INTERNAL ENERGY-BASED COMPETITION BETWEEN POLYPHOSPHATE-ACCUMULATING 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 feed ing ratio (wt/wt) was found to be a key factor influencing an ''intern al energy-based'' competition between polyphosphate-accumulating bacte ria (PAB) that mediate biological phosphorus removal and glycogen-accu mulating 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 ana erobic stage, and to use the reserved material for growth in the aerob ic stage. When excessive P was provided (P/C feeding ratio = 20/100), PAB could accumulate a high content of polyphosphate, and with a highe r 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 un der operation with a median P/C ratio, because the stored energy pool of PAB was not enough for the complete uptake of acetate under anaerob ic conditions. Thus, GAB could share what acetate remained, coexisting with PAB. These competitive outcomes were strongly supported by resul ts on the anaerobic metabolism of acetate, and by microscopic observat ions in this study. (C) 1997 Elsevier Science Ltd.