Transformation Of Typical Sulfonamides By Chlorination In Water Distribution Systems

Sulfonamide antibiotics have been frequently detected in urban drinking water distribution system in recent years.Sulfonamide antibiotics may harm human health,and they may cause gene mutation of biofilm in the water distribution systems,then resulting in the generation of antibiotic resistance genes,which makes drinking water safety difficult to be guaranteed.Two typical sulfonamides,sulfapyridine and sulfamethoxazole,which are widely used and frequently detected in water distribution systems,were used as target compounds.The influence factors and reaction kinetics of sulfapyridine and sulfamethoxazole in pilot-scale water distribution systems were studied,and degradation pathways and formation of antibiotic resistance genes under sulfapyridine chlorination were studied.According to the experimental results,the degradation of sulfapyridine and sulfamethoxazole chlorination in water distribution systems conforms to the first-order kinetic model and the pseudo-second-order kinetic model,and the first-order kinetic constant k1 and pseudo-second-order kinetic constant k2 were used to quantify degradation efficiency.The degradation rate of sulfapyridine was the fastest at pH 6.9,and the degradation rate of sulfamethoxazole was the fastest at pH 6.3.Based on the dissociation of residual chlorine,sulfapyridine and sulfamethoxazole,a model about chlorination rate and pH was proposed.It was found that when the flow velocity in water distribution systems changed from 0.7 m/s to 1 m/s,the chlorination rate of sulfapyridine and sulfamethoxazole was increased with flow velocity increasing,but when the flow velocity exceeded 1 m/s,the acceleration effect of flow velocity increasing was not obvious.The chlorination rates of sulfapyridine and sulfamethoxazole in different pipe materials as following order:stainless steel pipe>ductile iron pipe>PE pipe.The results about disinfection byproducts of sulfapyridine and sulfamethoxazole chlorination show that the total increment of trihalomethanes in the presence of sulfapyridine is significantly higher than that in the absence of sulfapyridine,while sulfapyridine hardly produced trihalomethanes in chlorination process in pure water.Therefore,it is speculated that organic matter in tap water is affected by sulfapyridine and produce more trihalomethanes.Four chlorination byproducts of sulfapyridine,4-amino-N-methylbenzenesulfonamide,3,4-dichlorobenzenesulfonic acid 4-amino-3-chloro-N-methylbenzenesulfonamide and chlorobenzenesulfinate acid,were identified.The presence of antibiotics can increase the toxicity of drinking water.After chlorination,the comprehensive toxicity of water first decreases,then increases,and then decreases to the level of dechlorinated tap water.In the resistance genes investigation,the relative abundances of sul1 and sul2 increased significantly under the pressure of sulfapyridine alone and chlorination products of sulfapyridine and low concentration of residual chlorine.