Kinetic and phylogenetic characterization of an anaerobic dechlorinating microbial community

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–b–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 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 intensive microscopic observation. Two of them were mainly responsible for anaerobic/aerobic P and PHA transformations. Fluorescence in situ hybridisation (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 utilise it aerobically