The Characteristic Of Secondary Effluent Improving To Quasi-Class Ⅳ Of Surface Waterby The Electro-hybrid Dissolved Ozone Flotation System

In response to the requirement of upgrading the quality ofsecondary effluent of sewage treatment plants to Quasi-Class Ⅳ standard of surface water,based on the coupling mechanism of ozone and coagulation,an Electro-hybrid Dissolved Ozone Flotation（EDOF）System is constructed,which takes the secondary effluent as the research object.Through the construction of a small test device and a pilot test device,the treatment characteristics of the secondary effluent by EDOF process were explored,and the key impact parameters of the system were clarified,which provides a theoretical basis and technical reference for the quality and efficiency improvement of Quasi-Class Ⅳof surface water in urban sewage treatment plants.Taking COD,TP and NH₃-N as the key control indicators,the treatment effects of EDOF,EC（Electrocoagulation）and Ozonation were analyzed and compared.The results showed that,compared with the electrocoagulation and Ozonation process,the removal effect of EDOF on pollutants has been significantly improved.In the EDOF process,there may be a mutual promotion and synergy coupling mechanism between the electrocoagulation and Ozonation.Based on the mechanism analysis of the EDOF process,the effects of electrode material,initial pH,current density and ozone dosage on the treatment characteristics of the system were explored.The results of the study indicate that the optimal conditions for the process are the use of iron electrodes,initial pH 7.0,ozone dosage of 10.0 mg/L,and current density of 5.0 m A/cm².The removal rates of COD,TP,and NH₃-N are 59.66%,71.43%and 12.96%.Based on the static experiment results,EDOF integrated pilot process system was developed.Under different current density,ozone dosage and inlet flow,the removal effect of EDOF integrated process on COD,TP and NH₃-N in the secondary effluent was studied.The experiment found that the optimal current density and ozone dosage were 3.66 mA/cm² and 6.8 mg/L,respectively,and the maximum allowable inlet flow was 1.0 m³/h.Under these conditions,the COD and TP of effluent can meet the quasi-Class Ⅳstandard of surface water standard,but NH₃-Nremoval effect is poor and cannot meet the standard.The optimal load carrying capacity of COD and TP is 82.9mgCOD/cm²·d and 1.72 mgTP/cm²·d.Three-dimensional fluorescence spectra and molecular weightdistribution results showed that the EDOF process has a significant effect on the removal of organic matter such as fulvic acid and soluble microbial metabolites.