Theoretical Analysis And Engineering Practice Of Improved A~2/O Process Under Low C/N

The improved A2/O technology was added a pre-denitrification zone as a selection area in the front of the traditional A2/O process.The improved process was that the returning activated sludge from the secondary sedimentation tank and partial wastewater had come into the microorganism selection area at first.And then denitrification was carried out by microorganisms using organic matter in the influent as carbon source,so some nitrate or nitrite were removed from return sludge and influent wastewater.The biological dephosphorus capacity of the system was improved because the adverse effects of nitrate nitrogen on anaerobic dephosphorus were eliminated.In this study,Fuxin Beikong sewage treatment plant as the research object,the operation status and the effluent of A-A2/O process and traditional A2/O process were compared and analyzed.The effect of key parameters such as water inflow on the effluent quality was investigated.The calculation equation of the residual activate sludge had been amended because of the deviation from actual.The following conclusions were:Compared with the traditional A2/O technology and improved A2/O process for biochemical treatment,the ability of denitrification and dephosphorus were enhanced and also improved the removal efficiency of COD,so some biological carbon sources come into selection area that the function of denitrification was increased and anaerobic phosphorus released with denitrification were respectively completed in different reaction zones.The analysis for operation parameters of Beikong sewage treatment plant showed that the average removal rate of COD increased about 3.47%and the effluent concentration of COD was lower about 7mg/L in the improved A2/O technology.The effluent concentration of TN could easily reach the national standard of first A level.Removal rate of TP has been greatly improved under the improved A2/O process with 11.3%higher than the traditional process.In general,the effect of nitrogen and phosphorus removal for the modified A2/O process was improved.The temperature and the quantity of water,C/N and C/P had certainly effect on water quality through analysis the operation parameter.It was showed that the effect of temperature reduction on denitrification was obvious.However,increased temperature improves COD removal rate slightly and presents low effect on nitrifying bacteria and polyphosphate bacteria and polyphosphate bacteria,but also has great influence on denitrifying bacteria and VAF.Overall,influent C/N,C/P ratio should meet the requirement of the denitrogen and dephosphorus in sewage treatment plant.The total influent has little influence on the removal rate of COD and TP and with its increasing,the removal rate of denitrification were decreased.In this paper,the calculation methods of three kinds for residual sludge were discussed.Combined with the actual production practice,The amended calculation formula of residual sludge was put forward so that it was more practical.