Effect Of Anoxic Treatment On Nitrogen And Phosphorus Removal In Sludge Reflux Process

During the process of the traditional AAO system,the competition of carbon source between denitrifying bacteria and phosphorus bacteria in the anaerobic stage will make PAO can not fully release phosphorus in the anaerobic section,resulting in AAO process is difficult to obtain a stable and efficient phosphorus removal effect.In order to improve the efficiency of nitrogen and phosphorus removal and reduce the concentration of nitrogen and phosphorus in the effluent,domestic and foreign scholars have made a lot of research.One of the solutions is to reduce the effect of nitrate on the anaerobic environment in the anaerobic tank,UCT,JHB and modified AAO process was designed to improve the efficiency of nitrogen and phosphorus removal by ensuring the anaerobic environment in the anaerobic tank.Considering that the effluent sludge contains the external carbon source and the intracellular polymer PHB,In this study,we proposed an addition of anoxic tank and changed sludge retention time in the process of reflux to reduce the concentration of nitrate in the sludge.The influence of different sludge residence time on the denitrification and phosphorus removal of the system was analyzed.The effects of different influent C / P on the process were investigated.The main results of this study are as follows:(1)The addition of sludge anoxic tank is more efficient than the traditional AAO process.Adding the sludge anoxic tank,the nitrate concentration in the sludge was significantly reduced,which ensured the anaerobic environment of the anaerobic tank and provided good conditions for the phosphorus removal in the subsequent aerobic pool,and the removal rate was improved.After the addition of sludge anoxic tank,the residence time of returning sludge was an important control factor for the denitrification and dephosphorization.At 40 min,the removal efficiency of phosphorus and COD was the best.Phosphorus efficiency decreased at 60 min.If Extending the sludge residence time,it will result in an anaerobic tank volume and an increase in engineering costs.Considering that the residence time of the reflux sludge should be controlled at 40 min.(2)With the increase of phosphate concentration in the influent,the concentration of COD in the effluent of the secondary sedimentation tank remained basically stable,and the removal rate of COD was not much affected.When the dosage of phosphate was 5 mg / L and 7.5 mg / L,the change of total nitrogen concentration in the effluent of the secondary sedimentation tank was not changed,and the removal efficiency of total nitrogen was about 91%.When the dosage of phosphate was 10 mg / L and 15 mg / L,The efficiency of denitrification of modified AAO process is deteriorated due to the competition of phosphate and denitrifying bacteria to matrix.When the dosage of phosphate in the influent was 7.5 mg / L,the concentration of total phosphorus in the secondary sedimentation tank was 0.97 mg / L,which reached Grade B and the efficiency of phosphorus removal was 87.16%,which was better than that of other Conditions.The concentration of phosphorus in domestic sewage is generally 4 ~ 7 mg / L,The modified AAO process has a better effect when the phosphorus concentration is 5 ~ 7.5 mg / L.while the influent phosphorus is greater than 10 mg / L,nitrogen and phosphorus removal efficiency was worse.Therefore,in the actual treatment process,the use of additional sludge anoxic tank treatment of domestic sewage,When the concentration of phosphorus was 7.5 mg / L,the treatment effect was the best.