Effect of temperature and aeration rate on co-composting of olive mill wastewater with olive stone wooden residues

Co-composting of the solid residues and wastewater from the olive oil production process was examined as a potential bioremediation treatment for these wastes. Experimental results from a semi batch laboratory pilot plant were reported. Composting was performed for 20 days under constant moisture 40% and the temperature ranged from 55 to 72°C and the oxygen partial pressure from 10 to 17%. An operational region of temperature and oxygen partial pressure was defined in order to achieve a ratio of total olive mill wastewater consumption to olive stone wooden residue stabilization equal or greater than 2.5, the typical ratio for an olive mill plant. Another critical parameter for the optimisation of the 20-day co-composting process that was examined was the biological efficiency of the process, as the carbon dioxide produced to the total carbon available to biomass. A strong sigmoid correlation of co-composting efficiency with temperature derived, reaching a maximum plateau of 0.50 at 68°C. The optimum conditions for a 20-day semi batch co-composting proved to be 68°C and 16–17% oxygen partial pressure, indicating that this process could be an integrated treatment scheme for olive mills.