Complete treatment of olive mill wastewaters by electrooxidation

Laboratory scale electrochemical experiments on a olive mill wastewater (OMW) were performed to obtain discharge quality which meets the regulations requirement without any pre- or additional treatment. The process has been examined through the dependence of chemical oxygen demand (COD), oil-grease, phenol and turbidity on electrolysis duration. The influence of current density (25, 45, 65, 75, 85, 105, 135 mA cm−2), sodium chloride concentration (1, 2, 3, 5 M), recirculation rate of OMW (1.1, 4.6, 7.9 cm3 s−1) and temperature (7, 20, 40 °C) on the rate of pollutants abatement and the response of the system and specific energy consumption were evaluated. Based on the results obtained from laboratory experiments, the removal rates of organics increased with the increase of applied current density, sodium chloride concentration, recirculation rate and temperature. The results also indicated that specific energy consumption (SEC) ranged between 5.35 and 27.02 kWh (kg COD)−1 decreased with increasing NaCl concentration, recirculation rate and temperature whereas it increased with increasing current density. The initial COD concentration of 41,000 mg L−1 was reduced to 167 mg L−1 (corresponding to 99.6% removal) which complies with legal requirements while almost complete conversion of phenol, 99.85% turbidity removal, 99.54% oil-grease removal were achieved with the running cost of 0.88€ (kg COD)−1 after 7 h electrolysis at the conditions of 135 mA cm−2, 2 M NaCl, 7.9 cm3 s−1, 40 °C.