Anaerobic metabolism of bacteria performing enhanced biological phosphate removal

Enhanced biological phosphate removal (EBPR) is an established activated sl udge process although many of the fundamental metabolic mechanisms are stil l poorly understood. Therefore, the stoichiometry and enzymatic reactions o f the anaerobic phase of this process were studied in a laboratory reactor with acetate as organic substrate. Enzyme assays showed that acetate activa tion is performed by acetyl-CoA synthetase. Results of C-13-NMR measurement s after feeding C-13-labeled acetate indicated that glycogen is degraded vi a the Entner-Doudoroff pathway. Energy is supplied by glycolysis, hydrolysi s of polyphosphate and probably also by hydrolysis of pyrophosphate and the efflux of MgHPO4. The ratio of phosphate released to acetate taken up is v ariable and apparently dependent on the contents of polyphosphate and glyco gen. A biochemical model is proposed explaining the experimental results in terms of carbon, redox. and energy balances. Anaerobic operation of an inc omplete tricarboxylic acid cycle (TCA) is proposed to explain the generatio n of extra reducing equivalents. (C) 2000 Elsevier Science Ltd. All rights reserved