Precursors of dichloroacetamide, an emerging nitrogenous DBP formed during chlorination or chloramination

Computational-aided analysis of the pathway and mechanism of dichloroacetonitrile formation from phenylalanine upon chloramination

Dichloroacetonitrile (DCAN) is an emerging disinfection by-product (DBP) that is widespread in drinking water. However, the pathway for DCAN formation from aromatic amino acids remains unclear, leading to a lack of an understanding of its explicit fate during chloramination. In this study, we investigated the specific formation mechanism of DCAN during the chloramination of phenylalanine based on reaction kinetics and chemical thermodynamics. The reason for differences between aldehyde and decarboxylation pathways was explained, and kinetic parameters of the pathways were obtained through quantum chemistry calculations. The results showed that the reaction rate constant of the rate-limiting step of the aldehyde pathway with 1.9 × 10-11 s-1 was significantly higher than that of decarboxylation (3.6 × 10-16 s-1 M-1), suggesting that the aldehyde pathway is the main reaction pathway for DCAN formation during the chloramination of phenylalanine to produce DCAN. Subsequently, theoretical calculations were performed to elucidate the effect of pH on the formation mechanism, which aligned well with the experimental results. Dehydrohalogenation was found to be the rate-limiting step under acidic conditions with reaction rate constants higher than those of the rate-limiting step (expulsion of amines) under neutral conditions, increasing the rate of DCAN formation. This study highlights the differences in DCAN formation between the decarboxylation and aldehyde pathways during the chloramination of precursors at both molecular and kinetic levels, contributing to a comprehensive understanding of the reaction mechanisms by which aromatic free amino acids generate DCAN.

High throughput identification of carbonyl compounds in natural organic matter by directional derivatization combined with ultra-high resolution mass spectrometry

Carbonyl compounds are important components of natural organic matter (NOM) with high reactivity, so that play a pivotal role in the dynamic transformation of NOM. However, due to the lack of effective analytical methods, our understanding on the molecular composition of these carbonyl compounds is still limited. Here, we developed a high-throughput screening method to detect carbonyl molecules in complex NOM samples by combining chemical derivatization with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). In six different types of dissolved organic matter (DOM) samples tested in this study, 20-30 % of detected molecules contained at least one carbonyl group, with relative abundance accounted for 45-70 %. These carbonyl molecules displayed lower unsaturation level, lower molecular weight, and higher oxidation degree compared to non-carbonyl molecules. More importantly, the measured abundances of carbonyl molecules were consistent with the results of 13C nuclear magnetic resonance (NMR) analysis. Based on this method, we found that carbonyl molecules can be produced at DOM-ferrihydrite interface, thus playing a role in shaping the molecular diversity of DOM. This method has broad application prospects in screening carbonyl compounds from complex mixtures, and the same strategy can be used to directional identification of molecules with other functional groups as well.

A sequencing electroreduction-electrooxidation system driven by atomic hydrogen for enhancing 2,4-dichloronitrobenzene removal from wastewater

The sequencing electroreduction-electrooxidation process has emerged as a promising approach for the degradation of the chloronitrobenzenes (CNBs) due to its elimination of electro-withdrawing groups in the reduction process, facilitating further removal in the subsequent oxidation process. Herein, we developed a cathode consisting of atom Pd on a Ti plate, which enabled the electro-generation of atomic hydrogen (H*) and the efficient electrocatalytic activation of H2O2 to hydroxyl radical (•OH). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra verified the existence of H* and •OH. The electroreduction-electrooxidation system achieved 94.7% of 20 mg L-1 2,4-DCNB removal with a relatively low H2O2 addition (5 mM). Moreover, the inhibition rate of Photobacterium phosphoreum in the effluent decreased from 95% to 52% after the sequencing electroreduction-electrooxidation processes. It was further revealed that the H* dominated the electroreduction process and triggered the electrooxidation process. Our work sheds light on the effective removal of electron-withdrawing groups substituted aromatic contaminants from water and wastewater.

Assessing the Health Impact of Disinfection Byproducts in Drinking Water

This study provides a comprehensive investigation of the impact of disinfection byproducts (DBPs) on human health, with a particular focus on DBPs present in chlorinated drinking water, concentrating on three primary DBP categories (aliphatic, alicyclic, and aromatic). Additionally, it explores pivotal factors influencing DBP formation, encompassing disinfectant types, water source characteristics, and environmental conditions, such as the presence of natural materials in water. The main objective is to discern the most hazardous DBPs, considering criteria such as regulation standards, potential health impacts, and chemical diversity. It provides a catalog of 63 key DBPs alongside their corresponding parameters. From this set, 28 compounds are meticulously chosen for in-depth analysis based on the above criteria. The findings strive to guide the advancement of water treatment technologies and intelligent sensory systems for the efficient water quality surveillance. This, in turn, enables reliable DBP detection within water distribution networks. By enriching the understanding of DBP-associated health hazards and offering valuable insights, this research is aimed to contribute to influencing policy-making in regulations and treatment strategies, thereby protecting public health and improving safety related to chlorinated drinking water quality.

Fluorescence spectroscopy in the detection and management of disinfection by-product precursors in drinking water treatment processes: A review

Monitoring and prevention of the formation of disinfection by-products (DBPs) is paramount in drinking water treatment plants (DWTP) to ensure human health safety. This review provides an overview of how fluorescence techniques are developed to predict DBP formation and to evaluate the reduction of fluorescence components and DBPs following individual DWTP processes. Evidence has shown that common DBPs, nitrogenous DBPs and specific emerging DBPs exhibit positive linear relationships with terrestrial, anthropogenic, tryptophan-like, and eutrophic humic-like fluorescence. Due to the interrelationships of both regulated and emerging DBP types with fluorescence components, the limitations arise when attempting to predict emerging DBPs solely through linear relationships. Monitoring the reduction of DBP precursors after each treatment process can be achieved by studying the relationship between fluorescence components and DBPs. During the coagulation process, highest reduction rates are observed for terrestrial humic-like fluorescence. Advanced treatments such as granular, powdered, silver-impregnated activated carbon, magnetic ion exchange resins, and reverse osmosis, have revealed a significant reduction of fluorescent DBP precursors, ranging from 53% to 100%. During chlorination, the reduction rate follows the order: terrestrial humic-like > microbial humic-like > protein/tryptophan-like fluorescence. This review provides insights into the reduction of fluorescence signatures following individual DWTP processes, which offers information regarding DBP formation. These insights could assist in optimizing the treatment process to more effectively manage DBP formation. For the identification of emerging DBP generation, the utilization of advanced models is imperative to precisely predict emerging DBPs and to more accurately trace DBP precursors within DWTPs.

Alkaline chlorination of drinking water: A trade-off between genotoxicity control and trihalomethane formation

The pH of chlorination is an important factor affecting the formation of disinfection byproducts (DBPs). In this study, we discovered that the genotoxicity induced by chlorination can be effectively reduced under alkaline conditions. As the pH of chlorination increased from 6.5 to 8.5, the genotoxicity of investigated waters reduced by ∼30-90 %. By assessing the genotoxicity of the mixture of measured DBPs, it was found that the contribution of measured DBPs to the overall genotoxicity was lower than 5 %, and the significant reduction of genotoxicity was largely associated with unknown DBPs. The result of Pearson's correlation analysis indicated that humified organics and soluble microbial byproducts were likely responsible for the genotoxicity, and their derived genotoxic compounds (i.e., unknown DBPs) tended to decompose during alkaline chlorination. However, the control of genotoxicity by alkaline chlorination was achieved at the expense of promoting trihalomethane (THM) formation. The highest genotoxicity reduction (93 %) was observed for chlorinated granular activated carbon-treated waters, but the formation of THMs was promoted to a level approaching that in untreated waters. The inconsistent trend of overall genotoxicity and THM concentration during alkaline chlorination suggested the inadequacy of THMs as metric for DBP exposure, and considerations should also be given to the toxicity of bulk water in addition to regulated DBPs.

Emerging disinfection by-products formation of various molecular weight organic matter fractions in raw water contaminated with treated wastewater

Combining dissolved organic matter (DOM) in raw water (RW) with DOM in treated wastewater (TWW) can react with chlorine and pose emerging disinfection by-products (DBPs). This study evaluated DOM based on the molecular weight (MW) size fractionation, trihalomethane, iodinated-trihalomethane, haloacetonitrile, and trichloronitromethane formation potential (THMFP, I-THMFP, HANFP, and TCNMFP) of the RW from the U-Tapao Canal, Songkhla, Thailand and the RW mixed with TWW (RW + TWW) samples. The RW and RW + TWW were treated by coagulation with poly aluminum chloride. The DOM of RW and RW + TWW and their treated water was distributed most in the MW below 1 kDa. The MWs of 3-10 kDa and 1-3 kDa were the active DOM involved in the specific THMFP for the RW + TWW. The MW of < 1 kDa in the RW + TWW resulted in a slightly high specific I-THMFP and HANFP. The MW of 1 - 3 kDa in the coagulated samples had a high specific I-THMFP. The MW of > 10 kDa in the coagulated RW + TWW was a precursor for a particular HANFP. Monitoring systems for measuring the level of TWW mixed with RW and an effective process to enhance the efficiency of traditional water treatment must be set up to produce a consumer-safe water supply.

