In this study the wastewaters generated from a water-based paint industry have been investigated with respect to their chemical treatability. As the industry under consideration currently houses sludge drying beds and a chemical treatment facility that consists of an equalization basin, a rapid mixing tank, a slow mixing tank and a sedimentation unit, the main objective of the study was to find out the optimum sodium bentonite dosage applicable to meet the effluent discharge standards by using the existing treatment plant. A wastewater volume of 0.23 m(3) per ton of water-based paint is produced by the process. The achieved pollutant removal efficiencies, sludge characteristics and calculated running costs covering sludge disposal and expenses of chemicals used show the introduction of a bentonite dosage of 500 mg/l at the original pH of the effluent as the optimum treatment alternative. The last part of the study is dedicated to evaluate the effect of optimum bentonite application on COD values of different molecular weight cut-off fractions. The results obtained indicate approximately 62% of the COD originated from the fraction over 1.2 mum, where highest COD removal efficiency is achieved with sodium bentonite.