Black-olive wastewater is easily degraded by the completely mixed activated-sludge treatment system. The bio-kinetic coefficients are calculated from the two-level activated-sludge operational processes by using four influent-COD concentrations and four values of solids-retention time. The results indicate that the effluent-COD is related to the influent-COD concentration. Furthermore, the effluent COD is proportional to the product of the influent-COD concentration and the specific growth rate. The multiple-substrate model of Adams et al. gives a good prediction of the effluent COD under variable influent-COD concentrations.