Formation characteristics and acute toxicity assessment of THMs and HAcAms from DOM and its different fractions in source water during chlorination and chloramination

The formation characteristics of trihalomethanes (THMs) and haloacetamides (HAcAms) from dissolved organic matter and its fractions were investigated during chlorine-based disinfection processes. The relationships between water quality parameters, fluorescence parameters, and the formation levels of THMs and HAcAms were analyzed. The fractions contributing most to the acute toxicity were identified. The trichloromethane (TCM) generation level (72 h) generally followed the order of Cl₂ > NH₂Cl > NHCl₂ process. The NHCl₂ process was superior to the NH₂Cl process in controlling TCM formation. Hydrophobic acidic substance (HOA), hydrophobic neutral substance (HON), and hydrophilic substance (HIS) were identified as primary precursors of 2,2-dichloroacetamide and trichloroacetamide during chlorination and chloramination. The formation of TCM mainly resulted from HOA, HON and HIS fractions relatively uniformly, while HOA and HIS fractions contributed more to the formation of bromodichloromethane and dibromomonochloromethane. UV₂₅₄ could be used as an alternative indicator for the amount of ΣTHMs formed during chlorination and chloramination processes. Dissolved organic nitrogen was a potential precursor of 2,2-dichloroacetamide during chlorination process. The fractions with the highest potential acute toxicity after the chlorination were water-dependent.

Identification of key precursors contributing to the formation of CX3R-type disinfection by-products along the typical full-scale drinking water treatment processes

Identification and characterization of disinfection by-product (DBP) precursors could help optimize drinking water treatment processes and improve the quality of finished water. This study comprehensively investigated the characteristics of dissolved organic matter (DOM), the hydrophilicity and molecule weight (MW) of DBP precursor and DBP-associated toxicity along the typical full-scale treatment processes. The results showed that dissolved organic carbon and dissolved organic nitrogen content, the fluorescence intensity and the SUVA₂₅₄ value in raw water significantly decreased after the whole treatment processes. Conventional treatment processes were in favor of the removal of high-MW and hydrophobic DOM, which are important precursors of trihalomethane and haloacetic acid. Compared with conventional treatment processes, Ozone integrated with biological activated carbon (O₃-BAC) processes enhanced the removal efficiencies of DOM with different MW and hydrophobic fractions, leading to a further decrease in almost all DBP formation potential and DBP-associated toxicity. However, almost 50% of the detected DBP precursors in raw water has not been removed after the coagulation-sedimentation-filtration integrated with O₃-BAC advanced treatment processes. These remaining precursors were found to be mainly hydrophilic and low-MW (< 1.0 kDa) organics. Moreover, they would largely contribute to the formation of haloacetaldehydes and haloacetonitriles, which dominated the calculated cytotoxicity. Since current drinking water treatment process could not effectively control the highly toxic DBPs, the removal of hydrophilic and low-MW organics in drinking water treatment plants should be focused on in the future.

Relating algal-derived extracellular and intracellular dissolved organic nitrogen with nitrogenous disinfection by-product formation

The dissolved organic nitrogen (DON) pool from algal-derived extracellular and intracellular organic matter (EOM and IOM) comprises proteins, peptides, free amino acids and carbohydrates, of which, proteins can contribute up to 100% of the DON. Previous reports of algal-derived DON character have focused on bulk properties including concentration, molecular weight and hydrophobicity. However, these can be similar between algal species and between the EOM and IOM even when the inherent molecular structures vary. A focus on bulk character presents challenges to the research on algal-derived nitrogenous-disinfection by-product (N-DBP) formation as N-DBP formation is sensitive to the changes in molecular structure. Hence, the main aim of this study was to characterize algal EOM and IOM-derived DON, specifically proteinaceous-DON, using a combination of bulk and molecular characterization techniques to enable a more detailed exploration of the relationship between the character of algal-derived proteins and the N-DBP formation potential. DON from the EOM and IOM of four commonly found algae and cyanobacteria in natural waters were evaluated, namely Chlorella vulgaris, Microcystis aeruginosa, Dolichospermum circinale, and Cylindrospermopsis raciborskii. It was observed that 77-96% of total DON in all EOM and IOM samples was of proteinaceous origin. In the proteins, DON concentrations were highest in the high molecular weight fraction of IOM-derived bulk proteins (0.13-0.75 mg N L^-1) and low to medium molecular weight fraction of EOM-derived bulk proteins (0.15-0.63 mg N L^-1) in all species. Similar observations were also made via sodium dodecyl sulphate polyacrylamide gel electrophoresis and liquid chromatography-high resolution mass spectrometry. Solid-state ¹⁵N nuclear magnetic resonance (NMR) spectroscopy of the EOM and IOM revealed the existence of common aliphatic and heterocyclic N-groups in all samples, including a dominant 2° amide peak. Species dependent variability was also observed in the spectra, particularly in the EOM; e.g. nitro signals were found only in the Cylindrospermopsis raciborskii EOM. Dichloroacetonitrile (DCAN) and N-nitrosamine concentrations from the EOM of the species evaluated in this study were lower than the guideline limits set by regulatory agencies. It is proposed that the dominant 2° amide in all samples decreased N-DBP formation upon chlorination. For chloramination, the presence of nitro groups and aliphatic and heterocyclic N-DBP precursors could cause variable N-nitrosamine formation. Compared to non-algal impacted waters, algae-laden waters are characterised by low organic carbon: organic nitrogen ratios of ∼7-14 and elevated DON and protein concentrations. Hence, relying only on bulk characterization increases the perceived risk of N-DBP formation from algae-laden waters.

Aspartame-Sweetened Tap Water: Transformation Products and 2,6-Dichloro-1,4-Benzoquinone Formation

Aspartame (APM), a dipeptide of aspartic acid (ASP) and phenylalanine (PHE), is a widely used artificial sweetener in beverages. It is unclear whether residual chlorine in tap water can react with APM to form disinfection byproducts (DBPs). Therefore, we investigated the formation of DBPs from the reaction of APM with residual chlorine in authentic tap water. APM and a commercial sweetener (CS) packet containing APM were studied under authentic and simulated tap water conditions. Eight chlorinated products of APM were detected using solid-phase extraction (SPE) and high performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS). These new chloro-products were tentatively identified based on accurate masses, isotopic patterns of 35,37Cl, and MS/MS spectra. Furthermore, we identified APM as a precursor to 2,6-dichloro-1,4-benzoquinone (DCBQ). DCBQ significantly increased to 2.3-12 ng/L with the addition of APM or CS in tap waters collected from different locations compared to 1.4-1.8 ng/L in the same tap water samples without sweetener. DCBQ and two of the chlorinated transformation products were identified in cold prepared tea containing APM. DCBQ formation was eliminated when the residual chlorine in tap water was reduced by ascorbic acid or boiling prior to the addition of APM or CS. This study found that eight new DBPs and DCBQ were produced by the reactions of residual chlorine with APM and CS. These findings show an unintended exposure source of emerging DBPs via APM sweetened beverages.

Characteristics of dissolved organic matter in two alternative water sources: A comparative study between reclaimed water and stormwater

Reclaimed water and stormwater are two important alternative water sources to mitigate water resource shortage. They can be reused by discharging into drinking water sources. Due to different sources, characteristics of dissolved organic matter (DOM, a precursor of disinfection by-products, DBPs) present in reclaimed water and stormwater would be different. This study selected reclaimed water to compare with stormwater (including both stormwater runoff and rainwater) by investigating their DOM characteristics, including concentrations, aromaticity, molecular weight, hydrophobicity/hydrophilicity, composition and DBPs formation potential. The results showed that reclaimed water had higher dissolved organic carbon (DOC) concentrations (6.02-10.8 mg/L) than stormwater (3.62-5.48 mg/L) while SUVA₂₅₄ values of stormwater runoff (1.92-2.53 L/(mg-C·m)) were higher than reclaimed water (1.11-1.24 L/(mg-C·m)). Additionally, reclaimed water is more hydrophobic while stormwater runoff and rainwater are more hydrophilic. Although all water types included the highest fraction of DOM with molecular weight <1 kDa (43.0 %-77.5 %), reclaimed water primarily contained soluble microbial products (SMPs)-like and humic acid-like substances while stormwater runoff primarily contained humic acid-like DOM. In terms of DBPs, reclaimed water showed relatively higher formation potential than stormwater runoff while rainwater had the lowest DBPs formation potential. These results can contribute to effective water resource management. Particularly, when reclaimed water or/and stormwater are discharged into drinking water sources, these outcomes can help on efficient drinking water treatment.

