Olive Mill Wastewater Treatment by Membrane Operations

The extraction of olive oil generates huge quantities of wastes having a great impact on land and water environments because of their high phytotoxicity. Pressure and three-phase centrifugation systems produce a liquid effluent called olive mill wastewater (OMW). Several waste management approaches, including physicochemical treatments (natural evaporation, treatment with lime and clay, oxidation), agronomic methods (land spreading), animal breeding, and biological treatments (both aerobic and anaerobic) have been proposed to reduce the polluting load and, consequently, the final waste disposal. The efficiency of the process, the complexity, and the costs involved may vary remarkably. In addition, different legislations existing in olive-oil producing countries play an important role in the selection of appropriated technologies. Pressure-driven membrane operations, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) have been proposed and combined in integrated processes to obtain effluent streams from OMWs of acceptable quality for safe disposal into the environment (surface water or soil) for irrigation or even for recycling and use in the olive mill. Basically, MF and UF processes are used for primary treatment purpose, while NF and RO are used for final treatment (Cassano et al. 2013; Paraskeva et al. 2007). Integrated systems based on the use of these processes permit to obtain a COD reduction of about 99 %, the recovery of high percentage of purified water (60-70 %) (permeate of RO membranes), a production of an organic fraction (retentate of MF and UF membranes) which can be submitted to anaerobic digestion for the production of biogas, the recovery of a phenolic fraction (retentate of NF and RO membranes) of potential interest for food, phytotherapic, or cosmetic applications.