EFFECT OF POLYPHOSPHATE LIMITATION ON THE ANAEROBIC METABOLISM OF PHOSPHORUS-ACCUMULATING MICROORGANISMS

There are two types of microbial populations described in the literatu re as being capable of anaerobic storage of acetic acid in activated-s ludge processes: the polyphosphate-accumulating organisms (PAO) and th e glycogen-accumulating non-polyphosphate organisms (GAO). Both groups use the conversion of glycogen to poly-hydroxyalkanoate to produce AT P and NADH; however, the first group can also produce ATP from polypho sphate (poly-P). No representative pure cultures are available from ei ther group. The question arises: is the observed activity of GAO due t o PAO that are depleted in poly-P? In this study, using a laboratory s equencing batch reactor containing an enriched culture, the ability of the enriched PAO to utilize organic substrate (acetate) anaerobically was investigated under conditions of poly-P limitation and surplus gl ycogen content of the biomass. This study showed clearly that, under t hese conditions, almost no acetate was taken up. Furthermore, this str ongly suggests that PAO can not use glycogen conversion to poly-hydrox yalkanoate as the sole energy source under anaerobic conditions, which seems to be the restricted to a separate group of GAO. On the basis o f the results and literature data, an improved scheme for the anaerobi c acetate accumulation is presented.