In this study, the transformation mechanisms of extracellular polymeric substances (EPS) during ultraviolet/peracetic acid (UV/PAA) disinfection were elucidated based on multiple molecular-level analyses. After UV/PAA disinfection, the contents of soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were reduced by 70.47 %, 57.05 % and 47.46 %, respectively. Fluorescence excitation-emission matrix-parallel factor and Fourier transform ion cyclotron resonance mass spectrometry analyses showed that during UV/PAA disinfection, EPS was transformed from the state characterized by high aromaticity, low saturation and low oxidation to the one with reduced aromaticity, increased saturation and higher oxidation. Specifically, sulfur-containing molecules (CHOS, CHONS, etc.) in EPS were converted into highly saturated and oxidized species (such as CHO), with the aromaticity index (AImod) decreasing by up to 53.84 %. Molecular characteristics analyses further indicated that saturation degree, oxidation state of carbon and molecular weight exhibited the most significant changes in S-EPS, LB-EPS and TB-EPS, respectively. Additionally, mechanistic analysis revealed that oxygen addition reaction was the predominant reaction for S-EPS (+O) and TB-EPS (+3O) (accounting for 31.78 % and 36.47 %, respectively), while the dealkylation was the main reaction for LB-EPS (29.73 %). The results were consistent with functional groups sequential responses analyzed by Fourier transform infrared and two-dimensional correlation spectroscopy, and were further verified by density functional theory calculations. Most reactions were thermodynamically feasible, with reaction sites predominantly located at functional groups such as CO, CO, CN and aromatic rings. Moreover, metabolomics analysis suggested that changes in metabolites in raw secondary effluent during UV/PAA disinfection were strongly correlated with EPS transformation. Our study not only provides a strong basis for understanding EPS transformation during UV/PAA disinfection at molecular-level but also offers valuable insights for the application this promising disinfection process.

中文翻译：

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追踪紫外线/过氧乙酸消毒过程中细胞外聚合物物质的转化：强调分子水平分析和被忽视的机制


在本研究中，基于多分子水平分析阐明了紫外线/过氧乙酸 （UV/PAA） 消毒过程中细胞外聚合物物质 （EPS） 的转化机制。UV/PAA 消毒后，可溶性 EPS （S-EPS） 、松散结合的 EPS （LB-EPS） 和紧密结合的 EPS （TB-EPS） 的含量分别降低了 70.47 %、57.05 % 和 47.46 %。荧光激发-发射矩阵-平行因子和傅里叶变换离子回旋共振质谱分析表明，在 UV/PAA 消毒过程中，EPS 由高芳香性、低饱和度、低氧化的状态转变为芳香性降低、饱和度增加、氧化度高的状态。具体来说，EPS 中的含硫分子（CHOS、CHONS 等）转化为高饱和和氧化的物质（如 CHO），芳香性指数 （AImod） 下降高达 53.84 %。分子特性分析进一步表明，S-EPS、LB-EPS 和 TB-EPS 的饱和度、碳氧化态和分子量分别表现出最显著的变化。此外，机理分析表明，氧加成反应是 S-EPS （+O） 和 TB-EPS （+3O） 的主要反应 （分别占 31.78 % 和 36.47 %），而脱烷基化是 LB-EPS 的主要反应 （29.73 %）。结果与傅里叶变换红外和二维相关光谱分析的官能团顺序响应一致，并通过密度泛函理论计算进一步验证。大多数反应在热力学上是可行的，反应位点主要位于 CO、CO、CN 和芳香环等官能团上。 此外，代谢组学分析表明，UV/PAA 消毒过程中原始二次流出物中代谢物的变化与 EPS 转化密切相关。我们的研究不仅为理解分子水平 UV/PAA 消毒过程中的 EPS 转化提供了强有力的基础，而且还为这种有前途的消毒过程的应用提供了有价值的见解。