Ultrafiltration has been accepted as a highly attractive separation process to treat oily wastewaters. The use of ultrafiltration is particularly interesting for the treatment of stable oil-in-water emulsions, such as cutting oil emulsions, since the value of the recovered solid oil waste is high. However, the efficiency of ultrafiltration is limited by membrane fouling and concentration polarisation, resulting in a permeate flux decrease, and therefore, increasing energy consumption of the process. The aim of this study was to investigate the potential for energy saving in cross-flow ultrafiltration of a stable oil-in-water emulsion by using a static mixer as a turbulence promoter. Experimental investigations were performed on a zirconia membrane with a nominal pore size of 20 nm using the Kenics(TM) static mixer as a turbulence promoter. The reduction of the specific energy consumption of over 40% accompanied by the flux increase of up to 600% has been observed during ultrafiltration of fresh cutting oil. Furthermore, the results showed the way how operation parameters should be selected in order to achieve optimal process performance of the ultrafiltration with inserted static mixer. (c) 2007 Elsevier B.V. All rights reserved.