In order to study the characterization of polyphosphate-accumulating organisms (PAOs) community structure in an enhanced biological phosphorus removal system

the phosphorus uptake of anaerobic-oxic (A/O) sludge and anaerobic-anoxic (A/A)sludge were investigated via batch tests.The experiment results indicated that the A/O sludge had a higher aerobic phosphorus uptake rate than the anoxic phosphorus uptake rate

however

the aerobic phosphorus uptake rate of the A/A sludge was less than the anoxic phosphorus uptake rate of that sludge.Based on these results

the presently used method

in which the ratio of the anoxic phosphorus uptake rate (qPa) to the aerobic uptake rate (qPo) gives the relative proportion of denitrifying polyphosphate-accumulating organisms (DPAOs) in the PAOs，is unreasonable.Furthermore

the PAOs community structure was related to the electron acceptor type.According to the type of electron acceptor

three groups of the PAOs could be proposed as follows：PON(using oxygen and nitrate as electron)

PO(using only oxygen as electron acceptor) and PN (using only nitrate as electron acceptor).