The mixture of olive-oil mill wastewater (OMW) and urban wastewater from secondary treatment (UWST) as culture medium was studied. Experiments were performed in a batch bioreactor on laboratory scale, using Scenedesmus obliquus CCAP 276/3A. In this sense, two experimental series were prepared. In the first, the culture medium was formed by 0%, 1%, 2.5%, 5%, 10% (v/v) of OMW added to UWST. In the second, a constant proportion (5% v/v) of bleached OMW was maintained and 0, 10, 25, and 50 (v/v) of UWST were added. From the experimental results, the highest values of maximum specific growth rate (mu(m) = 0.074h(-1)), volumetric biomass productivity (P-b =4 mg dm(-3) h(-1)), and net biomass generation (0.28 g dm(-3)) were determined in the culture formed by 25% (v/v) of UWST added to 5% (v/v) bleached OMW. The final biomass was characterized by an accumulation of energy-rich compounds, such as lipids and carbohydrates which are capable of being transformed into biofuels. (C) 2012 Elsevier Ltd. All rights reserved.