| Reservoir water in Northeast China often has high content of natural organic matter,and the removal efficiency of natural organic matter by conventional treatment process of drinking water is not good,which leads to the formation of more chlorinated disinfection by-products（DBPs）by the interaction of natural organic matter and chlorine disinfectant in chlorination process,threatening the safety of drinking water supply.Therefore,in this study,M reservoir water,a representative lake-reservoir water source in Northeast China,was selected as the research object,and its organic index and the monthly variation of chlorinated DBPs after chlorination disinfection were tracked for up to one year.In order to grasp the source,type,composition characteristics and variation rules of organic matter in source water and find out the correlation between it and DBPs formation potential,the molecular composition and structural characteristics of the precursors that mainly contribute to the production of DBPs were analyzed,and the reaction path,transformation mechanism and product toxicity of the main precursors during chlorination disinfection were revealed.It provides theoretical basis and data support for reducing the production of chlorinated DBPs in drinking water and health risks.Through the monthly water quality index monitoring of M reservoir for one year,the composition characteristics and variation rules of organic matter in water were clarified.The results showed that the pollutants in the water of M reservoir were mainly natural organic matter,and its carbon skeleton was mainly composed of aliphatic carbon,unsubstituted aromatic carbon andα-carbon.When the organic matter increased,the organic matter was mainly dominated by humic acid with high color and high unsaturation.The composition of fluorescent organic matter in M reservoir water was investigated by fluorescence spectroscopy.The results of three-dimensional fluorescence-parallel factor analysis showed that the organic matter in reservoir water was mainly attributed to five fluorescent components,two humic acid components（C2,C3）,two fulvic acid components（C1,C4）and a protein component（C5）.The results of fluorescence characteristics showed that the organic matter in M reservoir water mainly came from autochthonous and heterogenous sources,and had stronger terrestrial input characteristics and higher humification characteristics.The correlation analysis results of each fluorescent component showed that the four components had a transformational relationship with each other.On the basis of determining the composition,source and characteristics of organic matter in M reservoir water,the influence of organic matter on chlorinated DBPs in reservoir water and the correlation between organic matter index and chlorinated DBPs production were further studied.The results showed that the formation potentials of four typical chlorinated DBPs from high to low were trichloromethane（TCM）,trichloroacetic acid（TCAA）,dichloroacetic acid（DCAA）and chloral hydrate（CH）.The variation of formation potential of chlorinated DBPs was similar to that of organic matter concentration.DOC,UV254and the intensity of each fluorescent component showed a good linear relationship with the formation potential of four chlorinated DBPs.On this basis,a multivariate linear prediction model suitable for the local water matrix was constructed with the fluorescence intensity of each component as the independent variable and the formation potential of chlorinated DBPs as the dependent variable.The model was screened and verified by F test,residual independence test,error and mean square analysis of variance.The results showed that the ternary linear model constructed by C1,C2 and C4 was more effective in predicting the formation potential of DCAA and TCM,and the binary model constructed by C2 and C4 was more suitable for predicting the formation potential of TCAA.The binary model constructed by C1 and C2 can well predict the CH formation potentia.By studying the molecular weight（MW）distribution of organic matter in M reservoir water and the influence of organic matter with different molecular weight ranges on the production of chlorinated DBPs,the main precursors of CH and TCM can be identified.The results showed that the organic matter in the reservoir water was mainly distributed in the MW>3 k Da range,accounting for62%～70%of the total organic matter concentration.TCM and CH precursors were mainly distributed in MW<1k Da and 5<MW<10 k Da.The molecular characteristics and transformation characteristics of small molecular weight（MW<1 k Da）organic matter in water before and after chlorination disinfection were further studied by high resolution mass spectrometry.The results showed that after chlorination disinfection,macromolecular organic matter was transformed into small molecular organic matter,the number of organic molecules increased,and the average molecular weight decreased.Lignin is the main component of organic matter and the main precursor of chlorinated DBPs.The organic matter in the raw water is mainly lignin,accounting for about 40%;in chlorinated water samples,lignin accounted for 36.73%～42.22%;the proportion of chlorinated products was21.82%～38.43%.There are 15 types of reactions that occur during chlorination disinfection,of which oxygen-involved reactions are the main types,and chlorine-involved reactions mainly include substitution reactions and addition reactions.Among them,the precursors that can participate in the substitution reaction have higher H/C,the precursors that can participate in the addition reaction have higher aromatic index,and the chlorinated products formed by the addition reaction have higher H/C,O/C and lower aromaticity;the results of correlation analysis showed that TCM and CH had a good correlation with the weighted average of aromatic index and the weighted average of O/C.The organic compounds with stronger aromaticity were more likely to be the precursors of chlorinated DBPs.Based on the findings that lignin had the highest proportion of organic matter in M reservoir water and that it was an important precursor of chlorinated products,the production pattern of chlorinated DBPs in the presence of lignin during chlorination and disinfection was further investigated in depth.The results showed that different reaction conditions affected the production of chlorinated DBPs from lignin-based organics,and that prolonging the reaction time and increasing the reaction temperature promoted the production of chlorinated DBPs,with the highest yield of TCM under alkaline conditions,chloroacetic acid under acidic conditions and CH under neutral conditions.Fluorescence spectroscopy,ultraviolet spectroscopy and other methods were used to compare lignin and fulvic acid.The results showed that compared with fulvic acid with complex molecular structure and higher molecular weight,lignin contains more oxygen-containing functional groups and benzene ring structure.The ability of lignin to produce chloroacetic acid and CH was higher than that of fulvic acid,and the ability of fulvic acid to produce TCM was greater than that of lignin.Therefore,it is necessary to further explore the rule of DBPs formation after chlorination of lignin organic matter.Two lignin monomers were selected as model compounds to further explore the reaction mechanism of lignin chlorination disinfection process.The results showed that the degradation reaction of 4-propylphenol（4PP）and 4-propylguaiacol（4PG）followed pseudo-first-order reaction kinetics during chlorination disinfection.Both lignin monomers were dominated by the electrophilic reaction of chlorine during the reaction and during the reaction phenol radicals were generated to form dimeric intermediates through coupling reactions,which were further transformed in the process.The formation of intermediates P190,P156,P160 and P168 during chlorination and their further conversion was the rate-controlling step in the reaction process and determines the reaction rate.A conformational relationship（QSAR）toxicity risk assessment of the intermediates using the US EPA certified toxicology software ECOSAR and T.E.S.T.software showed that the toxicity of chlorinated intermediates was low. |
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