Restricted to the complex nature of dissolved organic matter (DOM) in various aquatic environments, the mechanisms of enhanced iodinated disinfection byproducts (I-DBPs) formation in water containing both I- and IO3- (designated as I-/IO3- in this study) during the ultraviolet (UV)-chloramine sequential disinfection process remains unclear. In this study, four machine learning (ML) models were established to predict I-DBP formation by using DOM and disinfection features as input variables. Extreme gradient boosting (XGB) algorithm outperformed the others in model development using synthetic waters and in cross-dataset generalization of surface waters. Shapley additive explanation (SHAP) analysis, partial dependence plots (PDPs), and individual conditional expectation (ICE) analysis were then employed to explain the models' workings and feature interactions, aiding in identification and quantification of underlying mechanisms. A type of DOM component (namely DC_b) was found as the greatest contributor and identified as reduced quinones associated with broken-down lignin within higher plant-derived fulvic substance, serving as precursors and electron shuttles for I-DBP formation. Based on the interactional effects acquired from explanation results, the ejection of e-aq from excited DOM and pre-existing I- in the I-/IO3- system were identified responsible for the enhanced generation of I-DBPs compared to that in the I- or IO3- alone systems; extra DOM scavenged reactive iodine species (RIS), contributing to a limited enhancement. These findings and the methodology developed here together enhance our understanding of the mechanisms how DOM limitedly promotes I-DBP formation during UV-chloramine sequential disinfection of I-/IO3--containing water and facilitate effective online monitoring in the future.

Pre-chlorination is commonly employed to remove algae cells in source water, reducing the burden on drinking water treatment. However, ammonia nitrogen and algal organic matter (AOM) can react with the free chlorine (FC) to form mixed chlor(am)ine conditions. The effects of mixed chlor(am)ines on algae cell removal and associated risks have long been overlooked. Herein, we elucidated the differences in algae cell inactivation by different chlor(am)ine species and mixed chlor(am)ine concentration ratios (CCRs). Furthermore, the effectiveness of algae removal by mixed chlor(am)ines under different pH levels and algal species was compared. Results indicated that FC was the most effective at removing chlorophyll-a from algae cells (98%), followed by monochloramine (NH2Cl) (95%) and dichloramine (NHCl2) (64%). Reactive nitrogen species produced by NHCl2 accelerated the damage to algae cells and led to release more AOM than NH2Cl. FC mainly caused algae cells dissolution, whereas NH2Cl and NHCl2 primarily induced shrinkage. A mixed CCR of FC:NH2Cl:NHCl2 = 1:2:1 exhibited higher removal efficiency, lower AOM release rates and chlor(am)ine consumption, enabling efficient and persistent algal removal. More carbonaceous disinfection by-products were generated under the action of FC, and the highest amounts of geosmin (GSM) and 2-methylisoborneol (2-MIB) were released. Fewer nitrogenous disinfection by-products and more N-chloroaldimine odorants were produced when treating by NH2Cl. Increasing the NH2Cl ratio in mixed CCRs reduced GSM and 2-MIB release. Our findings expand the theoretical understanding of traditional pre-chlorination for algae removal, which can achieve non-lytic algae inactivation and reduce water quality risks via easily-operated chlor(am)ine species regulation methods.

The efficient removal of 2-Methylisoborneol (2-MIB), a typical odour component, in water treatment plants (WTPs), poses a great challenge to conventional water treatment technology due to its chemical stability. In this study, the combination of ultraviolet light-emitting diode (UV-LED) and chlorine (UV-LED/chlorine) was exploited for 2-MIB removal, and the role of ultraviolet (UV) wavelength was investigated systematically. The results showed that UV or chlorination alone did not degrade 2-MIB effectively, and the UV/chlorine process could degrade 2-MIB efficiently, following the pseudo-first-order kinetic model. The 275 nm UV exhibited higher 2-MIB degradation efficiency in this UV-LED/chlorine system than 254 nm UV, 265 nm UV and 285 nm UV due to the highest mole adsorption coefficient and quantum yield of chlorine in 275 nm UV. center dot OH and center dot Cl produced in the 275 nm UV/chlorine system played major roles in 2-MIB degradation. HCO3- and Natural organic matter (NOM), prevalent in water, consumed center dot OH and center dot Cl, thus inhibiting the 2-MIB degradation by UV-LED/chlorine. In addition, NOM and 2-MIB could form a photonic competition effect. The degradation of 2-MIB by UV-LED/chlorine was done mainly through dehydration and demethylation, and odorous intermediates, such as camphor, were produced. 2-MIB was degraded through the alpha bond fracture and six-membered ring opening to form saturated or unsaturated hydrocarbons and aldehydes. Four DBPs, chloroform (CF), trichloroacetaldehyde (TCE), trichloroacetone (TCP) and dichloroacetone (DCP), were mainly generated, and CF was the most significant by-product.

