Composting the two phase olive oil mill residues

During the few last years 2-phase centrifugation is replacing both the traditional press technology and the relatively recent 3-phase centrifugation in the olive-oil extraction industry. Press and 3-phase centrifugation systems were unavoidably connected with the production of large amounts of highly polluting wastewater. Although the new, 2-phase systems do not produce wastewater, they have led to the formation of a new type of waste, the "alpeorujo". Alpeorujo is moist, almost slurry in texture and poses problems of transport, drying or solvent extraction. In addition, a second centrifugation often applied in 2-phase systems of olive extraction, leads to the production of another slurry-like waste, the olive pulp. The chemical composition of these wastes is suitable for composting, but their physical structure and lack of porosity do not allow this treatment approach. The addition of woody materials or straw as bulking agents is not feasible in most cases, as they are not usually available in the vicinity of olive producing areas. In this project a self-sustained fed-batch composting process was developed for alpeorujo, which does not require the addition of bulking materials, apart from the set up of the process, as it effectively recycles fresh compost into the staring mixture. The compost produced is of high agricultural value, as phytotoxic compounds such as polyphenols and soluble sugars are degraded, while it is rich in organic and inorganic compounds, especially potassium.