Construction of a wastewater management pilot plant for the Olive Mill owned by “P. Kantaris & Co”-Olympos (Vasilika, Municipality of Polixnitos, Lesvos).

The centrifugal (3-phase) olive mill has a processing capacity of about 2500 tn of olives per harvest period (maximum produce). It is estimated that approximately 3300 m³ of olive mill wastewater is produced as a by-product (over a 90 day-period of operation which is the longest harvest period).

Description of the Olive mill wastewater Management System selected for this Olive Mill:

In the case of this olive mill the technique for olive mill wastewater separation into phases (fractions), followed by subsoil disposal was selected. Parallel with the above, a system for the recycling of the (turbid) water of the vertical centrifuge (oil separator) will be installed, while the decanter “ARA” system will be applied. These two systems will result in a reduction of drinking water usage. Consequently, less wastewater will be produced.

More specifically, the basic parts of the management system are:

1.      Installation and operation of the system for the recycle of the (turbid) water of the oil separator and utilization of the “ARA” system in order to reduce the use of water by the decanter.

2.      The initial separation of the olive mill wastewater into 3 fractions (phases) by natural settling. For this purpose a concrete Phase Separation Tank (PST) will be constructed. This tank is dimensioned to provide a five (5) day hydraulic retention period.

3.      Disposal of the middle liquid fraction into Evaporation-Infiltration Ponds located 400m from the Phase Separation Tank.

4.      Periodical removal of the settled sludge from the PST and burial in deep (anaerobic) pits, near the Subsoil Infiltration Field (SIF).

5.      Periodical removal of the floating grease/oil from the PST and its return back to the olive mill for the separation of industrial olive oil.

6.      Removal of the sludge from the anaerobic pits once a year and its application to agricultural land.

Technical details of the Management System:

The total Management System of olive mill wastewater was initially designed and dimensioned without having the possibility of reducing the volume of the produced wastewater. Thus, the volume of the Phase Separation Tank (PST) initially was estimated (about 530 m³ total tank volume) according to the production capacity of a average conventional olive mills on Lesvos. However the olive mill of  “P. Kantaris & Co can reduce the volume of the wastewater it produces by: a) the application of the “ARA” system that its decanter technology provides (model NX-X20 by Alfa Laval) and b) the installation and operation of the system for the recycling of the (turbid) water produced by the oil separator (this recycling system is also proposed by Alfa Laval). Thus, at least a 40% reduction in the total volume of wastewater produced is expected. Consequently, the Phase Separation Tank (PST) was eventually dimensioned to be 40% smaller than initially calculated (318 m³ total volume). The PST is divided into three compartments communicating with each another via baffles and overflows (baffled reactor type). The bottom of the tank is given a slight inclination (2%). The PST is designed in such a way that the sludge and the floating grease/oil are temporarily stored inside the tank. These fractions will be periodically removed (2-3 times during the harvest period) with the help of pumps.

The middle fraction of the Phase Separation Tank will be disposed in three ponds of a total effective volume of 637m3. These ponds will be connected via overflow pipe, allowing phased repletion. Each pond will function as a separate subsoil infiltration disposal field and evaporation pond. This integrated system is fed from the uppermost section of the land, taking advantage of the natural declination. The slopes of the pond will be designed especially. Moreover, dry-stone walls will be built for soil retention. A special type of stone will be used and especially designed foundations will be laid.  The dry-stone wall will be 1 meter in thickness and 2 meters high on average, varying according to the pond’s location and the natural altitude of the building suite. The wastewater flows naturally from the Phase Separation Tank to subsoil infiltration / evaporation disposal field. Pond design was based on the acceptance that during a peak olive harvest season, the total volume of the middle fraction ending up in the ponds would be 1500m3. Other data which were taken into account for pond design were rainfall, evaporation and infiltration data of the landsite area. An important criterion used for the selection of the Subsoil-Infiltration Ponds was the assumption that their operation would not contaminate the ground water table or have any other negative impact on the neighboring crops.

A basic criteria for the selection of the Evaporation – Infiltration Ponds was the assumption that it their operation would have no negative impacts (pollution) on the ground water table and on the neighbouring cultivations. However the following precautions were taken in order to protect a neighbouring cultivated field, which belongs to a different landowner:

a)      the allowance of a 5m wide buffer zone towards the neighbouring field and

b)      at the site entrance as well as other locations where the level of the wastewater is perhaps higher than the altitude of the land, special safety and insulation measures will be taken by fitting 400μm thick HDPE sheets concluding at the pond coronation to insure their insulation. These sheets will be retained in position by depositing excavation material over the membrane.

The total (maximum) annual volume of the produced sludge is estimated to be 400m3. It will be stored in deep pits whose surface will be covered with various materials (e.g. leaves). Thus it is estimated that a 130 m² area will be needed for the storage of the sludge. It is also expected to have a sludge volume reduction inside the pits of about 70%-80% until the beginning of the next olive harvest period. The digested sludge will then be collected in order to be spread over non-cultivated lands (for safety reasons) and even over cultivated fields (olive groves, vineyards, etc.) as it is expected to serve as a soil enhancer / organic fertilizer.

The transfer of the produced sludge from the Phase Separation Tank to the pits will be achieved by a tank-car.

The total investment cost is estimated at € 138.300. The operational costs are estimated at approximately € 4.100/ year.

Note: The “ARA” system is an innovation in horizontal centrifuges (decanters) which operate in three (3) phases. It allows a reduction of up to 75% of the water used for the dilution of the olive paste (in the decanter) compared to decanters of older technology. This results in a direct reduction of the wastewater produced (roughly a 30% reduction in the total volume of wastewater produced by the olive mill).

In brief, the oil separator (turbid) water recycling system consists of a stainless steel tank that receives the (turbid) water of the oil separator and from a pump which feeds this water back to the decanter in order to (partially) substitute the water from the water supply system which is required for the dilution of the olive paste. It is a simple  system (to install and operate), which is expected to reduce the total volume of wastewater produced by the olive mill by 20% (recycled water from the rinsing of the oil separator is also included).

Photographs from the worksite

Photo 1 (Tank)

Photo 2 (Tank)

Photo 3 (Tank)

Photo 4 (Lakes-Infiltration Field)

Photo 5 (Lakes-Infiltration Field)

Photo 6 (Sludge pitch)



Mission and Prospects | Olive Mills in the North Aegean Region | Olive Mill Waste - Information for olive mill owners | ELAIA - Olive Mill Waste Management Network | Applications and pilot plants | NAIAS Programme |

Contact | News | Waste Management Laboratory | University of the Aegean



Στόχοι και Προοπτικές Εφαρμογές και Πιλοτικές Μονάδες Δράσης Απόβλητα Ελαιουργείων - Ενημέρωση για Ελαιουργούς North Aegean  Innovative Actions and Support Ελαιουργεία Περιφέρειας Βορείου Αιγαίου ΕΛΑΙΑ - Δίκτυο Διαχείρισης ΕΛΑΙουργικών Αποβλήτων Αρχική Σελίδα Επικοινωνία Εργαστήριο Διαχείρισης Αποβλήτων Πανεπιστήμιο Αιγαίου


Mission and Prospects Olive Mills in the North Aegean Region Olive Mill Waste - Information for olive mill owners ELAIA - Olive Mill Waste Management Network Applications and pilot plants Waste Management Laboratory Naias Programme home Contact News Waste Management Laboratory University of the Aegean