Disinfection by-product precursors introduced by sandstorm events: Composition, formation characteristics and potential risks.

Sandstorms, a natural meteorological event, occur repeatedly during the dry season and can accumulate large amounts of natural/anthropogenic pollutants during the deposition process, potentially introducing disinfection by-product (DBP) precursors into surface waters. In this study, the characteristics of sandstorm-derived dissolved organic matter (DOM) and its DBP formation potential were elucidated. Overall, sandstorm-derived DOM mainly consisted of low-molecular-weight, low-aromaticity, high-nitrogen organic matter, with a dissolved organic carbon (DOC) release yield of 14.4 mg-DOC/g. The halogenated DBP formation potential (calculated as total organic halogen) of sandstorm-derived DOM was comparable to that of surface water, while the normalized DBP-associated toxicity was 1.96 times higher. Similar to DOM introduced by other depositional pathways, sandstorm-derived DOM also had higher yields of highly cytotoxic DBPs (haloacetaldehydes [HALs], haloacetonitriles [HANs] and halonitromethanes [HNMs]). The average atmospheric deposition flux for DOM during the sandstorm event (50.4 ± 2.1 kg km-2 day-1) was 6.95 times higher than that of dry deposition, indicating a higher probability of contaminant input. Simultaneously, the estimation revealed that the sandstorm will increase the formation potential of toxicity forcing agents, such as HALs, HANs and HNMs, in surface water by 3.87%, 2.39% and 9.04%, respectively. Considering the high frequency of sandstorm events and the sorption of other organic pollutants by sand and dust, the impact of sandstorms on surface water quality should be of concern.

Leaching of organic matter and iodine, formation of iodinated disinfection by-products and toxic risk from Laminaria japonica during simulated household cooking.

Iodinated disinfection by-products (I-DBPs) exhibited potential health risk owing to the high toxicity. Our recent study demonstrated that I-DBPs from Laminaria japonica (Haidai), the commonly edible seaweed, upon simulated household cooking condition were several hundred times more than the concentration of drinking water. Here, the characterization of Haidai and its leachate tandem with the formation, identification and toxicity of I-DBPs from the cooking of Haidai were systemically investigated. The dominant organic matter in Haidai leachate were polysaccharides, while the highest iodine specie was iodide (∼90% of total iodine). Several unknown I-DBPs generated from the cooking of Haidai were tentatively proposed, of which 3,5-diiodo-4-hydroxybenzaldehyde was dominant specie. Following a simulated household cooking with real chloraminated tap water, the presence of Haidai sharply increased aggregate iodinated trihalomethanes, iodinated haloacetic acids, and total organic iodine concentrations to 97.4 ± 7.6 µg/L,16.4 ± 2.1 µg/L, and 0.53 ± 0.06 mg/L, respectively. Moreover, the acute toxicity of Haidai soup to Vibrio qinghaiensis sp.-Q67 was around 7.3 times higher than that of tap water in terms of EC50. These results demonstrated that the yield of I-DBPs from the cooking of Haidai and other seaweed should be carefully considered.

Degradation kinetics and formation of regulated and emerging disinfection by-products during chlorination of two expectorants ambroxol and bromhexine.

Ambroxol hydrochloride (AMB) and bromhexine hydrochloride (BRO) are classic expectorants and bronchosecretolytic pharmaceuticals. In 2022, both AMB and BRO were recommended by medical emergency department of China to alleviate cough and expectoration for symptoms caused by COVID-19. The reaction characteristics and mechanism of AMB/BRO with chlorine disinfectant in the disinfection process were investigated in this study. The reaction of chlorine with AMB/BRO were well described by a second-order kinetics model, first-order in both AMB/BRO and chlorine. The second order rate reaction constant of AMB and BRO with chlorine at pH 7.0 were 1.15 × 102 M-1s-1 and 2.03 × 102 M-1s-1, respectively. During chlorination, a new class of aromatic nitrogenous disinfection by-products (DBPs) including 2-chloro-4, 6-dibromoaniline and 2, 4, 6-tribromoaniline were identified as the intermediate aromatic DBPs by gas chromatography-mass spectrometry. The effect of chlorine dosage, pH, and contact time on the formation of 2-chloro-4, 6-dibromoaniline and 2, 4, 6-tribromoaniline were evaluated. In addition, it was found that bromine in AMB/BRO were vital bromine source to greatly promote the formation of classic brominated DBPs, with the highest Br-THMs yields of 23.8% and 37.8%, respectively. This study inspired that bromine in brominated organic compounds may be an important bromine source of brominated DBPs.