Treatment of bromate in UV/sulfite autoxidation process enhances formation of dibromoacetonitrile during chlorination

The integration of UV/sulfite autoxidation process (USAP, i.e., UV activation of sulfite in the presence of 5 ∼ 10 mg/L O₂) into conventional water to degrade micropollutants rises extensive attention, but its impact on water quality, and especially the formation of disinfection byproducts is still unclear. Herein, the formation of dibromoacetonitrile (DBAN) from bromate (BrO₃^-) upon treatment with USAP followed by chlorination was evaluated, in the presence of amino acids (AAs) selected as representative organic matter in drinking water. Results revealed that hydrated electrons (e_aq^-) produced during USAP contribute to the reduction of BrO₃^- to Br^-, which is then converted into HBrO/BrO^- during post-chlorination. At the same time, sulfate radicals (SO₄^•-) and hydroxyl radicals (•OH) generated in USAP mediated AAs' conversion via α-hydrogen abstraction and NH₂-hydrogen abstraction reactions to produce HN=C(CH₃)‒COOH, CH₃‒CH=NH, and CH₃‒CN, which are released into the post-chlorination stage and therefore, enhance the bromine utilization factor (BUF) value and DBAN formation. The effects of the USAP treatment time, BrO₃^- concentration, AA concentration, pH, and real waters were also evaluated. Although 63.5% of BrO₃^- was eliminated by USAP followed by chlorination, the toxicity index (TI) was increased by 1.5-fold due to the formation of the all brominated CX₃R-type nitrogenous disinfection byproducts (N-DBPs), demonstrating the potential risk of applying USAP as a treatment process in BrO₃^- containing waters.

Effects of biological activated carbon filter running time on disinfection by-product precursor removal

Biological activated carbon (BAC) filtration is usually considered to be able to decrease formation potentials (FPs) of disinfection by-products (DBPs) in drinking water treatment plant (DWTP). However, BAC filters with long running time may release microbial metabolites to effluents and therefore increase FPs of nitrogenous DBPs with high toxicity. To verify this hypothesis, this study continuously tracked BAC filters in a DWTP for one year, and assessed effects of old (running time 8-9 years) and new (running time 0-13 months) BAC filters on FPs of 15 regulated and unregulated DBPs. Results revealed that dissolved organic carbon (DOC) removal was slightly higher in the new BAC than the old one. All fluorescent components of dissolved organic matter evidently declined after new BAC filtration, but fulvic acid-like and soluble microbial product-like substances increased after old BAC filtration, which could be caused by microbial leakage. Correspondingly, new BAC filter generally removed more DBP FPs than the old one. 46.5% HAA₇ FPs from chlorination and 44.3% THM₄ FPs from chloramination were removed by new BAC filter. However, some DBP FPs, especially HAN FPs, were poorly removed or even increased by the old BAC filter. Proteobacteria could be a main contributor for DBP precursor removal in BAC filters. Herminiimonas, most abundant genera in new BAC filter, may explain its better DOC and UV₂₅₄ removal performance and lower DBP FPs, while Bradyrhizobium, most abundant genera in old BAC filter, might produce more extracellular polymeric substances and therefore increased N-DBP FPs in old BAC effluent. This study provided insight into variations of DBP FPs and microbial communities in the new and old BAC filters, and will be helpful for the optimization of DWTP design and operation for public health.

Degradation of sulfadiazine by UV/Oxone: roles of reactive oxidative species and the formation of disinfection byproducts

Sulfadiazine (SDZ) is a typical persistent sulfonamide antibiotic, which has been widely detected in natural drinking water sources. The degradation of SDZ by UV/Oxone (potassium monopersulfate compound) was explored in this study. The results showed that Cl^- can effectively activate PMS to promote rapid degradation of SDZ in the Oxone process by forming chlorine in the system. Radical quenching tests suggested that radical oxidation, including HO^•, SO₄^•-, and reactive chlorine species (RCS), played an important role by UV/Oxone. It further verified that concentration and distribution of HO^•, SO₄^•-, and RCS were pH-dependent; RCS act as a major contributor at pH 6.0 and pH 7.0 to degrade SDZ in this process. The SDZ degradation rate was firstly increased and then decreased by Cl^- and HCO₃^- (0-10 mM); HA (0-10 mg L^-1) exhibited insignificant influence on SDZ degradation. The degradation pathways of SDZ during UV/Oxone and formation pathways of five disinfection byproducts during subsequent chlorination were proposed. The possible DBP precursors formed by SO₂ extrusion, hydroxylation, and chlorination of SDZ during UV/Oxone pre-oxidation.

Unique On-Site Spinning Sampling of Highly Water-Soluble Organics Using Functionalized Monolithic Sorbents

Water utilities encounter unpredictable odor issues that cannot be explained by routine water parameters during spring runoff, even in the summer and fall. Highly water-soluble organics (e.g., amino acids and saccharides) have been reported to form odorous disinfection byproducts during disinfection, but the lack of simple and practical on-site sampling techniques hampers their routine monitoring at trace levels in source water. Therefore, we have created two functionalized nested-in-sponge silica monoliths (NiS-SMs) using a one-pot synthesis method and demonstrated their application for extracting highly soluble organics in water. The NiS-SMs functionalized with the sulfonic group and phenylboronic moiety selectively extracted amino acids and monosaccharides, respectively. We further developed a spinning sampling technique using the composites and evaluated its robust performance under varying water conditions. The spinning sampling coupled to high-performance liquid chromatography tandem mass spectrometry analysis provided limits of detection for amino acids at 0.038-0.092 ng L^-1 and monosaccharides at 0.036-0.14 ng L^-1. Using the pre-equilibrium sampling-rate calibration, we demonstrated the applicability of the spinning sampling technique for on-site sampling and monitoring of amino acids and monosaccharides in river water. The new composite materials and rapid on-site sampling technique are unique and efficient tools for monitoring highly soluble organics in water sources.

Enhanced formation of iodinated trihalomethanes in a mixed chlorine/chloramine system and attenuation by UV-activated process

Iodinated trihalomethanes (I-THMs) have drawn increasing concerns due to their higher toxicity than those of their chlorinated and brominated analogues. In this study, I-THM formation was firstly evaluated for three treatment scenarios - (i) chlorine alone, (ii) chloramine alone, and (iii) mixed chlorine/chloramine - in the presence and absence of UV irradiation for the iodide-containing humic acid solution or natural water. The results indicated that I-THM formation decreased in the order of mixed chlorination/chloramination > chloramination > > chlorination, which fitted the trend of toxicity evaluation results using Chinese hamster ovary cells. Conversely, total organic halide concentration decreased in the order of chlorination > > chloramination ≈ mixed chlorination/chloramination. Besides, I-THM formation can be efficiently controlled in a UV-activated mixed chlorine/chloramine system. Influencing factors including pH values and Br^-/I^- molar ratios were also systematically investigated in a mixed chlorine/chloramine system. Enhanced I-THM formation was observed with increasing pH values (6.0-8.0) and Br^-/I^- molar ratios (1: 1-10: 1). The results obtained in this study can provide new insights into the increasing risk of I-THM formation in a mixed chlorine/chloramine system and the effective control of I-THMs in the iodide-containing water using UV irradiation.

Molecular composition of halobenzoquinone precursors in natural organic matter in source water

Halobenzoquinones (HBQs) are emerging disinfection byproducts generated during the reaction of chlorine disinfectant with natural organic matter (NOM) in source water. In this study, the correlations between molecular weight and HBQs generation of river NOM was evaluated. The compositional and functional characteristics of primary HBQs precursors were revealed by using Orbitrap mass spectrometry combined with molecular tagging. The NOM fraction larger than 50 kDa resulted in approximately 9 times more HBQs (50.9 ± 2.7 ng/mgC) than low molecular weight fractions. Significant correlations were found between the yields of HBQs and lignin-like and highly oxygen compounds in NOM, suggesting their critical roles in HBQs formation. Derivatizating the aldehydes, ketones, hydroxyl and carboxyl groups in NOM could reduce HBQs yields by 90.7%-100%. Unraveling the molecular characteristics of HBQs precursors in NOM would greatly benefit the prediction of HBQs yields of different source water, and develop more efficient disinfection byproduct control strategies.

