The characteristics of removal of nitrogen and phosphorus were investigated by using denitrifying phosphorus activated sludge taken from an anaerobic/anoxic/oxic (A2/O)-biological contact oxidation (BCO) system. Different concentrations of NO2--N and NO3--N(NO2--N+NO3--N=30 mg·L-1) were used to evaluate the influence of different electron acceptor ratios (NO2--N:NO3--N0

0.2:0.8

0.4:0.6

0.5:0.5

0.6:0.4) on nitrogen and phosphorus removal of denitrifying polyphosphate accumulating organisms (DPAOs). The results showed that sodium acetate was the ideal carbon source for DPAOs to denitrify phosphorus removal and the best concentration was 200 mg·L-1. The more appropriate additive amount of NO3--N was 30 mg·L-1 when NO3--N was the electron acceptor in anoxic phosphorus absorption reaction. It was hard for the DPAOs that using NO3--N as electron acceptor and untamed with NO2--N to use NO2--N in a short time

but a low NO2--N concentration (6 mg·L-1) did not affected nitrogen and phosphorus removal by DPAOs when NO2--N was the electron acceptor. Additionally

the effect of NO2--N on phosphorus absorption was more significant than that of denitrification by NO3--N

and the reaction of phosphorus absorption almost ceased when the concentration of NO2--N achieved 18 mg·L-1. Furthermore

high concentration would inhibit the decomposition and utilization of PHA (polyhydroxyalkanoate)

and more energy from PHA decomposition would use for glycogen storage

where PHB (poly-β-hydroxybutyrate) accounted for more than 90% of the PHA decomposition and utilization.