Effects of UV-based oxidation processes on the degradation of microplastic: Fragmentation, organic matter release, toxicity and disinfection byproduct formation.

The occurrence and transformation of microplastics (MPs) remaining in the water treatment plants has recently attracted considerable attention. However, few efforts have been made to investigate the behavior of dissolved organic matter (DOM) derived from MPs during oxidation processes. In this study, the characteristics of DOM leached from MPs during typical ultraviolet (UV)-based oxidation was focused on. The toxicity and disinfection byproduct (DBP) formation potentials of MP-derived DOM were further investigated. Overall, UV-based oxidation significantly enhanced the aging and fragmentation of highly hydroscopic MPs. The mass scales of leachates to MPs increased from 0.03% - 0.18% at initial stage to 0.09% - 0.71% after oxidation, which were significantly higher than those leached by natural light exposure. Combined fluorescence analysis with high resolution mass spectrometer scan confirmed that the dominant MP-derived DOM are chemical additives. PET-derived DOM and PA6-derived DOM showed inhibition of Vibrio fischeri activity with corresponding EC50 of 2.84 mg/L and 4.58 mg/L of DOC. Bioassay testing with Chlorella vulgaris and Microcystis aeruginosa showed that high concentrations of MP-derived DOM inhibited algal growth by disrupting the cell membrane permeability and integrity. MP-derived DOM had a similar chlorine consumption (1.63 ± 0.41 mg/DOC) as surface water (1.0 - 2.0 mg/DOC), and MP-derived DOM mainly served as precursors for the investigated DBPs. Contrary to the results of previous studies, the DBP yields from MP-derived DOM were relatively lower than those of aquatic DOM under simulated distribution system conditions. This suggests that MP-derived DOM itself rather than serving as DBP precursor might be potential toxic concern.

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.

Decomposition of Total Organic Halogen Formed during Chlorination: The Iceberg of Halogenated Disinfection Byproducts Was Previously Underestimated.

Total organic halogen (TOX) is widely used as a surrogate bulk parameter to measure the overall exposure of halogenated disinfection byproducts (DBPs) in drinking water. In this study, we surprisingly found that the level of TOX in chlorinated waters had been significantly underestimated under common analytical conditions. After the addition of quenching agent sodium thiosulfate, total organic chlorine and total organic bromine exhibited a two-phase decomposition pattern with increasing contact time, and a significant decomposition was observed for different types of quenching agents, quenching doses, and pH conditions. More importantly, the decomposed TOX closely correlated with the acute toxicity of quenched water against luminous bacteria, implying that the DBPs responsible for TOX decomposition could be of important toxicological significance. Based on nontarget analysis by using high-resolution mass spectrometry, molecular formulas for the decomposed TOX were determined. After re-examining the mass balance of TOX in the context of unintentional decomposition, it was found that both the level and percentage of unknown TOX in chlorinated waters were considerably higher than historically thought. Overall, this study brings new insights into the knowledge of TOX formed during chlorination, providing important clues on the identification of toxicity driver in drinking water.

Does Snowfall Introduce Disinfection By-product Precursors to Surface Water?

