Composting of three phase olive mill solid waste using different bulking agents

Pilot-scale experiments were carried out to produce good quality, low-cost composting technology from three phase olive mill solid waste (olive pomace, OP) using rice husk (RH) and olive leaves (OL) as bulking agents. A series of parallel experiments was carried out to examine the effect of: (a) initial moisture content, (b) water addition during the composting process, and (c) material ratios. To monitor the composting process and evaluate compost quality, physicochemical parameters (temperature, moisture content, pH, electrical conductivity, organic matter, volatile solids, total organic carbon, total nitrogen, total phosphorus, potassium, sodium, and water soluble phenols) were measured at different phases of the composting period. Experimental results showed that even after short composting periods, the quality of the final product remained high. To achieve higher quality of the final product, OP should be used in higher quantities than the other two materials (OL and RH). A full-scale compost unit was designed based on the experimental results. For a typical small-sized olive mill, processing 30 tonnes of olives per day for a 90 days operation period, a total area of about 500 m2 is needed to compost the mill's entire waste production.