Formation Of Disinfection By-products Research Articles

Iodide enhances degradation of histidine sidechain and imidazoles and forms new iodinated aromatic disinfection byproducts during chlorination

Peptide-bound histidines and imidazoles are important constituents of dissolved organic matter in water, and understanding the formation of halogenated disinfection byproduct (DBP) formation from these compounds during disinfection is important for ensuring a safe drinking water supply. Previous studies suggested that histidine has low reactivity with chlorine only; this study indicates that iodide substantially enhances histidine reactivity with the disinfectant at a time scale from days to hours. Mono- and di-iodinated histidines were identified as dominant transformation products with cumulative molar yields of 3.3 % at 6 h and they were stable in water over 7 days. These products were formed via electrophilic substitution of iodine to imidazole ring when hypoiodous acid reacted with histidine sidechain. Bromide minimally influenced the formation yields of these iodinated products, and higher pH increased yields up to 12 % for pH in the range 5–9. The cumulative concentration of low-molecular-weight DBPs, such as trihalomethanes and haloacetic acids, was less than 0.3 % under the same conditions. Similar iodinated imidazole analogs were also identified from other imidazoles (i.e., imidazole-carboxylic and phenyl-imidazole-carboxylic acids). This study demonstrated that peptide-bound histidine and imidazoles can serve as important precursors to iodinated aromatic DBPs, facilitating the identification of less-known iodinated DBPs.

Novel sunlight-induced monochloramine activation system for efficient microcontaminant abatement

As an eco-friendly and sustainable energy, solar energy has great application potential in water treatment. Herein, simulated sunlight was for the first time utilized to activate monochloramine for the degradation of environmental organic microcontaminants. Various microcontaminants could be efficiently degraded in the simulated sunlight/monochloramine system. The average innate quantum yield of monochloramine over the wavelength range of simulated sunlight was determined to be 0.068 mol/Einstein. With the determined quantum yield, a kinetic model was established. Based on the good agreement between the simulated and measured photolysis and radical contributions to the degradation of ibuprofen and carbamazepine, the major mechanism of monochloramine activation by simulated sunlight was proposed. Chlorine radical (Cl∙) and hydroxyl radical (HO∙) were major radicals responsible for microcontaminant degradation in the system. Moreover, the model facilitated a deep investigation into the effects of different reaction conditions (pH, monochloramine concentration, and water matrix components) on the degradation of ibuprofen and carbamazepine, as well as the roles of the involved radicals. The differences between simulated and measured degradation data of each microcontaminant under all conditions were less than 10 %, indicating the strong reliability of the model. The model could also make good prediction for microcontaminant degradation in the natural sunlight/monochloramine system. Furthermore, the formation of disinfection byproducts (DBPs) was evaluated at different oxidation time in simulated sunlight/monochloramine with and without post-chloramination treatment. In real waters, organic components showed more pronounced suppression on microcontaminant degradation efficiency than inorganic ions. This study provided a systematic investigation into the novel sunlight-induced monochloramine activation system for efficient microcontaminant degradation, and demonstrated the potential of the system in practical applications.

Disinfection by-product formation potential in response to variability in dissolved organic matter and nutrient inputs: Insights from a mesocosm study

Changes in rainfall patterns driven by climate change affect the transport of dissolved organic matter (DOM) and nutrients through runoff to freshwater systems. This presents challenges for drinking water providers. DOM, which is a heterogeneous mix of organic molecules, serves as a critical precursor for disinfection by-products (DBPs) which are associated with adverse health effects. Predicting DBP formation is complex due to changes in DOM concentration and composition in source waters, intensified by altered rainfall frequency and intensity. We employed a novel mesocosm approach to investigate the response of DBP precursors to variability in DOM composition and inorganic nutrients, such as nitrogen and phosphorus, export to lakes. Three distinct pulse event scenarios, mimicking extreme, intermittent, and continuous runoff were studied. Simultaneous experiments were conducted at two boreal lakes with distinct DOM composition, as reflected in their color (brown and clear lakes), and bromide content, using standardized methods. Results showed primarily site-specific changes in DBP precursors, some heavily influenced by runoff variability. Intermittent and daily pulse events in the clear-water mesocosms exhibited higher haloacetonitriles (HANs) formation potential linked to freshly produced protein-like DOM enhanced by light availability. In contrast, trihalomethanes (THMs), associated with humic-like DOM, showed no significant differences between pulse events in the brown-water mesocosms. Elevated bromide concentration in the clear mesocosms critically influenced THMs speciation and concentrations. These findings contribute to understanding how changing precipitation patterns impact the dynamics of DBP formation, thereby offering insights for monitoring the mobilization and alterations of DBP precursors within catchment areas and lake ecosystems.