Snow with large specific surface area and strong adsorption capacity can effectively adsorb atmospheric pollutants, which could/might lead to the increase of disinfection by-product (DBP) precursors in surface water. In this study, the contents and characteristics of dissolved organic matter (DOM) in meltwater were investigated, and DBP formation and the DBP-associated cytotoxicity index during chlorination of meltwater was first explored. Overall, meltwater exhibited high nitrogen contents. Meltwater-derived DOM was mainly composed of organics with low molecular weights, low aromaticity, and high unsaturated degrees. DBP formation potentials and cytotoxicity indexes in chlorinated meltwater were positively correlated with air quality index and were significantly impacted by snowfall stages. The trihalomethane and haloacetic acid yields from meltwater were relatively low, while yields of highly cytotoxic DBPs, especially halonitromethanes (6.3-10.8 µg-HNMs/mg-DOC), were significantly higher than those of surface water (1.7 µg-HNMs/mg-DOC). Notably, unsaturated nonaromatic organic nitrates in meltwater were important precursors of halonitromethanes. The actual monitoring results showed that snowfall significant increased the haloacetaldehydes and nitrogenous DBP formation levels of surface water. Considering increased DBP formation and DBP-associated toxicity, it was demonstrated that DOM derived from snowfall in atmosphere-polluted areas could deteriorate surface water quality and pose potential risks to drinking water.

Insights into the formation and mitigation of iodinated disinfection by-products during household cooking with Laminaria japonica (Haidai).

Iodinated disinfection by-products (I-DBPs) have attracted extensive interests because of their higher cytotoxicity and genotoxicity than their chlorinated and brominated analogues. Our recent studies have firstly demonstrated that cooking with seaweed salt could enhance the formation of I-DBPs with several tens of µg/L level. Here, I-DBP formation and mitigation from the reaction of disinfectant with Laminaria japonica (Haidai), an edible seaweed with highest iodine content, upon simulated household cooking process was systematically investigated. The total iodine content in Haidai ranged from 4.6 mg-I/g-Haidai to 10.0 mg-I/g-Haidai, and more than 90% of iodine is soluble iodide. During simulated cooking, the presence of disinfectant simultaneously decreased iodide by 15.0-32.8% to 2.7-5.8 mg/L and increased total organic iodine by 1.3-10.9 times to 0.5-1.8 mg/L in Haidai soup, proving I-DBP formation. The concentrations of iodinated trihalomethanes and haloacetic acids were at the levels of several hundreds of µg/L and several µg/L, respectively, which are 2-3 orders and 1-2 orders of magnitude more than those in drinking water. Effects of key factors including disinfectant specie, disinfectant dose, temperature and time on I-DBP formation were also ascertained, and temperature and disinfectant specie played a decisive role in the formation and speciation of I-DBPs. In order to avoid the potential health risk from the exposure of I-DBPs in Haidai soup, it is prerequisite to soak and wash dry Haidai sample over 30.0 min before cooking, which could effectively remove major soluble iodide. In general, this study provided the new insight into I-DBP formation from daily household cooking with Haidai and the corresponding enlightenment for inhabitants to eat Haidai in daily life.

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.

[Disinfection By-products in Drinking Water and Their Control Strategies: A Review].

Disinfection by-products(DBPs) are secondary pollutants generated by the reaction of disinfectants with organic or inorganic precursors during drinking water disinfection. DBPs have received considerable global attention due to their carcinogenic, teratogenic, and mutagenic characteristics. Focusing on drinking water, this paper introduces the main classification and research history of DBPs, and then summarizes the concentration levels of common DBPs in drinking water, and DBPs regulatory compliance in global drinking water standards. Further, the control strategies for DBPs in drinking water, including source control, process control, DBPs removal and integrated control are introduced together with the advantages and disadvantages. Finally, a summary and review of the current level and future trends of DBPs research in China are presented with the proposed control strategies. On the one hand, when evaluating the control effect of a process or technology, the DBPs concentration and comprehensive toxicity should be considered; on the other hand, in order to realize the efficient control of DBPs in drinking water, the focus should be on the integrated methods coupling different DBPs control methods.

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.

Removal of disinfection by-product precursors by Al-based coagulants: A comparative study on coagulation performance.

