Waste oil serves as a heating oil substitute for industrial processes. Existing pretreatment of oil residues must be improved for a better combustion performance. Subsequently, the results of a dead end and cross-flow filtration for a waste oil refinement, following the conventional pretreatment, are given. Dead end filtration was performed in bench scale only. Different materials, pore sizes and pressures were tested. Due to the high particle load in the used oil, for dead end filtration, no successful results were obtained. Cross-flow microfiltration with a bench scale module and ceramic tubular membranes from different manufacturers provided acceptable results. Based on these encouraging findings, the scale up for the cross-flow filtration to the pilot plant scale was realized. Membranes from the best performing manufacturer (TAMI) at pore sizes of 300 kD as well as 0.14 mum were investigated. The ash content of the burned waste oil permeate was found to decrease by 55-75% compared to the conventional waste oil. Applied temperatures were about 60degreesC, cross-flow velocities 4-4.5 m/s and transmembrane pressures about 300 kPa. (C) 2004 Elsevier B.V. All rights reserved.