Research On The Reversed A~2/O Process For Municipal Wastewater Treatment

The eutrophication is exacerbated by the situation that removal of nitrogen and phosphorus can not both Reach the standard in sewage treatment plant running. It has become a hot issue that the methods used to ensure efficient removal of nitrogen and phosphorus and that the effluent quality at the same time reach the national integrated discharge standard.The process that the tradition of A2 / O process stop the return sludge and recycle ratio increased become inverted A2 / O process. With the conventional A2 / O process, it has the following features: first of all,the phosphorus uptake dynamics are fully utilized because the return sludge that participates in the process of phosphorus release and uptake increases and the bacteria after phosphorus release phosphorus directly enter into the aerobic environment; Secondly, denitrification rate is improved because the oxygen pool is before the anaerobic pool and the anaerobic denitrifying bacteria readily biodegradable COD as carbon source; Finally, the sludge return system combines within the return system, process simplicity, the operating cost [1-2].This test uses inverted A2 / O process and recearches the effect of urban sewage treatment in operating parameters of different conditions in this process. Test reaction column consists of four parts :hypoxia column - anaerobic column - aerobic column - secondary sedimentation column.The raw water from the hypoxia column followed through anaerobic column,aerobic column and secondary sedimentation column. At last part of treated water and sludge returned to hypoxia column. The experiment was divided into two stages: first, the stage is training of sludge .The sludge is exposed in aerobic environment to make micro-organisms remuse activity and then remove supernatant.After the sludge and sewage from city wastewater treatment plant to the ratio of 1:2 are added to reactor, microorganisms are acclimated.The stage is finished when the efficiency of COD and NH4 +-N removal stabilized at 75%. Second is the official pilot phase: by controlling the reactor temperature, dissolved oxygen, C / N ratio, reflux ratio and so on , the overall treatment efficiency of the process and the treatment effect of the reaction section are studied when these factors changes.The results show that municipal wastewater that is treated by inverted A2 / O process is good and basically meet an A standard of the Municipal Wastewater Treatment Plant Pollutant Emission Standards (GB18918-2002) . The inverted A2 / O process has a strong resistance to impact load and simple process and meet the requirements of nitrogen and phosphorus removal and appropriate for the new municipal wastewater treatment plant and the transformation of the old water plant.