Effects On Brominated Disinfection By-products From Pre-chlorination

With the rapid economic development, the drinking water sources are polluted in different ways. Therefore the pre-chlorination process is applied to the polluted water treatment. But during the process, it also generates the disinfection by-products(DBPs). Considering the toxicity of brominated DBPs is much higher than chlorinated DBPs, and the brominated DBPs is often detected in the drinking water, this study focuses on the effects of pre-chlorination on brominated DBPs.In this study, the source water of a waterworks in Tianjin was treated on a laboratory scale. The effect of water treatment processes on trihalomethanes(THMs),haloacetic acids(HAAs) and total organic carbon(TOC) were studied, and the relationship between TOC and THMs, HAAs were also analyzed. In addition, the changes of brominated DBPs in the processes associated with bromide ions and available chlorine concentration were studied, as well as the distribution of bromine in THMs and HAAs.The results showed that pre-chlorination had a significant influence on the DBPs of finished water, which could increase the final concentration of THMs and HAAs to1.3 and 1.4 times. The removal rates of coagulating sedimentation and filtration on THMs were 10.3% and 18.5%. While for the HAAs, the coagulating sedimentation had no effects and the filtration could only remove 9.25% of HAAs. Pre-chlorination could strengthen the removal of TOC, but the impact of TOC on THMs and HAAs was little, while chlorine was an important limiting factor of both THMs and HAAs.The bromide incorporation factors of THMs and HAAs were increased with the increase of bromide ion concentration, while the proportion of brominated DBPs increased with the decrease of chlorinated DBPs. However, the bromide ions concentration had little influence on the distribution of bromide in THMs and HAAs in this study. And in all processes, only pre-chlorination and disinfection could change the proportion of brominated DBPs and chlorinated DBPs.When the concentration of TOC was adequate, the concentration of THMs and HAAs were increased with increase of the chlorine concentration and extention of the reaction time. The chlorine dosage in pre-chlorination should be controlled strictly,because it had a direct impact on the final concentration of THMs and HAAs.