Metal removal by adsorption and precipitation in the activated sludge process

Abstract Metal removal in the activated sludge process has been determined by adding metals to samples of mixed liquor developed in a synthetic sewage, followed by separation of soluble and particulate forms of the metals using membrane filtration. The importance of precipitation in metal removal was evaluated by adding metals to mixed liquor filtrates and removing precipitates by filtration. The removal efficiencies of Pb, Cr(III) and Cu, to a lesser extent, were unaffected by changing sludge age or increasing metal concentration due to their low solubility. The predominantly soluble metals responded to sludge age in similar ways, with maximum removal generally occurring at a sludge age of 12 days. The percentage removals of the soluble metals decreased as increasing concentrations were added, but there was no evidence of saturation of the biomass. Experiments undertaken to investigate synergistic or antagonistic reactions between metals indicated that competition for activated sludge binding sites did not occur to any significant extent, but some interactions between metals having a tendency to precipitate were observed.

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