Ecological aspects of biological phosphorus removal in activated sludge systems

Inorganic polyphosphate (poly-P) is a linear polymer of many tens or hundreds of inorganic phosphate (Pi) residues linked by high-energy phosphoanhydride bonds (Fig. 1) and usually consists of mixtures of different molecular sizes. Thermodynamically the standard free energy of hydrolysis of the anhydride linkage yields about 38 kJ per phosphate bond at pH 5. The energy storage function of poly-P depends on the ability of the bond cleavage reaction to effect phosphorylation and thereby conserve the energy associated with the hydrolytic action (Dawes, 1990).