A Preliminary Study to Optimize the Managing of Waste and By-Products in a Small-Scale Olive Mill

Olive oil extraction process produce huge amount of by-products and waste. Furthermore, these are produced in a short period of time, not justifying the investment in expensive systems to be created for their disposal, especially in small/medium sized mills. Particularly, olive mill generates two types of waste. One is a solid waste called pomace, while the second one is wastewater. Olive oil wastes are considered highly pollutant and phytotoxic due to the presence of natural compounds like phenols. An improper disposal of wastewater on soil could results in a decreasing of water retention and infiltration rate, and could affect soil acidity and salinity. As for the pomace, this represents a by-product that can be reused as a raw material in a pomace factory. This depends greatly on the way in which the solid-liquid separation is carried out. Specifically, a three-phase decanter centrifuge produces a drier pomace than that obtained with a two-phase centrifuge. In the latter case, the pomace needs to be dried before sending it to the pomace factory. In this study, a preliminary feasibility was conducted to optimize the reuse of the by-products of a small/medium sized oil mill equipped with two extraction lines in parallel: one with a two-phase decanter, one with a three-phase decanter. The possibility of introducing a machine for concentrating the pomace leaving the two-phase process and a new line for wastewaters management has been evaluated. This relatively cheap solution would allow the entire dry pomace to be sent to a pomace factory and the wastewater, mixed to light solids, to a biogas plant as a new product identified as biphasic pomace. If the material balances are appropriately completed, this solution would make it possible to drastically reduce the waste coming out of a small/medium mill.