Study On The Denitrification Efficiency During Anaerobic-aerobic Switched BAF Process

With the water pollution situation continuously intensified,request of receiving water for drainage water quality has been increasing,thus the effluent water quality of urban sewage treatment plant have to meet higher emission standard.Due to the discontinuous and seasonal changed discharge of industrial wastewater treatment plant in our country,the effluent ammonia nitrogen and total nitrogen many urban sewage treatment plants can't reach first grade A standard of Discharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002).So it's necessary to upgrade the existing wastewater treatment processes.This study adopted anaerobic-aerobic switched BAF process in urban sewage advanced treatment to ensure the discharge standard.For anaerobic-aerobic BAF process,the effects of hydraulic loading(1.5 m3/(m2·h),2.0 m3/(m2·h),2.5 m3/(m2·h)),carbon and nitrogen ratio(4:1,6:1,8:1),dissolved oxygen(0.5 mg/L?1.2 mg/L,1.5 mg/L?2.2 mg/L)on pollutants removal efficiency were investigated.The results showed that the optimum process condition for pollutant removal were determined to be hydraulic load=2.0 m3/(m2·h),COD/TN=4,DO<1.2 mg/L.The optimal removal rate of COD,TN and nitrate reached 97%,85%and 83%,respectively.For aerobic-anaerobic BAF process,the effect of HRT(0.5 h,1.0 h,1.5 h)on pollutants removal efficiency was studied.The result showed that the pollutants removal efficiency became better with the increasing of HRT when the hydraulic load and COD/TN were 2.0 m3/(m2·h)and 4:1.And the average removal rate of COD,TN and ammonia nitrogen reached 85%,85%and 95%when HRT was 1.5 hIn the field test stage,the anaerobic-aerobic switched BAF process was adjusted according to the effluent property in different stages of Changge sewage purification company.The anaerobic-aerobic BAF combined process was adopted when total nitrogen concentration exceeded the standard,and TN removal rate reached 92%.The aerobic-anaerobic BAF combined process was adopted when ammonia nitrogen exceeded the standard.And the effluent ammonia nitrogen concentration was less than 0.5 mg/L when the influent water concentration was 15.0 mg/L,the average removal rate reached 97%.The discharged wastewater quality could meet first grade A level under two kinds of operation conditions.Microbial populations of the field trial reactor were investigated,and 7 kind of bacteria were found:Proteobacteria,Chloroflexi,Bacteroidetes,Acidobacteria,Planctomycetes,Chlorobi,Nitrospirae..No significant changes on microbial abundance and dominant population were observed before and after switching anaerobic-aerobic switched BAF process.Pilot solution of anaerobic-aerobic switched BAF process was designed based on the results of the laboratory test,field test and the actual situation of Changge sewage purification company.