Treatment of acidic wastewater arising from the refining of vegetable oil by crossflow microfiltration at very low transmembrane pressure

The refining process of vegetable oils generates acidic wastewater with the following characteristics: pH (1–1.5), COD (10–30 g O₂ 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 μm) 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 h. With a 0.5 μm 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.