The optimal removal efficiencies of COD

N and P were investigated by using denitrifying phosphorus activated sludge taken from an anaerobic/anoxic/oxic (A2O)-biological contact oxidation (BCO) system. Response surface methodology using Central Composite Design (CCD) of Design-Expert was used to evaluate the influence and specific function of four important factors (initial COD concentration

nitrate concentration

temperature and anoxic reaction time) on the three responses

which were marked removal rate of COD

N and P as Ycod

Yn and Yp

respectively. Among all the factors

initial COD concentration greatly influenced the three responses. In addition

anoxic reaction time had a major impact on Yn and temperature had a greater influence on Yp than other two factors. The three response model equations were all significant

where R2 were 0.9853

0.9118 and 0.9972 respectively. When initial COD concentration

nitrate concentration

temperature and anoxic reaction time were 316.95 mg·L-1

42.26 mg·L-1

27.19℃

and 237.37 min respectively

the model predictions of Ycod

Yn and Yp were 93.54%

99.96% and 99.56%

and test responses were 92.03%

91.15% and 81.64%

respectively.