Effect of chromium (VI) on heterotrophic maximum specific growth rate (μm) in activated sludge systems

The effect of hexavalent chromium, Cr(VI), on the maximum specific growth rate, mu(m) of heterotrophic biomass was studied in batch tests conducting under high (=10) and low (<2) substrate to biomass ratios (S-0/X-0). The effect of sludge age and acclimatization of biomass to Cr(VI) on the bacterial kinetics was also studied. The mu(m) values were determined by measuring oxygen uptake rate (OUR) and volatile suspended solids (VSS) simultaneously. Concentrations of Cr(VI) equal or higher to 10 mg l(-1) inhibited severely mu(m) values. The acclimatization of biomass and the selection of high operating sludge age reduced the inhibitory effect of Cr (VI). Concentrations of Cr(VI) up to 10 mg l(-1) stimulated the mu(m) values of the microorganisms for sludge ages of 20 days.