Influence of Dissolved Oxygen on Catalyzed Iron Internal Electrolysis Process for Mixed Chemical Wastewater Pretreatment

75% of the total amount of wastewater discharged from an industrial area in the northwest of Shanghai is chemical industrial and pharmaceutical wastewater,which is a typical mixed chemical industrial wastewater.Currently,SBR process is used in the wastewater treatment plant of this area and its effluent fails to meet the discharge standard,especially the color index standard.Therefore,the pilot-scale experiment using catalyzed iron internal electrolysis for pretreatment of the mixed chemical industrial wastewater was carried out.The results show that dissolved oxygen has great influence on the pretreatment.Under the conditions that dissolved oxygen depletion is 0.5 mg/L,the removal of the color level appears efficiently and averages 42%.However, only about 14% of COD is removed.At high dissolved oxygen(5.3-5.9 mg/L),the average removal efficiencies of COD and color are 44.0% and 34% respectively.At low dissolved oxygen(0.9-1.4 mg/L),the average removal efficiencies of COD and color are 54.5% and 43%,which is a more appropriate operation condition.