Electrochemical mineralization of anaerobically digested olive mill wastewater

Abstract

A novel approach was developed for the energetic valorisation and treatment of olive mill wastewater (OMW), combining anaerobic digestion and electrochemical oxidation. The electrochemical treatment was proposed as the final step to mineralize the remaining OMW fraction from the anaerobic reactor. The electrooxidation of anaerobically digested OMW was investigated over dimensionally stable anodes (DSAs). RuO2 based anode was significantly more efficient than IrO2-type DSA, mainly for the COD removal. IrO2 based anode promoted a selective oxidation of phenols and colour removal. For instance, after an electrolysis charge of 10.4 × 104 C L−1, COD removals of 14 and 99%, phenols removals of 91 and 100% and colour removals of 85 and 100% were obtained for IrO2 and RuO2 DSAs-type, respectively. The electrochemical post-treatment was effectively performed without using a supporting electrolyte and in the presence of the solids that remained from the anaerobic process. The achievement of the required effluent quality for sewer systems disposal depends on the operating conditions of the anaerobic process. Consequently, special care must be taken with the chloride and nitrogen levels that may surpass the legal discharge limits. The electrochemical oxidation over RuO2 based DSA is an appropriate second-step treatment for OMW disposal, after the recovery of its energetic potential.