预氧化混凝去除原水中铜绿微囊藻及同步控制消毒副产物生成

Removal of Microcystis aeruginosa in Raw Water and Control of DBPs by Pre-Oxidation Coagulation

湘江流域长沙段夏季藻类频繁暴发,然而常规混凝工艺对原水中的藻类及其生成的消毒副产物前驱体的去除效果欠佳,对供水安全造成一定的威胁。预氧化混凝法由于除藻效果较好,而且不需在水处理工艺流程中增设处理构筑物,具有很好的应用前景。文中以长沙市水厂藻类暴发时的主要藻种--铜绿微囊藻为例,探讨了预氧化混凝法的除藻效果和消毒副产物控制情况。结果表明,单独混凝时,10 mg/L聚合硫酸铝(PAS)的除藻率为92.7%,分别使用K_(2)FeO_(4)、ClO_(2)、KMnO_(4)、O_(3)或NaClO对藻类进行预氧化处理后再混凝,除藻率最高提升至100.0%、99.1%、98.2%、98.2%或96.4%。0.2 mg/L K_(2)FeO_(4)或KMnO_(4)使溶解性有机碳(DOC)的去除率较单独混凝分别提高了12.3%和19.4%,而同等用量的ClO_(2)、O_(3)和NaClO则造成藻液中的DOC水平增加。质量浓度≤1.0 mg/L的K_2FeO_(4)、KMnO_(4)或ClO_(2)处理样品中未检出土臭素、2-甲基异莰醇和微囊藻毒素-LR。K_(2)FeO_(4)对三氯甲烷(TCM)、总卤乙酸(HAAs)和总三卤甲烷(THMs)的去除效果最佳,0.5 mg/L的K_(2)FeO_(4)对上述消毒副产物的去除率分别为59.8%、73.4%和59.7%。综合除藻效果、DOC去除率、藻源有机物和消毒副产物控制效果,推荐水厂用0.5~1.0 mg/L K_(2)FeO_(4)+10 mg/L PAS去除铜绿微囊藻,其成本低至2.225×10^(-2)元/m^(3)。

Algae outbreaks occur frequently in Changsha section of Xiangjiang River Basin in summer.However,the conventional coagulation process is not effective in removing algae and the precursors of disinfection by-products in raw water,which poses a threat to the safety of water supply.The pre-oxidation coagulation method has a good application prospect because it has a good effect on removing algae and does not need to add treatment structures in the water treatment process.Microcystis aeruginosa was the main algal species in the algal outbreak in the water treatment plant(WTP)of Changsha City.This paper discussed the algal removal effect of pre-oxidation coagulation method and the control of disinfection by-products.The results showed that pre-oxidation of Microcystis aeruginosa with K_(2)FeO_(4),ClO_(2),KMnO_(4),O_(3) or NaClO increased the algae removal rates of 10 mg/L PAS from 92.7% to 100%,99.1%,98.2%,98.2%or 96.4%,respectively.Meanwhile,the dissolved organic carbon(DOC)removal rate of 0.2 mg/L K2FeO4 or KMnO_(4) was 12.3% or 19.4%higher than that of single coagulation,respectively,while the same amount of ClO2,O3 or NaClO increased the DOC content in the algal fluid.In addition,when the dosage of K_(2)FeO_(4),KMnO_(4) or ClO_(2) was less than 1.0 mg/L,no geosmin,2-methylisokanol and microcystin-LR were detected in the treated samples.Futhermore,K2FeO4 exhibited the best removal effects on trichloromethane(TCM),total haloacetic acid(HAAs)and total trihalomethane(THMs).The removal rates of 0.5 mg/L K2FeO4 for the above three disinfection by-products were 59.8%,73.4% and 59.7%,respectively.In summary,the stratagy of 0.5~1.0 mg/L K_(2)FeO_(4)+10 mg/L PAS is recommended for Microcystis aeruginosa removal in WTPs,with a cost as low as 2.225×10^(-2) yuan/m^(3) of algae-containing raw water.