The speciation of metals in sewage and activated sludge effluent

A gel filtration chromatography technique was used to separate soluble species of Cd, Cu, Co, Mn, Ni, and TI in the influent and effluent of a laboratory scale activated sludge simulation operated at a range of sludge ages from 3 to 18 days. It was found that, whilst there was no general trend for all six metals, Cd and Mn associated mainly with low molecular weight fractions; Co, Cu, and Ni with a range of predominantly high molecular weight fractions; and TI tended towards association with high molecular weight fractions which influenced metal solubility and appeared to be significant in determining metal removal. It appeared that all metals exhibited high affinity for mixed liquor suspended solids (MLSS) and that this affinity was strongest for Cu and Cd. Nickel, Co, Cu, and TI appeared to show a high affinity for polymeric microbial products produced at longer sludge ages. The gel filtration technique was found to be useful in the separation of metal species in conjunction with a sufficiently sensitive detector provided their concentrations in the original sample were relatively high.