SEM-EDS for determining the phosphorus content in activated sludge EPS

Not all phosphorus removed in activated sludge systems can be accounted for by polyphosphate accumulating organisms (PAO). A method for the qualitativ e and quantitative in situ characterization of PAO cell clusters and closel y associated extracellular polysaccharides (EPS) is described. X-ray microa nalysis was performed on samples from four activated sludge plants situated in Pretoria, South Africa. Analyses were done by means of Scanning Electro n Microscopy (SEM) combined with Energy Dispersive Spectrometry (EDS). Cell clusters with associated EPS on average contained between 57 and 59% phosp horus, while EPS alone contained on average between 23 and 30% phosphorus. Results suggest that phosphorus removal in activated sludge might be due no t only to PAO, but also by EPS acting as a phosphorus reservoir. Extraction of EPS from two different activated sludge plants yielded different amount s of EPS, which, in combination with SEM-EDS, may shed light on different p hosphate uptake abilities of different activated sludges.