Study On The Characteristics Of Algal-Derived Chlorination By-Products In Chongqing

The presence of high concentration of algae in drinking water sources increases the total organic carbon（TOC）and disinfection by-products（DBPs）formation potential in the effluent of water plants,which seriously affects the safety of water supply.With the operation of the Three Gorges project,the drinking water sources of Chongqing is threatened by both lake-reservoir algal blooms dominated by cyanobacteria and river algal blooms dominated by diatoms and dinoflagellates.At present,the researches on the mechanism of by-products produced by algogenic organic matter（AOM）in the disinfection process is mainly focused on cyanobacteria,but there is no relevant research on diatoms and dinoflagellates.In this study,three typical dominant algal species of blooms,Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa,which have the highest frequency in drinking water sources of Chongqing over the years,were selected as the research objects.Firstly,the hydrophobicity,molecular weight distribution and three-dimensional fluorescence of entracellular organic matters（EOM）and intracellular organic matters（IOM）in different growth phases were characterized.Then,the correlations between the formation potential of disinfection by-products of EOM and IOM and their characteristics were studied.Finally,according to the different dominant algae species,the species of disinfection by-products which need to be controlled in different phases of blooms and the basic characteristics of their precursors were identified.The main conclusions are as follows:（1）The formation potential of chlorination by-products of Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa was correlated with the growth phase.There were chloroform（TCM）,dichloroacetic acid（DCAA）and dichloroacetonitrile（DCAN）produced by the EOM and IOM of Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa.Monochloroacetic acid（MCAA）,trichloroacetic acid（TCAA）,trichloroacetonitrile（TCAN）and trichloronitromethane（TCNM）were not detected.The chloroform formation potential（TCMFP）at different growth stages was always greater than dichloroacetic acid formation potential（DCAAFP）and dichloroacetonitrile formation potential（DCANFP）.For EOM and IOM of Synedra sp.,TCMFP and DCANFP were the highest in stationary phase,and DCAAFP was the highest in decline phase.For Peridinium umbonatum,the TCMFP,DCANFP and DCANFP of EOM reached the maximum in the decline phase,and the TCMFP,DCANFP and DCANFP of IOM reached the maximum in the stationary phase.For EOM and IOM of Microcystis aeruginosa,the TCMFP,DCAAFP and DCANFP reached the maximum at the stationary phase.（2）The formation potential of disinfection by-products in different growth phases of Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa was correlated with hydrophobicity.The TCMFP of hydrophobic components in different growth stages was much higher than that of hydrophilic and transphilic components.For EOM and IOM of Synedra sp.and Peridinium umbonatum,there was no significant correlation between DCAAFP and hydrophobicity in exponential phase,but transphilic fraction（TPI）>hydrophobic fraction（HPO）>hydrophilic fraction（HPI）in stationary phase and decline phase.For EOM and IOM of Microcystis aeruginosa,there was no significant correlation between DCAAFP and hydrophobicity in exponential phase and stationary phase,but in decline phase,DCAAFP of hydrophobic component and transphilic component was higher in EOM,while DCAAFP of hydrophilic component was higher in IOM.For Synedra sp.and Peridinium umbonatum,the order of DCANFP of EOM was TPI>HPO>HPI in exponential phase,and it changed to TPI>HPI>HPO with the growth.The precursors of DCANFP in EOM of Microcystis aeruginosa changed from hydrophobic component to hydrophilic component with the increase of growth phase.（3）The formation potential of disinfection by-products in different growth phases of Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa was correlated with the molecular weight range.For EOM of Synedra sp.in the exponential phase,the TCMFP of the components with molecular weight of 1-10kda and>100kda was larger,the DCAAFP of the components with molecular weight of 1-10kda was the largest,and the DCANFP of the components with molecular weight of<1k Da was the largest.For EOM of Peridinium umbonatum in the exponential phase,the components with molecular weight>100 k Da,10-50 k Da and<1 k Da were the main precursors of TCM.The DCAAFP with molecular weight between 10-50 k Da was the largest,and the DCANFP with molecular weight>50 k Da was the largest.In the exponential phase,the main precursor of TCMFP was the macromolecular component in EOM of Microcystis aeruginosa,and the components with molecular weight>100 k Da was the main contributors of DCAAFP and DCANFP.With the increase of growth period,the main contributors of TCMFP,DCAAFP and DCANFP were the components with molecular weight>50 k Da in EOM of Synedra sp..For EOM of Peridinium umbonatum in the stationary phase,the components with molecular weight less than 1 k Da in EOM was the main precursors of TCM.The DCAAFP of components with molecular weight more than 100 k Da and 1-10 k Da was the largest,and the DCANFP of components with molecular weight between 1-10 k Da was the largest.In the EOM of Microcystis aeruginosa,the components with molecular weight of>100 k Da were the main precursors of TCMFP,and the components with molecular weight of>100 k Da were the main contributors of DCAAFP and DCANFP.（4）TCM,DCAA and DCAN were the priority disinfection by-products for the different growth phases of Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa.When the concentration of Synedra sp.is greater than 2*10⁷ cells/L,the water purification plant needs to take control measures.When the concentration of Peridinium umbonatum is greater than 3*10⁷ cells/L,the water purification plant needs to control.When the concentration of Microcystis aeruginosa is greater than 3*10⁷cells/L,the water purification plant needs to control.In view of the difficulties in judging the stage of bloom occurrence in the water treatment plant,it is suggested to adopt the pre-oxidation enhanced coagulation+activated carbon adsorption+O₃/BAC process when the bloom occurs.The conclusions of this study will provide some theoretical guidance for the water treatment plant to deal with the bloom of Synedra sp.,Peridinium umbonatum and Microcystis aeruginosa.in different stages.It is very important to ensure the safety of drinking water in Chongqing.