Study On Advanced Municipal Wastewater Treatment And Ecological Risk Control After Chlorination

Municipal reclaimed water is an important way for energy-saving emission reduction,wastewater resources,as well as resolving water shortage and pollution.As the final part of treatment process,disinfection plays a vital role in the public security of recycling system.Based on the analysis of basic features and components of municipal secondary effluent,aimed at two advanced treatment process,"magnetic resin-coagulation"("NDMP-PAC") and ultrafiltration-ozone ("UF-O3") process,the purification effects and removal characteristics for municipal secondary effluent were studied in this thesis.The treated water was chlorinated and then the evaluation of disinfected water quality and security index was carried out. At last, through analysis and contrast, a most suitable technology for municipal wastewater advanced treatment was selected.Secondary effluent from three representative municipal wastewater plants in Zhengzhou, Henan province,Nanjing and Yancheng, in Jiangsu province, represented by plant A,B and C,was selected to experiment with. Research showed that municipal wastewater contained dissolved organic matter (EfOM) with different molecular weight and hydrophilicity.The proportion of components with low molecular weight (<1000Da,1000-2500Da) and hydrophobicity (HPO-A+HPO-N) was large,and quite a few functional groups such as conjugated double bond, benzene ring, carbanyl group and conjugated carbonyl group(all represented by characteristic ultraviolet absorbancy degree,SUVA) were existed.These components or functional groups were exactly significant disinfection by-products (DBPs) precursors. Corresponding to the SUVA as well as proportion of components with low molecular weight and hydrophobicity, the trihalomethane(THMs) and haloacetic acid(HAAs) formation potential per TOC(THMPC\HAAPC) of municipal secondary effluent from plant C was highest, plant A came second, and plant B was the last.After the chlorination of secondary effluent,acute and chronic biological toxicity significantly increased due to the formation of DBPs.The organic concentration,DBPs formation potential of secondary effluent,and biological toxicity of disinfected water were effectively reduced by "NDMP-PAC" and "UF-O3" process respectively.But in contrast,"NDMP-PAC" was superior to " UF-O3" process.The TOC removal for secondary effluent of plant A,B,C by "NDMP-PAC " process were49.88%,54.03%,44.35%,and the UV254removal were60.14%,79.80%、59.02%respectively."NDMP-PAC" process showed a better removal capability for the SUVA as well as components with low molecular weight and hydrophobicity,whose DBPs formation potential were strong, than "UF-O3" process.As a result of the superiority of organic concentration and DBPs formation potential reduction,"NDMP-PAC" process was more efficient for the reduction of biological toxicity of disinfected water than " UF-O3" process.Futhermore,"NDMP-PAC" process had lower cost-in-use, thus had stronger economy.All in all,compared to " UF-O3" process,"NDMP-PAC " process was more appropriate for advanced treatment of municipal wastewater,and thus was an efficient,feasible,safe and economic method for preparation of reclaimed water.