It was demonstrated that glycogen-accumulating organisms (GAOs) were able to compete with phosphorus-accumulating organisms (PAOs) for acetate in a biological phosphorus removal (BPR) process, leading to a loss of BPR capability. Cellular fatty acid composition, which serves as a fingerprint for microbial identification, was used to determine microbial population change and to investigate the competition mechanisms of PAOs and GAOs. Analysis of cellular fatty acid composition indicated that PAOs grown with acetate and glucose were different species and that GAOs and PAOs grown with the same substrate were also different species. Glycogen-accumulating organisms seemed to coexist with PAOs even in a well-developed BPR process. The GAOs were able to accumulate more poly-β-hydroxybutyrate (PHB) and glycogen than PAOs during the anaerobic stage of the BPR process. The GAOs synthesized more in-cell glycogen than PAOs. The growth rate for PAOs was always greater than that for GAOs at various acetate or glucose concentrations, while GAOs had higher acetate uptake and PHB synthesis rates than PAOs. Therefore, GAOs are thought to compete with PAOs only at long solids retention times (≥ 20 days).
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