Spectral And Molecular Characteristics Of DOM In Municipal Domestic Wastewater And Its Relationship With Microbial Community Composition

With the rapid development of social economy and urbanization,the water demand of residents has increased greatly,and the increasing amount of urban domestic sewage discharge has a great impact on the aquatic ecosystems of the watershed.Although there are a large number of wastewater treatment plants(WWTPs)have reached the primary A discharge standard,but the urban domestic wastewater plant effluent will be injected into the river with the outfall,causing impact on the surface water quality and aquatic ecosystems.The DOM from WWTPs effluent discharge is also an important source of DOM in aquatic ecosystems,these inputs are the major energy source for microorganisms and could influence the structure of microbial communities in coastal waters.Besides,these DOM also participate in the migration transformation of pollutants and change their biological activity and stability.Thus,a comprehensive evaluation of the presence and the fate of DOM in both influent and effluent in WWTPs with various processes and clarifying the interactions between DOM with microbial communities is crucial.The main conclusions of this study are as follows:(1)In this study,the molecular types of DOM in domestic wastewater were found to be dominated by CHO,CHON,and CHOS.The effluent water has a higher molecular weight and contains more double bonds or ring structures.Geographical location and economic level both determine the DOM components in the influent of WWTPs,and the influent contains more lipid and protein components.There were no significant regional differences of DOM in the effluent,which was dominated by humic-like component and lignin,and the relative percentage of protein-like component C4 increased.In addition,the fluorescence index(FI)of DOM in the influent and effluent of the WWTPs did not vary significantly and were in the range of 1.9-2.3.(2)The fluorescent component C3 identified in the culture experiments was a UVC humic-like component that can be utilized by microorganisms for metabolism,and C5 is a protein-like component secreted by microorganisms during the metabolism.The dominant microbial genera in the sodium lignosulfonate,humic acid,polyglyceryl fatty ester,peptone fish powder and sucrose addition groups were Nitrosomonas spp.,while the tannic acid group had a higher bacterial diversity and several genera tended to coexist,consisting of Comamonas,Bacillus,Hydrogenophaga,Oligotrophomonas Hydrogenophaga,Stenotrophomonas,and Sphingopyxis.(3)The results of the culture experiments showed that the relative abundance of functional genes related to nitrification reaction increased in all groups except tannic acid treatment,and the diversity of functional genes related to carbon metabolism decreased in the humic acid treatment group.Bacterial community,carbon and nitrogen metabolism functional gene composition were all strongly correlated with lipid,humic acid and protein fractions,suggesting that heterogeneity of different DOM components could affect the expression of functional genes by influencing bacterial community composition.This study systematically analyzed the component composition,spectral characteristics and variation of DOM in the influent and effluent of WWTPS in Shaanxi Province,clarified the main component composition of human-derived DOM and its potential threat to the ecosystem.The interactions between different types of DOM components and microbial communities were explored through indoor incubation experiments,and the effects of each component on the structure of microbial communities and their functional gene expression were clarified,providing a reference for the risk assessment of effluent from WWTPs and the management of aquatic ecosystem ecological health.