To investigate the possible biochemical metabolisms for excess phosphate uptake in a sequencing batch reactor (SBR) with single-stage oxic process, which was reported using glucose as the sole carbon source previously, glucose and acetate were fed to two SBRs as the sole carbon source, respectively. The changes of polyhydroxyalkanoates (PHAs), glycogen and the removal of phosphorus were compared between two SBRs. It was observed that the phosphorus removal efficiency was 91.8-94.4% with glucose, and 23.3-28.5% with acetate, although the former showed much lower accumulations/transformations of PHAs. Instead, the former showed a much higher transformation of glycogen. The facts suggested that glycogen could replace PHAs to supply energy for phosphate uptake under the single-stage oxic condition. Furthermore, the possible biochemical metabolisms were proposed to describe the relation between phosphate uptake and energy storages formations under Such a single-stage oxic process. Such a process may serve as a prototype for the development of alternative biological and chemical options for phosphate removal from wastewaters. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.