Analysis of the microbial community structure and function of a laboratory scale enhanced biological phosphorus removal reactor

Abstract

Summary A laboratory scale sequencing batch reactor (SBR) operating for enhanced biological phosphorus removal (EBPR) and fed with a mixture of volatile fatty acids (VFAs) showed stable and efficient EBPR capacity over a four‐year‐period. Phosphorus (P), poly–β–hydroxyalkanoate (PHA) and glycogen cycling consistent with classical anaerobic/aerobic EBPR were demonstrated with the order of anaerobic VFA uptake being propionate, acetate then butyrate. The SBR was operated without pH control and 63.67 ± 13.86 mg P l −1 was released anaerobically. The P% of the sludge fluctuated between 6% and 10% over the operating period (average of 8.04 ± 1.31%). Four main morphological types of floc‐forming bacteria were observed in the sludge during one year of in‐tensive microscopic observation. Two of them were mainly responsible for anaerobic/aerobic P and PHA transformations. Fluorescence in situ hybridization (FISH) and post‐FISH chemical staining for intracellular polyphosphate and PHA were used to determine that ‘ Candidatus Accumulibacter phosphatis’ was the most abundant polyphosphate accumulating organism (PAO), forming large clusters of coccobacilli (1.0–1.5 µm) and comprising 53% of the sludge bacteria. Also by these methods, large coccobacillus‐shaped gammaproteobacteria (2.5–3.5 µm) from a recently described novel cluster were glycogen‐accumulating organisms (GAOs) comprising 13% of the bacteria. Tetrad‐forming organisms (TFOs) consistent with the ‘G bacterium’ morphotype were alphaproteobacteria , but not Amaricoccus spp., and comprised 25% of all bacteria. According to chemical staining, TFOs were occasionally able to store PHA anaerobically and utilize it aerobically.

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