BACKGROUND Biodiesel produced from renewable energy sources has gained significant attention in the arena of fuel diversification from fossil sources. However, the conventional treatment to separate biodiesel from glycerol produces large volumes of wastewater, causing environmental concerns. The present study aims to assess ceramic membrane technology for improving biodiesel separation and purification, and overcome the traditional process constraints. RESULTS Biodiesel was obtained by ethylic transesterification of crude, degummed and refined soybean oil. The tangential ultrafiltration (alpha-Al2O3/TiO2) performance in separating and purifying the produced biodiesel was evaluated based on the glycerol retention capacity and on the permeate flux values. The separation was improved by use of acidified water [0.5% and 1% (m/m)] which promoted the demulsification of the reaction final mixture. In the proposed system, the glycerol was retained, and the biodiesel was the continuous phase. Higher free fatty acid content in the crude and degummed soybean oil, not only favoured the glycerol transfer over the aqueous phase, which was retained by the membrane, but also resulted in the lowest flux decline rates. An increase in the oil acidity reduced the consumption of acidified water. As the pore diameter (0.05 mu m and 20 kDa) and the transmembrane pressure (1 and 2 bar) decreased, the glycerol retention increased allowing the system to fulfill commercialization requirements. CONCLUSION The results of this study showed that the novel ultrafiltration process is efficient in separating biodiesel from glycerol and reducing wastewater generation when compared with the conventional process. (c) 2020 Society of Chemical Industry