CONTRIBUTION OF PRECIPITATED PHOSPHATES AND ACID-SOLUBLE POLYPHOSPHATE TO ENHANCED BIOLOGICAL PHOSPHATE REMOVAL

The amount of precipitated metal phosphates and the acid-soluble polyphosphate concentration were measured in several sludges and pure cultures of Acinetobacter strains. The percentage of metal phosphates of the total phosphorus content of the sludges varied between negligible and about 80%. Increasing ability to release phosphate anaerobically was frequently parallelled by a decreasing contribution of precipitated metal phosphates to the total phosphorus concentration in 10 different sludges. Sludges from fill and draw systems with over 100 mg P/g dry wt, were almost completely devoid of these precipitates. The same was true for polyphosphate-accumulating cultures of Acinetobacter. Besides high molecular weight polyphosphate, the sludges also contained low polymeric polyphosphates (LPP), ranging from 0 to 50% of the total phosphate content. The LPP fraction in polyphosphate-accumulating cultures of Acinetobacter strains was between 3 and 23% of their total phosphate content. Sludges developed in the fill and draw systems could release more than 50% of the accumulated phosphate within 60 min. About 66% of this phosphate originated from LPP. Pure cultures of Acinetobacter strains released less than 1 mg P/g dry wt in the same time. Reduction of phosphate release by an increase of the pH in the medium as a result of denitrification could only partly be explained by formation of precipitated phosphates.