Sulfonamides Degradation And Disinfection Byproducts Formation In A Pilot-scale Water Distribution System

In recent years,due to the pressure of economic and population,sulfonamides have been widely used in human and veterinary clinics,animal husbandry and aquaculture.The serious abuse resulted in more and more sulfonamides in natural water,which even detected in drinking water system.If human was long-term exposed to sulfonamides,the bodies will produce a large number of resistant strains,breaking the organism's health.Moreo-ver,sulfonamides in natural water and water distribution systems cannot be completely removed through conventional water treatment processes.Disinfection is a key step in drinking water treatment process to prevent water-borne infections.However,reactions between chlorine,one of the most common disinfectants,and natural organic matter(NOM)often lead to the formation of hazardous disinfection byproducts(DBPs).However,now there is still little research on the degradation of sulfonamides and the formation of DBPs in water distribution systems.These knowledges are essential for the correct selection of disinfect in disinfectant process and sulfonamides control.Sulfamethazine(SMZ)and sulfadiazine(SDZ)were selected as target compounds in this study.The pilot-scale water distribution system in Yuquan campus of Zhejiang University was selected as experimental equipment in this study.The reaction kinetics of SMZ and SDZ chlorination were studied in this pilot-scale water distribution system under the influence of different factors,including pH,temperature,flow rate and pipe materials,to determine the optimal factors for removing SMZ and SDZ in urban drinking water systems.Besides,the detection of intermediate products and formation of DBPs,the analysis of microbial community structures,possible degradation pathways were also studied.According to the experimental results,the kinetics models of SMZ and SDZ chlorination fitted a second-order reaction.With the increase of the concentration of free chlorine,the degradation rate also increased.The degradation of SMZ was not only affected by the water quality conditions but also the operating temperatures,flow rates and pipe materials.The rate constants of SMZ and SDZ chlorination under different temperatures were related to the Arrhenius equation.Neutral pH had the fastest rate of destruction of SMZ and SDZ.But different flow rates had little effect on degradation.In different pipes,the degradation rates of SMZ followed the order stainless-steel pipe>polyethylene pipe(PE)>ductile iron pipe.Based on the less complex bacterial diversity and more chlorine-resistant by 16S ribosomal ribonucleic acid(rRNA)gene analysis,stainless-steel pipe and PE pipe were more suitable in SDZ degradation in water distribution system than ductile iron pipe.Eight reaction intermediates during SMZ degradation were observed and identified by GC-MS.Six reaction intermediates during SDZ degradation were observed and identified by GC-MS and LC-MS.Combined with discrete fourier transform(DFT)calculation,the possible degradation pathway of SMZ and SDZ were proposed.The concentrations of trihalomethanes(THMs),haloacetic acids(HAAs),haloacetonitriles(HANs)and trichloroacetaldehyde(TCA)during the degradation in water distribution system were also determined.Toxicity tests further confirmed that the toxicity of SMZ and SDZ chlorination was higher,which indicated the more toxic intermediate products were produced.Finally,the effects of DBPs on mouse acute liver injury and Hep3B cells were also investigated.The exacerbation of liver damage increased with the DBPs concentrations,likely due to the increased hepatic macrophages.Haloacetonitriles(HANs)and haloketones(HKs)are more toxic to Human Hepatocellular(Hep3B)cells than trihalomethanes(THMs).Cytotoxicity of DBPs were governed by the halogen type(brominated DBPs>chlorinated DBPs)and the numbers of halogen atoms per molecule.Then,we used the pilot-scale water distribution systems to study the best conditions for reducing the formation of DBPs.The result showed that the formation of DBPs followed the order:stainless-steel(SS)>ductile iron(DI)>polyethylene(PE)pipe.Higher flowrate promoted the formation of DBPs in all three pipes.The results suggest that the formation of DBPs in chlorine disinfection can be reduced by using PE pipes and low flow rate in water distribution systems.