Research On Fluorescence Characteristics And Disinfection By-products Formation Potential Of Source Water Based On 3D-EEM And Fraction Technology Of DOM

Dissolved organic matter（DOM）is the main precursor of disinfection by-products（DBPs）.It is important to reveal the relationship between the characteristics of DOM and the formation of DBPs to ensure the safety of regional drinking water.In this study,the water quality indexes of four water sources in Xiamen（Beixi sluice,Tingxi reservoir,Lianhua reservoir and Bantou reservoir）were determined.The compositional characteristics of DOM in Xiamen were investigated by DAX-8 resin and UV₂₅₄.The source and three-dimensional fluorescence spectroscopy（3D-EEM）characteristics of DOM among fractions were compared by traditional peak-seeking method of 3D-EEM,fluorescence region integral（FRI）and fluorescence indicators.The formation potential of trihalomethanes（THMs）and haloacetamides（HAc Ams）,their species distribution and the main precursors of DOM in Xiamen were determined using chlorination and chloramination potential tests,combined with liquid-liquid extraction and gas chromatography detection technologies.The fractions with greater acute toxicity were identified by the luminescent bacterial acute toxicity technology after the two formation potential tests.The relationship between the fluorescence index,water quality index and DBPs formation potential of DOM among fractions was investigated by 3D-EEM technology combined with correlation and multiple linear regression analysis.The main findings are as follows:（1）The UV₂₅₄of hydrophobic acidic（HOA）fraction was the highest（36.07%～48.69%）and the hydrophobic basic（HOB）fraction was the lowest（0.00%～10.86%）in the water sources of Xiamen.The hydrophobic organic matter content(characterized by UV₂₅₄)exceeded 70%of the total organic matter in the source water.The HOB fraction contained mainly tyrosine-like protein substances and tryptophan-like protein substances,while the HOA,hydrophobic neutral（HON）and hydrophilic（HIS）fractions contained more fulvic acid-like substances in the ultraviolet region compared to the HOB fraction.Fluorescence index（FI）analysis indicated that the humus source in the HOA fraction was mainly terrestrial input.The humus in the HOB fraction of reservoir-type water sources（Bantu,Lianhua and Tingxi reservoirs）showed mixed sources,while the humus in the HOB fraction of river-type water sources（Beixi sluice）showed terrestrial inputs.（2）The concentration of THMs compounds generated by chlorine and chloramine disinfection of each separated fraction of reservoir-type water sources followed the following order:trichloromethane（TCM）>monobromodichloromethane（BDCM）>dibromomonochlori-ne（DBCM）>tribromomethane（TBM）.The concentration ranking of HIS components of river-type water sources disinfected by chlorine and chloramine to form THMs follows the following pattern:DBCM>TBM>BDCM>TCM.The chlorination potential test provides a more accurate assessment of the concentration of dichloroacetamide（DCAc Am）precursors in the source water,while the chloramination potential test provides a more accurate assessment of the concentration of trichloroacetamide（TCAc Am）precursors.（3）Ф_3,n,Ф_5,nand(Ф_3,n+Ф_5,n)have a significant negative correlation with the freshness index（β:α）among fractions（Pearson’s r<-0.89）,while a significant positive correlation with HIX（Pearson’s r>0.85）,so（β:α）and HIX can be used as a proxy forФ_3,n,Ф_5,nand(Ф_3,n+Ф_5,n).There is a good correlation between UV₂₅₄and TCM formation potential during chlorination and chloramination（R²>0.55）.UV₂₅₄can be used as a predictor of TCM formation potential among fractions.DON correlates well with trichloroacetamide（TCAc Am）formation potential during chloramination（R²>0.6）.DON can be used as a predictor of TCAc Am formation potential during chloramination.The integrated volume of the fluorescence region has a good multiple linear regression relationship with the formation potential of DBPs（THMs and dichloroacetamide（DCAc Am））during chlorination（R²>0.89）,and it has a good multiple linear regression relationship with the formation potential of DBPs（TCM,BDCM,DBCM and TCAc Am）during chloramination（R²>0.87）.