Coagulation is well-established for controlling regulated disinfection by-products (DBPs), but its effectiveness for controlling unregulated DBPs remains unclear. The efficiency of coagulation in controlling unregulated DBPs requires clarification owing to their relatively high toxicity. In this study, three Al-based coagulants, aluminum sulfate (Alum), polyaluminum chloride (PAC), and a novel type of covalently bond hybrid coagulant (CBC, synthesized using AlCl3) were selected, and the coagulation performance of these Al-based coagulants in controlling DBPs and DBP-associated toxicity was compared over 5 classes of DBPs, including trihalomethanes, haloacetic acids, haloacetaldehydes, haloacetonitriles, and halonitromethanes. The results showed that Alum was the least efficient in removing DBP precursors among the three coagulants. The effectiveness of CBC and PAC for DBP control varied with the characteristics of source waters. CBC had an advantage in water with a low content of humic acids, and reduced DBP concentration and DBP-associated toxicity by 47% and 25%, respectively. For water rich in aromatic organics, CBC might serve as DBP precursors at a high-required dosage, suggesting that a trade-off between enhanced DBP control and serving as DBP precursors should be considered for CBC coagulation; PAC achieved the most reduction in DBP concentration and DBP-associated toxicity by 50% and 34%, respectively.

Ultrasound-enhanced coagulation for Microcystis aeruginosa removal and disinfection by-product control during subsequent chlorination.

Ultrasound techniques have gained increased interest in environmental remediation because of their promising performance and reagent-free nature. This study investigated the effects of ultrasound-coagulation on Microcystis aeruginosa removal, disinfection by-product (DBP) formation during subsequent chlorination, and acute toxicity and DBP-associated toxicity variations in chlorinated effluents. Compared with coagulation using polymeric aluminum chloride (5 mg-Al/L) alone, ultrasound-coagulation showed significantly enhanced turbidity removal, with the removal ratio increasing from 51% to 87%-96%. Although the addition of ultrasound may not substantially improve and even deteriorate the coagulation removal of DOC following the leakage of intracellular organic matter, the significantly improved DBP control was achieved as the cells dominated DBP formation. With the addition of ultrasound, the chlorine demand, aggregate DBP concentration and total organic halogen concentration reductions in the chlorinated M. aeruginosa solution increased from 15%, 47% and 52% (coagulation alone), respectively, to 56%-78%, 56%-80% and 68%-89%. The enhanced DBP mitigation was mainly attributed to the enhanced algal removal. Similarly, the acute toxicity and DBP-associated toxicity of chlorinated effluents further decreased from 100% and 0.0092 (coagulation alone) to 30%-88% and 0.0029-0.0060. Therefore, ultrasound-enhanced coagulation is a promising strategy for urgent algal removal, DBP mitigation and toxicity abatement.

Simultaneous mitigation of disinfection by-product formation and odor compounds by peroxide/Fe(II)-based process: Combination of oxidation and coagulation.

To remove disinfection by-product (DBP) precursors and mitigate odor compounds, peroxide (peroxymonosulfate and persulfate)/Fe(II)-based process was applied as a combination of coagulation and oxidation. Compared with traditional Fe-based salt coagulation (FeSO4 and FeCl3), peroxide/Fe(II)-based process was more efficient in dissolved organic carbon, UV254 and turbidity removal, and peroxymonosulfate showed better performance than persulfate. The better coagulation performance arose from a combination of enhanced neutralization and different characteristics of flocs. Even though the combined process would increase the bromine substitution factor of DBPs, DBP formation and DBP-associated toxicity after peroxide/Fe(II)-based process were 9.2-38.8% and 5.2-27.2% lower than that after conventional Fe(III) coagulation. Both enhanced dissolved organic matter removal and oxidation of DBP precursors played vital roles in DBP control. Conventional Fe-based salt coagulation could hardly remove odor compounds (less than 10%, generally), whereas 28.2-84.9% of odor compounds were degraded during peroxide/Fe(II)-based process, due to free radical formation. This study demonstrated that PMS/Fe(II)-based process might be a promising treatment process for simultaneous DBP control and odor removal in source water.

Transformation of antiviral ribavirin during ozone/PMS intensified disinfection amid COVID-19 pandemic.

