Speciation of chromium(III) in activated sludge

Abstract

An understanding of the fate of metals in the activated sludge process is necessary. Such knowledge is needed to assess the potential adverse effects of metals that may be associated with activated sludge and ultimately discharged into the natural environment. As an example, an equilibrium approach was developed to quantify the distribution of trivalent chromium, Cr(III) in activated sludge. Cr(III) adsorption on activated sludge exhibited linear characteristics. Cr(III) formed a 1:2 complex with soluble organic compounds remaining in wastewater treatment plant effluents. Both pH and the mean cell retention time significantly affected Cr(III) adsorption and complexation. Intracellular Cr(III) uptake was estimated by comparing the observed overall Cr(III) uptake with the predicted Cr(III) adsorption. This comparison revealed that more Cr(III) is transported to the solid phase than predicted. The predicted speciation of Cr(III) suggested that intracellular Cr(III) accounted for more than 70% of the total Cr(III) in activated sludge. Thus, intracellular uptake was an important consideration.