Research On High Ammonia Nitrogen Domestic Wastewater Treatment By Step-feed A/O Nitrogen Removal Process Under Low DO Concentration

The step-feed A/O nitrogen removal process is a new process with high nitrogen removal efficiency developed based on the traditional A/O process.It have become a hot research both at home and abroad because of its significant advantages.The dissolved oxygen concentration,aeration mode and hydraulic retention time were researched to investigate the effect on property of nitrogen removal by four stage step-feed A/O process treating domestic wastewater.Water quality variation in each reaction tank was measured to analysis the reason of difference between the theory of nitrogen removal efficiency and actual nitrogen removal efficiency.In addition,the sludge distribution condition and activated sludge sedimentation performance were investigated in the trial.The main research results are as follows:First,step-feed A/O nitrogen removal process had better removal efficiency of organism and ammonia nitrogen.The average removal efficiency of COD,ammonia nitrogen and total nitrogen reached 92.80%,96.63%and 64.30%respectively.COD and ammonia nitrogen removal had little effect under different dissolved oxygen concentration,but the organic carbon source was fully utilized and the total nitrogen and COD removal was enhanced to some degree because of simultaneous nitrification and denitrification while maintaining lower DO concentration in the aerobic tank.The TN removal efficiency reached 68.98%when the influent carbon nitrogen ratio was 4.2,the DO concentration in the aerobic tank was 0.8-1.3mg/L,which is about 10%higher than the same condition of higher DO concentration.Second,after researching the water quality variation in each reaction tank,we found that COD concentration reduced greatly after getting through the anoxic tank because of dilution and denitrification and function of microbe-assimilation,which provided a good environment for nitrifying bacteria and nitration reaction.The ammonia nitrogen concentration was very low in each aerobic tank and the effluent ammonia nitrogen concentration could reach the standard.The denitrification was incomplete and the nitrogen removal efficiency was not high because of the shortage of carbon source,and the effluent total nitrogen was nitrate mainly.Total nitrogen was decreased in the aerobic tank and TN removal efficiency was increased a lot under lower dissolved oxygen concentration because of SND.MLSS was high in the reaction tank and the sludge sedimentation performance was good and no sludge bulking phenomena.Third,the aeration mode of constant aeration rate and constant DO concentration under lower DO concentration could reached 93.24%and 91.94%of COD removal efficiency.The effluent ammonia nitrogen concentration increased gradually along with the increase of influent ammonia nitrogen load,even far more than 5mg/L,it proved that constant aeration rate could meet the requirements of nitration when influent ammonia nitrogen concentration was under a certain range.The effluent ammonia nitrogen was always less than 5mg/L under constant DO concentration mode.The adding of ammonia nitrogen to wastewater could cause poor sludge sedimentation performance when the water quality fluctuated rapidly at constant aeration rate,and the SVI value increased gradually to 221.04mL/g.However,the control mode of constant dissolved oxygen could improve sludge sedimentation performance effectively and the SVI value decreased to 170mL/g and then kept stability.And the system was in the limited filamentous bulking condition,it caused no sludge loss,and could get good effluent quality.In addition,it achieve the purpose of saving energy.Forth,different HRT had certain influence on organic removal effect and nitrogen removal efficiency.The COD,NH3-N and TN removal efficiency were gradually increased as the hydraulic retention time increased,but the increase rate became smaller and smaller.Take economic factors into consideration,Hydraulic retention time was not as long as possible.In actual operation,the optimal HRT should be determined considering the technical and economic aspects comprehensively.