RELEASE OF PHOSPHORUS FROM WASTE-ACTIVATED SLUDGE

The dynamics of Prelease from a primarily domestic waste-activated slu dge was investigated, More than 70% of the P in the sludge was in mine ral form, The inorganic rather than the organic fraction controlled th e release of P. Phosphorus release from soil-sludge mixtures into soil solution during 100 d of incubation was measured with and without a c orn (Zea mays L.) crop, in both a calcareous and a noncalcareous sandy soil. The kinetics of inorganic P dissolution from the sludge was als o measured in aqueous suspensions during 9 d of incubation. Sludge con centrations 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 exper iments 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 fr om that of hydroxyapatite to that of dicalcium phosphate dihydrate. Tr ansformations of N compounds in the sludge-containing systems had stro ng effects on the dynamics of P dissolution, mainly through the influe nce of the ammonification and nitrification processes on the pH and th e ionic strength and composition of the aqueous solution.