Due to the spread of coronavirus disease 2019 (COVID-19), large amounts of antivirals were consumed and released into wastewater, posing risks to the ecosystem and human health. Ozonation is commonly utilized as pre-oxidation process to enhance the disinfection of hospital wastewater during COVID-19 spread. In this study, the transformation of ribavirin, antiviral for COVID-19, during ozone/PMS­chlorine intensified disinfection process was investigated. •OH followed by O3 accounted for the dominant ribavirin degradation in most conditions due to higher reaction rate constant between ribavirin and •OH vs. SO4•- (1.9 × 109 vs. 7.9 × 107 M-1 s-1, respectively). During the O3/PMS process, ribavirin was dehydrogenated at the hydroxyl groups first, then lost the amide or the methanol group. Chloride at low concentrations (e.g., 0.5- 2 mg/L) slightly accelerated ribavirin degradation, while bromide, iodide, bicarbonate, and dissolved organic matter all reduced the degradation efficiency. In the presence of bromide, O3/PMS process resulted in the formation of organic brominated oxidation by-products (OBPs), the concentration of which increased with increasing bromide dosage. However, the formation of halogenated OBPs was negligible when chloride or iodide existed. Compared to the O3/H2O2 process, the concentration of brominated OBPs was significantly higher after ozonation or the O3/PMS process. This study suggests that the potential risks of the organic brominated OBPs should be taken into consideration when ozonation and ozone-based processes are used to enhance disinfection in the presence of bromide amid COVID-19 pandemic.

Rejection of chlorinated, brominated, and iodinated trihalomethanes by multi-stage reverse osmosis: Efficiency and mechanisms.

Reverse osmosis (RO), a promising technology for removing inorganic salts and a wide range of trace organic pollutants, is widely used in water treatment industry. In this study, the rejection of chlorinated, brominated, and iodinated trihalomethanes (THMs) by a multi-stage RO system was investigated. The results showed that the multi-stage RO system is effective in rejecting THMs, and THMs with large size, high hydrophobicity and low polarity were highly rejected. In the first stage, high percentage of THMs was adsorbed on RO membrane, and the THM rejection was dominated by both hydrophobic adsorption and size exclusion. The contribution of hydrophobic adsorption to THM rejection decreased significantly along RO stages due to decreased feed concentration, but the enhancement of size exclusion still ensured high rejection efficiencies for most THMs, indicating a compensation effect between two rejection mechanisms. Finally, to further understand the rejection in the multi-RO system from a perspective of THM property, multiple linear regression models were built. The impact of n-octanol-water partition coefficient (Log Kow) was slightly higher than that of stokes radius in the first stage, which was consistent with the rejection mechanism. But dipole moment played an increasingly important role in the second and third stage, weakening the impact of Log Kow on THM rejection.

Has the formation of disinfection by-products been overestimated? Membrane leakage from syringe filter heads serves as unexpected precursors.

Syringe filters are widely used for sample pretreatments in laboratories. This study found that, surprisingly, these filters can leak dissolved organic carbon (DOC) that can potentially serve as precursors of disinfection by-products (DBPs). Nine common types of syringe filters were assessed. The results showed that the DOC of ultrapure water increased after syringe filtration. The DOC shed from filter membranes was characterized, whose spectra showed that the main compounds exhibited a low apparent molecular weight. Five classes of DBPs were investigated including trihalomethanes, haloacetaldehydes, haloacetonitriles, haloacetamides and halonitromethanes, among which trichloromethane (TCM), dichloroacetaldehyde (DCAL), trichloroacetaldehyde (TCAL), dichloroacetonitrile (DCAN), and trichloronitromethane (TCNM) were principally detected. The DBP formation was affected by chlorination time and membrane types. In general, the use of the poly vinylidene fluoride membrane resulted in the highest formation of TCM and TCAL, whereas nylon and mixed cellulose esters membranes contributed significantly to the formation of DCAN and TCNM, respectively. The shedding DOC and the formation of TCM, DCAL and TCAL from filter membranes were mitigated effectively by pre-washing; however, the contribution of membrane leakage to DCAN and TCNM formation was still notable, even with a pre-wash volume of 50 mL. When unwashed syringe filters were used for a real water sample, the DBP formation increased by up to 73.2% compared to the pre-washed ones; particularly for TCNM it was always over 15%. Therefore, for better quality control in laboratories, more attention should be paid to the syringe filters during sample pre-treatments, particularly when DBP formation is being investigated.

