observed to be slightly decreased,

observed to be slightly decreased, while the abundance of the microorganisms was considerably increased. A greater decrease of the PHB density in the activated sludge of the A2O-B process than the A2O-C process was strongly correlated to the removal of nitrogen species. This was because the denitrifying bacteria used NO2− ions in the absence of O2, and NO3− ions as electron acceptors under anoxic conditions, for phosphate uptake and denitrification (Meinhold et al., 1999). The contents of the PHB in the activated sludge from the oxic reactors disappeared completely, since the PHB under the oxic conditions was used as an energy source for the growth of microorganisms and their storage of PO43- ions (Akin and Ugurlu, 2004). The lower PHB content in the activated sludge of the A2O-B process compared to that of the A2O-C process strongly suggests that the inoculation of beneficial microorganisms into the sludge digestion tank might facilitate the biological removal of phosphorus species in the A2O process.