Study on the Control of Dichloroacetonitrile Generation by Two-Point Influent Activated Carbon-Quartz Sand Biofilter

Aiming at the problem of highly toxic Nitrogenous disinfection by-products (N-DBPs) produced by disinfection in the process of drinking water, two-point influent activated carbon-quartz sand biofilter, activated carbon-quartz sand biofilter, and quartz sand biofilter are selected. This study takes typical N-DBPs Dichloroacetonitrile (DCAN) as the research object and aromatic amino acid Tyrosine (Tyr), an important precursor of DCAN, as the model precursor. By measuring the changes of conventional pollutants in different biofilters, and the changes of Tyr, the output DCAN formation potential of the biofilters, this article investigates the control of DCAN generation of the two-point influent activated carbon-quartz sand biofilter. The results show that the average Tyr removal rate of the three biofilters during steady operation is 73%, 50%, and 20%, respectively, while the average effluent DCAN generation potential removal rate is 78%, 52%, and 23%, respectively. The two-point influent activated carbon-sand biofilter features the highest removal rate. The two-point water intake improves the hypoxia problem of the lower filter material of the activated carbon-quartz sand biofilter, and at the same time, the soluble microbial products produced by microbial metabolism can be reduced by an appropriate carbon sand ratio, which is better than traditional quartz sand filters and activated carbon-quartz sand biofilters in the performance of controlling the precursors of N-DBPs.

Towards carbon neutrality and water sustainability: An integrated anaerobic fixed-film MBR-reverse osmosis-chlorination process for municipal wastewater reclamation

Freshwater resilience is facing to an increasing challenge, while carbon neutral wastewater reclamation has been put onto agenda in more and more countries. The activated sludge-microfiltration (MF)-reverse osmosis (RO) process has been currently adopted for reclamation of municipal wastewater to high-grade product water (e.g. NEWater). However, the conventional activated sludge (CAS) unit in this process has the drawbacks of excessive sludge generation, high energy consumption, greenhouse gases (GHGs) emissions etc. To address these emerging issues, an integrated anaerobic fixed-film membrane bioreactor (AnfMBR)-RO-chlorination process was developed in this study. Results showed that about 99.9% of COD, 99.3% of phosphate and 95.3% of NH₄⁺-N were removed in the AnfMBR-RO process, while breakpoint chlorination served as a polishing step when the NH₄⁺-N concentration in RO permeate exceeded the typical NH₄⁺-N concentration (e.g. 1 mg/L) of NEWater. The net energy consumption and total GHG emissions in the proposed integrated process were estimated to be 0.33 kWh/m³ and 310.2 g CO₂e/m³ influent wastewater treated, respectively, which were 64% and 74% less than those in the current municipal wastewater reclamation process. Consequently, this study offers an alternative path to bring municipal wastewater reclamation one step closer to carbon neutrality and water sustainability.

Catalytic hydrolysis: A novel role of zero-valent iron in haloacetonitrile degradation and transformation in unbuffered systems

Efforts to remove highly toxic haloacetonitriles (HANs) is an important step to reduce health risks associated with disinfection by product exposure. Zero valent iron (ZVI) is a versatile material, whose reductant, sorbent and coagulant role has been well understood. However, their catalytic role is less known. In this study, the degradation and transformation of HANs in ZVI system were investigated. Significant decreases of the four HANs in ZVI system were observed, and haloacetamides and haloacetic acids (hydrolysis products of HANs) were the dominant transformation products of HANs. However dehalogenated HANs, Fe (II) and Fe (III) were rarely detected after reaction, indicating that the ZVI acted as a catalyst to promote the hydrolysis of HANs, rather than other previously reported causes (dehalogenation or redox reaction). The HAN degradation rates were dramatically affected by the initial pH, ZVI doses and initial HAN concentration. Kinetic analysis indicated that HAN removal was enhanced with the increase of initial pH (5-9), ZVI doses (1-10 g/L), and initial HAN concentration (25-200 μg/L). ZVI induced the transformation of HANs to haloacetamides, haloacetic acids and other de-halogenated compounds, which reduced the cytotoxicity and genotoxicity by 88% and 85%, respectively. This study helped to understand the fate of HAN during the transmission in cast iron pipes, and provided a theoretical foundation for future HAN control and monitoring efforts.

Integration of fluorescence quenching correction into trihalomethane formation prediction models

Despite there being numerous models of trihalomethane (THM) formation, they are limited by high estimation errors, which can be close to the regulatory limits for THMs, due to the fluorescence quenching effect. In this research, the estimation error for THM formation was reduced by correcting the quenching effect. The trihalomethane formation potential (THMFP) test was conducted in the presence of chlorine and bromine, individually and in mixtures. The THM precursors used in this study were protein (bovine serum albumin; BSA), amino acids (tryptophan and tyrosine), chlorine, bromine, and Suwannee River natural organic matter (SWNOM). BSA tended to form bromodichloromethane (BDCM) rather than trichloromethane (TCM) during chlorination in the presence of bromide (Br^-). In contrast, SWNOM tended to form chlorinated THMs (TCM) rather than brominated THMs (BDCM and dibromochloromethane; DBCM), and no TBMs were formed in these processes. BSA with SWNOM decreased the formation of TCM due to the decrease in the amount of TCM precursor in SWNOM through binding with BSA. The concentration of each THM species was predicted from the fluorescence intensity of peak C, corrected fluorescence intensity of peak T, and Br^- concentration. The use of humic-like and corrected protein-like fluorescence in the excitation-emission matrix model for predicting THM species reduced the prediction error. In this research, correction of the fluorescence quenching decreased the mean percentage estimation error for TCM, BDCM, and DBCM from 47%, 35%, and > 100% in classical approaches to 6.6%, 26.9%, and 2.0%, respectively. This study is expected to make contributions in reporting the relationship between the concentration of natural organic matter compositions and the formation of THM species.

Degradation of carbamazepine and disinfection byproducts formation in water distribution system in the presence of copper corrosion products

Copper ion (Cu²⁺), a common corrosion product released from copper pipes, is widely present in water distribution system (WDS). Cu²⁺ was confirmed to be capable to catalyze the decay of monochloramine (NH₂Cl), which is a commonly used disinfectant and need to maintain a minimum concentration in WDS. Cu²⁺ and NH₂Cl form a system in WDS and their interaction with other substances in WDS is unclear. In this study, the performance of Cu²⁺/NH₂Cl system on degradation of trace pollutants, taking carbamazepine (CBZ) as an example, in WDS was investigated, and significant promotion on CBZ degradation was observed. The acceleration was due to the generation of Cl, OH and other oxidants, which were identified by scavenge experiments. CBZ degradation in Cu²⁺/NH₂Cl system was highly pH-dependent, because the catalytic effect of Cu²⁺ can only work at low pH (Cu²⁺ precipitating at pH > 6.0). The removal of CBZ increased with the concentration of Cu²⁺ increasing. Water matrix (NOM, HCO₃^- and Br^-) can inhibit the removal of CBZ in Cu²⁺/NH₂Cl system. Further, five disinfection byproducts (DBPs), namely, trichloromethane (TCM), dichloroacetonitrile (DCAN), dichloroacetone (DCP), trichloronitromethane (TCNM) and trichloroacetone (TCP), were detected in chloramination in the presence/absence of Cu²⁺. Compared with chloramination without Cu²⁺, the cytotoxicity and genotoxicity of formed DBPs increased significantly in the presence of Cu²⁺, indicating that the chemical safety in WDS deserves more attention.

Iron particle formation under chlorine disinfection considering effects of deoxidizers in drinking water

Iron oxidation inevitably occurs in drinking water distribution systems (DWDSs) and can cause water quality problems such as increased turbidity and discoloration of tap water. Considering that chlorine disinfection is also widely used in DWDSs, the role of disinfectant and disinfection byproducts (DBPs) in iron oxidation should not be neglected. Interestingly, here the well-known deoxidizer ascorbic acid (VC), which is also a food additive, could induce the formation of Fe₃O₄ besides FeOOH resulting in the color change from yellow to black in the presence of trichloroacetic acid (TCA, one of the most typical DBPs) and NaClO (disinfectant). The oxygen-containing functional groups in TCA and VC may bind Fe(II) to guide the crystal growth. Though the particles generated in the presence of TCA and NaClO together with VC had higher content Fe₃O₄ which would be more difficult to suspend, once disturbance happened, these particles could increase the turbidity and color of water into higher value than the particles formed without VC and those generated in the absence of TCA and NaClO. Therefore, the deoxidizer VC may control "yellow water" without disinfectant, but may deteriorate the water quality under disinfection conditions.