A group of emerging heterocyclic nitrogenous disinfection byproducts: Formation and cytotoxicity of halopyridinols in drinking water

Recently, a new group of halopyridinol disinfection byproducts (DBPs) was reported in drinking water. The in vivo developmental and acute toxicity assays have shown that they were more toxic than a few commonly known aliphatic DBPs such as bromoform and iodoacetic acid. However, many pyridinol DBPs with the same main structures but different halogen substitutions were still unknown due to complicated water quality conditions and various disinfection methods applied in drinking water treatment plants. Studies on their transformation mechanisms in drinking water disinfection were quite limited. In this study, comprehensive detection and identification of halopyridinols were conducted, and five new halopyridinols were first reported, including 2-chloro-3-pyridinol, 2,6-dichloro-3-pyridinol, 2-bromo-5-chloro-3-pyridinol, 2,4,6-trichloro-3-pyridinol and 2,5,6-trichloro-3-pyridinol. Formation conditions and mechanisms of the halopyridinols were explored, and results showed that chlorination promoted their formation compared with chloramination. Halopyridinols were intermediate DBPs that could undergo further transformation/degradation with increasing contact time, disinfectant dose, bromide concentration, and pH. The in vitro cytotoxicity of the halopyridinols was evaluated using human hepatocellular carcinoma cells. Results showed that the cytotoxicity of 3,5,6-trichloro-2-pyridinol was the highest (EC50 = 474.3 μM), which was 13.0 and 1.6 times higher than that of 2-bromo-3-pyridinol (EC50 = 6214.5 μM) and tribromomethane (EC50 = 753.6 μM), respectively.

The Role of Ferrate (VI) in the Pretreatment of Algal Cells and Algal Organic Matters: A Review

Algal blooms are caused by excessive levels of nitrogen, phosphorus, and other plant nutrients in water. Algae and algal organic matter (AOM) pose a great threat to the quality of drinking water. This manuscript offers a systematic review of algal removal by ferrate (Fe(VI)) oxidation, including the conditions for the removal of different algae by Fe(VI) and the factors affecting the removal efficiency. On this basis, the oxidation and coagulation mechanisms of algae removal by Fe(VI) are discussed. Then, the review introduces the process combining Fe(VI) pre-oxidation with aluminum sulfate action. The addition of aluminum sulfate can further enhance the coagulation effect and reduce the formation of disinfection byproducts (DBPs) in the subsequent chlorination process by effectively removing AOM, which is recognized as a precursor of DBPs. In addition, recent studies on the combined application of Fe(VI) and Fe(II) are also reviewed. In a reasonable dose range, the synergistic effect of Fe(VI) and Fe(II) can significantly improve the removal of algae and algal toxins. Finally, this review provides a comprehensive evaluation of the applicability of Fe(VI) in removing algal material, offers guidance for the harmless treatment of algae with Fe(VI), and identifies future research questions.

