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 fracti onation (extraction) procedure for distinguishing chemically and biological ly stored phosphorus compounds in activated sludge. For this-purpose, it wa s necessary to select appropriate methods for measurement of total phosphat e(total P) and orthophosphate (orthoP) and to make approximations in respec t of the nucleic acid content of activated sludge. The selected fractionati on procedure appeared to be capable of broadly distinguishing between chemi cal and biological forms of. stored phosphorus-in activated:sludge systems. Satisfactory agreement was obtained with results for biological polyphosph ate (polyP)- accumulation predicted using a mathematical model applied to s uch systems. The recovery of chemical phosphate precipitate formed in vitro was found to be satisfactory, although me addition of metal precipitant ap peared to cause particular artefacts in the fractionation pattern which nee d to be taken into account when interpreting the data. It was concluded:tha t the chemical fractionation procedure developed would be useful for assess ing the relative sizes of biological and chemical phosphors "pools" in acti vated sludge simultaneously dosed with chemical precipitants (typically iro n or aluminium salts).