The refining process of vegetable oils generates acidic wastewater with the following characteristics: pH (1-1.5), COD (10-30 g O-2 L-1), suspended solids (7-12 g L-1) and fats (2-4 g L-1). In order to reduce the effluent load and recover a fraction of the fats without using any additives. a microfiltration (0.2-1.4 mu m) process involving ceramic membranes at very low transmembrane pressure values (0.1-1 bar) was assessed. Four batches of acidic wastewater from different manufacturing runs were tested. Trials with a constant volumetric reduction ratio of 30 were carried out for periods of more than 5 It. With a 0.5 mu m membrane it was possible to maintain a permeate flux of 100 L h(-1) m(-2) for 24 h and achieve a 91% reduction in SS, a 96% reduction in fat and a COD reduction of more than 60%. In addition, the retentate thus extracted separated spontaneously into two phases, both of which could be exploited: the upper phase mainly consisting of fats as a by-product and the lower clarified phase which could be mixed into the permeate. (c) 2006 Elsevier Ltd. All rights reserved.