Trial Study On The Anoxic-Oxic Biological Filters For Municipal Wastewater Treatment

The Aerated Biological Filter has been extensively used in treatment and reuse of sewage wastewater. It has faction of removing SS, COD, BOD, nitrogen, phosphorus, which is characterized by setting biological oxidation and suspended solids in one interception, saving a follow-up sedimentation tanks(secondary sedimentation tank).The volume load, hydraulic load of BAF is strong. The hydraulic retention time is short . The investment of necessary infrastructure is less than others . It's discharge water is good. It's operation costs is province. To strengthen the effect of nitrogen, we add the anaerobic paragraph to compose the anoxic-oxic process, whose oxic biological filter is composed by two aerated biological filters.How to start-up the process and impact factors of this process, the relevant of denitrification process control technology and features of backwashing were studied in this paper.The linked membrane in this test was separated in two phases: nausea exposures phase (3d), natural biofilm formation phase (17d), and the removal rate of NH₃-N and COD_Cr were about 75 percent, hanging film is success.The process has been proved to be effective for nitrogen in this experiment.The system discharge water quality is good enough to meet the A-level standards in the " pollutant discharge standards of urban sewage treatment plant " (GB18918-2002).The system has strong impact capacity, when the volume load changes in 0.05～0.91kgNH₃-N/(m³Â·d), the average removalrate of NH₃-N in this system is about 90.8%, the effluent concentration of NH₃ -N is less than 5mg/L mostly. Considering the large number of returning nitrification, the Anoxic filtration (columnl) has the multiple functions of removing COD_Cr, NH₃-N and denitrification.,the average removal rate ofCOD_Cr is 32.1 percent, the average rate of nitrification is 23.94 percent, the average rate of denitrification is 57.03 percent. Carbonation (column2) completed the removal of most COD_Cr, NH₃-N .The average removal rate ofCOD_Cr is 24.4 percent, the average rate of nitrification is 38.58 percent Thenitrification-filtration has evident result in Simultaneous Nitrification and Denitrification, NH₃-N concentration reduced 2.76mg/L by an average, butNO_x^--N concentration only increased 0.87mg/L by an average. Because of urban sewage COD_Cr/NH₃-N average value is 7.15, which is good formicrobial nitrification-denitrification process, the accumulated problems is not found in the experimental process. The system optimized operating parameters: HRT = 48min = 0.8h (20 min in Anoxic paragraph, 28 min in aerobic paragraph, is the shortest HRT), the ratio of gas and water change from1:1 to 2:1, the system back ratio also change from 1:1 to 2:1.Backwashing is the key operation to maintain Aerated Biological Filter function. The backwashing procedure is: the individual gas washing strength is 8 L/(s·m²), the separate gas washing time is 3 min, the joint gas washing strength is 8L/(s·m²), the joint washed strength is 3 L/(s·m²), the joint irrigation washing time is 6 min, the separate washed strength is 3 L/(s·m²), the separate washing time is 4 min. The backwashing cycleis: column 1:24～36h, column 2:2～3d, column 3:5～6d; the ratio of backwash water and production is about 7～9%. The backwash water and gas in the Anaerobic Filter (column 1), to a certain extent, undermine the anaerobic environment, resulting in the denitrification efficiency is not very high (only reach to 57.03%).