Operation Optimization In A Combined Multistage AO And Advanced Treatment For Nitrogen And Phosphorus Removal

The multistage AO process is a multipoint water sewage treatment technology based on traditional AAO process.This technology owns higher carbon source utilization and nitrogen removal efficiency,and lower energy consumption.However the system optimization of the process does not remain the best performance.Besides,some sewage treatment plants in some areas need to reach the standard of effluent to achieve an advanced treatment in nitrogen and phosphorus removal.For example,the wastewater effluent standard A in Tianjin requires the effluent should meet TN?10 mg/L and TP?0.3 mg/L when the scale of urban sewage treatment plants are designed over 10 000 m3/d.However,it is hard to reach above standard only relaying on the optimization of biologicaltreatment.In order to meet this standard,chemical phosphorus removal and denitrification are needed combinating with biological treatment.In this research,multistage AO as a main body process,which was optimized on the system.After the multistage AO process,the chemical phosphorus removal and the deep bed denitrification filter were used to ensure the effluent meet the standard of TN?10 mg/L and TP?0.3 mg/L.Lab-scale experiments of the multistage AO process was conducted and the main parameters were optimized.Meanwhile,traditional AAO process was compared with the multistage AO process.The results showed that the optimal influent feed ratio was 60%:40%,the mixed liquor returnrd ratio of two sections was 50% and 150%,respectively,HRT was 10 h,and volume ratio of anoxic zone and aerobic zone was 0.8.Under the best conditions,the effluent could reach the standard A of first level.When compared with the traditional AAO process,the results reflected that the removal efficiency of COD and TP were similar,but the denitrification ability of multistage AO process was better than traditional AAO process.In the study of chemical phosphorus removal,different phosphorus reagents,drug dosing and reaction time were discussed and examined under different water quality condition.The test results showed that the optimal reagent was polyaluminium chloride.When the initial TP was 0.50 mg/L,0.75 mg/L and 1.00 mg/L,the corresponding drug dosing quantity were 10 mg/L,15 mg/L and 20 mg/L respectively.The best reaction time was 15 min.For the deep bed denitrification filter,methanol was an appropriate adding carbon source,and the C/N of adjusted water was 3:1.The HRT was 0.25 h,and the effluent TN could meet the requirements of TN?10 mg/L.Based on the study of multistage AO,chemical phosphorus removal and deep bed denitrification filter,the integration of three units were optimized.The integration system characteristics of continuous running were investigated in this study.The experiment results indicated that the effluent of multistage AO process was stable,and the water quality could meet the standards A of first level.The effluent TP of chemical phosphorus removal was below 0.20 mg/L.The effluent TN,TP and COD of deep bed denitrification filter were 7.27 mg/L,0.16 mg/L,and 19.58 mg/L.As can be seen that this system met the need of nitrification and phosphorus advanced treatment.