| Halonitromethanes(HNMs),as a typical nitrogen-containing disinfection by-products(NDBPs),have attracted special attention due to its higher cytotoxicity and genotoxicity,even they has the characteristics of low concentration levels in the environment.Combined Ultraviolet(UV)and chlor(am)ine Disinfection has broad application prospects in the field of water treatment,which can effectively inactivate various microorganisms in water and has subsequent anti-virus ability.However,UV/chlor(am)ine disinfection may bring more HNMs.Nowadays,it is insufficient to study on the formation law of HNMs in the UV/chlor(am)ine disinfection process.Therefore,by choosing nitrate as the nitrogen source and humic acid as the carbon source,this research investigated the formation law of HNMs during the process of UV/chlor(am)ine disinfection in the presence and absence of bromide ion.This paper firstly discussed the formation of HNMs form nitrate during UV/chlorine disinfection.In the presence and absence of bromide ion,the influence factors on the formation of HNMs(e.g.the concentrations of free chlorine,nitrate,bromide ion and temperature,p H)were investigated in the experiments.Further analysis was conducted to examine the bromine substitution factor(BSF)of HNMs under different reaction conditions,and to compare the differences in toxicity of HNMs with or without additional bromide ion.In the absence of bromide ion,the results showed that chloronitromethane(CNM),dichloronitromethane(DCNM),and trichloronitromethane(TCNM)were detected during UV/chlorine disinfection,of which TCNM formation was the most advantageous.With the increase of free chlorine concentration,the formation of HNMs increased first and then decreased.The formation of HNMs increased with the increase of nitrate concentrations and temperature,and was highest at p H 7.In the presence of bromide ion,CNM,DCNM,TCNM,bromochloronitromethane(BCNM),bromodichloronitromethane(BDCNM),dibromochloro-nitromethane(BDCNM),dibromonitromethane(DBNM)and tribromonitromethane(TBNM)were detected during UV/chlorine disinfection,of which TBNM formation was the most advantageous.With the increase of bromide ion concentration,HNMs formation increased first and then decreases,ClHNMs and Cl Br-HNMs were converted to Br-HNMs.The formation of HNMs increased with the increase of free chlorine and nitrate concentration,decreased with increasing p H,and was less affected by temperature.Under UV/chlorine disinfection process,the BSF values increased with the increase of bromide ion,free chlorine and nitrate concentration,and decreased with the increase of temperature and p H.The additional bromide ion increased the calculated index of cytotoxicity and genotoxicity of HNMs.Secondly,chloramine was instead of free chlorine as the disinfectant,this paper discussed the formation of HNMs form nitrate during UV/chloramine disinfection.In the presence and absence of bromide ion,the influence factors on the formation of HNMs(e.g.the concentrations of chloramine,nitrate,bromide ion and temperature,p H)were investigated in the experiments.During the UV/chloramine disinfection process,further analysis was conducted to examine the BSF values of HNMs under different reaction conditions,and to compare the difference in toxicity of HNMs with or without bromide ion.In the absence of bromide ion,the results showed that CNM,DCNM,TCNM were detected during UV/chloramine disinfection,of which DCNM formation was the most advantageous.With the increase of nitrate concentration,HNMs formation increased first and then decreased.HNMs formation increased with increasing chloramine concentration,and decreased with the increase of temperature and p H.In the presence of bromide ion,CNM,DCNM,TCNM,BCNM,DBNM were detected during UV/chloramine disinfection,and the formation of Bromide-containing HNMs was the most advantageous.The increase of bromide ion,chloramine,nitrate concentration and temperature all promoted the formation of HNMs.And HNMs formation was highest at p H 7,followed by p H 6,p H 8.Under UV/chloramine disinfection,the BSF values increased with the increase of bromide ion,temperature,chloramine and nitrate concentration,and was highest at p H 7.The additional bromide ion significantly increased the calculated index of HNMs cytotoxicity by1～2 orders and increased the calculated index of HNMs genotoxicity by 6.5 times.Finally,this study explored the effects of bromide ion and nitrates on the formation of HNMs in actual water samples of sewage and water supply plants,which was filtered without disinfection.The results showed that CNM,DCNM,TCNM,BCNM,DBNM were detected in actual water sample under chlor(am)ination alone and UV/chlor(am)ine disinfection.Under chlor(am)ination alone,the formation of HNMs in the actual water sample slowly increased with reaction time,while HNMs formation increased first and then decreased during UV/chlor(am)ine disinfection process.In the actual water sample,the increase of bromide ion concentration led to the formation of Br-HNMs increased,and the increase of nitrate concentration can promote the formation of HNMs,which was basically consistent with the laboratory law.However,due to the wide variety of organic matter and large amount of inorganic ions in the actual water sample,there were differences in the types and concentration of HNMs formation compared with laboratory water samples. |
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