Study On The Formation Of Halonitromethanes From Amines In The UV/Chloramine Disinfection

In the disinfection process of the water treatment plant,the dissolved organic nitrogen(DON)in the water can react with chlor(am)ine to produce nitrogen-containing disinfection byproducts(N-DBPs),which may cause threat to water safety.Halonitromethanes(HNMs),as a kind of typical N-DBPs,currently lack systematic researches on their formation,control methods and precursors.Therefore,HNMs were selected as the research object,to explore their formation from amines in the UV/chloramine disinfection,discuss the influence of bromide ion concentration,chloramine concentration,precursor concentration,p H and UV light intensity on the formation of HNMs,as well as the transformation of nitrogen forms and the toxicity effect caused by HNMs during the reaction.At last,the formation pathway of HNMs was deduced.Firstly,this paper revealed the law of amines forming HNMs in the UV/chloramine disinfection without bromide ions.The results demostrated that methylamine(MA),dimethylamine(DMA)and polydiallyldimethylammonium chloride(poly DADMAC)could all generate Cl-HNMs in the UV/chloramine disinfection,and the formation of Cl-HNMs enhanced at the beginning,then gradually decreased with the extention of the reaction time.The formation of Cl-HNMs increased with the increase of chloramine concentration and precursor concentration,and decreased with the increase of p H.In the chloramine disinfection,Cl-HNMs were produced in a small amount,and the production gradually increased with the extention of the reaction time.As a contrast,the formation of Cl-HNMs had a significant promotion and increased with the increase of UV light intensity in the UV/chloramine disinfection.During the reaction,ammonia nitrogen and dissolved organic nitrogen gradually transformed to nitrate nitrogen.Secondly,this paper revealed the law of the formation of HNMs from amines in the UV/chloramine when bromide ion presented.The results demostrated that,in the presence of bromide ion,MA,DMA and poly DADMAC all had the potential to generate brominecontaining HNMs in the UV/chloramine disinfection,and the formation of HNMs first increased and then decreased with the extention of the reation time.When the bromide ion concentration increased,Cl(Br)-HNMs were gradually converted to Br-HNMs.When the chloramine concentration increased,Br-HNMs were gradually converted to Cl(Br)-HNMs.The formation of HNMs increased with the increase of precursor concentration and UV light intensity,and decreased with the increase of p H.In the chloramine disinfection,MA,DMA and poly DADMAC could also produce a small amount of HNMs,and their formation kept increasing with the extention of the reaction time.During the reaction,ammonia nitrogen and dissolved organic nitrogen gradually transformed to nitrate nitrogen,and the concentration of different forms of nitrogen in the bromine-added system changed more than that in the nonbromine system.The toxicity of HNMs increased first and then decreased with the extension of the reaction time,and it continued to increase with the increase of the bromide ion concentration.Finally,this paper revealed the law of the formation of HNMs in actual water samples of sewage and water supply plants(before disinfection)in the UV/chloramine disinfection,and compared it with the law obtained in laboratory water samples.The results demostrated that,the actual water samples could generate HNMs during both the chloramination and UV/chloramine disinfection.With the extention of the reaction time,the formation of HNMs kept increasing in the chloramine disinfection,but increased first and then decreased in the UV/chloramine disinfection.With the addition of bromine ions in actual water samples,the formation of Br-HNMs and Br(Cl)-HNMs increased,the formation of Cl-HNMs decreased.The law of amines generating HNMs in actual water samples was basically similar to that in laboratory water samples,but there were certain differences in the amount and maximum time of HNMs formation.