Investigation into the content and formation of trihalomethanes and molecular change of dissolved organic matter from a typical water plant in south China

Trihalomethanes (THMs) are a class of disinfection by-products that were proved to have adverse effects to human health. Investigation into its content change and molecular composition variation of its main precursor, which is believed to be dissolved organic matter (DOM) during water purification process, can help understand the formation mechanism of THMs and optimize the processes in drinking water treatment plant (DWTP). This is of great significance to ensure the safety of urban water supply. In this study, detailed changes of THMs' content and formation potential were determined during the water purification process in summer and winter at a typical DWTP in south China. Specific molecular composition changes of DOM were also characterized by ultrahigh-resolution mass spectrometry, to comprehensively study its correlation with the formation of THMs in different water processing units and seasons. The result showed that chlorination will cause drastic changes of water quality and a sharp increase in the concentration of THMs (18.7 times in summer and 13.9 times in winter). Molecular-level characterization of DOM indicates that a range of lignin-like substance with lower O/C (< 0.5) and H/C (< 1.25) vanished and considerable amount of protein-like and tannins-like substance with higher H/C (> 1.25) and O/C (> 0.5) was formed after chlorination. Analysis of Cl-containing products demonstrated that a bulk of CHOCl₁ and CHOCl₂ compounds with moderate molecular weights were formed in both winter and summer. However, the newly formed CHOCl₁ molecules showed a relatively higher mass weight in summer (> 500 Da) compared to winter (300-500 Da). Seasonal differences also emerged in the result of correlation between the trihalomethanes formation potential and total organic carbon. The correlation coefficient in summer (0.500) was lower than that in winter (0.843). The results suggested that the exhaustive reaction and contribution of DOM to THMs may vary in different seasons.

Iodinated disinfection byproduct formation in a MnO2/I-/EPS system

Manganese dioxide (MnO₂) is a Mn deposit widely accumulated in the corrosion layer of pipelines, and iodide (I^-) is a halogen ion frequently detected in waters. The biofilm dwelling on the corrosion scales often secretes extracellular polymeric substances (EPS) into drinking water. The paper aimed to study the I^- oxidation by MnO₂ and iodinated disinfection byproducts (I-DBPs) formation with biofilm EPS as a precursor. More than 93% of formed free iodine was finally converted into organic iodine in the MnO₂/I^-/EPS system. Compared with humic acid, EPS had a lower carbonaceous I-DBPs (C-IDBPs) formation while a higher nitrogenous I-DBPs (N-IDBPs) formation. The formation of iodomethanes (I-THMs), iodoacetonitriles (I-HANs) and iodoacetic acids (I-HAAs) decreased with the increase of pH due to the weakening of polarization effect and redox potential, while the iodoacetamides (I-HAcAms) formation achieved the maximum at pH 6.0 due to the difference between the hydrolysis rate of I-HANs and decomposition rate of I-HAcAms. The I-DBPs formation was positively correlated with I^- concentration, while negatively correlated with MnO₂ dose. Protein components displayed a higher formation of N-IDBPs and C-IDBPs than polysaccharide components due to higher nitrogen proportion and more iodination sites. Among 20 protein monomers, aspartic acid was considered as the most important precursor of the four investigated I-DBPs species. The paper is helpful to understand the I-DBPs formation when I^- in the bulk water come into contact with Mn deposits attached by biofilm.

Enhanced coagulation for mitigation of disinfection by-product precursors: A review

The unintended formation of disinfection by-products (DBPs) has received considerable attention as it may pose risks to human health. Coagulation is the most common process for removing particulates as well as dissolved organic matter (DOM) (i.e., DBP precursors) during drinking water and wastewater treatments. With the improvement of water quality standards and the increased fluctuation in source water quality, conventional coagulation becomes challenging. Thus, significant efforts have been made to enhance coagulation to promote the removal of DOM in source water and mitigate the formation of DBPs in drinking water. This review provides a brief summary of the properties of DBP precursors and summarizes the effectiveness of enhanced coagulation involving three types of coagulants (metal-based coagulants, organic polymers, and organic-inorganic hybrid coagulants) in controlling the formation of DBPs during chlor(am)ination disinfection. Metal-based coagulants can achieve a reduction in DBP formation potential of approximately 20%-60% in natural water under enhanced coagulation conditions. Both the organic polymers (used as coagulant aids) and novel hybrid coagulants increase the removal of DOM and exhibit high potential for mitigating DBP formation. In addition, integrated treatments combining coagulation with other treatment processes (e.g., oxidation, membrane filtration, ion exchange, and adsorption) to enhance DBP precursor removal are evaluated in terms of performance, mechanisms, and features. Advanced treatments, such as membrane filtration and activated carbon adsorption, are effective coagulation-assisted processes, and can further control chlorinated DBPs; however, the elevated formation of bromate or highly brominated DBPs is of particular concern.

Characterization of Dissolved Organic Matter and Its Derived Disinfection Byproduct Formation along the Yangtze River

The Yangtze River basin covers one-fifth of China's land area and serves as a water source for one-third of China's population. During long-distance water transport from upstream to downstream, various sources of dissolved organic matter (DOM) lead to considerable variation in DOM properties, significantly impacting water treatability and disinfection byproduct (DBP) formation after chlorination. Using size-exclusion chromatography and fluorescence spectroscopy, the spatial variation in DOM characteristics was comprehensively investigated on a basin scale. The formation of 36 DBPs and speciated total organic halogen in chlorinated samples was determined. Overall, the Yangtze River waters featured a high proportion of terrestrially derived humic substances that served as important precursors for trihalomethanes and haloacetic acids, which was responsible for the increase in total DBP formation along the Yangtze River. The downstream waters were characterized by high levels of microbially derived protein-like biopolymers, which significantly contributed to the formation of haloacetaldehydes and haloacetonitriles that dominated DBP-associated mammalian cell cytotoxicity. Moreover, the precursors of haloacetaldehydes and haloacetonitriles in downstream waters were highly hydrophilic, posing a challenge for water treatment. This study presents an extensive basin-scale study, providing insights into DOM variations along the Yangtze River, illustrating the impact of DOM properties on drinking water from a DBP perspective.

Enhanced formation of dichloroacetamide and dichloroacetonitrile during chloramination of drinking water and model organic matters in the presence of copper corrosion products

The formation of nitrogenous disinfection byproducts (N-DBPs) occurs in chloraminated water in drinking water distribution systems and may be affected by metal pipe materials and their corrosion products. The effect of copper corrosion products, including Cu²⁺, CuO, and Cu₂O, on the formation of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) was investigated during chloramination of natural organic matter (NOM), model precursors (carboxylic acids and amino acids), and real water samples. Copper corrosion products enhanced DCAN and DCAcAm formation during chloramination of NOM by 33%-72% and 11%-80%, respectively. Addition of ¹⁵N-labeled monochloramine showed that the copper corrosion products primarily enhanced the formation of DCAN using organic nitrogen and monochloramine as nitrogen sources, and the formation of DCAcAm using monochloramine as the nitrogen source, but had a limited impact on the formation of DCAcAm using organic nitrogen as the nitrogen source. A distinct N-DBP formation pathway in the presence of Cu²⁺ and CuO was observed using tyrosine as a model compound, which included the formation of 1,4-benzoquinone as a dominant intermediate. On reaction with monochloramine, the 1,4-benzoquinone greatly contributed to enhancement of DCAN and DCAcAm formation using monochloramine as the nitrogen source. During chloramination of real water samples, Cu²⁺ and CuO enhanced DCAN formation by 9-40% and DCAcAm formation by 16-33%. This study increases our knowledge of copper catalyzed DCAN and DCAcAm formation in copper pipes, which will be meaningful for water safety in distribution systems using chloramine disinfection.

Effects of process factors on the performance of electrochemical disinfection for wastewater in a continuous-flow cell reactor

Although electrochemical disinfection has been shown to be an effective approach to inactivate bacteria in saline water, the effects of process parameters and reactor design for its application in low-salinity water have not been well understood. In this study, factorial experiments were performed to investigate the direct and confounded effects of applied current (5-20 mA), contact time (2.5-20 min), anode surface area (185-370 cm²), and chloride concentration (50-400 mg L^-1) on the disinfection efficiency in fresh water and the secondary effluent of municipal wastewater. An electrochemical disinfection reactor cell with an internal volume of 75 cm³ was designed and fabricated. Residence time distribution analysis showed that the internal mixing of the reactor is similar to that of a dispersed plug-flow reactor. All studied process parameters showed significant effect on the kill efficiency, with the applied current and contact time having the most dominant effect. Although the effect of chloride concentration, which is responsible for electrochemical production of free chlorine in water, is statistically significant, it is not as prominent as those reported for high salinity water. A synergistic effect between chloride concentration and anode surface area was identified, leading to high kill efficiency (99.9%, 3 log kill) at low current density (0.0135 mA cm^-2). Response surface modeling results suggested that a scaled-up disinfection reactor can be designed using large anode surface area with long contact time for high chloride water (400 mg L^-1) or high current density with short contact time for low chloride water (50 mg L^-1). The power requirement of a portable system treating 37.85 m³ day^-1 (10,000 gpd) of municipal wastewater was estimated to be 1.9 to 8.3 kW to achieve a 3 log kill, depending on the reactor design.

