Microbial community profile of a biological excess phosphorus removal (BEPR) activated sludge system using a cultivation-independent approach

It is generally accepted that biological release of phosphorus in the anaer obic zone of a nutrient removal system and phosphorus accumulation in the s ubsequent aerobic zone is directly proportional to the quantity of volatile fatty acid or the readily biodegradable COD fraction (f(bs)) entering the system. This will enrich For polyphosphate accumulating organisms (PAOs) in the system and an increase in biological phosphorus removal will be observ ed. Enrichment for PAOs during the present study was essentially achieved b y increasing both the phosphorus and f(bs) concentrations (maintaining cons tant total COD loads) in the influent to the system. Fluorescence in situ h ybridisation (FISH) using kingdom-, subdivision- and genus-level probes was used to identify and enumerate the bacterial community implicated in biolo gical excess phosphorus removal (BEPR). Hybridisation of up to 78% of the c ells (in relation to DAPI staining) with probe EUB338 indicated that a high proportion of the sludge comprised metabolically active bacteria. Bacteria l predominance in the BEPR sludge appeared, in descending order, as such: b eta Proteobacteria (22%); alpha Proteobacteria (19%): gamma Proteobacteria (17%); and. Actinobacteria(11%). Incidence of Acinetobacter spp. appeared t o be relatively low with counts amounting to < 9% of the total bacterial co unt. The results indicate that the beta and alpha Proteobacteria are metabo lically functional (either directly or synergistically) in BEPR processes a nd reiterate the functional misconception of Acinetobacter spp. in these sa me systems.