Disposal and Management
From the Book of M. Niaounakis and C.P. Halvadakis " Olive Processing Waste Management-Literature Review and Patent Survey", Waste Management Series No 5, Elsevier, 2nd Ed. 2006.
The terms used for olive-mill wastes are neither standardized nor country specific. This causes some confusion in the publications which makes it sometimes difficult to identify clearly the particular by-products concerned. The Spanish term for OMWW is alpechín; the name alpechín, comes from the Latin faecinus, and alludes to the latter characteristic. Other Spanish terms such as murga, morga or amorca as well the French term margine come from the Latin amurca, which means stinking juice. The Italians refer to OMWW as acqua di vegetazione, while the covered basin in an olive-mill (generally underground), where OMWW is collected and stored, is called inferno or hell. The Turks refer to it as kara su or black water, due to its appearance; the Arabs call it zubar, and the Greeks call it liozumia or olive juice (in Crete they call it katsigaros).
Current Practices for Olive Processing Waste Management
The largest average annual production of olive oil in Spain comes from the Region of Andalusia, where are located most of the 1700 olive-mills that operate in Spain. Andalusia has more than 1.5 million hectares of olive trees. The number of olive orchards in Andalusia is 320.354, the 44% of which are located in Jaén (the darker green provinence in the map).
In Andalusia the most common size of olive orchards is between 1.0 and 5.0 hectares (47% of total farms and 24% of total olive trees surface in Spain).
Until the year 1980, the majority of olive-mills were traditional press systems and evaporation ponds were used for the liquid effluent. In the early 1980s, the three-phase extraction system started to dominate. In 1982, in Spain a law forbade river disposal of OMWW and subsidized construction of storage ponds to promote evaporation during the summer period. Around 100 evaporation ponds were constructed, which improved the water quality, but raised annoyances in ambient air quality because of odor problems. In 1992, the two-phase extraction system was introduced in the region of Andalusia. Nowadays, almost all olive-mills in Spain use two-phase centrifugal decanters. There is still some liquid effluent from the process, but existing evaporation ponds are more than adequate to handle it. Since olive-mills have already started to use water recycling, it is expected that eventually most of the evaporation ponds can be closed down. However, the semi-solid residue(TPOMW or 2POMW) has reached an amount of more than 4 million tons/year and a lot of effort has been put on finding a solution for its management.
Although there is an absence of a definite valorization strategy,the most common practices for TPOMW management in Spain are second extraction for energy recovery, composting and use in agriculture, disposal in evaporation ponds, and use of wastes for animal feeding.
The use of TPOMW for energy recovery by applying second extraction of residual oil is the most accepted technology and the first treatment option in Spain. However, the high poisture content of TPOMW makes the extraction difficult when performed in classic extraction plants and intial drying in power plants is considered necessary. Co-generation power plants use natural gas to produce electricity. The thremal energy produced during combustion is used for TPOMW drying. After this stage the dried wastes can be used for 2nd oil extraction. After the residual oil extraction, the oil-free wastes ares old for energy production or used as biomass in the same plant
Up to 300.000t of TPOMW are treated annualy by this technology while it is estimated that the treatment cost per kg of TPOMW is 0,012€ + VAT + transport costs to plant
In Italy, 5000–6000 olive-mills are operating with most common extraction technology still based on simple pressure. Italy is the only olive oil producing country with a special legislation for the disposal and/or recycling of olive processing wastes. Land spreading of wastes arising from olive processing is specifically regulated under the Law no. 574 of 11/11/1996 on OMWW and olive cake. However, the prescriptions of the law have been criticized because they make the inspections quite difficult as the regional and provincial authorities, from which the inspection depend, do not know the exact dates and places of the spreading. A typical disposal scheme applied in Italy for the treatment of olive-mill wastes is outlined here.
Almost the 70% of the Greek olive oil mills are of a three-phase centrifugal type and the rest of classical type or combinations thereof. In addition, there are 40–45 (active only 32) seed-oil extraction plants, more than 200 enterprises of standardization-packaging plants and around 25 refineries. There are only a very small number of olive-mills that uses two-phase centrifugal decanters. Some olive oil producers tried this technology, but they had to abandon it because there was no viable alternative for the management of 2POMW, while the existing extraction plants cannot handle it and do not accept it. In Greece there is no specific regulation regarding the discharge of OMWW. The olive oil producing prefectures have their own environmental requirements and, on the gained local experience and the results of sponsored research projects, they encourage different waste management approaches. Nowadays, the issuing of an olive-mill operation permit is subject to measures taken to treat the olive-mill waste. More specifically, the Prefecture of Lesvos has stipulated that OMWW must be pretreated with lime before disposal in the natural recipients. However, this solution was not enforced and the olive-mills were granted a two-year extension of the validity of their operation permits. The Prefecture of Chios decided to construct open ponds, large enough to accommodate the entire quantity of wastewater produced in one olive cultivation season. Twelve of the fourteen olive-mills on the island dispose of their wastewater in such mud ponds. The Prefecture of Samos has granted all its olive-mills a two-year extension with regard to issuing an operation permit. Meanwhile, a wastewater management technique is due for evaluation for real-scale application by an olive-mill on Samos. This method — proposed by Professor Georgacakis D. of the Agricultural University of Athens — initially includes pretreatment/fractionization of OMWW by natural sedimentation. Separate management of the individual fractions then takes place. A general conclusion drawn from research to date is that there is no single technical solution that can ensure a satisfactory level of treatment efficiency whose application cost will be within the economic means of each individual olive-mill owner. This conclusion accounts especially in the case of Greece, given its geographical distribution and the size of its olive-mill plants. In other parts of the country, evaporation ponds (lagoons) are commonly used for the treatment and disposal of OMWW, optionally after neutralization with lime. In practice, all the generated OMWW results in creeks (58%), or in sea and rivers (11.5%), or in soil (19.5%).
