Dietrich Uhlmann

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.

Sediment and pore water composition as a basis for the trophic evaluation of standing waters

Sediments and pore water samples from four reservoirs in eastern Germany with different trophic characteristics have been examined (Neunzehnhain I – oligotrophic; Muldenberg – oligotrophic, dystrophic; Saidenbach – mesotrophic; Quitzdorf – highly eutrophic). Several parameters were analyzed regarding the dependence on the trophic state and the possibility to use them for the trophic evaluation of standing waters. The strongest influence of the trophic state could be found in the case of the parameters SRP, alkalinity and ammonium in the pore water. For the dry sediment, it could be concluded that the most important factor affecting the trophic state is the ratios of Fe:P and Al:P, which were summarized to a metal:phosphorus sum ratio (MPS) and showed a clear threshold value for the potential to immobilize phosphorus in the sediment. Also, with the P fractions of the sediment samples, differences between the trophic levels became evident. Higher percentages of the reductively soluble, iron-bound fraction and of the biogenic fraction occurred in the reservoirs with higher trophic state, while comparitively higher percentages of the stable aluminum-bound fraction could be measured in the reservoirs with lower trophic state.