Study On The Control Technologies Of Chlorination Typical Algal-derived Disinfection By-products Of Water Treatment Plant In Chongqing

The main water source of Chongqing water treatment plants are the main stream of the Yangtze River and its tributary,Jialing River.Water blooms occur frequently and eutrophication increases year by year in the Three Gorges Reservoir area and the Chongqing section of the Jialing river.High-concentration algae in drinking water sources will not only reduce the efficiency of the coagulation and sedimentation process,but also increase disinfection by-products formation potential in the effluent of the water plants,seriously affecting the quality of the water supply.In this paper,the dominant algal species of typical bloom of Chongqing water treatment plants are taken as the research object.Through small-scale experiments,the inactivation effects of KMnO₄ pre-oxidation method,O₃ pre-oxidation method,and ultrasonic treatment on Microcystis aeruginosa,Synedra sp.and Peridinium umbonatum were studied,respectively.Based on conventional water treatment process of Chongqing water treatment plants and the inactivation effects of dominant algae species,the corresponding feasible integrated control processes of the algal-derived disinfection by-products formation potential（DBPs-FP）were proposed,respectively.The water treatment plants in Chongqing urban areas mostly adopts conventional water treatment processes,and the control effect on the algal-derived DBPs-FP in Chongqing water treatment plants was not significant.The conventional water treatment process cann’t control the trihalomethanes formation potential（THMs-FP）of Microcystis aeruginosa to below the standard limit.In addition,the THMs-FP,the haloacetic acids formation potential（HAAs-FP）and the haloacetonitrile formation potential（HANs-FP）of Synedra sp.and Peridinium umbonatum couldn’t be controlled below the standard limit by conventional water treatment.Slightly acidified and low-dose KMnO₄ pre-oxidation cuold effectively inactivate Microcystis aeruginosa and Synedra sp.with inferior fifth-level bloom concentrations,and had no inactivation effect on Peridinium umbonatum.After being treated with KMnO₄ at a dose of 1.5mg/L for 30min at p H 5,both Microcystis aeruginosa and Synedra sp.could be effectively inactivated.Slightly acidified low-dose KMnO₄+Powder activated carbon（PAC）+conventional water treatment process could effectively control DBPs-FP from Microcystis aeruginosa.The concrete parameters are as follows:KMnO₄dosage of 1.5mg/L,treatment time is not less than 30min;when PAC adsorption time is from 0.5h to 1h,PAC optimal dosage is 60mg/L;when PAC adsorption time is from 1h to 2.5h,PAC optimal dosage is 20mg/L;when PAC adsorption time exceeds 2.5h,PAC optimal dosage is 20mg/L.The low-dose O₃ pre-oxidation could effectively inactivate Microcystis aeruginosa and Synedra sp.with inferior fifth-level bloom concentrations,and had no inactivation effect on Peridinium umbonatum.After being treated with O₃ at a dose of 1.5mg/L for15min,both Microcystis aeruginosa and Synedra sp.could be effectively inactivated.Low-dose O₃ pre-oxidation+conventional water treatment+O₃-BAC process could effectively control DBPs-FP from Synedra sp..The concrete parameters are as follows:pre-O₃ dosage of 1.5mg/L,treatment time is not less than 15min;O₃ dosage of 2.0 mg/L,treatment time is 5min,BAC retention time is 15min.High-frequency and low-power sonication could effectively inactivate Peridinium umbonatum.After being treated with sonication at 400k Hz for 8min,Peridinium umbonatum could be effectively inactivated.According to the numerical simulation of the ultrasonic sound field of algae removal by COMSOL Multiphysics software,the ultrasonic effective distance of algal removal was 0.44m at 400k Hz.High-frequency and low-power sonication+PAC+conventional water treatment+O₃-BAC process could effectively control DBPs-FP from Peridinium umbonatum.The concrete parameters are as follows:ultrasonic frequency of 400k Hz,power density of 0.19W/m L,treatment time is 8min;PAC dosage of 40mg/L,the adsorption time is 0.5h;O₃ dosage of 2.0 mg/L,treatment time is 5min,BAC retention time is 15min.