Peracetic acid-induced nanoengineering of Fe-based metallic glass ribbon in application of efficient drinking water treatment

This study presents a novel approach utilizing Fe-Si-B metallic glass-based advanced oxidation processes (AOPs) with peracetic acid (PAA) exposure to mitigate disinfection by-products (DBPs) formation in drinking water treatment. Under optimal conditions, it achieved a 98.21% removal of natural organic matter (NOM) and an 80.64% reduction in DBPs formation. The efficacy is attributed to the galvanic cell effect induced by nanoflower structures on the ribbon surface, produced via PAA exposure, thereby enhancing degradation efficiency. High-valent iron Fe(IV) was identified as the primary reactive species, showing robust cycling efficiency under near-neutral conditions. Continuous flow experiments and toxicity assessments using luminescent bacteria further validated the method, demonstrating minimal metal leaching (<0.146 mg/L) and reduced biotoxicity with a 37.68% inhibition rate decrease in 24 h. These findings underscore the promising potential of PAA-integrated Fe-based amorphous alloys for comprehensive water disinfection and purification.

Secondary risks induced by polyethylene microplastics during the disinfection processes of chlorination, UV irradiation, and ozone treatment

ABSTRACT The presence of microplastics in surface waters poses potential hazards to both organisms and human health. Traditional water treatment processes have proven to be inadequate in effectively removing microplastics. Besides, previous studies have often utilized disinfectant dosages that surpass those commonly employed in drinking water treatment plants (DWTPs), and the biotoxicity changes induced by microplastics after disinfection remain largely unexplored. To address these knowledge gaps, our study aimed to investigate the impact of practical disinfectant dosages on the leaching of organic compounds from microplastics and the formation of disinfection byproducts (DBPs). Furthermore, the resulting acute and genetic toxicity was evaluated through bioassays. Our findings revealed an elevated release of dissolved organic matter (DOM) derived from microplastics. Additionally, both acute and genetic toxicity increased following various disinfection processes. Specifically, chlorination exhibited the highest level of toxicity in short-term disinfection, while the pretreatment of ozonation followed by residual chlorination demonstrated the highest toxicity in the long-term disinfection, which was correlated with the concentration of CHCl3 formed. These findings will advance our understanding of the potential risks associated with microplastics during various disinfection processes, with the ultimate goal of safeguarding water supplies.

Disinfection byproducts and their cytotoxicity contribution from dissolved black carbon in source water during chlor(am)ination

Dissolved black carbon (DBC), the soluble component of black carbon, which mainly comes from the incomplete combustion of fossil fuels or biomass, is widely spread in source water and significantly contributes to the formation of dissolved organic matter (DOM). However, the origin of DBC in different types of source water in China has not been well studied, as well as its subsequent transformation and toxicity contribution during disinfection of source water DOM by chlor(am)ine. In this study, DBC from 17 different source water in East China at different seasons was collected. The δ13C compositions indicated that straw burning was the main origin of DBC in source water. After simulated chlor(am)ination of DBC, 5 categories of aliphatic disinfection byproducts (DBPs) including trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, halonitromethanes and 6 categories of aromatic DBPs including halophenols, halonitrophenols, halohydroxybenzaldehyde, halohydroxybenzoic acid, halobenzoquinones and haloaniline were detected. Compared with chlorination of DBC, higher levels of nitrogenous DBPs and aromatic DBPs were generated during chloramination. Detected DBPs accounted for 42 % of total organic halogen. What's more, Chinese hamster ovary cells cytotoxicity tests showed that the cytotoxicity of DBPs formed by chlor(am)ination of DBC was 4 times higher than that by chlor(am)ination of DOM. Haloacetonitriles contributed to the highest cytotoxicity in the chloramination of DBC, and haloacetic acids contributed to the highest cytotoxicity in chlorination. 67 % of the total cytotoxicity attributed to the undetected DBPs. As a result, DBPs generated from DBC contributed to 11.7 % of the total cytotoxicity in the chlor(am)ination of the source water DOM although DBC only took up 2 % of DOC in the source water. Results obtained from this study systematically revealed the DBPs formation from DBC and their potential cytotoxicity contribution in the chlor(am)ination of source water DOM, which should not be ignored in drinking water treatment.

