Abstract
Denitrifying polyphosphate-accumulating organisms (DN-PAOs) in the biological phosphorus removal process treating municipal wastewater were studied. On the basis of the ratio of anoxic phosphate uptake rate (PUR) to aerobic PUR, it was suggested that the minimized aeration for mixing the anaerobic tank is fatal to DN-PAOs even if the dissolved oxygen concentration was nearly equal to zero. The results also suggested that DN-PAOs preferred the anoxic followed by anaerobic conditions although they could be significantly observed in the processes without anoxic conditions. Moreover, the ratio serves as one of the parameters of the activated sludge model No.2d (ASM2d). From the sensitive analysis of the parameter in an A2O process, we could conclude that the phosphorus removal ability depended on the ratio of DN-PAOs. On the other hand, it did not affect the nitrogen removal ability (both nitrification and denitrification) very much. The parameter observed in the present experiments showed that we had to calibrate or measure it in each plant for the valid simulation of simultaneous nitrogen and phosphorus removal systems based on the ASM2d.
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