Internal energy-based competition between polyphosphate- and glycogen-accumulating bacteria in biological phosphorus removal reactors--effect of P/C feeding ratio

In acetate-fed, anaerobic-aerobic alternated bioreactors, the P/C feeding ratio (wt/wt) was found to be a key factor influencing an `internal energy-based' competition between polyphosphate-accumulating bacteria (PAB) that mediate biological phosphorus removal and glycogen-accumulating bacteria (GAP) that do not. Both groups were previously known to use internally stored polyphosphate and glycogen, respectively, as energy sources for storing acetate as polyhydroxyalkanoate in the anaerobic stage, and to use the reserved material for growth in the aerobic stage. When excessive P was provided (P/C feeding ratio = 20/100), PAB could accumulate a high content of polyphosphate, and with a higher and faster acetate uptake ability, successfully out-competed GAB. In contrast, reduction of the P/C ratio to 2/100 caused the depletion of the polyphosphate content in PAB, eventually leading to a replacement by GAB as the majority. Stable coexistence of both groups occurred under operation with a median P/C ratio, because the stored energy pool of PAB was not enough for the complete uptake of acetate under anaerobic conditions. Thus, GAB could share what acetate remained, coexisting with PAB. These competitive outcomes were strongly supported by results on the anaerobic metabolism of acetate, and by microscopic observations in this study.