An experimental study of olive mill wastewater (OMW) treatment is undertaken in an external ceramic membrane bioreactor (MBR). The main objective of this work is the study of OMW treatment feasibility using an MBR with a biomass specially acclimated to phenol. The used reactor, equipped with an external ceramic microfiltration membrane gave stabilized permeate flux, around 92 L h(-1) m(-2), with zero suspended solid and no phenolic compounds. No fouling problems occur during all the experiments. The short backpulse method adopted allows the use of the MBR in a continuous way. The chemical oxygen demand (COD) remains quite high, and its abatement improvement can be achieved by enhancing the oxygen transfer to the mixed liquor contained in the MBR. The combination of biological and membrane separation for the OMW treatment seems to be a serious alternative in the reduction of the environmental impact of the olive oil extraction processes effluents. The OMW treatment in a membrane bioreactor call be used as a pre-treatment stage, essentially for phenolic compounds removal before a conventional biological process. (C) 2008 Elsevier B.V. All rights reserved.