Anoxic biological phosphorus uptake and the effect of excessive aeration on biological phosphorus removal in the A2O process

The occurrence of denitrifying phosphate accumulating organisms (DNPAOs) and the contribution of DNPAOs to biological nutrient removal performance were investigated in a bench-scale A2O system. Moreover, the effect of excessive aeration on biological phosphorus removal (BPR) was studied. The experimental results suggested that anoxic phosphorus uptake could occur in the A2O process, as compared with the conventional A2O process. Good COD, phosphorus, ammonia nitrogen and total nitrogen removal efficiency (92.3%, 95.5%, 96% and 79.5% respectively) could be achieved. Furthermore, sludge analysis demonstrated that the ratio of anoxic P uptake rate to aerobic P uptake rate reached 69% in such a system and nitrate concentration in the anoxic phase and different organic substrate introduced into the anaerobic phase had significant effects on the anoxic P uptake. It was also found that if the air supply was not adjusted properly under good anoxic P uptake conditions, excessive aeration of activated sludge at the end of aerobic zone could lead to the deterioration of BPR.