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Spectroscopic insights into photochemical transformation of effluent organic matter from biological wastewater treatment plants

Zhang, Xin, Yang, Chuan-Wang, Li, Jing, Yuan, Li, Sheng, Guo-Ping
The Science of the total environment 2019 v.649 pp. 1260-1268
Fourier transform infrared spectroscopy, absorption, amides, carbohydrates, effluents, fluorescence, moieties, organic matter, photolysis, proteins, quinones, spectral analysis, ultraviolet radiation, wastewater treatment
The photodegradation of discharged effluent organic matter (EfOM) changes its composition and shifts its impacts on pollutant migration and transformation in receiving waters. However, to date, EfOM photodegradation processes are not well understood due to the complexity and heterogeneity of EfOM. Herein, the spectroscopic analysis including ultra violet-visible (UV–Vis), fluorescence and FTIR spectroscopies coupled with two-dimensional correlation analysis (2D-COS) were used to draw a comprehensive view of EfOM photodegradation and involving mechanisms. Results revealed that the photolability of each component in EfOM followed the order: tannin-like > humic-like > protein-like > carbohydrate-like and aliphatic compounds. The photolability of different components of EfOM were found to be related to the photolability of their functional groups. Specifically, the aromatic, carboxylic, phenolic and quinonoid groups associated with humic or tannin-like compounds were more prone to be photodegraded than amides in proteins or C-OH and C-O-C in carbohydrates. Furthermore, the humic-like components, dominating the light absorption of EfOM, were found to be degraded by direct photolysis. Nevertheless, the photodegradation of tannin-like and protein-like components were mainly due to the indirect photodegradation by ROS and 3OM⁎. Furthermore, results indicated that UV light, rather than visible light, was responsible for the photodegradation of EfOM. The spectroscopic techniques integrated with 2D-COS analysis could serve as a powerful tool with which to clarify complex EfOM photodegradation process as well as to improve our understanding of the fate of discharged EfOM and related environmental processes.