Analysis And Distribution Of Dissolved Organic Matter In Municipal Wastewater

Dissolved organic matter(DOM)in municipal wastewater has wide origin and complex chemical composition.It is greatly affected by the wastewater source,treatment technology and spatial and temporal variations.A comprehensive and indepth analysis of DOM is the premise and foundation for studying DOM distribution in wastewater,improving treatment technology and ensuring water quality safety.This study targets the DOM in influents and secondary effluents of municipal wastewater treatment plants(WWTPs)in China.Firstly,the analytical method for DOM fluorescent composition of municipal wastewater in China has been established.Separate parallel factor analysis(PARAFAC)models and self organized map models have been established on excitation emission matrix(EEM).Then,the distribution of fluorescent dissolved organic matter(FDOM)in municipal wastewater has been explored.FDOM components difficult to remove have been confirmed.The similarities/differences between fluorescent components in municipal wastewater and their key influencing factors have been confirmed.The optimal index to characterize fluorescent composition of municipal wastewater has been determined.Secondly,the analytical method for DOM molecular composition of municipal wastewater has been established.The hydrophilic and hydrophobic compositions of DOM in municipal wastewater were clarified through resin separation.Then,the retention effects of different polar solid phase extraction(SPE)columns on dissolved organic carbon(DOC)and FDOM were investigated to determine the column for DOM pretreatment.A pretreatment method suitable for DOM molecular composition analysis of municipal wastewater has been established.Fourier ion cyclotron high resolution mass spectrometry(FTICRMS)has been used to explore the distribution of DOM at the molecular level in municipal wastewater,and the properties of DOM difficult to remove have been determined from the aspects of elements and compounds.The results provide a theoretical basis for effectively removing DOM from municipal wastewater.The main conclusions are as follows:(1)The analysis and distribution of FDOM in municipal wastewater.PARAFAC models have been established separately for samples from each municipal wastewater treatment plant to obtain properties and abundances of fluorescent components.The similarities/differences between fluorescent compositions of municipal wastewater have been analyzed by SOM.Key influencing factors have been obtained by multiple factor analysis(MFA)and spearman analysis.Results show that FDOM of municipal wastewater in 15 provincial capitals(municipalities)contains six kinds of components: free tryptophan-like amino acids,terrestrial humic acid-like components,microbial humic-like fluorescence,hydrophobic humic-like compounds with large molecular size,free tyrosine-like amino acids,humic-like substance.The main components in municipal wastewater are tryptophan-like components,terrestrial humic-like components and microbial humiclike components.The components most difficult to remove are hydrophobic humic-like compounds with large molecular size and microbial humic-like fluorescences.Fluorescent compositions of wastewater in middle and east regions are different from others regions.That is to say,the properties of municipal wastewater are related to the geographical locations,economic developments and human activities of cities.The compositions of FDOM in secondary effluents mainly depend on influents,and are less affected by biological treatment processes.Besides,it has found that humification index(HIX)is the most suitable index to describe the fluorescent compositions of municipal wastewater.The ratio of main fluorescent components and its change in municipal wastewater can be predicted by HIX.(2)The analysis and distribution of DOM at molecular level in municipal wastewater.It is clear that hydrophobic components mainly consist of DOM in influents,about 54-97%.The removal of hydrophobic components are higher than hydrophilic components during bio-treatment.The hydrophobic components of DOM in secondary effluents account for 34%~67%.On this basis,a pretreatment method suitable for DOM molecular composition analysis of municipal wastewater is established.The extraction recovery of secondary effluent DOC using PPL column is the highest,and the recoveries of microbial humic-like substances,free tryptophan-like components and hydrophobic humic-like components in influents and secondary effluents are relatively consistent.That is to say,PPL could truly retain FDOM components.It is suitable for analyzing the variation of DOM in wastewater treatment process.C18 OH column has the highest recovery of influents DOC,and mainly retains hydrophobic humic-like components with large size.It is suitable for extracting hydrophobic humic-like components with large size in influents.The results of FTICRMS show that CHO and CHOS are the main element compounds in the influents of municipal wastewater.The relative contents of CHO,CHOS and CHON compounds were the highest in the secondary effluents.The degradability of one class of compounds is up to the degradability of easily degradable parts.When the two types of compounds contain the same element,the degradability of different elements determines the degradability of them.CHO3S1-CHO7S1 are main CHOS compounds in the influents and secondary effluents of municipal wastewater,which are difficult to remove during biological treatment.CHO1N1-CHO4N1 are main CHON compounds in the influents,and CHO1N1-CHO4N1 and CHO1N2-CHO4N2 are main compounds after biological treatment.The number of CHO1N3-CHO2N3 compounds also increases after biotreatment.In the process of bio-treatment,new compounds with higher nitrogen content are produced,mainly from the decomposition of microorganisms.