A novel process has been developed at pilot scale for the treatment of olive mill wastewater (OMW), which combines electro-Fenton, anaerobic digestion and ultrafiltration. Application of electro-Fenton procedure in semi-continuous mode permitted high removal efficiencies of chemical oxygen demand (COD) (50%) and monophenolic compounds (95%). This pre-treatment was found to enhance the anaerobic activity of an up-flow anaerobic filter (3001) significantly. In the bioreactor, COD removal efficiency of 75% was reached at a hydraulic retention time of 4.5 d and an organic loading rate of 10 g CODI-1 d(-1). The use of ultrafiltration technology as a post-treatment completely detoxified the anaerobic effluent and removed its high molecular mass polyphenols. An economic calculation of this treatment process revealed that a surplus of energy of 73.5 kWh could be recovered after the treatment of 1 m(3). (c) 2008 Elsevier B.V. All rights reserved.