Study On The Halonitromethanes Formation From Nitrate Threonine Under UV/chlorine Disinfection

In the process of chlorine disinfection,nitrate and dissolved organic matter(DOM)can react with chlorine disinfectants to generate nitrogenous disinfection by-products(N-DBPs).As a representative N-DBPs,halonitromethanes(HNMs)has received widespread attention because of its strong toxicity,especially its genetic toxicity and teratogenic which are harm to human health.Therefore,the three representative HNMs of monochloronitromethane(CNM),dichloronitromethane(DCNM)and trichloronitromethane(TCNM)were chosen as the research object to explore the potential and regularity of HNMs generated from nitrate under UV/chlorine disinfection.The experimental resulds could provide reference for drinking water and wastewater disinfection process to controls the formation of HNMs.This study selected the three nitrate of ammonium nitrate,sodium nitrate and calcium nitrate as the precursor of HNMs to explore those factors,carbon source types(humic acid and glucose),concentration of carbon source,types of nitrate,nitrite initial concentration,ultraviolet light intensity,concentration of free chlorine,pH and chlorine/nitrogen ratio,on the effects of HNMs formation from nitrate under UV/chlorine disinfection.The experimental results showed that the humic acid had the potential to generate HNMs under chlorine disinfection,while only glucose in the water could not formed HNMs,But the glucose could generate HNMs with nitrate under chlorine disinfection.The potential of ammonium nitrate to generate the productions of CNM,DCNM,and TCNM was higher than that of sodium nitrate and calcium nitrate.With the carbon source concentration increased,the initial concentration of nitrate and the intensity of UV light,the productions of CNM,DCNM,and TCNM increased.The productions of CNM,DCNM,and TCNM decreased with the increase of pH value(6-8).When the ratio of chlorine and nitrogen was between 0.5:1 and 5:1,the production of CNM decreased with increasing the chlorine/nitrogen ratio,while the production of DCNM and TCNM increased with increasing the chlorine/nitrogen ratio.When the ratio exceeded 3:1,the change of DCNM concentration was not obvious.During the course of UV/chlorine disinfection,the experimental results showed that the concentration of nitrate nitrogen and ammonia nitrogen gradually decreased,and the concentration of dissolved organic nitrogen(DON)gradually increased,which was probably due to the ammonia nitrogen and nitrate nitrogen produced HNMs and other nitrogen-containing organics.Based on the above results and other relevant references,this study speculated on the pathway of HNMs formation from nitrate.Nitrate produced nitrite and related active substances such as NO2·,Cl·,and·OH under UV/chlorine disinfection,then these substances reacted with simple organic matters to generate CNM,DCNM,and TCNM in the solution.This study took raw water samples from a sewage plant and a water supply plant in jiangning district,nanjing city to verify the formation rules of HNMs in the laboratory.The results showed that the rule of HNMs formation in raw water from sewage plant was different from that in laboratory.This was because the organic compounds in sewage were complex and had a great influence on the generation of HNMs.When glucose was added to the raw water,the rank of three HNMs concentrations was CNM>TCNM>DCNM.The HNMs formation in raw water from water supply plant was significantly lower than that from sewage plant.The rules of HNMs generated by raw water from water supply plant was consistent with the results of the laboratory,indicating that the quality of water from water supply plant was similar to that in the laboratory.The results of this study could be used in the disinfection process of water plants and provide a reference for controlling the formation of HNMs under UV/chlorine disinfection.