Assessment of electrocoagulation as a pretreatment method of olive mill wastewater towards alternative processes for biofuels production

Abstract

In the present study, electrocoagulation (EC), alone or in combination with precipitation or centrifugation, was assessed as a potential pretreatment method for enhanced production of biofuels from 3-phase decanter olive mill wastewater (OMW). Experiments were performed using undiluted and diluted OMW in an EC reactor, operating with a current of 2 A and either Al or Fe electrode materials. Subsequently, diluted OMW was subjected to EC followed by precipitation or centrifugation. The effect of current density (0.05, 0.5 or 1 A) on the combined EC – centrifugation process was assessed and a high reduction of organics was observed for the higher current applied. The different fractions of the pretreated effluents were used as substrates for methane, hydrogen as well as for bioethanol production and the maximum energy recovery was determined in each case. It was shown that, EC at a current of 2 A or further combination with physical methods led to low biofuels yields. However, reduction of the current during EC to 0.05 A or 0.5 A, led to high methane and ethanol yields, with the best scenario being the production of methane yielding an energy equivalent of 1902 kJ/L OMW.