Study of a demonstration plant for the co-composting of olive-oil-processing wastewater and solid residue

The co-composting of the solid residue and wastewaters from the olive-oil production process has been studied as a new method for the treatment of wastewater containing high organic and toxic pollutants. The experimental results for a demonstration plant using solid residue from olive extraction as bulking material and olive-oil-processing effluents as continuously fed wastewater are reported. Composting temperature was controlled between 45 and 65°C by air supply and the wastewater addition was fed mainly in order to keep the moisture in the range of 45 to 60% and secondly to replace the carbon substrate. During 23 days of operation in the thermophilic region, the system was fed with 263 m 3 wastewater in total, which means an average rate of 11.4 m 3/day wastewater or 2.9 kg wastewater per kg solid residue. The total bioenergy production was estimated to be about 90 000 000 kcal. Then followed a 3 months stabilization period in the mesophilic region until the final product reached ambient temperature.