Role Of Ammonia On HANs And HNMs Formation During Ultraviolet Irradiation Followed By Chlorination

Combination of ultraviolet?UV?disinfection and chlorination,which can both well-control disinfection byproducts?DBPs?and ensure disinfection efficiency,became a common multi-barrier approach taken by water utilities.Compared with regulated DBPs,nitrogenous DBPs?N-DBPs?,like haloacetonitriles?HANs?and halonitromethanes?HNMs?,are more potent genotoxic and cytotoxic.Ammonia contamination of source drinking water is common in China,and ammonia in water could be nitrogen origin of N-DBPs.This study examined the effect of ammonia nitrogen?NH₃-N?on N-DBPs formation during UV disinfection of drinking water followed by chlorination/chloramination.Two kinds of N-DBPs,dichloroacetonitrile?DCAN?and chloropicrin?TCNM?,were detected after UV combined with chlorination.DCAN yield reached peak when HA water contained 0.5 mg/L-N NH₃-N after UV combined with chlorination treatment?LP/MP UV:0¹00mJ/cm²;Chlorination:10mg/L-Cl₂?.The formation of DCAN increased with increasing chlorine-nitrogen ratio?Cl:N?,and DCAN could significantly increase when Cl:N exceed breakpoint of chlorination.DCAN yield increased with increasing MP UV irradiation dose,while LP UV irradiation had no significant influence on DCAN generation.With increasing total organic carbon?TOC?concentration of synthetic water,TCNM decreased while DCAN increased.Under alkaline condition,DCAN yield decreased with increasing pH value of synthetic water.TCNM generation was positively correlated with pH value.When treated with MP UV combined with chlorination,TCNM yield could be significantly increased with nitrate in water,and it could be further increased when ammonia and nitrate coexisted in water.Prechlorination before UV irradiation could increase yield of DCAN and TCNM.Effect of ammonia and UV irradiation on N-DBPs formation in filtered waters from GUO and TD water treatment plants was different from results of synthetic water.Firstly,ammonia and UV irradiation had no significant effect on DCAN formation in GUO water.However,UV irradiation could decrease formation of chloro-bromoacetnitrile?BCAN?in TD water,and MP UV irradiation decreased DCAN yield in ammonia-contaminated TD water.Furthermore,UV irradiation could increase TCNM yield in GUO water,and ammonia contamination further increased the increasing rate of TCNM yield caused by UV irradiation.For TD water,UV irradiation decreased TCNM formation,but ammonia contamination could decrease the increasing rate of TCNM yield caused by UV irradiation.N-DBPs formation in waters treated by UV followed by chloramination was in a low level?<0.2?g/L?,and NH₃-N contamination and UV irradiation showed no influence on N-DBPs formation,The changes of the three-dimensional fluorescence spectra?EEM?and UV absorption spectra of filtered water were analyzed.UV irradiation could decrease fluorescence intensity,change the position of fluorescence center,and increase the UV absorbance during 200-240nm wave range of GUO and TD water.Ammonia pollution could increase the increasing amplitude of UV absorbance of GUO and TD water after MP UV irradiation.Effect of MP UV irradiation on the EEM and UV absorbance of water was much more significant than LP UV irradiation.The results indicated that ammonia pollution and UV irradiation could change the aromatic structure,chromophores and molecule size of organic matters in water,and further influence N-DBPs formation.