Study On The Regression Models Of DBPs Formation About Drinking Source Water

Tai Lake,Qiantang River and Jinlan Reservoir are three important drinking water sources in Yangtze River Delta.The water quality of jinlan reservoir is good,however,the source water of Qiantang River and Tai Lake have a high concentration of organic and bromide due to the impact from domestic sewage,industrial and agricultural wastewater and salty tide etc.During disinfection process,they will react with disinfectants to form disinfection by-products(DBPs),which have genotoxicity and cytotoxicity.Although there are a few studies on the formation of DBPs about these water sources,there is no information about the key factors and prediction models of DBPs formation.Based on the above information,present study investigated the formation of trihalomethanes(THMs),haloacetonitriles(HANs)and haloacetic acids(HAAs)upon chlorination and chloramination of source water derived from Tai Lake,Qiantang River and Jinlan Reservoir.The key factors influenceing the formation of THMs,HANs and HAAs were identified and the regression models were developed.The conclusions are as following:1)Under chlorination,THMs regression model showed good prediction effect,and the accuracy was 86-97%.However,the predictive ability of HANs model is weak,and the accuracy rate is only 75-83%.DOC,UVA54 and bromide ions are the most important factors in the formation of HANs.However,for THMs,in addition to DOC,UVA254,chlorination reaction time is also a key factor.Moreover,it was found that the regression models of the low SUVA source waters may have low DOC coefficients,but have high bromide coefficients as compared with those from the high SUVA waters comparing the models of total THMs(T-THMs)in this study with previous literatures.2)Under chlorination,the formation of HAAs was dominated by dihaloacetic acid(DHAA)and trihaloacetic acid(THAA),and the total HAAs level was ranked as following:Tai Lake>Qiantang River>Jinlan Reservoir.The regression models of dichloroacetic acid(DCAA),?DHAA(sum of DHAA),HAA5(regulated by USEPA),and HAA9(sum of nine HAAs)showed good predicting potential(the accuracy rate reached 83.3%-94.4%);while the models of trichloroacetic acid(TCAA),bromodichloroacetic acid(BDCAA),?THAA(sum of THAA)showed low predicting ability(predicting accuracy ranged from 47.2%to 61.1%).According to the partial correlation coefficients,the key factors influencing the HAAs formation was DOC(key factors for DCAA,?DHAA and HAAs),chlorine dose(key factors for TCAA??THAA?HAA9)and bromide level(key factors for BDCAA).3)Under chloramination,the regression models for trichloromethane(TCM),dichloroacetonitrile(DCAN),dichloroacetic acid(DCAA),dihaloacetic acids(DHAAs),5 HAAs species regulated by U.S.EPA(HAA5)and total haloacetic acids(HAA9)have good evaluation ability(prediction accuracy reached 81-94%),while the models for total haloacetonitriles(HAN4),trichloroacetic acid(TCAA),trihaloacetic acids(THAAs)and total trihalomethanes(THM4),they appeared relative low prediction accuracy(53-72%).For THMs,dissolved organic nitrogen(DON)was their key organic precursor,yet for HAN,DHAAs and THAAs,UVA254 played the dominant role.The other key factors influencing DBPs formation included the bromide(THM4,DCAA,DHAAs and HAA9),reaction time(DCAN,HAN4),chloramine dose(TCM,HAA5,TCA and THAAs).In spite of these results,control DHAAs may be the keystone to reduce the health risks of DBPs for these waters.4)The key factors of DBPs formation vary greatly,which will bring trouble to the decision-making of water workers.This study calculated the potential toxicity of THMs,HANs and HAAs using the toxicity data from references and the DBPs formation data in the present study.The results showed the order of potential genotoxicity and cytotoxicity toxicity(chlorination/chloramination)were as following:HAN4(2.46*10-2/1.62*10-3)>HAAb(2.30*10-3/2.96*10-4)>THM4(7.99*10-5/1.03*10-5).The potential toxicity of DBAN and BAA was higher than that of other DBPs.In addition,by comparing the potential genotoxicity and cytotoxicity of the three water sources under two disinfection methods,we found that Tai Lake ranked the highest,followed by Qiantang River,the least was Jinlan Reservoir.