Influencing Factors The Formation Of Disinfection Byproducts Of The Water Supply Network In Jiaxing

In recent years,in order to ensure the safety of drinking water for residents,the upgrading of urban water supply pipelines and the switching of water sources have been continuously implemented.However,the generation of disinfection byproducts?DBPs?in water supply pipelines with increasingly complex topologies has been rarely reported.Based on the background of pipeline upgrading in Jiaxing City and the project of“Qiandao Lake Diversion”,the law of DBPs generation in water supply pipelines was examined to ensure the safety of drinking water safety for residents.Firstly,the quality of the finished water of Shijiuyang Water Plant and the DBPs levels of key nodes in Jiaxing water supply network were investigated.According to water quality survey results,several key factors affecting the DBPs generation in water supply network were studied.Besides,the influences of water source switching and metal corrosion products on the DBPs formation were also investigated.The results of the follow-up investigation on water quality characteristics of Shijiuyang finished water in Jiaxing indicated that the turbidity,p H value,COD_Mn,residual chlorine and the metal ions concentration in water produced by Shiusyang Water Plant from January 2018 to November 2018 were generally within the specified limits of Standard for Drinking Water Quality?GB5749-2006?.The maximum generation potential of trihalomethane?THMs?and haloacetic acids?HAAs?in finished water in summer was greater than that in winter.The concentrations of THMs and HAAs in water supply network of Jiaxing City were in the range of 29?66?g/L and 2?20?g/L,respectively,both of them fluctuated in different locations.With the increase of chlorine dosage,the maximum DBPs production increased and HAAs concentration was significantly higher than THMs.The main species of DBPs were determined to be dichloroacetic acid?DCAA?,trichloroacetic acid?TCAA?and trichloromethane?TCM?.The production of THMs and HAAs both increased with the extension of reaction time.HAAs were mainly composed of TCAA and DCAA,while THMs were mainly composed of TCM and bromodicloromethane?BDCM?.With the p H increasing from 6 to 8,the production of THMs gradually increased,while the production of HAAs reduced.The increase of p H exerted the most obvious promoting effect on the formation of TCM and BDCM,while the decrease of HAAs production was mainly reflected in DCAA production.With the increase of temperature,the production of both THMs and HAAs presented an obvious increasing trend,and the influence of temperature on HAAs generation was more significant than that of THMs.With the increase of bromide concentration,the production of HAAs and THMs increased,and the production of Br-DBPs also increased significantly.The influence of three kinds of pipes on the production of HAAs and THMs followed the order of plastic steel pipe>ductile iron pipe>PE pipe,which was related to the properties and corrosion degree.With the switch of water source,the concentration of HAAs and THMs changed.When the ratio of the finished water from Shijiuyang Water Plant to the finished water from the Qiandao Lake Water Plant reached 80%:20%,the increase in HAAs and THMs production was the most significant.With the further increase of the proportion of finished water from Qiandao Lake Water Plant,the production of HAAs and THMs gradually decreased.The presence of metal corrosion products including Fe₃O₄,Zn O,Cu O,and Mn O all promoted the formation of HAAs and THMs.Cu O was found to be the most obvious promoter,while Fe₃O₄,Zn O and Mn O were relatively weak.The metal ions released from their corrosion products also promoted the yield of HAAs and THMs,and the rule was consistent with the effect of metal corrosion products.