| In recent years,urban and rural integrated regional water supply is rising,however,researches on formation and distribution rules of disinfection by-products(DBPs)in long-distance complex water delivery pipelines are reported fewly.In this paper,formation and distribution rules of DBPs in long-distance water delivery pipelines are investigated,it depends on the project of urban and rural integrated regional water supply in Yancheng city and focuses on ensuring water quality stability in long-distance water delivery pipelines.First,characteristic qualities of outflow water and con-centration of DBPs in key nodes of water distribution system in Yancheng area are studied.Then,effects of eight key factors on formation of DBPs in water delivery pipelines are explored based on previous study findings.Furthermore,formational and variational regulations of DBPs in pipelines are investigated based on simulating operational conditions of practical long-distance water delivery pipelines.For water quality analysis of outflow water in Yancheng area,main conclusions are as follows:the turbidity,CODMn,temperature,pH,residual chlorine,total number of colonies and ammonia nitrogen can meet drinking water health standards on the whole during 2014 and 2017.For raw water,the concentration level of bromide is high and the content of Mn2+ is overproof seriously because of geographical factors and the location of headwaters,these characteristics of water quality shall be paid attention to although they can meet relevant standards after treatment.The concentration of total THMs of outflow water keeps decreasing year by year during 2014 and 2017,mainly dominated by DBCM and TBM.For HAAs,its concentration ranges from 4.05 to 10.27μg/L and MBAA/TCAA/DBAA are the major components,moreover,the concentration level is high in summer but low in winter.During study period,THMFP varies from 95.24 to 201.57 μg/L and THMFP varies from 43.03 to 286.24 μg/L and seasonal changes are significant for both.In 2016,the total amounts of THMs in the four monitoring points in the Yancheng water delivery pipelines decrease significantly compared with that in 2014 and 2015,it may be related to the improvement of product water quality from the waterwork and the renewal of pipelines.During three years,DCAA and TCAA contents in the four sampling points are monitored for six times,results show that the contents all remain low.For the influencing factors of DBPs formation such as HRT,chlorine quantity,TOC,pH,temperature,Mn2+ and Br-in water delivery pipelines,main conclusions can be concluded as follows:Production of THMs in the pipelines is increased along with extension of HRT and then to be stable,the composition of THMs are dominated by DBCM and TBM.HAAs production is increased at first then decreased along with time,and its main components are TCAA and DBAA.Content of DBPs and proportion of high-chlorinated DBPs will increase along with the enhancement of chlorine quantity.The raise of TOC concentration will lead to the increase of DBPs in the pipelines,and the concentration of each component will increase accordingly.The higher pH value will promote production of all four THMs in pipelines.The production of HAAs in alkaline and acidic conditions is higher than that in neutral,mainly embodies in the generating differences of DCAA.The increase of temperature has a positive effect on the formation of DBPs,and effects on BDCM/DBCM/DCAA/MBAA are more significant.Mn2+content has a certain effect on the formation of THMs,while has no significant effect on the formation of HAAs.Br-content has a significant effect on the formation of DBPs in pipelines,and the increase of Br-concentration will increase the brominated degree of DBPs.The generation of DBPs in UP VC pipes is the highest,followed by galvanized steel pipes,ductile iron pipe,PE pipe is the least.Ductile iron pipe and UP VC pipe is beneficial to the formation of Br-THMs,while galvanized steel pipe is more conducive to the generation of TCM and TCAA.Chlorine Attenuation in long-distance water delivery pipelines follows the exponential attenuate law.It is found that THMs is increased along with extension of HRT and then to be stable,HAAs is increased at first then decreased along with time.In addition,DBPs analyzed are dominated by some bromated and high halogenated DBPs,such as DBCM,TBM,TCAA and DBAA.Booster chlorination can ensure bio-stability but will cause DBPs increased again at the same time.It will also increase the proportion of chlorinated DBPs.Generation of THMs in pipelines is lower when the flow rate is high in main pipelines than low flow rate.However their composition is similar with the priority to DBCM and TBM and the difference mainly reflects in TBM content.On the contrary,the flow rate in main pipelines has no significant effect on the content and composition of HAAs,which all take TCAA and DBAA as the main compositions. |
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