Efficiency Of Advanced Treatment Of Electroplating Wastewater By O₃/H₂O₂-A/O Combined Process

In recent years,the emission standards of electroplating pollutants in some cities have been raised to the stricter limits of the indicators between the standards in "Table 3Special Emission Limits for Water Pollutants" of the Emission Standards of Pollutants for Electroplating(GB21900-2008)and the standards in the Environmental Quality Standards for Water(GB3838-2002)IV standards(except total nitrogen,the emission limit of total nitrogen is 10 mg/L).The standard are referred to as "the high emission standards" below.However,the wastewater after treated in the electroplating industrial park can not meet the high emission standards.In order to solve this problem,this dissertation takes the high emission standards as the treatment target,and takes the mixed discharge wastewater from an industrial park as the treatment object,and proposes the "O3/H2O2 advanced oxidation-anoxic/ aerobic(A/O)" combined process and and optimizes the process parameters.The treatment efficiency of the physicochemical process was studied through laboratory research,which was "O3/H2O2 advanced oxidation" process.The results showed that this process could achieve the standard treatment of total nickel,total chromium,total zinc,total iron,total copper and total phosphorus,but had limited effect on the removal of chemical oxygen demand,ammonia nitrogen and total nitrogen.The better working conditions were: the p H adjusting reagent of the primary chemical precipitation system was calcium hydroxide,the p H of the primary chemical precipitation system was 9.0,the dosage of polyacrylamide(PAM)was 2 mg/L,and the O3/H2O2 oxidation reaction time was 60 min,the p H of the O3/H2O2 oxidation reaction system was9.0,the dosage of O3 was 96 mg/L,the dosage of 30% H2O2 was 1.0 m L/L,the adjusting reagent of p H for the secondary chemical precipitation was calcium hydroxide,and the p H of the secondary chemical precipitation system was 10.0.The A/O process was used as the follow-up process of the physicochemical section to remove chemical oxygen demand,ammonia nitrogen and total nitrogen.The high emission standards can be achieved through optimization of process parameters.The better working conditions were: the dissolved oxygen is 5.0 ± 0.4 mg/L,the reflux ratio of the nitrification solution was 300%,the influent carbon-nitrogen ratio was 6.5,and the hydraulic retention time was 33.6 h.On the basis of optimizing the physicochemical process and the A/O process respectively,the two were coupled to form a combined process.The combined process’ s efficiency and operational stability of treatment of electroplating mixed discharge wastewater were studied.The experimental results showed that the concentrations of chemical oxygen demand,total nitrogen,ammonia nitrogen,total phosphorus,total nickel,total chromium,total copper,total iron and total zinc in the influent are 158～180,84～102,44～54,0.8～1.3,33～36,0.3～0.5,3～4,113～126,80～89 mg/L,the corresponding average concentrations of the effluent indicators were 17.84,6.96,0.39,0.05,0.04,0.004,0.01,0.01 and 0.01 mg/L respectively,meeting the high emission standards.