Using UV/H2O2 pre-oxidation combined with an optimised disinfection scenario to control CX3R-type disinfection by-product formation.

The effects of UV/H2O2 pre-oxidation or disinfection methods on the formation of partial disinfection by-products (DBPs) have been studied previously. This study assessed the effect of UV/H2O2 pre-oxidation combined with optimisation of the disinfection method on the formation of six classes of CX3R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloacetamides (HAMs). Experimental results showed that a simulated distribution system (SDS) in-situ chloramination or pre-chlorination followed by chloramination effectively decreased total CX3R-type DBP formation by 51.1-63.5% compared to SDS chlorination, but little reduction in DBP-associated toxicity was observed. The dominant contributors to the calculated toxicity were HANs and HALs. UV/H2O2 pre-oxidation was able to destroy the aromatic and dissolved organic nitrogen components of natural organic matter. As a consequence, THM, HAA, and HAL formations increased by 49.5-55.0%, 47.8-61.9%, and 42.0-67.1%, respectively, whereas HAN, HNM, and HAM formations significantly decreased by 52.1-83.6%, 42.9-87.3%, and 74.1-100.0%. UV/H2O2 pre-oxidation increased total CX3R-type DBP formation, during SDS chlorination, whereas SDS in-situ chloramination or pre-chlorination followed by chloramination of UV/H2O2-treated water produced lower total CX3R-type DBPs than water without UV/H2O2 pre-oxidation. Nevertheless, the DBP-associated toxicity of water with UV/H2O2 pre-oxidation was substantially lower than the toxicity for water without UV/H2O2 pre-oxidation, decreased by 24.1-82.7%. HALs followed by HANs contribute to major toxic potencies in UV/H2O2 treated water. The best DBP concentration and DBP-associated toxicity abatement results were achieved for water treated by UV/H2O2 coupled with in-situ chloramination treatment.

Effect of oxoanions on oxidant decay, bromate and brominated disinfection by-product formation during chlorination in the presence of copper corrosion products.

The present study investigated the effect of oxoanions on catalytic behaviour of copper corrosion products (CCPs) during chlorination of bromide-containing waters. Three types of oxoanions (carbonate, sulphate, and phosphate) and four types of CCPs (Cu2+, Cu(OH)2, Cu2O, and CuO) were involved in investigation and the effect of oxoanions concentration was also examined. The result indicated that carbonate and sulphate slightly inhibited oxidant decay in the presence of CCPs, but the formation of brominated disinfection by-products (Br-DBPs) remained largely unchanged. In contrast, the presence of phosphate (0.2-1 mM) almost eliminated the catalytic effect of Cu2+. For CCP solids (i.e. Cu(OH)2, Cu2O, and CuO), phosphate preferentially inhibited the formation of bromate rather than Br-DBPs. Despite the catalysis by CCP solids was reduced to some extent, the oxidant decay rate and bromate and Br-DBP formation were still significantly higher than blank groups, even at high phosphate concentration. By testing different addition scheme (simultaneous/sequential addition), it was proposed that phosphate was a strong competitor for hypohalites, rapidly destroying CCPs-hypohalites complexes on some adsorption sites. However, there were some specific sites that can only be adsorbed by hypohalites, leading to the incomplete inhibition of phosphate. Finally, the inhibition effect of phosphate on CCPs catalysis was tested in real water matrix. For Cu2+, higher reduction of bromate and Br-DBPs was found in raw water rather than filtered water, while converse pattern was true for Cu(OH)2 and Cu2O, and this discrepancy can be ascribed to the difference in catalytic mechanism between Cu2+ and CCP solids.