Olive oil mill wastewater treatment by means of electrocoaculation with punts aluminium electrodes
Olive mill wastewater (OMWW) generated by the olive oil extraction process is the main waste product of this industry. These effluents have been characterized, followed by an experimental study of the elimination of organic matter (chemical oxygen demand (COD), phenolic compounds, suspended solids (SS) and colour), mineral matter (phosphate and ammonium nitrogen) and heavy metals (zinc and iron) using an electrocoagulation technique with aluminum electrodes. It was found that an increase in electrolysis time and voltage improved treatment significantly. However, a simultaneous increase in electrode and energy consumption was observed. The results of these analyses showed that the olive mill wastewater (OMWW) effluent, diluted five times, is acidic (pH 4.2), has a very high organic matter concentration (chemical oxygen demand (COD) 20,000 g•L‐1) and is high in salts (Electric Conductivity E.C = 3.6 mS•cm‐1), ammonium nitrogen (NH4+) (32 mg•L‐1) and orthophosphate (PO43‐) (22 mg•L‐1). The OMWW also contains considerable amounts of heavy metals, in particular zinc (3.69 mg•L‐1) and iron (13.80 mg•L‐1). The trend in physicochemical parameters during the electrocoagulation treatment shows that, after 15 minutes of electrolysis using an electrical voltage of 20 volts (corresponds to 250 A•m‐2), the discolouration of the OMWW, diluted five times, lay between 96-99%, the reduction of the chemical oxygen demand (COD) was approximately 80-85%, the reduction of phenolic compounds was approximately 75‐80%, the elimination of colloidal material (suspended solids) reached 7-8 kg•m‐3, the reduction of orthophosphates was 94-99% and the reduction of ammonium was 80-85%. The reduction of zinc was 70-75%, the reduction of iron was 71-76%, the electrode consumption was 0.6-0.7 kg•m‐3 and the amount of energy consumed was 12-14 kWh•m‐3. Under these optimal operational conditions, acceptable degradation of the OMWW was achieved.