紫外/氯联用作为一种高级氧化工艺,可利用其产生的多种活性物种去除微污染物和强化消毒效果。在此过程中,水体中存在的天然有机质(NOM)和溴离子会导致氯代和溴代消毒副产物的生成,从而对生态安全和人类健康构成潜在风险。由于检测技术的限制,之前的研究大多只关注常规消毒副产物,针对紫外/氯联用工艺中NOM在分子层面的转化以及未知卤代副产物生成的研究非常缺乏。本研究采用傅里叶变换离子回旋共振质谱技术(FT-ICRMS),从分子层面解析溴离子对紫外/氯联用工艺中NOM转化以及卤代副产物生成的影响。研究发现,紫外/氯联用工艺中,溴离子转化生成次溴酸和含溴自由基(例如Br•、BrO•、和BrOH•−),使得NOM中更多的CHO化合物发生转化,特别是芳香性较高的物质,并生成主要为单宁酸类及富含羧基的脂环类CHO化合物。NOM经紫外/氯联用工艺处理后,共检出222个含溴化合物(CHOBr),与单独氯化处理后生成的CHOBr化合物相比具有明显更低的含碳数和芳香性指数。通过对其前体物的解析发现CHOBr化合物对应的前体物主要是NOM中O/C值较低或H/C值较高的物质,包括NOM中的木质素类似物、高度不饱和类和酚类化合物,而发生取代反应的前体物比发生加成反应的前体物的芳香值更低。单独氯化生成的大部分CHOBr化合物会在后氯化阶段被去除,但紫外/氯生成的大量CHOBr化合物在后氯化阶段依然存在。有溴离子存在时,紫外/氯联用工艺中识别出的CHOCl化合物数量远远低于无溴离子存在时的数量。在没有Br−参与的紫外/氯联用工艺中,识别出333个一氯化合物。当体系中加入Br−后,紫外/氯联用体系中只识别出33个一氯化合物。研究同时也检出了既含Cl又含Br的化合物。本研究从分子层面表征了紫外/氯联用工艺中新型含溴副产物的生成,并阐明了其前体物的转化机理。这些发现凸显了含溴副产物的重要性,并为该工艺在实际应用中需重视的问题提供了参考。

The  UV/chlorine  advanced  oxidation  process  (AOP),  which  generates  various  highlyreactive  radical  species,  effectively  degrades  micropollutants  and  inactivates  microorganisms.  Theubiquitous presence of natural organic matter (NOM) in water leads to the generation of chlorinateddisinfection  byproducts,  while  the  presence  of  bromide  induces  the  generation  of  brominateddisinfection  byproducts,  which  are  known  to  pose  threats  to  ecological  safety  and  human  health.However,  research  has  primarily  focused  on  conventional  disinfection  byproducts  due  to  thecomplexities  associated  with  NOM,  the  diversity  of  halogenated  byproducts,  and  the  limitations  ofanalytical techniques. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was applied to elucidate the influence of bromide ions on the transformation of NOM and thegeneration  of  halogenated  byproducts  in  the  UV/chlorine  AOP.  The  introduction  of  bromide  in  theUV/chlorine AOP facilitated the generation of hypobromous acid and bromine-containing radicals (suchas Br, BrO, , and BrOH). This alteration in radical speciation led to significant transformations ofCHO  compounds  in  NOM,  particularly  those  with  higher  aromaticity.  The  newly  generated  CHOcompounds  were  mainly  tannin-like  and  alicyclic  molecules  rich  in  carboxyl  groups.  A  total  of  222bromine-containing compounds (CHOBr) were detected after the UV/chlorine AOP. Compared with theCHOBr  compounds  detected  in  dark  chlorination,  these  CHOBr  compounds  had  significantly  lowercarbon numbers and AI values. Analysis of the precursors of these CHOBr, considering both additionreactions (AR) and substitution reactions (SR) as pathways, showed that these precursors had low O/Cratios  or  high  H/C  ratios.  These  precursors  were  predominantly  lignin-like  compounds  and  highlyunsaturated  and  phenolic  compounds.  The  SR  precursors  had  lower  aromaticity  compared  to  ARprecursors. The majority of CHOBr compounds generated during chlorination were removed during thepost-chlorination  process,  while  most  of  the  CHOBr  compounds  generated  in  the  UV/chlorine  AOPremained during the post-chlorination phase. In addition to CHOBr compounds, the number of CHOClcompounds identified in the UV/chlorine AOP in the presence of bromide ions was significantly lowerthan  that  in  the  absence  of  bromide  ions.  For  example,  there  were  333  one-chlorine-containingcompounds in the UV/chlorine AOP without bromide ions, but only 33 CHOCl compounds with thepresence of bromide ions. Meanwhile, compounds containing both Cl and Br were also detected in thisstudy. This study characterizes the formation of unknown brominated byproducts at the molecular leveland  elucidates  the  transformation  mechanisms  of  their  precursors.  These  findings  highlight  theimportance  of  brominated  byproducts  and  provide  a  reference  for  addressing  critical  issues  in  thepractical application of the UV/chlorine AOP.