PROJECT DESCRIPTION
BACKGROUND
High organic content process water from olive oil manufacturing (OMW - olive mill wastewater) represents one of the most important environmental problems in the Mediterranean region. During production of olive oil OMW, a high organic content wastewater, is generated as a liquid by product of mechanical extraction. With a chemical oxygen demand (COD) of 50 to 150 g/l, this wastewater has one hundred times the contamination potential of communal wastewater. The production processes employed in the manufacture of the oil have a significant impact on the amount and composition of the OMW. Evaporation ponds reduce the problem of OMW only marginally, and OMW is not suited for application on fields. Although its contents are a good fertilizer, negative affects on soil quality and ground water cannot be ruled out. Wastewater from olive processing contains valuable organic and mineral components that are extracted from the soil by the olive trees. One cubic meter of wastewater contains 50-80 kg of organic constituents and 20-30 kg of minerals, as well as 60-80 kWh of energy. This LIFE project investigated a technologically and economically suitable solution for the disposal of OMW.
OBJECTIVES
This project was to demonstrate the advantages of a economically viable, multi-use process for the exploitation of the solid and energetic components from olive mill wastewater (OMW). The ultimate aim is to minimise the extensive organic pollution of rivers and ground water, potential drinking water contamination risks as well as typical odours which are associated with oil presses. The core element of the technology was to be a multiple-stage anaerobic biological process. In this process, biogas obtained from the organic wastewater content would be converted into electrical and thermal energy (regenerative energy). In addition, high quality fertilizer and other valuable substances would be obtained from the residues. The purified wastewater would be used as process water or for the irrigation of agricultural land. It was intended that in the future the process would be available as an integrated solution for small and medium-sized oil presses, as well as the engineering basis for large oil presses or centralised disposal plants in the Mediterranean region. AquaTec, Dresden, was to develop this technology and be responsible for the engineering aspects of the demonstration plant. In addition, AquaTec would lead the scientific tasks related to the plant and be responsible for the further development and optimisation of the wider application of the process. WIP-Munich, a recognised research and technology establishment, would support the scientific tasks and be responsible for the exploitation of the results. The oil pressing company AFOI Boudourakis, Crete, which produces about 350 tonnes of olive oil per season, would in addition to its role as the industrial partner, also be the contact point for future users.
RESULTS
A demonstration system based on the AquatecOLIVIA process was erected in 1999 on the island of Crete and began operating at the beginning of the oil pressing season in November of the same year. The system operates successfully roughly 5 months out of the year and purifies the wastewater from an oil mill that produces approximately 400 tons per year of olive oil (three-phase decanter). The level of purification achieved is over 95%. It has been estimated that applying the technology would increase the price of olive oil by 3%. Expansion of the system to accommodate additional oil mills in the Apokorounou region was under planning at the end of the LIFE project. The technology consisted of three processing lines: 1) Wastewater purification 2) Sludge treatment 3) Biogas processing. 1) Wastewater purification In a mechanical-biological pretreatment stage, the wastewater is separated into dissolved and undissolved constituents, which reduces the organic load by 40- 60%. As an option, the remaining olive oil can also be separated in the wastewater of 0.5 - 1.5 Vol.%. Because the wastewater is generated for a short period of only a few months, economic considerations call for an intermediate storage solution. Existing pond or storage systems can be integrated into the solution. In a special anaerobic stage, up to 95% of the dissolved or undissolved constituents are removed from the wastewater and converted to biogas. The wastewater is treated subsequently in an anaerobic or membrane filtration stage to ensure the necessary discharge quality. This subsequent treatment can also be handled in an existing communal water treatment plant. The purified wastewater can be used for irrigation of agricultural land or as industrial process water, or fed into surface waters. 2) Sludge treatment During pretreatment the undissolved constituents of the wastewater are separated as sludge (OMW sludge) by sedimentation and, depending on the project concept, subsequently processed for energy or fertilizer. Where recovery of energy is the primary objective, the sludge is converted to biogas in the methane stage and subsequently dewatered and dried. One cubic meter of OMW sludge yields energy equivalent to 140 - 200 kWh of electrical power. For the production of fertilizing material, the OMW sludge is stabilized aerobically and solar-dried after pretreatment. The fertilizer (in the form of a powder or granulate) can be mixed with nitrogen and phosphorous sources, resulting in a purely plant-based potassium fertilizer with a high content of humus-building material. One cubic meter of wastewater yields 40 - 60 kg of fertilizer. 3) Biogas processing. Approximately 30 m³ of biogas can be produced from each m³ of OMW (COD approx. 100 g/l), from which roughly 70 kWh/m³ of electrical and 150 kWh of thermal energy or, where a cogeneration plant is not used and the biogas is used only thermally, 210 kWh of thermal energy can be generated. Simultaneous treatment of other organic waste or wastewater Other high organic content waste or wastewater such as in meat, vegetable, or fruit processing operations, are often generated in the disposal areas of the oil mills and can be removed and handled in a treatment system that uses the AquaTecOLIVIA technology.
