Combined effects of Ni(II) and Cr(VI) on activated sludge

The combined effects of Ni(II) and Cr(VI) on activated sludge kinetics were studied in this paper. The metals were added to a synthetic medium with a chemical oxygen demand (COD) of 1300 mg 1−1 to give various combinations of Ni(II) and Cr(VI). Activated sludge performance, in terms of COD removal, was not adversely affected in an acclimatized culture by the metal combinations, compared with the single metals. The combination effects of Ni(II) and Cr(VI) on biokinetic constants, i.e. the maximum specific growth rate, μm, was found to be stimulatory in general. The same effect was observed on the half-saturation substrate concentration, Ks. Effects were therefore classified as synergistic with respect to these constants.