An attempt has been made to remove chemical oxygen demand (COD) from olive mill wastewaters (OMW) as well as oil-grease and turbidity in the presence of H2O2 and polialuminum chloride (PAC), as a coagulant-aid by an electrochemical method using either iron or aluminum as sacrificial electrodes. The effects of current density, electrode material and polarization, amount of hydrogen peroxide using as an oxidizing agent and addition of coagulant-aid, on percent removal and energy consumption have been investigated. According to the results, Fe was determined more effective than Al as an electrode. The removal efficiency of COD was in the range of 62-86% whereas oil-grease and turbidity removal was 100% at the current density range of 20-75 mA cm(-2) depending on the concentrations of H2O2 and coagulant aid. It is obtained that the electrocoagulation in the absence of coagulant aid and oxidant is not too efficient for the treatment of this type of wastewater. The polarity of the electrodes played an important role in the treatment of OMW. (c) 2006 Elsevier B.V. All rights reserved.