The use of simultaneous chemical precipitation in modified activated sludge systems exhibiting biological excess phosphate removal Part 2: Method development for fractionation of phosphate compounds in activated sludge

An experimental investigation was conducted into the use of a simple fractionation (extraction) procedure for distinguishing chemically and biologically stored phosphorus compounds in activated sludge. For this-purpose, it was necessary to select appropriate methods for measurement of total phosphate(total P) and orthophosphate (orthoP) and to make approximations in respect of the nucleic acid content of activated sludge. The selected fractionation procedure appeared to be capable of broadly distinguishing between chemical and biological forms of. stored phosphorus-in activated:sludge systems. Satisfactory agreement was obtained with results for biological polyphosphate (polyP)- accumulation predicted using a mathematical model applied to such systems. The recovery of chemical phosphate precipitate formed in vitro was found to be satisfactory, although me addition of metal precipitant appeared to cause particular artefacts in the fractionation pattern which need to be taken into account when interpreting the data. It was concluded:that the chemical fractionation procedure developed would be useful for assessing the relative sizes of biological and chemical phosphors "pools" in activated sludge simultaneously dosed with chemical precipitants (typically iron or aluminium salts).