ABSTRACT
197There are two types of microbial populations described in the literature as being capable of anaerobic storage of acetic acid in activated sludge processes: the poly-phosphate accumulating organisms (PAOs) and the glycogen accumulating non-poly-phosphate organisms (GAO). Both groups use the conversion of glycogen to poly-hydroxy-alkanoate (PHA) to produce ATP and NADH; however, the first group can also produce ATP from poly-phosphate (poly-P). No representative pure cultures are available from either group. The question arises: is the observed activity of GAO due to PAO that are depleted in poly-P? In this study, using a laboratory sequencing 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 glycogen content of the biomass. This study showed clearly that, under these conditions, almost no acetate was taken up. Furthermore, this strongly suggests that PAO can not use glycogen conversion to PHA as the sole energy source under anaerobic conditions, which seems to be restricted to a separate group of GAO. On the basis of the results and literature data, an improved scheme for the anaerobic acetate accumulation is presented.