Iodinated X-ray contrast media (ICM) are ubiquitously present in water sources and challenging to eliminate using conventional processes, posing a significant risk to aquatic ecosystems. Ultraviolet light-emitting diodes (UV-LED) emerge as a promising technology for transforming micropollutants in water, boasting advantages such as diverse wavelengths, elimination of chemical additives, and no induction of microorganisms' resistance to disinfectants. The research reveals that iohexol (IOX) degradation escalates as UV wavelength decreases, attributed to enhanced photon utilization efficiency. Pseudo-first-order rate constants (k(obs)) were determined as 3.70, 2.60, 1.31 and 0.65 cm(2) J(-1) at UV-LED wavelengths of 255, 265, 275 and 285 nm, respectively. The optical properties of dissolved organic matter (DOM) and anions undeniably influence the UV-LED photolysis process through photon competition and the generation of reactive substances. The influence of Cl- on IOX degradation was insignificant at UV-LED 255, but it promoted IOX degradation at 265, 275 and 285 nm. IOX degradation was accelerated by ClO2-, NO(3)(-)and HA due to the formation of various reactive species. In the presence of NO3-, the k(obs) of IOX followed the order: 265 > 255 > 275 > 285 nm. Photosensitizers altered the spectral dependence of IOX, and the intermediate photoactivity products were detected using electron spin resonance. The transformation pathways of IOX were determined through density functional theory calculations and experiments. Disinfection by-products (DBPs) yields of IOX during UV-LED irradiation decreased as the wavelength increased: 255 > 265 > 275 > 285 nm. The cytotoxicity index value decreased as the UV-LED wavelength increased from 255 to 285 nm. These findings are crucial for selecting the most efficient wavelength for UV-LED degradation of ICM and will benefit future water purification design.

Fungi represent a considerable challenge given their ubiquitous inhabitation and growth in drinking water distribution systems (DWDSs), yet the germination behavior of fungal spores in DWDSs is largely unknown. This study investigated germination of three chlorine-resistant fungal spores (Penicillium chrysogenum, Cladosporium halotolerans, and Penicillium spinulosum) in synthetic tap water (STW) under varying conditions of disinfectants (free chlorine, FC; monochloramine, NH2Cl), humic acid (HA), and pH. The germination ratios of the tested fungal spores in STW(+HA) were <10% without FC/NH2Cl, while surprisingly increased to a maximum of 67.5% and 44.14% with 2 mg/L FC and 0.4 mg/L NH2Cl, respectively, for C. halotolerans spores. With increasing initial concentrations of FC (0-4 mg/L) and NH2Cl(0-2 mg/L), germination ratios of C. halotolerans spores in STW+HA showed a first increasing and then decreasing trend, suggesting that the stimulation effect was outweighed by inactivation at high CT values. Nontargeted metabolomics analysis identified the decrease of several potential self-inhibitors for spore germination by chlor(am)ination. Patterns of significantly changed metabolites and pathways involving lipid, sugar, and amino acid metabolism were significantly different for C. halotolerans spores treated by FC versus NH2Cl. The results provide new insights into survival strategies and germination mechanisms of fungal spores in chlor(am)ine-disinfected DWDSs.

The sludge produced by urban drinking water treatment plants has a high yield, low organic content, and a high risk of inorganic pollution. Its green and low-carbon treatment, as well as resource utilization, has become urgent issues in achieving the "dual-carbon" goals in China's water supply industry. This paper discusses and analyzes national industry policies and the characteristics of sludge from drinking water treatment plants, and summarizes the treatment methods and development trends in resource utilization. Currently, commonly used treatment methods for drinking water treatment plant sludge include water body discharge, municipal sewage discharge, and landfilling, which present environmental risks, facility clogging, land occupation, and significant carbon emissions. Based on the characteristics of sludge from urban drinking water treatment plants, potential methods for resource utilization include the production of synthetic adsorption materials, coagulation/precipitation materials, regenerated salt materials, construction materials, and agroforestry materials. Breaking through the aforementioned key technologies to realize the transformation of drinking water treatment plant sludge from "treatment" to "resource utilization" will play a crucial role in promoting the green and low-carbon operation of China's urban water supply industry.

Dredged sediment, reed straw and algae are three kinds of wastes generated during the ecological construction and operation of the water source reservoir. Efficient treatment and disposal of them is an important guarantee for realizing the ecological cycle of the reservoir, and is of great significance for improving the water quality and sustainable development. Firstly, this paper summarizes the current situation of resource utilization technology of dredged sediment in farmland, forest land, landscaping and other aspects of land use and building materials production, filling materials and other aspects of building materials utilization, and summarizes the development status of resource utilization technology of reed straw in agriculture, aquaculture, energy, industrial raw materials and other aspects, as well as the recovery of blue-green algae in anaerobic digestion, extraction of useful substances, feed application, aerobic composting and other aspects. Furthermore, the applicability of the above resource utilization technologies in the process of resource utilization of water source reservoir wastes is analyzed, and it is pointed out that land use is the best way of resource utilization of dredged sediment, and aerobic composting is the mainstream technology of treatment and disposal of reed straw and blue-green algae wastes. Finally, targeted suggestions are put forward for waste resource reutilization technologies in water source reservoir.

