UV/H_(2)O_(2)促进饮用水氯化消毒中高毒性卤代乙醛生成的机制

UV/H_(2)O_(2) oxidation promotes the formation of highly toxic haloacetaldehydes during chlorination of drinking water

饮用水消毒过程中,氯不可避免地与溶解性有机质(dissolved organic matter,DOM)发生反应,进而生成消毒副产物(disinfection byproducts,DBPs).随着紫外/过氧化氢高级氧化技术(UV/H_(2)O_(2)advanced oxidation process,UV/H_(2)O_(2)AOP)广泛应用于水中新污染物的去除,DOM的结构及其DBPs生成潜能也将发生改变.但目前关于该工艺对不同类型DOM生成DBPs的影响及反应机制尚不清楚,特别是Br^(-)存在下高毒性溴代DBPs的生成潜能亟待研究.本研究通过生成潜能试验探究了Br^(-)存在和不存在下UV/H_(2)O_(2)对6种天然有机质(natural organic matter,NOM)和藻类有机质(algal organic matter,AOM)在氯化消毒过程中DBPs的生成潜能及反应机制.结果表明,UV/H_(2)O_(2)均显著促进了NOM和AOM的DBPs生成潜能,且AOM的上升趋势更为显著.当Br-存在时,UV/H_(2)O_(2)氧化后使AOM的DBPs生成潜能和毒性分别增加了4.1~4.7倍和49~81倍.荧光光谱分析结果表明UV/H_(2)O_(2)主要通过改变AOM的蛋白质或微生物代谢物等结构促进氯化过程中高毒性溴代乙醛(brominated haloacetaldehydes,Br-HALs)生成.进一步利用模型化合物探究UV/H_(2)O_(2)影响Br-HALs生成的机制,结果表明UV/H_(2)O_(2)改变了AOM中氨基酸等的分子结构,生成的氧化产物在后氯化过程中与HOBr(由氯与Br^(-)反应而成)反应生成高毒性Br-HALs.采用MIEX?DOC树脂预处理和氯胺替代消毒的方式可以使DBPs的生成潜能分别降低48.1%~96.7%和83.5%~97.7%,其中氯胺替代消毒可使DBPs的总毒性降低84.2%~98.2%.本研究可为饮用水厂应对含溴高藻水污染问题提供科学参考并指导生产.

Dissolved organic matter(DOM),a ubiquitous component of source water,serves as a significant precursor to hazardous disinfection byproducts(DBPs)in chlorinated drinking water.Recently,the UV/H_(2)O_(2) advanced oxidation process(UV/H_(2)O_(2) AOP),known for generating highly reactive hydroxyl radicals(HO·),has become increasingly favored for micropollutant abatement in drinking water treatment plants.This process can alter the structural composition of DOM and its potential for DBP formation.However,the specific impact of UV/H_(2)O_(2) on DBP formation from various types of DOM,particularly the production of highly toxic brominated DBPs during harmful algal bloom events in bromide(Br^(-))-enriched waters,remains poorly understood.This knowledge gap impedes the optimization of water treatment processes and the improvement of water quality.To address this gap,six DOM isolates were selected,including three natural organic matters(NOMs)and three algal organic matters(AOMs),to evaluate the influence of UV/H_(2)O_(2) AOP on DBP formation,under both Br^(-)-enriched and Br^(-)-free conditions.At concentrations typical of those used(0.50 mW/cm^(2) UV and 0.3 mmol/L H_(2)O_(2))in drinking water treatment plants,UV/H_(2)O_(2) significantly increased the formation of DBP from both NOM and AOM.Specifically,the concentrations of DBPs formed from Microcystis aeruginosa AOM(MAAOM),Anabaena AOM(AAOM),and Chlorella AOM(CAOM)increased by 198.6%,117.9%,and 103.4%,respectively,compared to only 33.8%,45.5%,and 17% increments for Suwannee River NOM(SRNOM),Pahokee Peat fulvic acid(PPFA),and Elliott Soil humic acid(ESHA),respectively.Furthermore,under Br^(-)-enriched conditions,UV/H_(2)O_(2) further augmented DBP formation,predominantly as brominated DBPs.Notably,the concentrations of brominated-haloacetaldehydes(Br^(-)HALs)produced after AOM oxidation were higher than those from NOM,especially for bromodichloroacetal and dibromochloroacetaldehyde.Due to the elevated toxicity of Br^(-)HALs,the calculated cytotoxicity induced by DBPs from AOM was 49~81 times higher than that of the control group.Analysis using fluorescence spectroscopy showed a positive correlation between changes in the fluorescence intensities of the soluble microbial by-product-like regions before and after the oxidation of each DOM and the formation potential of HALs(R^(2)=0.59),suggesting that UV/H_(2)O_(2) may alter the structures of proteins or microbial metabolites in AOM,thereby boosting HAL formation.We investigated the moieties responsible for altering HAL formation and found that UV/H_(2)O_(2) modified the molecular structure of amino acids,facilitating HAL formation,especially Br^(-)HALs in the presence of Br^(-).Additionally,based on the analysis of oxidation products and bromination experiments,the formation pathway of Br^(-)HAL from histidine(HIS,representative of amino acids)was proposed:HO·attacks the heterocycle of HIS to produce 2-oxo-HIS;during post-chlorination,Br−in water can be rapidly oxidized by HOCl to active HOBr,which further reacts with 2-oxo-HIS to form Br^(-)HAL.Finally,we proposed two strategies to control DBP formation:treatment by MIEX®DOC resin prior to chlorination and switching to chloramination.The results indicate that these strategies could reduce DBP formation by 48.1%-96.7% and 83.5%-97.7%,respectively,with a more significant reduction in DBP toxicity(84.2%-98.2%)under the chloramination scenario.In conclusion,UV/H_(2)O_(2) significantly enhances DBP formation from both NOM and AOM,with a more pronounced increase observed in AOM.Under Br^(-)-enriched conditions,UV/H_(2)O_(2)-treated AOM exhibits a remarkably high potential for Br^(-)HAL formation,contributing to an increase in the total toxicity of DBPs.This study provides substantial insights into the mechanisms of DOM oxidation and HAL formation by UV/H_(2)O_(2),offering guidance for safer and more reliable drinking water treatment strategies during harmful algal blooms.