Derivates variation of phenylalanine as a model disinfection by-product precursor during long term chlorination and chloramination

Dissolved nitrogenous organic matter in water can contain precursors of disinfection by-products (DBPs), especially nitrogenous DBPs (N-DBPs). Amino acids are ubiquitous as dissolved nitrogenous organic matter in source water and can pass through drinking water treatment processes to react with disinfectants in finished water and in the distribution system. Phenylalanine (Phe) was selected as a model amino acid precursor to investigate its derived DBPs and their variations during a chlorination regime that simulated water distribution with residue chlorine. The 7-day DBPs formation potential (DBPsFP) test with chlorine revealed chlorination by-products of phenylalanine including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and halonitromethanes (HNMs), but not trichloronitromethane (TCNM) which was a significant N-DBP detected during the first 48 h of chlorine contact. The formation of most carbonaceous DBPs (C-DBPs) increased with chlorination time; however N-DBPs and non-chlorinated byproducts of phenylacetonitrile and phenylacetaldehyde reached their highest concentration after 2 h of reaction, and then gradually decreased until below detection after 7 days. The chlorination influencing factors indicated that light enhanced the peak yield of DBPs; the pH value showed different influences associated with corresponding DBPs; and the presence of bromide ions (Br^-) generated a variety of bromine-containing DBPs. The DBPsFP test with chloramine reduced C-DBPs generation to about 1/3 of the level observed for chlorine disinfection and caused an increase in dichloroacetonitrile. Surveillance of DBPs during drinking water distribution to consumers should consider the varying contact times with disinfectants to accurately profile the types and concentrations of C-DBPs and N-DBPs present in drinking water.

Tetracycline antibiotics as precursors of dichloroacetamide and other disinfection byproducts during chlorination and chloramination

Pollution of natural water and even source water with pharmaceuticals is problematic worldwide and raises concern about the possibility of disinfection byproduct (DBP) formation during subsequent water treatment. In this study, the formation of DBPs, especially dichloroacetamide (DCAcAm), was investigated during chlorination and chloramination of tetracyclines, which are a class of broad-spectrum antibiotics. DBPs including DCAcAm were formed during chlorination and chloramination of tetracycline (TC). Although the concentrations and theoretical cytotoxicity of the DBPs formed from TC were affected by the contact time, disinfectant dose, and pH, DCAcAm was the main contributor determining the yields and cytotoxicity of the measured DBPs. The DCAcAm yields from four tetracycline antibiotics ranged from 0.43% to 54.26% for chlorination. For chloramination, the DCAcAm yields reached 44.57%, and the nitrogen in DCAcAm mainly came from tetracycline antibiotics rather than chloramines. ClO₂ pre-oxidation and UV photolysis decreased DCAcAm formation during chlorination and chloramination of TC. The high yields observed in this study suggest that tetracycline antibiotics are possible precursors of DCAcAm.

Formation of disinfection by-products in a UV-activated mixed chlorine/chloramine system

In recent years, ultraviolet (UV) irradiation coupled with chlor(am)ination process is ubiquitous in secondary water supply systems in many cities of China. However, the disinfection by-products (DBPs) formation in a UV-activated mixed chlorine/chloramine system (MCCS) still remains unclear. In this study, the DBPs formation in a UV-activated MCCS was systematically investigated, considering influencing factors including the mass ratios of free chlorine to NH₂Cl, UV irradiation, pH values, NOM types, Br^- concentration and toxicity of the DBPs. Results indicated that DBPs formation decreased remarkably as mass ratio of free chlorine to NH₂Cl changed from 5:0 to 0:5. The DBPs formation in humic acid (HA)-containing water was the highest, followed by those in fulvic acid (FA) and algal organic matter (AOM). Besides, better control of the DBP-related calculated toxicity can be achieved in acidic conditions regardless of the UV irradiation. Furthermore, in the presence of Br^-, a significant reduction of DBPs formation could be achieved in a UV-activated MCCS. The findings also demonstrated that DBPs formation in real water can be effectively reduced at high UV fluence in a MCCS.

Ozonation Treatment Increases Chlorophenylacetonitrile Formation in Downstream Chlorination or Chloramination

Chlorophenylacetonitriles (CPANs) are an emerging group of aromatic nitrogenous disinfection byproducts (DBPs). However, their dominant precursors and formation pathways remain unclear, which hinders the further development of effective control strategies. For the first time, CPAN precursors were screened by conducting formation potential (FP) tests on real water samples from six drinking water treatment plants (DWTPs). The average overall removal of CPAN precursors across all six DWTPs was only 10%. Moreover, ozonation increased CPAN precursors by 140% on average. Fluorescence spectroscopy showed a dramatic reduction in aromatic proteins, tyrosine-like proteins, and tryptophan-like proteins following ozonation. Low-apparent-molecular-weight (AMW) (<1 kDa) substances were correlated with the CPAN FP in these samples. We therefore hypothesized that protein fragments with low AMW, such as amino acids, are important CPAN precursors during downstream chlor(am)ination. Two aromatic free amino acids, tyrosine and tryptophan, were selected to investigate the formation of CPANs during chlor(am)ination. Both amino acids were found to act as CPAN precursors for the first time. CPAN formation pathways from these model precursors were proposed based on the frontier molecular orbital theory and intermediate products identified using high-resolution mass spectrometry. This study provides a powerful theoretical foundation for controlling CPAN formation in drinking water.

Formation of carbonaceous and nitrogenous iodinated disinfection byproducts from biofilm extracellular polymeric substances by the oxidation of iodide-containing waters with lead dioxide

Lead dioxide (PbO₂) is an important form of lead mineral scales in drinking water pipes. Iodide (I^-) widely presents in source waters and can be thermodynamically oxidized by PbO₂ to the reactive iodine species (I₂/HOI). Biofilm extracellular polymeric substances (EPS) are nonnegligible precursors of disinfection byproducts (DBPs). The aim was to study the oxidation of I^- by PbO₂ and formation of iodinated DBPs (I-DBPs) from EPS. At a high molar ratio of PbO₂ to I^- (> 100), the observed rate constants of I^- oxidation decreased as pH increased from 6.0 to 9.0 with an H⁺ dependence of 0.79, and the rate constant (k) was 1.6 × 10¹¹ M^-2.79 s^-1. Most of formed I₂/HOI (> 92%) was transformed to organic iodine in the presence of EPS. EPS had a lower formation potential (FP) of carbonaceous I-DBPs (C-IDBPs), while a higher that of nitrogenous I-DBPs (N-IDBPs) than HA, resulting in a higher Chinese Hamster Ovary cell cytotoxicity. Generally, the formation of I-DBPs decreased with the increase of pH due to the reduction of surface positive charge and electrochemical driving force. PbO₂ dose and I^- concentration also had a significant effect on the I-DBPs formation. EPS proteins had a higher FP of both C- and N-IDBPs than polysaccharides on account of more electrophilic sites and higher nitrogen content. In proteins, aspartic acid was the main contributor to triiodomethane and iodoacetic acids formation, whereas aspartic acid, asparagine and tyrosine were the major precursors of diiodoacetonitrile and diiodoacetamide. The study helps to improve the control strategy of I-DBPs when biofilm outbreaks in lead-containing water pipes.

Highly efficient chloramphenicol degradation by UV and UV/H2 O2 processes based on LED light source

In this study, UV-LED was employed as a novel light source to investigate the degradation of a representative antibiotic compound, chloramphenicol (CAP), in the absence or presence of H₂ O₂ . The UV-LED irradiation showed a higher capability for degradation of CAP than conventional UV-Hg vapor lamps. Effects of the initial CAP concentration, UV wavelength, and light intensity on the degradation of CAP by UV-LED were evaluated. Introduction of H₂ O₂ evidently enhanced the degradation efficiency of CAP due to the production of reactive hydroxyl radicals. Results showed that the UV-LED/H₂ O₂ removed CAP by up to 95% within 60 min at pH 5.0, which was twice as that achieved by the UV-LED alone. The degradation products were identified to propose plausible degradation pathways. Moreover, the formation potentials of typical carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs) were assessed for the CAP polluted water treated by the UV-LED alone and UV-LED/H₂ O₂ processes. Results indicate unintended formation of certain DBPs, thereby highlighting the importance of health risk assessments before practical application. This study opens a new avenue for developing environment-friendly and high-performance UV-LED photocatalytic reactors for abatement of CAP pollution in water. PRACTITIONER POINTS: UV-LED bore higher capability to degrade CAP than low-pressure Hg lamp. The optimal performance to degrade CAP can be achieved at the UV wavelength of 280 nm. The degradation efficiency under UV-LED/H₂ O₂ process was double of that under UV-LED process. TCM, DCAN, and TCNM formation were higher under the existence of UV-LED radiation. The addition of H₂ O₂ had greater influence on the formation of DCAcAm than the introduction of UV-LED.