Mixed chlorine/chloramines are commonly occurring in real drinking water distribution systems (DWDSs) but often overlooked. This review provides a comprehensive overview of the occurrences, characteristics, analysis methods, and control strategies of mixed chlorine/chloramines in DWDSs. The characteristics of mixed chlorine/ chloramine species are summarized for treated water in drinking water treatment plants (DWTPs), secondary disinfection facilities, and DWDSs where different disinfectants could be blended. The key to differentiating and quantifying mixed chlorine/chloramine species is to separate organic chloramines (OCs) from di/tri-chloramines and overcome certain interferences. The complex interactions between water matrixes and chlorine/chloramine species could accelerate pipeline corrosions, enhance emerging disinfection by-products risks, lead to off-flavors in drinking water, and induce bio-instability issues (such as nitrification, microorganism regrowth, and promotion of horizontal gene-transfers). Three promising strategies for alleviating mixed chlorine/chloramine species are recommended, which include (i) removing precursors intensively and reconditioning the treated water, (ii) combining UV irradiation to eliminate undesired chlorine/chloramines species, and (iii) strengthening monitoring, operation, and maintenance management of DWDSs. Finally, the challenges for gaining insights into the mechanisms of mixed chlorine/chloramine species conversion are discussed and promising research directions are proposed.

A novel UV light, UVC laser, was used to activate persulfate (PS) for degrading bisphenol A (BPA) in this study. This new light source can emit concentrated beam, and achieve 74.5% of BPA removal within only 60 s when activating PS. Sulfate radicals (SO4 center dot- ) and hydroxyl radicals (OH center dot) were identified in the UVC laser/PS system. In the case of the same total irradiance energy, the concentrated beam performed a better removal efficiency of BPA than the diffused beam. Compared with the diffused beam, the steady-state concentrations of SO4 center dot- and OH center dot under concentrated beam increased by 26.21% and 361.25%, respectively. In addition, the depth-to-diameter ratio (h/D) of the reaction vessels also had a significant effect on the removal efficiency of BPA and the highest degradation rate obtained at h/D = 0.65. High UVC laser intensity, high PS dosage, and circumneutral pH conditions could promote BPA degradation, whereas the presence of water matrix (including chloride, bromide, bicarbonate, and natural organic matter) exhibited opposite effects. The BPA degradation intermediates in the UVC laser/PS system were identified by LCMS and the BPA degradation pathways were proposed accordingly. This study is the first one illustrating the influence of laser beam types, h/D ratio of the reactor vessel, and water matrix on UVC laser/PS application in water treatment process, which can provide essential knowledge for removing micropollutants in water using the novel UVC laser/PS AOP.

UV/peroxymonosulfate(UV/PMS)advanced oxidation process has attracted significant at-tention for removal of micropollutants in water.However,during practical water treatment applications,the PMS treatment must be performed before the UV treatment to achieve full contact.In this study,sulfamethoxazole(SMX)was selected as the target micropol-lutant.Four different operational approaches,including UV alone,PMS alone,simultane-ous UV/PMS and sequential PMS-UV,were compared for their differences in SMX removal and disinfection by-product(DBP)formation potentials during chlorine-driven disinfection.Among the four approaches,UV/PMS and PMS-UV achieved over 90％removal efficiencies for SMX without substantial differences.For raw water,the trichloronitromethane(TCNM)formation potential after treatment with PMS-UV was lower than that after UV/PMS treat-ment.The time interval over which the PMS-UV process was conducted had little effect on the final removal efficiency for SMX.However,a brief(5 min)pre-PMS treatment signifi-cantly reduced the TCNM formation potential and the genotoxicity from DBPs.The forma-tion risk for TCNM during chlorination increased markedly with increasing PMS dosages,and the appropriate dosage under these experimental conditions was suggested to be 0.5-1.0 mmol/L.Under alkaline conditions,PMS-UV treatment can enhance SMX degradation as well as dramatically reduced the formation potentials for haloketones,haloacetonitriles and halonitromethanes.This study suggests that proper optimization of UV/PMS processes can remove SMX and reduce its DBP formation.

相较于塑料、不锈钢等其它管材,给水用铜管可以更有效地提高饮用水供给质量,保障供水安全.但铜管在某些特殊情况下可能出现铜离子溶出情况,甚至出现"蓝水"现象,导致用户对给水用铜管的使用产生错误认识.分析和总结了铜管的电化学腐蚀原理与特性,并针对建筑给水领域用铜管可能存在的电化学腐蚀提出了防护建议.