Release of phosphorus from waste-activated sludge

The dynamics of Prelease from a primarily domestic waste-activated sludge was investigated, More than 70% of the P in the sludge was in mineral form, The inorganic rather than the organic fraction controlled the release of P. Phosphorus release from soil-sludge mixtures into soil solution during 100 d of incubation was measured with and without a corn (Zea mays L.) crop, in both a calcareous and a noncalcareous sandy soil. The kinetics of inorganic P dissolution from the sludge was also measured in aqueous suspensions during 9 d of incubation. Sludge concentrations were 10 to 100 g kg(-1) in the soil-sludge mixtures and 1 and 10 g L(-1) in the P-dissolution experiments, The dissolution experiments revealed that up to 40% of the total sludge P dissolved, under the experimental conditions. A continuum of solubilities was displayed by the solid inorganic P components present in the sludge, ranging from that of hydroxyapatite to that of dicalcium phosphate dihydrate. Transformations of N compounds in the sludge-containing systems had strong effects on the dynamics of P dissolution, mainly through the influence of the ammonification and nitrification processes on the pH and the ionic strength and composition of the aqueous solution.