Construction of a wastewater management pilot plant for the Olive Mill owned by “Theodoros Giannakas” (Afalonas, Municipality of Mytilene, Lesvos).

The centrifugal (3-phase) olive mill of Theodoros Giannakas has a processing capacity of about 2000 tn of olives per harvest period (maximum produce). It is estimated that approximately 2660 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:

Olive mill wastewater separation process takes place in phases (fractions) and is followed by subsoil disposal. Meanwhile, a recycling system for the decanter vegetation water will be installed. This will result in a reduction in water consumption (municipal water supply). Consequently less wastewater will be produced.

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

  1. Decanter vegetation water is recycled at the olive mill, and this recycled water is fed back to the decanter where it is used again while the decanter is fed with olive paste.

  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 (light) liquid fraction over a Subsoil Infiltration Field (SIF) located 50m 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 management system of “Theodoros Giannakas” olive mill will include a decanter vegetation water recycle system. This will result in a 50% reduction of the total produced wastewater. Specifically the vegetation water coming out of the decanter will return to the latter to be used again for the dilution of the olive paste, replacing a certain amount of the water that would be supplied to the decanter if no recycling took place. Thus water is saved, while at the same time less wastewater is produced.

In brief, the recycling system consists of a stainless steel tank, with three compartments, in which the decanter vegetation water is collected. A pump transfers the vegetation water back to the decanter - (re)used for the dilution of the olive paste.

This system for the decanter vegetation water recycling has already been installed and operated at the private olive mill of Mr. Kokkinoforos at Moria, Lesvos. The estimated 50%  reduction in the wastewater produced was based on data provided by Mr. Kokkinoforos’s olive mill.

The Olive Mill Wastewater Management System which is to be applied at Mr. Giannakas Olive Mill was designed and dimensioned under the basic condition that the decanter vegetation water recycle system operates. Thus, the volume of the Phase Separation Tank (PST), the area of the Subsoil Infiltration Field (SIF) and the area of the anaerobic pit for sludge burial were calculated considering a produced volume of 1330 m³ wastewater (for a maximum productive harvest period - for 90 days of operation annually) and not 2660 m³ as initially estimated.

The Phase Separation Tank (PST) total volume resulted in 207 m³. The tank 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 Subsoil Infiltration Field (SIF) will have an effective area of 457 m². It will be landscaped in order to be flat (without inclinations). With the SIF initially being dug at a total depth of 1m, starting from the bottom towards the top (natural ground level), it will be filled with rocks of 0,3m - 0,6m diameter reaching a height of 0,70m. Then a 15 cm layer of pebbles will follow. The rest of the SIF, until it reaches the normal level of the ground, will be filled with soil. For the uniform distribution of the middle (light) liquid fraction of the olive mill wastewater over the SIF, a collector and diffusion pipes will be placed under the ground. The transfer of the light fraction of the wastewater to the SIF, which is located a few meters from the Phase Separation Tank, has been designed to be operated by natural (gravitational) flow.

A basic criteria for the selection of the Subsoil Infiltration Field was the assumption that its 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)      the installation of a protective membrane between the SIF and the cultivated field, whose ground level is below the ground level of the SIF.

The total (maximum) annual volume of the produced sludge is estimated to be 260m³. It will be stored in deep pits (with a 3m effective depth, near the SIF) whose surface will be covered with various materials (e.g. leaves). Thus it is estimated that a 90 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 pump.

The total investment cost is estimated at € 72.600. The operational costs are estimated at approximately  € 2.000/ year.

Photographs from the worksite

Photo 1 (tank)

Photo 2 (tank)

Photo 3 (Infiltration field)

Photo 4 (Infiltration field)

Photo 5 (Recycling system)




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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