Combined bioremediation and advanced oxidation of green table olive processing wastewater

A novel method has been developed for the treatment of green table olive processing wastewater, which combines biological treatment using a selected strain of Aspergillus niger and electrochemical treatment in the presence of H2O2. Results are reported for the different stages of the scale-up procedure, from laboratory shake-flask cultures to a pilot plant of 4 m3/day capacity. In the biological treatment step COD removal efficiency varied between 66-86% while the concentration of selected phenols was reduced by 65%. The efficiency of the electrochemical step depended on pH and the concentration of H2O2 used. In laboratory experiments using a 500 ml electrolysis cell, 96% removal efficiency was achieved for both COD and measured phenols with 2.5% H2O2. In the pilot plant 75% COD removal efficiency was achieved with 1.6% H2O2. Coagulation with Ca(OH)2 finally gave an effluent COD of 360 mg/l and an overall removal efficiency of 98% for the combined treatment.