Bromate Formation Characteristics And Optimal Control In Drinking Water Treatment Process

In the micro-polluted drinking water treatment, ozone oxidation technologyhas been increasingly applied to drinking water treatment process. Containingbromide water in the ozone oxidation can generate bromate, which belongs to2Blevel carcinogen，and the bromate concentration control is important to ensure thewater quality security. At present, the relevant studies were mainly on Applicationof various applied methods in the removal of bromate, which ignoring theconventional water treatment process itself. It has not been reported that thebromate in the conventional process could be removed in the recent related research.In the existing water treatment technology, to solve the pollution problem ofbromate is the most practical and easily applied and the most economical method.For the whole system of drinking water treatment, this paper investigatedwater bromate formation characteristics, conventional treatment on bromate andcontrolling its precursor bromide ion, controlling bromate in ozone-activatedcarbon process, ultraviolet radiation treatment on the control of bromate in water,construction and optimization of bromine containing drinking water treatmenttechnology.Through the research on the characteristics of bromate formation in water, weascertained the quantitative relation between BrO3-and intermediate within theconventional range of0~500μg/L initial concentration of bromide ions in water, soas to find out the reason for low bromate production with0~4mg/L ozone dosage.Ozone dosage and the initial concentration of bromide ion in water are directlyrelated to the formation of bromate in water quantity. Ammonia nitrogen forms haveinfluence on pH and formation amount of BrO3-. Compared with water sampleswhich contained no ammonia nitrogen, the formation amount of BrO3-was relativelylowe in pH value close to the ammonia water samples. In the same ammonianitrogen content, when improved pH value, the formation amount of BrO3-wasslightly elevated. It means that the influence of the ammonia nitrogen on theformation amount of BrO3-was more than pH value. The experiment of addingammonium salt and adding ammonia to water respectively showed that theinfluence of ammonium group on bromide ion converting to bromate ion in water is more than that of free ammonia due to its low pH.Based on the experiment with bromine chloride, we ascertained the effect ofchloridizing disinfection of drinking water on bromine and bromate. Water addingchlorine within360min, the formation amount of bromate was small. Whenchlorine dosage was5mg/L, the conversion rate of bromine ion to bromate wasless than1.3%. After long time for Sodium hypochlorite contacted with bromideions, the formation amount of BrO3-was slightly elevated. In the water with higherconcentration of organic matter, chlorination did not lead to bromate. Whenchloridizing bromine water, bromate were not detected with chlorine dosage of1mg/L and3mg/L. With chlorine dosage up to5mg/L, bromate was detected byvery small amount in raw water. When chlorine residual level was0.11～0.26mg/Land TOC was1.4~1.8mg/L, BrO3-were not detected in drinking water. Thatmeant the existence of low concentration of residual chlorine could not oxidize thebromide ions to bromate, let alone bromate exceed standard.By experiment of PAC and FeCl3as coagulant, the article made clear thatcoagulation and sedimentation have certain control effect on bromate and bromideions, and its effect by coagulant dosage, pH, turbidity, water temperature and otherconditions. The control effect of FeCl3on bromate and bromide ions was better thanthat of PAC coagulation sedimentation. With the dosage of FeCl3of70mg/L, theaverage removal rate of bromate was58.5%in the raw water.A silicic acid modified polymerized ferrous coagulant was developed, whichhad turbidity removal and control of bromate in the dual function. characterized byinfrared spectroscopy, we found that the modified polymerized ferrous coagulantpreparation effect was reliable. The operty of turbidity removal of modifiedpolymerized ferrous coagulant was stronger than common salt and ferrous salt. Theeffect of polymer modified ferric coagulation on removal of bromate and bromideions was very good. Modified polymerized ferrous with ferrosilicon ratio1:2hadbest effect on control of bromate.When the dosage of16.8mg/L, bromate averageremoval rate was83.8%, that meant modified polymerized iron could be used asefficient coagulant for the control of bromate in water.The Control Action of filtration on bromate and bromide ion was limited.When the initial turbidity water was40NTU, pH=6.86, T=23℃, filter depth1.2m,bromate removal rate was14.4%, bromide ion removal rate was13.6%. The filterlayer thickness had most important influence on bromate and bromide ions concentration. Next came the water turbidity, in the range of50~200g/L, the initialconcentration of bromate and bromide ion effect can be ignored.Based on the pilot experiment，we determined the method which controlledbromate by ozone-activated carbon process with the optimal parameter. On onehand, by controlling the ozone oxidation process parameter limits the bromateformation amount to not exceed the standard. On the other hand, if the bromateproduction had already exceed the standard, by controlling the operating parametersof the active carbon water bromate amount to not exceed the standard. The initialconcentration of bromide ion in water, ozone dosage and contact time were thecontrol of bromate production key elements. In the ozone processing unit,established the mathematical model of controlling bromate production. In theactivated carbon processing unit, an activated charcoal column contact time andwater bromate concentration were the key factors of controlling bromate removal,established control of bromate removal rate mathematical model. We Studied12months of continuous operation of the activated carbon surface microorganismsand biomass change,and proved that the biological activated carbon for waterbromate removal efficiency was better than activated carbon, It was ascertained thatthe mechanism of action of biological activated carbon on bromate in water, andthe effect of microorganisms on activated carbon surface.Ultraviolet radiation containing bromate in water was researched, thendetermined the shortwave ultraviolet UVC radiation can be used as effective meansin the removal of bromate in drinking water, but the radiation dose required larger.UVA was a disturbance factor for reducing bromate, so we should reduce theradiation dose to ensure water bromate reduction effect.This paper revealed the change law of bromate and bromide ions in watertreatment process, and built the control technology system of bromate, proved theparameters combination in bromate processing unit for safety. We optimizedprocess operating conditions for bromate control, provided theoretical and technicalguidance for bromate control technology in drinking water treatment in the actualproject application.