Study On The Oxidation Of Pyrazolone During UV/chloramine Disinfection Process: Transformation Behavior And Water Toxicity

Pyrazolones,typical anti-inflammatory and analgesic drugs,are frequently detected in the water environment,posing a potential threat to human health and ecological environmentsafety.Various disinfection processes based on advanced oxidation processes have broadened the way for the removal of trace drug contaminants.Chloramine is a disinfectant which has been proved to produce fewer disinfection by-products.In order to improve the efficiency of chloramine,the UV/chloramine coupling process has been attracted more and more attention in removing trace organic micropollutants in recent years.In this study,three widely used pyrazolones including isopropyl antipyrine?PRP?,aminopyrine?AMP?and antipyrine?ANT?were selected as the aim contaminants.And their degradation efficiencies,degradation pathways and changes of genetic toxicity during UV/chloramine disinfection were explored.The results showed that dark chloramine could hardly degrade pyrazolones,while UV irradiation could degrade them partly and the UV/chloramine coupling process could degrade pyrazolones effectively at the higher reaction rates(k_obs?PRP?=0.0594 min^-1s^-1,k_obs?AMP?=0.2761 min^-1s^-1,k_obs?ANT?=0.0400 min^-1s^-1).Through quenching experiments and probe experiments,it was found that radical chlorine species?RCS?played a major role in PRP removal,HO^?played a major role in AMP removal and UV direct photodegradation played a major role in ANT degradation.In addition,the verification experiments of ammonia radicals showed that ammonia radicals could hardly degrade the pyrazolones.And the degradation rates of pyrazolones in the UV/chloramine process decreased with p H increasing.With the increase of chloramine concentration,the degradation rates of pyrazolones gradually increased and reached a plateau in the high concentration range?0.2-0.5 m M?.The present background carbonate,chloride and natural organic matter exhibited inhibition impacts on pyrazolones degradation.In addition,the intermediates/products of pyrazolones were identified and their general degradation pathways were proposed to be hydroxylation,deacetylation,and dephenylization.Specifically,Cl-substitution was inferred during PRP and AMP degradation,while demethylation in tertiary amine group was only observed in AMP degradation.These mechanisms including the main reactive sites of pyrazolones were further confirmed by the frontier orbitals calculation.Moreover,the results of the genetic toxicity according to the micronucleus test of Viciafaba root tip indicated that UV/chloramine treatment could partially reduce the genetic toxicity of pyrazolones.