Research On Reformation Of Coventional Chlorine Disinfection Process In Drinking Water Treatment Plant

Recently,the potential health effects of DBPs on human body have brought to the attention of the public,the problem of DBPs level exceeding the standard and the safety risks in disinfection process in drinking water treatment system using traditional chlorine disinfection method is easy to occur,but chlorine disinfection is still the most widely used method of disinfection.Although the transformation of disinfection process in water plants is becoming more and more common at home and abroad,it is relatively rare to evaluate these disinfectants and their application effects in specific water plants by comparing various of aspects.This paper mainly aims at the proposal and evaluation of the technical scheme of disinfection process transformation in drinking water treatment system,firstly,the main DBPs in P are trichloromethane(TCM),chloral hydrate(CH),trichloracetic acid(TCAA)and dichloracetic acid(DCAA),and the CH have the highest mass fraction(39.60 %)when liquid chlorine is used for disinfection.The DBPs level has significant difference between seasonal groups(the maximum of CH level was 26.00 ?g/L in autumn,and the minimum of 14.83 ?g/L in spring),but there does have some of the exceptions between two seasons,and there nearly have no intra-seasonal and inter-annual significant difference.The parameters of CODMn and chromaticity in raw water are highly correlated with the change of DBPs levels(r = 0.517,0.458 respectively).The influence of precipitation on DBPs levels in P has a two-month delay(r = 0.466).The DBPs levels in non-arid months showed a significant downward trend(the total DBPs = 39.29 ?g/L)compared with that in marginal and arid months(the total DBPs = 70.15 ?g/L,60.33 ?g/L respectively),while,no significant difference has been found between the marginal and arid months.Secondly,the storage unit of chlorine gas was a secondary major hazard source of hazardous chemicals during the use of liquid chlorine in P,the CH in P also has a high risk of exceeding the standard(10 ?g/L).The experimental results of sodium hypochlorite disinfection(CH = 17.7 ?g/L)in water treatment system show that DBPs have a slightly decrease than the liquid chlorine disinfection method(CH = 21.4 ?g/L).The sodium hypochlorite disinfection method can save the alkali adding process in water treatment system,although there still has a risk of cancer according to the DBPs levels in drinking water treatment system after using sodium hypochlorite disinfection method,it is all within the acceptable range.Under laboratory conditions,chloramine disinfection method can more effectively reduce the DBPs levels than sodium hypochlorite disinfection method(CH = 5.88 ?g/L,16.10 ?g/L respectively after 4 h reaction),the formation potential of DBPs in different water body is different,however,with the extension of the contact time the DBPs level still tends to increase.Finally,the reconstruction plan of disinfection method in drinking water treatment system has been preliminarily determined.The project will be accomplished in two stages,the construction of sodium hypochlorite adding system will be completed in the recent,and in the long run,the installation of ammonium sulfate feeding equipment will be considered,and then the conversion of the final chloramine disinfection process will be completed,two-phase process a total investment of 7.086 million yuan.By comparing the opearating costs of the above three disinfection methods,it is found that there is little difference in the per ton water cost of sodium hypochlorite and chloramine disinfection(0.043 yuan/m3,0.044 yuan/m3 respectively).Although liquid chlorine disinfection has significant safety risks,its per ton water consumption is 0.02 yuan/m3(0.026 m3)lower than the other two disinfection methods.Fuzzy comprehensive evaluation of the above three kinds of disinfection methods in plant P has been used,the evaluation results show that the sodium hypochlorite and chloramine disinfection method are both have significant advantages than liquid chlorine disinfection method,the comprehensive evaluation of chloramine disinfection is the best.The safety of production processes has been assured by using sodium hypochlorite disinfection method,it is suggested that the construction of ammonium sulfate adding system should be included in the future construction plan of the water treatment system as soon as possible.