In Turkey too, there is no specific regulation regarding the discharge of OMWW. The Turkish water pollution control regulation oversees protection of the water resources against pollution and sets discharge standards both for protection of the receiving media and for effluents of olive-mills. The biggest and main obstruction for the safe disposal of OMWW is that olive-mills are small and scattered in a large geographical area. In regard to solid olive-mill waste, the Ministry of Environment in Turkey has permitted the combustion of dried solid cake only in olive-mill beginning in 2003, with the condition that the gas emission limits are met.
In Tunisia, a common way of dealing with OMWW is to convey it from the mills to a central point and discharge it into a purpose-built lagoon. Here, the volume reduces by evaporation, providing that the lagoon base has been sealed (thereby preventing possible groundwater contamination); this can be a very reasonable way of containing the problem. Recently, in the Sfax area of Tunisia, a new facility has been built to receive OMWW. Four lagoons have been constructed with a combined surface area of 50 ha and a total storage capacity of 40,000m3. A charge of around 7 Tunisian Dinars per ton of OMWW is levied for reception at these lagoons.
In Portugal there are around 1000 olive-mills most of which use the traditional discontinuous pressing process, although over the last few years several units have introduced continuous solid–liquid centrifugation systems. The olive oil sector has been subject to a specific intervention that started in 1997 and was completed in 1999 with the signing of an agreement. Both the Ministry of Environment and the Ministry of Agriculture were involved, while the agreement was technically supported by a University that did exhaustive characterization of the sector, studied technical solutions for OMWW and performed cost–profit analysis for their implementation. The olive-mills are subjected to monitoring under the agreement and the new legislation that has been produced (regulation for the use of OMWW in irrigation, interpretation for excluding the olive cake from classicization as ‘‘waste’’ and selection of representative sample for air emission characterization). The use of OMWW for irrigation is also subject to restrictions similar to those applicable in Italy. Namely, the limits for the spreading of OMWW on soil for agricultural use are 50m3/ha/y from a traditional press system and 80m3/ha/y from the three-phase centrifugation system. Furthermore, it is forbidden to spread within 300m from a drinking water source; within 200m from a habitation center; over territories where in the same moment some crops are being grown; over soils where there may be any kind of contact with groundwater, or where the groundwater flow is within 10m from the surface. It is also forbidden to discharge in surface waters and in the sea.
The annual olive-oil production comes from four regions: Provence-Alpes-Coˆ te d’Azur (61%), le Languedoc-Roussillon (17%), Rhoˆ ne Alpes (12%), and Corse (10%). In France there are more than 25,000 olive farms and 152 mills and cooperatives. Land spreading is the disposal practice most commonly used in France. The creation of evaporation ponds has been encouraged as an alternative disposal treatment. The construction costs of an evaporation pond are subsidized up to 30% by the Water Agency and supplementary by regional and departmental authorities. The norms of construction of evaporation ponds are regulated by a ministerial decree concerning the pollution control of farming effluents (JO 21/03/2002).
There are 35 olive-mills in Cyprus today, with an average capacity of 1000 tons of olives per year, producing around 7500 tons/year of olive oil. Due to the small size of olive-mills in Cyprus, it is rather unreasonable to assume that each mill will have its own liquid waste treatment facility. Existing permitting system provides for liquid and solid waste conditions. Since facilities are SMEs they do not have to comply with Emission Limit Values (EVLs) relevant to treatment of wastes. The permit conditions are based on techniques/practices rather than treatment technologies of the wastes. The most useful practice is the storage of OMWW in artificial ponds and remaining there for evaporation (evaporation rate is about 550mm per year). Most of the plants are situated in the peripheries of villages. No discharge in the sea or in the surface waters and rivers is allowed. It is estimated that 95% of stones are used for heating, 85% of OMWW are stored in ponds and/or discharged to soil and, approximately 10% are discharged in central industrial treatment facilities, especially constructed and operated for SMEs.
There are about 4 million olive trees, covering 16,000 ha — 94% private farmsteads, 0.5% of total planted agricultural land — and 41,000 olive growers. During recent years, the annual production of olive oil ranges from 2000 to approximately 5000 tons/year. There are 86 olive-mills most of which use two-phase systems. There is no seed-oil extraction plant and 2POMW is usually applied to the soil as conditioner/compost.
There are presently five olive-mills in operation: two of these mills have a productive capacity of 0.5 and 0.4 tons/ha, respectively; the largest mill has a productive capacity of 3.5 tons/ha; and the two smaller ones have a productive capacity of 0.15 tons/ha each. The viable amount of olive oil that can be produced locally in the existing mills is estimated at 1052 tons. It is a typical practice in Malta to recycle the generated olive waste. The crude olive cake is left to dry and then it is mixed with natural manure for composting and used as fertilizer in the farmer’s fields. Some of it is left in a cylindrical form and wrapped in newspapers to absorb water and then dried. This is in turn used as combustion fuel, instead of wood logs. OMWW produced from the traditional plant is sprayed back in the orchard. The operation of an olive-mill requires: (i) planning permit — for the building up of the pressing room; (ii) Public Sewer Discharge Permit — this binds them with the following effluent limit values as established in LN 139 of 2002 and the Sewerage Master Plan for Malta and Gozo - November 1992. In the case of non-compliance, a fine of 240 E ‘‘for every day the default continues after the expiration of the said time’’. In any case, no mill raised any complaints from the public. In short, the olive oil sector in Malta, being a cottage industry, generates relatively small amounts of waste, which is reused within the same industry.