Control of chlorination disinfection by-products in drinking water by combined nanofiltration process: A case study with trihalomethanes and haloacetic acids

Disinfection by-products (DBPs) are prevalent contaminants in drinking water and are primarily linked to issues regarding water quality. These contaminants have been associated with various adverse health effects. Among different treatment processes, nanofiltration (NF) has demonstrated superior performance in effectively reducing the levels of DBPs compared to conventional processes and ozone-biological activated carbon (O3-BAC) processes. In this experiment, we systematically investigated the performance of three advanced membrane filtration treatment schemes, namely "sand filter + nanofiltration" (SF + NF), "sand filter + ozone-biological activated carbon + nanofiltration" (SF + O3-BAC + NF), and "ultrafiltration + nanofiltration" (UF + NF), in terms of their ability to control disinfection by-product (DBP) formation in treated water, analyzed the source and fate of DBP precursors during chlorination, and elucidated the role of precursor molecular weight distribution during membrane filtration in relation to DBP formation potential (DBPFP). The results indicated that each treatment process reduced DBPFP, as measured by trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP), with the SF + O3-BAC + NF process being the most effective (14.27 μg/L and 14.88 μg/L), followed by the SF + NF process (21.04 μg/L and 16.29 μg/L) and the UF + NF process (26.26 μg/L and 21.75 μg/L). Tyrosine, tryptophan, and soluble microbial products were identified as the major DBP precursors during chlorination, with their fluorescence intensity decreasing gradually as water treatment progressed. Additionally, while large molecular weight organics (60–100,000 KDa) played a minor role in DBPFP, small molecular weight organics (0.2–5 KDa) were highlighted as key contributors to DBPFP, and medium molecular weight organics (5–60 KDa) could adhere to the membrane surface and reduce DBPFP. Based on these findings, the combined NF process can be reasonably selected for controlling DBP formation, with potential long-term benefits for human health.

An analytical view of disinfectant degradation and disinfection by-product formation

An analytical view of disinfectant degradation and disinfection by-product formation

Simultaneous time-resolved inorganic haloamine measurements enable analysis of disinfectant degradation kinetics and by-product formation.

We demonstrate the application of proton transfer time-of-flight mass spectrometry (PTR-TOF-MS) in monitoring the kinetics of disinfectant decay in water with a sensitivity one to three orders of magnitude greater than other analytical methods. Chemical disinfection inactivates pathogens during water treatment and prevents regrowth as water is conveyed in distribution system pipes, but it also causes formation of toxic disinfection by-products. Analytical limits have hindered kinetic models, which aid in ensuring water quality and protecting public health by predicting disinfection by-products formation. PTR-TOF-MS, designed for measuring gas phase concentrations of organic compounds, was able to simultaneously monitor aqueous concentrations of five inorganic haloamines relevant to chloramine disinfection under drinking water relevant concentrations. This novel application to aqueous analytes opens a new range of applications for PTR-TOF-MS.

Response of a source water quality through a heavy precipitation event: Nutrients, dissolved organic matter and their DBPs formation

To better understand the influence of heavy precipitation event on water supply security, the change of nutrients, dissolved organic matter (DOM) and their corresponding disinfection by-products (DBPs) generation in river were investigated through a heavy precipitation event. The results show that short-term sustained heavy precipitation causes additional load on the river. Significant temporal variations and increases in dissolved oxygen (DO), turbidity, dissolved organic carbon (DOC) and molecular weight of raw water were observed during the heavy precipitation, and dissolved organic nitrogen (DON) showed a remarkably decline with the continuation of precipitation. The molecular weight and aromaticity of DOM increased dramatically with the continuous superposition of precipitation and flow, and the proportion of hydrophobic fraction increased during the study period. Four different fluorescent components were identified, including humic-like (C1, C2 and C3), and protein-like fluorophore C4. Heavy precipitation events affected the mobilization of DOM, while the generation of DBPs increased by 4%–47% during the chlorination, and the elevated river level further increased the DBPs formation. In particular, the HOA fraction was the main contributor of DBPs (up to 70%). The risk of haloacetic acids (HAAs) generation caused by heavy rainfall was concentrated in the river runoff producing and regression periods for both hydrophobic and hydrophilic fractions of DOM. Humification index (HIX) was positively correlated with the yield level of TCM, DCAA, TCAA, and DCAN during chlorination. Chlorination disinfection of raw water during river runoff producing and regression period is likely to increase the haloacetonitriles formation potential (HANsFP), thus posing a vital threat to water supply safety, while chloramination disinfection may significantly relieve the threat. This study provides a theoretical basis for the direct/indirect link between short-term precipitation events and their impact on water quality.

