A sequencing batch reactor (SBR) was operated for enhanced biological phosphorus removal (EBPR) and dramatic differences in the P removing capabilities were obtained in different stages of the operation. At one stage extremely poor P removal occurred and it appeared that bacteria inhibiting P removal overwhelmed the reactor performance. Changes were made to the reactor operation and these led to the development of a sludge with high P removing capability. This latter sludge was analysed by fluorescent in situ hybridisation (FISH) using a probe specific for Acinetobacter. Very few cells were detected with this probe indicating that Acinetobacter played an insignificant role in the P removal occurring here. Analysis of the chemical transformations of three sludges supported the biochemical pathways proposed for EBPR and non-EBPR systems in biological models. A change in operation that led to the improved P removal performance included permitting the pH to rise in the anaerobic periods of the SBR cycle.

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