Ultrafiltration (UF) is an alternative option that can be used to clarify glycerin-rich solutions in the oleo-chemical industry. However, the UF membranes used in the process were observed to have been seriously fouled in our preliminary study. Thus, the ultrafiltration of a glycerol-water-fatty acid mixture was carried out to investigate the membrane binding properties of the components and their contributions to membrane fouling. Palmitic, stearic, and oleic acid were used as fouling substances in the glycerol-water mixture. The flux decline experiments were carried out using polyvinylidenefluoride (PVDF) as well as polyethersulphone (PES) membranes with a MWCO of 30 and 25 kDa, respectively at specific conditions (T = 40 degrees C: Delta P = 2 bar). It was found that the PES membrane exhibited severe fouling for all types of fatty acids in solution with glycerol-water. As the pH decreased to acidic conditions, the PES membrane tended to exhibit more severe fouling than the PVDF membrane. (c) 2010 Elsevier Ltd. All rights reserved.