Chlorination of Aromatic Amino Acids: Elucidating Disinfection Byproducts, Reaction Kinetics, and Influence Factors.

In the face of ongoing water pollution challenges, the intricate interplay between dissolved organic matter and disinfectants like chlorine gives rise to potentially harmful disinfection byproducts (DBPs) during water treatment. The exploration of DBP formation originating from amino acids (AA) is a critical focus of global research. Aromatic DBPs, in particular, have garnered considerable attention due to their markedly higher toxicity compared to their aliphatic counterparts. This work seeks to advance the understanding of DBP formation by investigating chlorination disinfection and kinetics using tyrosine (Tyr), phenylalanine (Phe), and tryptophan (Trp) as precursors. Via rigorous experiments, a total of 15 distinct DBPs with accurate molecular structures were successfully identified. The chlorination of all three AAs yielded highly toxic chlorophenylacetonitriles (CPANs), and the disinfectant dosage and pH value of the reaction system potentially influence chlorination kinetics. Notably, Phe exhibited the highest degradation rate compared to Tyr and Trp, at both the CAA:CHOCl ratio of within 1:2 and a wide pH range (6.0 to 9.0). Additionally, a neutral pH environment triggered the maximal reaction rates of the three AAs, while an acidic condition may reduce their reactivity. Overall, this study aims to augment the DBP database and foster a deeper comprehension of the DBP formation and relevant kinetics underlying the chlorination of aromatic AAs.

Effects of cupric ions on the formation of chlorinated disinfection byproducts from nitrophenol compounds during UV/post-chlorination

Cupric ions (Cu2+) are ubiquitous in surface waters and can influence disinfection byproducts (DBPs) formation in water disinfection processes. This work explored the effects of Cu2+ on chlorinated DBPs (Cl-DBPs) formation from six representative nitrophenol compounds (NCs) during UV irradiation followed by a subsequent chlorination (i.e., UV/post-chlorination), and the results showed Cu2+ enhanced chlorinated halonitromethane (Cl-HNMs) formation from five NCs (besides 2-methyl-3-nitrophenol) and dichloroacetonitrile (DCAN) and trichloromethane (TCM) formation from six NCs. Nevertheless, excessive Cu2+ might reduce Cl-DBPs formation. Increasing UV fluences displayed different influences on total Cl-DBPs formation from different NCs, and increasing chlorine dosages and NCs concentrations enhanced that. Moreover, a relatively low pH (5.8) or high pH (7.8) might control the yields of total Cl-DBPs produced from different NCs. Notably, Cu2+ enhanced Cl-DBPs formation from NCs during UV/post-chlorination mainly through the catalytic effect on nitro-benzoquinone production and the conversion of Cl-DBPs from nitro-benzoquinone. Additionally, Cu2+ could increase the toxicity of total Cl-DBPs produced from five NCs besides 2-methyl-3-nitrophenol. Finally, the impacts of Cu2+ on Cl-DBPs formation and toxicity in real waters were quite different from those in simulated waters. This study is conducive to further understanding how Cu2+ affected Cl-DBPs formation and toxicity in chlorine disinfection processes and controlling Cl-DBPs formation in copper containing water.

