Effluent derived from the washing of virgin olive oil in a new manufacturing process was found to be readily treated using a completely mixed activated sludge process. The biokinetic coefficients for the process were derived by operating laboratory-scale plant at four different input chemical oxygen demand (COD) concentrations and four differing solids retention times. Results showed effluent COD to be correlated with input feed strength and proportional to the product of feed strength and specific growth rate. The multiple-substrate model of Adams et al. fitted the data well and could be used predictively to determine effluent COD from a wide range of input substrate concentrations.