Investigation Of Simultaneous Nitrogen And Phosphorus Removal By AOA-SBBR Process In Municipal Wastewater Treatment

The laboratory-scale Anaerobic/aerobic/anoxic(AOA)-SBBR process and Anoxic/anaerobic/aerobic(reversed A2O) process fed with synthetic municipal wastewater was designed to investigate the effect of changing COD/TN/TP ratios on the performance of biological nutrient remova(BNR).Specific objectives of the research were to investigate the effect of COD/TN/TP ratio on the rates of phosphorus removal, COD removal, nitrogen removal.The system was operated at normal temperature.The AOA-SBR process was stably operated over more than three months. The influent phosphorus concentration was held approximately constant while the COD concentration was varied to obtain the desired COD/TP ratios of 25,35,45,55,65 and 73.When the ratio of COD:TP=73:1,the average COD, nitrogen and phosphorus removal efficiencies were 100%, 84% and 93%, respectively. The concentration of effluent reached A grade of first grade discharge standard of GB18918-2002.It was demonstrated that the increment of carbon substrate has an adverse effect on phosphate-accumulating organisms (PAO) competing carbon substrate with glycogen-accumulating organisms (GAO), which inhibits aerobic phosphate uptake. The ratio of anaerobic acetate uptake by PAO and GAO is 1:9. Moreover, the ratio of anoxic phosphate uptake to aerobic phosphate uptake, which indicates the fraction of DNPAO in total PAO, was experimentally evaluated. The results indicate that the AOA-SBR process is much larger anoxic/ aerobic phosphate uptake than that of A2O and AO processes.It was also observed that the changes in the COD/TP ratio did not significant affect COD and nitrogen removal, but strongly affect the MLSS concentration. The MLSS concentration at COD/TP=73 was only 60% of that at COD/TP=25. The amount of phosphorus removal and MLVSS concentration in AOA-SBBR system increased as the COD/TP ratio increased.From this reseach, the amount of COD removal required to removal 1mg/L phosphorus decreased as COD/TP ratio increased.In reversed A2O process, the effect of COD/TN/TP ratio on simultaneous nitrogen and phosphorus removal was studied by changing the influent COD and nitrate concentration.When COD:TN:TP=50:3:1,the average nitrogen and phosphorus removal efficiencies were 75% and 83% respectively.In addition, the efficiencies of nitrogen and phosphorus removal by pre-denitrification (reversed A2O) and post-denitrification (AOA) were compared.It is proved that the reversed A2O process was influenced by COD/TN/TP ratios and adapt to treat municipal wastewater with low COD/TN ratios while AOA-SBBR process was not influenced by COD/TN.The AOA-SBBR is adapt to treat municipal wastewater with COD/TP>70.