Formation potential of disinfection byproducts during chlorination of petroleum hydrocarbon-contaminated drinking water

Recent leaks of underground fuel storage tanks in the Pearl Harbor region have led to direct release of un-weathered petroleum hydrocarbons (PHCs) into drinking water sources, which then directly underwent chlorination disinfection treatment. Since the control of disinfection byproducts (DBPs) traditionally focuses natural organic matters (NOM) from source water and little is known about the interactions between free chlorine and un-weathered PHCs, laboratory chlorination experiments in batch reactors were conducted to determine the formation potential of DBPs during chlorination of PHC-contaminated drinking water. Quantitative analysis of regulated DBPs showed that significant quantities of THM4 (average 3,498 μg/L) and HAA5 (average 355.4 μg/L) compounds were formed as the result of chlorination of un-weathered PHCs. Amongst the regulated DBPs, THM4, which were comprised primarily of chloroform and bromodichloromethane, were more abundant than HAA5. Numerous unregulated DBPs and a large diversity of unidentified potentially halogenated organic compounds were also produced, with the most abundant being 1,1-dichloroacetone, 1,2-dibromo-3-chloropropane, chloropicrin, dichloroacetonitrile, and trichloracetonitrile. Together, the results demonstrated the DBP formation potential when PHC-contaminated water undergoes chlorination treatment. Further studies are needed to confirm the regulated DBP production and health risks under field relevant conditions.

MnO2-based capacitive system enhances ozone inactivation of bacteria by disrupting cell membrane

The application of ozone (O3) disinfection has been hindered by its low solubility in water and the formation of disinfection by-products (DBPs). In this study, capacitive disinfection is applied as a pre-treatment for O3 oxidation, in which manganese dioxide with a rambutan-like hollow spherical structure is used as the electrode to increase the charge density on the electrode surface. When a voltage is applied, the negative-charged microbes are attracted to the electrodes and killed by electrical interactions. The contact between microbes and capacitive electrodes leads to changes in cell permeability and burst of reactive oxygen species, thereby promoting the diffusion of O3 into the cells. After O3 penetrates the cell membrane, it can directly attack the cytoplasmic constituents, accelerating fatal and irreversible damage to pathogens. As a result, the performance of the capacitance-O3 process is proved better than the direct sum of the two individual process efficiencies. The design of capacitance-O3 system is beneficial to reduce the ozone dosage and DBPs with a broader inactivation spectrum, which is conducive to the application of ozone in primary water disinfection.

Sunlight enhanced the formation of tribromomethane from benzotriazole degradation during the sunlight/free chlorine treatment in the presence of bromide

The coexistence of free chlorine and bromide under sunlight irradiation (sunlight/FC with Br−) is unavoidable in outdoor seawater swimming pools, and the formation of brominated disinfection byproducts could act more harmful than chlorinated disinfection byproducts. In this study, benzotriazole was selected as a model compound to investigate the degradation rate and the subsequent formation of disinfection byproducts via sunlight/FC with Br− process. The rate constants for the degradation of benzotriazole under pseudo first order conditions in sunlight/FC with Br− and sunlight/FC are 2.3 ± 0.07 × 10−1 min−1 and 6.0 ± 0.7 × 10−2 min−1, respectively. The enhanced degradation of benzotriazole can be ascribed to the generation of HO•, bromine species, and reactive halogen species (RHS) during sunlight/FC with Br−. Despite the fact that sunlight/FC with Br− process enhanced benzotriazole degradation, the reaction results in increasing tribromomethane (TBM) formation. A high concentration (37.8 μg/L) of TBM was detected in the sunlight/FC with Br−, which was due to the reaction of RHS. The degradation of benzotriazole was notably influenced by the pH value (pH 4 − 11), the concentration of bromide (0 − 2 mM), and free chlorine (1 − 6 mg/L). Furthermore, the concentration of TBM increased when the free chlorine concentrations increased, implying the formation potential of harmful TBM in chlorinated seawater swimming pools.

