A pilot plant using ceramic microfiltration membranes which could be regularly back-flushed with air for fouling control was evaluated for the treatment of spent cutting-oil. It was found that membrane fouling could be effectively controlled with regular air back-flushes (every 3 min for 1 s) and chemical cleaning using caustic soda. Permeate flux remained approximately constant and varied from 78 to 126 ./hEm2 for the first six runs and from 114 to 150 ./hEm2 for three more runs. An increase in feed temperature from ambient to 40‹C and cleaning of the membrane with 1% caustic soda, increased permeate flux from 183 to 282 ./hEm2 and from 195 to 264 ./hEm2 in two more runs. Excellent COD (75.5 to 90.3%) and O&G (97.2 to 99.1%) removals were obtained. The permeate quality should be suitable for discharge to the municipal sewer system (O&G < 500 mg/.) and the concentrated oil should be a useful energy source. Treatment of spent cutting-oil with microfiltration rather thanlandfilling should save valuable landfilling space.