The role of extracellular exopolymers in the removal of phosphorus from activated sludge

Bio logical phosphorus removal in activated sludge systems is thought to be a result of the action of polyphosphate accumulating organisms (PAO). Howe ver, not all phosphorus removed can be accounted for by PAO. A method for t he qualitative in sim characterization of PAO cell clusters and closely ass ociated extracellular exopolymers (EPS) is described. X-ray microanalysis w as performed on samples from two activated sludge plants situated in Pretor ia, South Africa. Analysis was done by means of scanning electron microscop y combined with energy dispersive spectrometry (EDS). Cell clusters with as sociated EPS, on average, contained between 57% and 59% phosphorus, while E PS alone contained, on average, between 27% and 30% phosphorus. Results sug gest that phosphorus removal in activated sludge might be due not only to P AO, but also by EPS acting as a phosphorus reservoir. (C) 2001 Elsevier Sci ence Ltd, All rights reserved.