Precursors of typical nitrogenous disinfection byproducts: Characteristics, removal, and toxicity formation potential

The emergence of nitrogenous disinfection byproducts (N-DBPs) in drinking water has become a widespread concern. In this study, dichloroacetonitrile (DCAN), dicholoacetamide (DCAcAm) and trichloronitromethane (TCNM) were chosen as representatives to clarify the characteristics of N-DBP precursors in the raw waters of Taihu Lake, the Yangtze River, and Gaoyou Lake. Removal of DCAN and DCAcAm precursors must focus on nonpolar and positively charged organics, but more attention should be paid to micromolecular, polar and non-positively charged organics as TCNM precursors. Compared to molecular weight (MW) and hydrophilicity fractionation, polarity and electrical classification have higher selectivity to intercept N-DBP precursors. The properties of N-DBP precursors are relatively fixed and traceable in water systems, which could contribute to their targeted removal. Based on investigation of their characteristics, the removal efficiency and preferences of organic precursors under different processes were studied in three drinking water treatment plants (DWTPs). The TCNM precursors produced in preozonation can be effectively removed during coagulation. The cumulative removal efficiency of conventional processes on N-DBP precursors was approximately 20-30%, but O₃/BAC process improved removal by about 40%. The key to improving the removal efficiency of N-DBP precursors by O₃/BAC is that it can significantly remove low-MW, nonpolar, positively charged, hydrophilic and transphilic organics. In combined toxicity trials, both cytotoxicity and genotoxicity showed a synergistic effect when DCAN, DCAcAm, and TCNM coexisted, which means that low-level toxicity enhancement in the actual water merits attention. DCAN precursors dominated in the toxicity formation potential (TFP), followed by TCNM precursors. In addition, the removal rate of total N-DBP precursors may be higher than that of TFP, leading to overly optimistic evaluation of precursor removal in water treatment practice. Therefore, the removal effect on TFP must also be considered.

Haloacetonitriles and haloacetamides precursors in filter backwash and sedimentation sludge water during drinking water treatment

Haloacetonitriles (HANs) and haloacetamides (HAMs) are nitrogenous disinfection byproducts that are present in filter backwash water (FBW) and sedimentation sludge water (SSW). In many cases FBW and SSW are recycled to the head of drinking water treatment plants. HAN and HAM concentrations in FBW and SSW, without additional oxidants, ranged from 6.8 to 11.6 nM and 2.9 to 3.6 nM of three HANs and four HAMs, respectively. Upon oxidant addition to FBW and SSW under formation potential conditions, concentrations for six HANs and six HAMs ranged from 92.2 to 190.4 nM and 42.2 to 95.5 nM, respectively. Therefore, at common FBW and SSW recycle rates (2 to 10% of treated water flows), the precursor levels in these recycle waters should not be ignored because they are comparable to levels present in finished water. Brominated HAN and chlorinated HAM were the dominant species in FBW and SSW, respectively. The lowest molecular weight ultrafiltration fraction (< 3 kDa) contributed the most to HAN and HAM formations. The hydrophilic (HPI) organic fraction contributed the greatest to HAN precursors in sand-FBW and SSW and were the most reactive HAM precursors in both sand- or carbon-FBWs. Fluorescence revealed that aromatic protein-like compounds were dominant HAN and HAM precursors. Therefore, strategies that remove low molecular weight hydrophilic organic matter and aromatic protein-like compounds will minimize HAN and HAM formations in recycled FBW and SSW.

Removal of CX3R-type disinfection by-product precursors from rainwater with conventional drinking water treatment processes

In addition to surface water and groundwater, rainwater is used as an important drinking water source in many parts of the world, especially in areas with serious water pollution or insufficient water resources. Conventional drinking water treatment technologies can remove dissolved organic matter and therefore reduce the formation of disinfection by-products (DBPs) during subsequent disinfection using surface water or groundwater as drinking water sources. However, little information has been known about the effect of conventional water treatment processes on DBP formation when rainwater is used as drinking water source. This study evaluated CX₃R-type DBP precursors removal from rainwater by conventional drinking water treatments and the corresponding decrease of CX₃R-type DBP (trihalomethanes (THMs), haloaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs)) formation and toxicity during the subsequent chlor(am)ination. The result showed that both sand filtration (SF) and activated carbon filtration (GAC) were able to remove DBP precursors and GAC outperformed SF, but no DBP precursors removal was observed during coagulation-sedimentation treatment. Among all treatments, SF + GAC was the most effective for DBP precursors removal, with removal efficiencies of 64.2% DOC, 98% DON and 76.6% UV₂₅₄. Correspondingly, both SF and GAC decreased the formation of THMs, HALs, HANs and HAMs, and GAC performed better than SF. The combination of SF and GAC, especially SF + GAC, greatly decreased DBP formation, with average reduction of 79.2% and 85% during chlorination and chloramination respectively. After different treatments, the comprehensive toxicity risk of CX₃R-type DBPs was all reduced, among which GAC + SF exhibited superior performance. Generally, the main contribution of integrated toxicity was HANs during chlor(am)ination. The formation potential of THMs, HALs, HANs and HAMs and the corresponding integrated toxicity were greater during chlorination than that during chloramination. Therefore, the combination of GAC and chloramination was promising in mitigating the comprehensive toxicity risk of THMs, HALs, HANs and HAMs for rainwater.

Removal of trihalomethanes and haloacetamides from drinking water during tea brewing: Removal mechanism and kinetic analysis

Disinfection by-products (DBPs) are associated with various adverse health effects. Diversiform advanced treatment processes have been applied for the control of DBPs, but DBPs can still be frequently detected in tap water. Tea-leaves can be made into popular beverage and is itself a porous bio-adsorbent. By simulating tea brewing process, this study evaluated the removal of DBPs from drinking water during the tea brewing process. Removal of four trihalomethanes (THMs) and four haloacetamides (HAMs) by different fermentation degree tea-leaves was investigated. Little DBPs were removed by unfermented and semi-fermented tea-leaves (i.e., Meitan turquoise bud and Dahongpao tea) with less than 5% removal of HAMs, whereas 40% HAMs can be removed by fermented tea (i.e., Jinjunmei tea and Shuixian tea). Tea soup is neutral and slightly acidic, so little DBP hydrolysis was observed under typical tea-leaf brewing process. DBPs were mainly removed by volatilization and adsorption during tea brewing. Removal difference caused by DBP volatilization is very small. The DBP removal difference of four kinds of tea-leaves may be caused by fermentation degree. The surface of unfermented Meitan turquoise bud had a smooth and regular morphology, whereas a rough, irregular, hollow and spongy surface of fermented tea (i.e., Jinjunmei and Shuixian tea) was observed. Generally, the higher the degree of tea fermentation, the more adsorption sites, and the more removal of DBPs. Finally, the model, which takes the DBP initial concentration, tea-leaf dose and brewing time into account, was established under the experimental conditions to predict the variation of DBP concentration during tea brewing, and suggestions for DBP removal were provided to reduce DBP exposure risk. The integrated toxic risk during tea brewing was also investigated, and about 30% integrated cytotoxicity and 26% genotoxicity was reduced during Jinjunmei and Shuixian tea-leaf brewing.

Enhanced formation of carbonaceous and nitrogenous disinfection byproducts from biofilm extracellular polymeric substances undercatalysis of copper corrosion products

Biofilm formation is ubiquitous on the corroded inner surface of water distribution pipes. Extracellular polymeric substances (EPS) secreted by biofilm microorganisms are nonnegligible precursors of disinfection byproducts (DBPs). The aim was to study the catalysis of copper corrosion products (CCPs, CuO and Cu²⁺) on the formation of carbonaceous and nitrogenous DBPs (C-DBPs and N-DBPs) with EPS as a precursor. Results indicate that CCPs had a remarkable enhancement on the formation of DBPs, especially N-DBPs. The enhancement by Cu²⁺ was mainly via homogeneous catalysis initiating from its complexation with EPS, while that by CuO was primarily through heterogeneous catalysis initiating from the polarization of Cl atom in HOCl/OCl^-. The enhancement was more evident as pH increased because an alkaline condition favored the electrostatic interactions of CCPs with EPS and HOCl/OCl^-. The presence of Br^- weakened the enhancement, which may be attributed to that HOBr/OBr^- had a much higher reaction rate than HOCl/OCl^- towards the low reactive moieties in EPS. Due to more phenolic or unsaturated/conjugated groups, EPS proteins had a higher catalytic formation of DBPs than EPS polysaccharides. Among the major amino acids in EPS proteins for DBPs formation, tyrosine had the highest enhancement on the formation of trihalomethanes, while histidine had the highest catalytic formation of halogenated acetic acids, acetonitriles and acetamides. The study helps to understand the formation of DBPs by the joint actions of EPS and CCPs in drinking water distribution systems.

