1.     Olive oil production in the North Aegean Region

2.     Olive mill waste and treatment methods

3.     Legislation in force regarding the Disposal of Olive Mill Waste  

Olive oil production in the North Aegean Region

For many centuries olive oil production has been a particularly developed practice on the islands of the North Aegean. The high economic growth the island economies enjoyed from the 19th century until the beginning of the 20th century is largely attributed to the flourishing olive oil production sector. This economic growth was due to the fact that the olive products (olive oil, pomace, soap) were of significant economic value on one hand, and that a particular trading relationship, based on these products, was developed between the N. Aegean islands and the coasts of Minor Asia and Istanbul. Even today olive production plays a leading role in the economy of most islands which is confirmed by its contribution to the GDP. On Lesvos for example, the olive industry accounts for 3,6% up to 15,3% of the GDP, depending on the olive-growing period. 

There are 107 olive mills in operation in the Northern Aegean Region; 71 of these are found on Lesvos, 14 on Chios, 13 on Samos and 9 on Ikaria island. Most of the olive mills are of a relatively low capacity (between 1,5 and 2,5 tons of olives per hour) and are scattered all over the island. About 75% of them are located within settlements. The dominant type of olive mill is the centrifugal type with the exception of only 4 olive mills on Chios and Ikaria, that apply the traditional hydraulic press process for olive oil extraction. On Lesvos 55% of the olive mills are co-operative based, unlike the case on other islands where almost all of the olive mills are privately owned.


Olive Mill Waste Treatment Methods

A number of by-products are produced during the olive oil production process. These are the pomace, which consists of mainly the pits of the fruits and solids after pressing,  olive leaves, that are carried away with the olives as the latter are being collected, and a significant quantity of vegetable water of high organic load, known as “liozoumi”, “katsigaros” or “mourga”.

The vegetable water or  “katsigaros” (OMW) consists of the liquid fraction of the olive juice and the water used during the different phases of olive mill processing. Essentially it is an aqueous vegetable extract, containing a number of substances such as sugers, nitrogenous compounds, organic acids, polyalcohols, polyphenols and oil residue. The direct impact that vegetable water has on the environment is the aesthetic degradation caused by its strong odor and dark color. Furthermore, due to its high organic load, this vegetable water is likely to cause eutrophication in cases where it ends up in recipients where exchanging rates are low (closed gulfs, lakes etc). Of all components, the polyphenols are the most interesting. This is owing to their toxic properties that may affect plants. Furthermore they have a relatively slow degradability rate by specialized groups of micro-organisms. On the other hand the polyphenols ensure that olive oil retains its quality over time (low acidity), acting as a natural preservative. It should be noted that the production of olive oil is a natural process, and thus the olive mill wastewater does not contain other substances that are highly toxic, such as heavy metals and synthetic organic compounds. 

Direct dumping of olive mill wastewater in the environment is unacceptable due to its high organic load and the presence of polyphenols. Thus treatment is required prior to disposal. Various olive mill wastewater treatment and disposal methods have been tested both in vitro and in vivo. However, despite efforts, an integrated solution has not yet been proposed and the techniques that have been applied in each individual case present certain technical and/or economic disadvantages and have failed to provide a satisfactory solution to the problem.

More specifically, evaporation ponds have been applied in Crete, simple ground pits in Chios and soil applications in Cyprus which are methods that require large areas of land for the disposal of the waste and often create aesthetic problems as a result of the frequently occurring poor layout and construction of these systems. Olive mills in Spain have been transformed into two-phase mills rather than three-phase, which considerably reduces the volume of water required by the olive mill and volume of wastewater produced accordingly. However it alters the problem, by producing an olive pomace/ wastewater mixture which must then be treated. At the same time, in Kalamata an effort was made on a pilot scale to produce a liquid soil enhancer or compost from OMW (Crete, Kalamata), which is a process that presupposes the existence of a sufficient market for the products produced. Chemical oxidation and anaerobic digestion of olive mill wastewater have been applied in Crete, which are techniques with high operational and construction costs. Another effort initiated on Crete is to achieve the co-treatment of OMW and municipal sewage in artificial biotopes or in active municipal waste water treatment plants. This technique requires a significant dilution of the OMW. Finally, the separation of OMW into fractions by natural sedimentation has been attempted on Samos, which is a technique that requires combination with one of the other methods mentioned above in order ensure a satisfactory level of treatment. 

Over the last years the recovery of polyphenols from OMW has been achieved in the laboratory using membranes, for the purpose of application in the perfume and pharmaceutical industry. Although the above utilization of olive mill waste is technically feasible, it is too early to achieve large-scale application.  

It should be noted that, due to the great variation in the characteristics of the olive mills (geographic position, capacity, location, water usage etc.), but also in the quality and quantity of the waste produced, a single solution that would be immediately applicable in all the olive mills of the North Aegean Region does not appear to exist.  


Regulations in force for OMW Disposal

Lesvos: The standing practice in the 71 olive mills on the island continues to be the unrestrained dumping of OMW in torrents/streams and ends up reaching its final recipient, the sea. A provisionary attempt to confront the problem was proposed by the Prefecture of Lesvos. This consisted of the addition of lime to the OMW before its disposal to the natural recipients, in order to lower the pollutant load. There is overall agreement that the proposed treatment system (that has been applied in only 2 olive mills on Lesvos where it is not applied in daily practice) requires improvements and additions. Thus the Prefecture of Lesvos has extended the period of putting technical applications into practice and a final decision based on the results of NAIAS programme currently underway is expected to be reached.   

Chios: The Prefecture of Chios recently went ahead with a provisionary solution to the problem, with its decision to construct simple tanks/ reservoirs for the storage of the total volume of OMW produced. So far the proposed solution has been applied in 12 of the 14 olive mills on the island. The system consists of soil reservoirs or concrete tanks, with the capacity to store the entire amount of waste produced during one olive production year. In certain cases however, because of the small size of the reservoir and the soil’s limited absorption capacity, the island’s torrents/streams continue to be the OMW’s final recipients.  

-Samos - Ikaria: To be updated shortly.

Information for olive mill owners who would like to participate in the currently running program for the construction and operation of waste management plants.







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