalyst and provided the sites for the reaction. The alloy particles are obtained by mechanical milling and stable under ambient conditions. The proposed method for chemical degradation of DBPs possesses the advantages of relatively constant degradation performance, long-term durability, no secondary contamination, and ease of handling, storage and maintenance in comparison with nanoparticle systems.

Degradation of Disinfection Byproducts by Carbonate Green Rust

Disinfection byproducts (DBPs) in drinking water flowing through corroded iron or steel pipes may encounter carbonate green rust (GR(CO32-)), a mixed Fe(II)/Fe(lll) hydroxide mineral and potent reductant. This research was performed to investigate the kinetics and pathways of the degradation of selected halogenated DBPs in the presence of GR(C032-). Trichloronitromethane was rapidly degraded to methylamine via sequential hydrogenolysis followed by nitro-reduction. Haloacetic acids reacted solely via sequential hydrogenolysis. Trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldehyde hydrate were transformed via hydrolysis and hydrogenolysis. Chloroform was unreactive over 300 h. The buffer identity affected reductive dehalogenation rates of DBPs, with faster rates in MOPS buffer than in carbonate buffer, the latter being representative of the buffer in drinking water systems. GR(CO32-) was unstable in both buffers and transformed to magnetite within 48 h. Thus, slower reacting compounds (half life >3 hours) were transformed by a combination of minerals. Reductive dehalogenation kinetics were influenced by DBP chemical structure and correlated with one-electron reduction potential.

Degradation of Disinfection Byproducts in Drinking Water

An investigation of the behavior of different categories of disinfection byproducts (DBPs) in ultrapure water and in spiked drinking water samples was performed. The influence of sunlight, pH, and time was examined. Several of the compounds were subject to degradation with time, while others showed increasing trends, possibly due to natural production by bacteria. Chloroform, monochloroacetonitrile, and monochloroacetic acid slightly increased in the presence of sunlight, while d ichloroacetonitrile, dibromoacetic acid, tribromoacetic acid, and mixed bromo-chloro acetic acids were subject to decomposition, especially under sunlight. However, sunlight was found to decelerate decomposition of trichloropropanone and to prevent decomposition of bromochloro-acetonitrile and chloral hydrate. Trichloropropanone decomposed to chloroform, while mixed haloacetic acids decomposed to the corresponding trihalomethanes. Multiple regression equations were obtained for the concentrations of i ndividual DBPs in drinking water as a function of time, pH, and sunlight. Most of the volatile DBPs decreased with increasing pH both in sunlight and in darkness, while haloacetic acids remained unaffected from pH. However, haloacetic acids seemed to be influenced by sunlight to a significantly greater extent than volatile DBPs. Knowledge of the behavior of individual compounds during exposure to sunlight is essential towards the development of photolysis-based removal techniques. pH influence needs to b e considered, especially in the case of volatile DBPs.