Effects of cadmium on the completely mixed activated sludge process

A laboratory study was conducted to measure the effect of cadmium on chemical oxygen demand removal efficiency, degree of nitrification, and on the kinetic coefficients Y(max) and b. Data were obtained from the operation of bench scale reactors which were fed 0, 5.15, and 9.98 mg/l solutions of cadmium. Mean cell residence time was used as the primary operational control parameters and values between approximately 3 and 15 days were used to obtain data. The chemical oxygen demand removal efficiencies for the reactors containing cadmium were slightly less than those obtained for the control reactor. No distinguishable difference was obtained for the kinetic coefficients Y(max) and b. Nitrification, however, was found to be significantly altered in the presence of cadmium. Results clearly show that the degree of nitrification decreased as cadmium concentrations increased at a given mean cell residence time.