Study On Raw Water Of Xiamen By 3D-EEM:the Changes Of DOM And Generation Of THMS During Disinfection Process

Dissolved organic matter（DOM）has a large number of functional groups containing carbon,nitrogen,oxygen and other elements.DOM will react with chlorine-containing disinfectants to form disinfection by-products（DBPs）in the water purification process,such as trihalomethanes and haloacetic acids,which are carcinogenic,teratogenic,and mutagenic.Therefore,investigating the pollution characteristics and sources of DOM in water bodies and studying its impact on the generation of DBPs are of great significance for protecting the ecological environment and ensuring the safety of drinking water for residents.Traditional UV,¹³C NMR,FT-IR and other characterization techniques require sample pre-processing and can only analyze specific types of DOM,so their application has limitations.Three-dimensional fluorescence technology（3DEEM）has been widely used at present because it can quickly and efficiently characterize the DOM.This paper is based on three-dimensional fluorescence spectroscopy combined with the fluorescence area integration method（3DEEM-FRI）,taking the water body of the water source in Xiamen area as the research object to characterize and analyze the DOM in water,and study the dosage of disinfectant in different disinfection processes.In addition,the influence of disinfectant dosage and disinfection time in the traditional Na Cl O disinfection process and the UV-LED/Na Cl O process on the DOM removal rate and DBPs generation was studied.The specific research contents are as follows:（1）Taking the natural water from six Reservoirs（Jiangdong,Beixi,Tingxi,Lianhua,Bantou and Shidou）as the research objects in Xiamen area.Through the three-dimensional fluorescence spectrum characteristics of water DOM,combined with other water quality indicators（TOC and NH₄⁺-N）,as well as UV₂₅₄,SUVA,fluorescence index（FI）,humification index（HIX）,biological source index（BIX）and freshness index（β:α）,we analyzed the pollution characteristics of DOM in the water bodies of each water source and traced the source of the pollutants.The main components of DOM are fluorescent protein components(P_1,n+P_2,n are all above 60%),and the content of humic acid-like components is the least(P_5,n are all less than 6%).Fluorescent protein components and soluble microbial metabolites are homologous,mainly from endogenous input,while humic acid-like and fulvic-like acid are mainly imported from external sources.The water samples from Jiangdong,Beixi and Lianhua Reservoir have a high degree of humification.（2）Taking the Lianhua Reservoir water sample collected in the autumn of 2020（October）as the research object,the water body was treated with the traditional Na Cl O disinfection process and the UV-LED/Na Cl O process.Based on the analysis of3DEEM-FRI,and combined with UV₂₅₄,TOC and other indicators,the effects of the two factors of Na Cl O dosage and disinfection time on the removal effect of DOM in the two disinfection processes were investigated.It can be concluded that the removal effect of UV-LED/Na Cl O process on DOM is significantly better than that of Na Cl O process.The influence of the dosage of Na Cl O on DOM in the UV-LED/Na Cl O process was investigated.When the dosage of Na Cl O increased from 1.0 mg/L to 5.0 mg/L,the removal rate ofФ_T,n increased to 65.2%from 11.7%.Besides,the effect of disinfection time on DOM in the UV-LED/Na Cl O process was investigated.The removal rate ofФ_T,nincreased with the progress of the reaction.The reaction was 30 min and the RФ_T,n was39.8%,and when the reaction was increased to 120 min,the RФ_T,n was 56.8%.（3）Taking the Lianhua Reservoir water sample in October 2020 as the research object,the GC/MS detection method was used to accurately quantify the generation of THMs in the raw water after different disinfection processes.The acute toxicity detection method of luminescent bacteria was used to determine the changes in acute toxicity of raw water after different disinfection processes,and then the correlation between THMs and acute toxicity changes was analyzed.The results showed that the THMs produced after the disinfection of the raw water of the Lianhua Reservoir were mainly CHCl₃ and CHCl₂Br,of which the CHCl₃ was between 7.2μg/L～58.07μg/L,CHCl₂Br was between 0～7.4μg/L,while CHBr₃ and CHBr₂Cl were not detected.In short,UV-LED devices can increase the generation rate of THMs and also accelerate the degradation rate of THMs.The results of correlation analysis showed that the humus and soluble microbial metabolites in DOM were prone to generate THMS during the disinfection process.However,the relationship between the content of THMs in water and acute toxicity is still unclear.