Demulsification of oily wastewater by electrocoagulation in a batch cell with horizontally oriented electrodes was studied. The anode of the cell was an array of separated horizontal cylinders made of aluminium, the cathode was a rectangular aluminium plate placed on the cell bottom below the anode. The effect of pH, temperature, current density, and sodium chloride concentration on separation efficiency was studied. The suggested cell design was found to be more efficient than the traditional vertical parallel plate cell. The horizontal electrode cell could reduce oil concentration in wastewater from 500 to 6 ppm within 30 min (i.e. below the maximum permissible value which is 10 ppm) with a separation efficiency of 99.8%. The use of an anode made of horizontal tubes offers the advantage of using the inner side of these tubes as heat exchanger to control cell temperature if necessary. (c) 2008 Elsevier B.V. All rights reserved.