The purpose of this investigation was to conduct batch and continuous flow laboratory experiments with bench scale activated sludge units to determine the effects of nickel on the completely mixed activated sludge process. The model units were located in a constant temperature room maintained at 20±2°C. The batch reactors were operated under acclimated and shock loaded condition with various nickel concentration to determine its effects on the rate of COD removal. The continuous flow units were operated until steady state conditions were obtained at each mean cell residence time studied and then data were recorded for an approximate 7 days period and averaged to obtain one steady state data point. Nickel was added to the waste water at various concentration to determine its effects on COD removal efficiency, degree of nitrification and on the biokinetic constants Ymax and kd.Ph. D.