The formation of disinfection by-products from the chlorination and chloramination of amides

This study examined the potential of six aliphatic and aromatic amides, commonly found in natural waters or used as chemical aids in water treatment, to act as organic precursors for nine haloacetamides (HAcAms), five haloacetonitriles (HANs), regulated trihalomethanes (THMs) and haloacetic acids (HAAs) upon chlorination and chloramination. The impact of key experimental conditions, representative of drinking water, including pH (7 & 8), retention time (4 & 24 h) and bromide levels (0 & 100 μg/L), on the generation of the target DBPs was investigated. The highest aggregate DBP yields upon chlor(am)ination were reported for the aromatic and hydrophobic hydroxybenzamide; 2.7% ± 0.1% M/M (chlorination) and 1.7% M/M (chloramination). Increased reactivity was observed in aliphatic and hydrophilic compounds, acrylamide (2.5 ± 0.2% M/M) and acetamide (1.3 ± 0.2% M/M), in chlorination and chloramination, respectively. The addition of bromide increased average DBP yields by 50-70%. Relative to chlorination, the application of chloramines reduced DBP formation by 66.5% (without Br^-) and by 46.4% (with Br^-). However, bromine incorporation in HAAs and HAcAms was enhanced following chloramination, of concern due to the higher toxicological potency of brominated compounds.

Characterization of organic matter by HRMS in surface waters: Effects of chlorination on molecular fingerprints and correlation with DBP formation potential

In order to understand and minimize the formation of halogenated disinfection by-products (DBPs), it is important to investigate how dissolved organic matter (DOM) contributes to their generation. In the present study, we analysed the DOM profile of water samples from the Barcelona catchment area by high resolution mass spectrometry (HRMS) and we studied the changes after chlorination. Chlorination produced significant changes in the DOM, decreased the average m/z and Kendrick mass defect (KMD) of their spectra and decreased the number and abundance of lignin-like features. The Van Krevelen (VK) fingerprint exhibited several noticeable changes, including the appearance of highly oxidized peaks in the tannin-like region (average O/C, 0.78 ± 0.08), the appearance of features with low H/C and the disappearance of more than half of the lipids-like features. Up to 657 halogenated peaks were generated during sample chlorination, most of which in the condensed hydrocarbons-like and the lignin-like region of the VK diagram. Around 200 features were found to be strongly correlated (ρ ≥ 0.795) to the formation potential of trihalomethanes (THMs) and 5 were correlated with the formation potential of haloacetonitrile (HANs). They all were plotted in the lignin fraction of the VK diagram, but both groups of features exhibited different nitrogen content: those features related to HANs FP had at least one nitrogen atoms in their structures, whilst those related to THMs did not.

Removal of disinfection by-products and their precursors during drinking water treatment processes

In this study, we investigated the control efficiency of a wide variety of disinfection by-products (DBPs) (including trihalomethanes [THMs], haloacetic acids [HAAs], haloacetonitiles [HANs], haloketones [HKs], haloaldehydes [Has], and trihalonitromethanes [THNMs]) with different drinking water treatment processes including pre-ozonation, coagulation-sedimentation, sand filtration, and ozone combined with biological activated carbon (O₃ -BAC) advanced treatment processes. The assessment of the treatment efficiency regarding the removal of organic matter was measured by the excitation emission matrix (EEM) spectra. There was a superior efficiency in reducing the formation of DBPs and their precursors by different drinking water treatment processes. Though some DBPs such as THMs could be promoted by ozonation, these by-products from ozonation could be degraded by the following BAC filtration process. In addition, the organic matter from the aromaticity, fulvic acid-like, protein, and soluble microbial by-products-like regions could be further degraded by the O₃ -BAC treatment. PRACTITIONER POINTS: A wide variety of DBPs in different drinking water treatment processes was investigated. The treatment efficiency regarding the removal of organic matter was measured. Some DBPs such as THMs and HAAs could be increased by ozonation. The removal percentage of nitrogen precursors and organic carbon would be increased by BAC filtration.

GAC to BAC: Does it make chloraminated drinking water safer?

Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4-27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.

Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation

Disinfection by-products (DBPs) precursors can be regarded mainly from the drinking water sources and the water treatment processes. A recent study showed that dissolved organic matter (DOM) in atmosphere is an important precursor source of DBPs through atmospheric wet deposition. However, little information is available on the characteristics of DOM derived from dry deposition particulate matter (PM) and the impact of dry deposition on CX₃R-type DBP formation. This study determined whether dry deposition directly contributed the production of DBPs during chlor (am)ination and investigated the mechanism behind the contribution based on the combination of the resin and membrane for fractionating DOM fractions. The results showed that the hydrophilic fraction (HPI) contributed the most DOM and low molecular weight DOM (<10 kDa) was the main component of HPI. In addition, aromatic proteins and soluble microbial products-like compounds were the dominant fluorescent species in DOM derived from PM, and <10 kDa transphilic was the most abundant. The concentrations of C-DBPs and N-DBPs in disinfected PM solution were trihalomethanes (THMs) > haloacetic acids (HAAs) > haloaldehydes and haloacetamides > haloacetonitriles > halonitromethanes for both chlorination and chloramination. The main contributors of calculated toxicity are transphilic and hydrophobic in chlorination and chloramination respectively. Dry deposition PM was deduced to contribute DOM and DBP formation after chlorination in surface water, especially THMs and HAAs. These results presented herein provide key information for controlling DBPs from the perspectives of atmospheric dry deposition, especially in the case of heavy air pollution.

Comparison of different disinfection processes for controlling disinfection by-product formation in rainwater

With increasing shortage of clean water, rainwater has been considered as a precious alternative drinking water source. The processes applied to rainwater treatment are responsible for the safety of drinking water. Therefore, we systematically compared different disinfection processes to evaluate the control of disinfection by-product (DBP) formation and integrated cyto- and genotoxicity of the treated rainwater for the first time. The evaluated disinfection processes included chlorination and chloramination, pre-oxidation by potassium permanganate (KMnO₄) and potassium ferrate (K₂FeO₄), ultraviolet/hydrogen peroxide (UV/H₂O₂), and ultraviolet/persulfate (UV/PS) processes. The results revealed that chloramination was effective for controlling the formation of carbonaceous DBPs (C-DBPs), but not nitrogenous DBPs (N-DBPs). Compared to KMnO₄ pre-oxidation, better reduction of almost all DBPs was observed during K₂FeO₄ pre-oxidation. According to the calculation of cytotoxicity index (CTI) and genotoxicity index (GTI), cyto- and genotoxicity of the samples decreased obviously at the dosage of ≥ 2.0 mg/L KMnO₄ and K₂FeO₄. The control of the cyto- and genotoxicity of the formed DBPs from the two UV-related AOPs was more effective at the dosage of ≥ 1.0 mM PS and ≥ 5.0 mM H₂O₂. Moreover, UV/PS was much more powerful to alter the structure of DBP precursors in rainwater.

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.

Formation of disinfection byproducts during Fenton's oxidation of chloride-rich landfill leachate

Because of the production of chlorine species in leachate during Fenton's oxidation, harmful disinfection byproducts (DBP) can be formed but this has not been well studied before. Herein, we have investigated five classes of DBP: trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, and halonitromethanes during Fenton's oxidation of landfill leachates. The results show that the DBP concentration increased with the increase of [H₂O₂]: [Cl^-] ratio due to the increased concentration of chlorine species. The highest total DBP concentration was 4860 μg L^-1 at [H₂O₂]: [Cl^-] = 4.0 and the lowest was 84 μg L^-1 at [H₂O₂]: [Cl^-] = 0.25. Both the DBP concentration and DBP toxicity increased with the increase of the [H₂O₂]: [Fe²⁺] ratio, because of the increased concentration and lifetime of the chlorine species. Most of the DBP were formed during the first minute of the reaction and stayed stable up to 3 h, indicating that DBP may not be preferred targets of hydroxyl radicals in the presence of a large amount of organics. In most cases, trihalomethanes dominated the DBP concentration, while haloacetonitriles dominated the total additive toxicity. This study has provided important implications to understand DBP formation during Fenton's oxidation.