Floc-forming properties of polyphosphate accumulating organisms in activated sludge.

The physico-chemical characteristics of polyphosphate-accumulating organisms (PAO) involved in enhanced biological phosphorus removal (EBPR) was investigated in order to find a novel method for phosphorus recovery. If the physico-chemical characteristics of PAO are different from those of other main floc components, it may be possible to enrich PAO in bulk water or in the floc material for improved recovery of phosphorus. A combination of shear tests, chemical manipulation, and quantification of PAO by fluorescence in situ hybridization was applied. The microcolony strength of both Rhodocyclus-related PAO and Actinobacteria-related PAO was generally high as no treatment could break up more than 20% of all PAO in microcolonies. In contrast, it was possible to remove 20-40% of the organic matter and other bacterial cells by applying a high pH value or adding EDTA. With that a selective enrichment of PAO in the remaining floc material was possible. The feasibility of applying this selective PAO enrichment in flocs remains to be evaluated in full-scale plants for P-recovery.