Chlorite and bromate alter the conjugative transfer of antibiotic resistance genes: Co-regulation of oxidative stress and energy supply

The widespread use of disinfectants during the global response to the 2019 coronavirus pandemic has increased the co-occurrence of disinfection byproducts (DBPs) and antibiotic resistance genes (ARGs). Although DBPs pose major threats to public health globally, there is limited knowledge regarding their biological effects on ARGs. This study aimed to investigate the effects of two inorganic DBPs (chlorite and bromate) on the conjugative transfer of RP4 plasmid among Escherichia coli strains at environmentally relevant concentrations. Interestingly, the frequency of conjugative transfer was initially inhibited when the exposure time to chlorite or bromate was less than 24 h. However, this inhibition transformed into promotion when the exposure time was extended to 36 h. Short exposures to chlorite or bromate were shown to impede the electron transport chain, resulting in an ATP shortage and subsequently inhibiting conjugative transfer. Consequently, this stimulates the overproduction of reactive oxygen species (ROS) and activation of the SOS response. Upon prolonged exposure, the resurgent energy supply promoted conjugative transfer. These findings offer novel and valuable insights into the effects of environmentally relevant concentrations of inorganic DBPs on the conjugative transfer of ARGs, thereby providing a theoretical basis for the management of DBPs.

Molecular-weight dependent promotion and competition effects of natural organic matter on dissolved black carbon removal by coagulation

Dissolved black carbon (DBC) is the ubiquitous component of dissolved organic matter pools with the high reactivity for disinfection byproducts formation. However, it is unknown that the influence of molecular weight (MW) of natural organic matter (NOM) on the DBC removal from potable water sources. Therefore, it was studied that the DBC removal by coagulation in the presence of the NOM with various molecular weights. The DBC removal was promoted due to the presence of NOM and the promotion degree decreased with decreasing MW of NOM. Furthermore, the removal ratio of humic-like component increased as the MW of NOM decreased, suggesting that the competition between DBC and NOM increased with decreasing MW. The functional groups after coagulation were the same with that before coagulation as the MW of NOM varied, suggesting that the molecular structure was not the key factor of influencing the DBC removal. This study will give the deep insight into the prediction of the DBC removal ratio by coagulation based on the MW of NOM in water sources.

Comparative analysis of chlorinated disinfection byproducts formation from 4-nitrophenol and 2-amino-4-nitrophenol during UV/post-chlorination

Nitrophenol compounds (NCs) are widely distributed in water environments and regarded as important precursors of disinfection byproducts (DBPs). Herein, 4-nitrophenol and 2-amino-4-nitrophenol were selected as representative NCs to explore chlorinated DBPs (Cl-DBPs) formation during UV/post-chlorination. Dichloronitromethane (DCNM), trichloronitromethane (TCNM), dichloroacetonitrile (DCAN), and trichloromethane (TCM) were formed from 4-nitrophenol and 2-amino-4-nitrophenol during UV/post-chlorination, and the yields of individual Cl-DBPs from 2-amino-4-nitrophenol were higher than those from 4-nitrophenol. Meantime, increasing chlorine contact time, UV fluence, and free chlorine dose could enhance Cl-DBPs formation, while much higher values of the three factors might decrease the yields of Cl-DBPs. Besides, alkaline pH could decrease the yields of halonitromethane (HNMs) and DCAN but increase the yields of TCM. Also, higher concentrations of 4-nitrophenol and 2-amino-4-nitrophenol would induce more Cl-DBPs formation. Subsequently, the possible formation pathways of DCNM, TCNM, DCAN, and TCM form 4-nitrophenol and 2-amino-4-nitrophenol during UV/post-chlorination were proposed according to transformation products (TPs) and density functional theory (DFT) calculation. Notably, Cl-DBPs formed from 2-amino-4-nitrophenol presented higher toxicity than those from 4-nitrophenol. Among these generated Cl-DBPs, DCAN and TCNM posed higher cytotoxicity and genotoxicity, respectively. Furthermore, 4-nitrophenol, 2-amino-4-nitrophenol, and their TPs exhibited ecotoxicity. Finally, 4-nitrophenol and 2-amino-4-nitrophenol presented a high potential to produce DCNM, TCNM, DCAN, and TCM in actual waters during UV/post-chlorination, but the Cl-DBPs yields were markedly different from those in simulated waters. This work can help better understand Cl-DBPs formation from different NCs during UV/post-chlorination and is conducive to controlling Cl-DBPs formation.