Characterization Of Dissolved Organic Matter Released From Fast-growing Eucalyptus In Southern China,and Its Risk And Control Of Disinfection By-products

Fast-growing eucalyptus is widely cultivated in south of China due to its high economic benefits.However,after the deforestation of rapid eucalyptus litters,different degrees of"black water"phenomenon will often occur in rivers,streams and even reservoirs.This phenomenon can indicates that the eucalyptus forest have potential to release dissolved organic matter（DOM）to the water sources,which worsens the water quality and finally bring environmental health risks in water bodies.Although disinfection processes,act as key role in the treatment of water as well as protect treated drinking water enters the pipe networks,especially pathogenic microorganisms,however generated chlorinated disinfection by-products（DBPs）is one of potential threat to human health.In this study,we investigated the regularity of DOM release from eucalyptus into water sources along with characterization of different types of DOM.Moreover,DBPs generated by DOM released from eucalyptus and its toxicity during various disinfection processes were investigated,and the correlation between DOM and DBPs was analyzed.In addition,the removal rate of DOM released by eucalyptus in drinking water treatment plant was measured.The results showed as the following:（1）Comparative analysis was conducted on DOC,UV₂₅₄,SUVA₂₅₄and DON of DOM extracted under different leach time,tree species,tree organs,temperature and p H conditions.DOM extracted from eucalyptus leaves was characterized by ultraviolet visible spectrum and three-dimensional fluorescence spectrum,and the DOM molecular weight was separated by ultrafiltration method.The results demonstrated that organic matter in eucalyptus leaves was basically dissolved within a week,and DOM less than 1000Da accounted for nearly 60 percent of dissolved DOM.The dissolution of organic matter was easy to leached from eucalyptus leaf litter under the alkaline and high temperature conditions.Fluorescent dissolved organic matter（FDOM）is almost containing protein-like organic composition.Four fluorescence components were detected by three-dimensional fluorescence parallel factor analysis:amino acid components,free or combined in proteins may indicate integrity of protein-like（C1）,terrestrial humus（C2）,tyrosine-like（C3）,and amino acid tyrosine components（C4）.According to the results derived from the V-K diagram and the detected elements by high resolution mass spectrometry,lignin and lipids accounted for a relatively large proportion in the leaches,and CHO and CHON were composed of more organic matter.（2）Simulated water sample with eucalyptus leaf litter leach solution and Suwannee River Natural Organic Material（SRNOM,purchased from International Standard Humic Acid Association）was taken as the research object.The reactivity of simulated water samples with different disinfectants was explored,and the cytotoxicity and genotoxicity of the disinfection by-products generated after disinfection were evaluated.The correlation analysis between DOM as the precursors of DBPs and the generation potential of disinfection byproducts（DBPFP）of eucalyptus leaf leachate was also studied.The results showed that the DBPFPs produced by the disinfected leach solution of eucalyptus leaf litter were significantly higher than that of SRNOM and the raw water from drinking water plant.After disinfection,some nitrogen-containing DBPs（N-DBPs）of eucalyptus leaf litter leach solution,especially after reaction with monochloramine.When bromine and iodide ions were added,the amount of DBPs produced by the reaction of eucalyptus leaf leach solution containing three disinfectants increased,and the calculated toxicity of chlorine dioxide to produce disinfection byproducts increased,considerably.39（hypochlorous acid）,70（monochloramines）,and 21（chlorine dioxide）suspected unknown DBPs were identified by non-targeted analysis by high resolution mass spectrometry.Among themes,there were 14（hypochlorous acid）,45（monochloramines）,and11（chlorine dioxide）aliphatic DBPs;and 46 suspected N-DBPs were detected after reaction with monochloramines,much higher than hypochlorous acid and chlorine dioxide,indicating that monochloramines may produce more N-DBPs as a disinfectant for drinking water.According to the correlation analysis results between the concentration of DOM in the leach solution of eucalyptus leaves and the concentration of DBPs after disinfection,the longer the soaking time of eucalyptus leaves（within 14 days）,the more trihalomethanes（THMs）were generated in the solution.The fluorescence components of C1 and tryptophan proteins in the leavers had a greater impact on formation potential of haloacetic acid（HAAFP）of the leach solution.Nitrogen-containing organic matter and lignin are important precursors of halogenated acetamide（HAc Ams）,and C1 protein fluorescent components in solution,refractory lignin,are important precursors of disinfection byproducts.（3）DOM removal efficiency and optimal coagulation conditions of four sample solutions（eucalyptus leaf litter leach solution,reservoir water,raw water from drinking water plant,and SRNOM）were studied after the treatment of coagulation-sand filter-activated carbon adsorption-ultrafiltration.The results show that coagulation is the most effective process to remove DOM from water,which can remove most of the organic matter.Moreover,it can effectively remove three of the four fluorescent components（protein like and humic acid like organic matter）of eucalyptus leaf leach solution,two of the three fluorescent components（protein like and humic acid like organic matter）of raw water from drinking water plant,and two of the four fluorescent components（humic acid like and new organic matter）of reservoir water.Sand filtration was used to remove part of the insoluble impurities,and has little effect on the removal of DOM.Activated carbon adsorption as an advanced treatment process has further effect on the removal of organic matter in water samples.Ultrafiltration has a good effect on the removal of protein organics in water.It is concluded that one of the influences of eucalyptus on drinking water may be the introduction of fluorescent components of protein organic matter,which can be reduced by ultrafiltration.