A simple method to distinguish between polyphosphate and other phosphate fractions of activated sludge

Abstract A procedure of sequential extraction steps proposed by Psenner et al. ( Arch. Hydrobiol. Suppl. 70 ,111–155, 1984; Arch. Hydrobiol. Beih. Ergebn. Limnol. 30 ,98–103, 1988) to quantify ecologically relevant phosphate fractions in lake sediments has been applied to activated sludge from waste treatment plants for biological phosphate removal. By this method, the following phosphate fractions of technological significance may be distinguished: (a) redox-sensitive phosphate, mainly bound to Fe(OH) 3 ; (b) phosphate adsorbed to surfaces (Al 2 O 3 ), exchangeable against OH − , and alkali-soluble phosphate; (c) phosphate bound to CaCO 3 , MgCO 3 and in apatite; and (d) a fraction which hitherto has been designated as “organically bound phosphate”. By means of nuclear magnetic resonance spectroscopy and by inclusion of a hot water extraction step it became evident that fraction (d) mainly contained polyphosphate (PP). In activated sludge samples with phosphate-accumulating bacteria, the PP content amounted to 80 mg/g MLVSS. By combination of the Psenner fractionation and hot water extraction, indications of a significant proportion of PP in lake sediments have also been found.