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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:
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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.
-
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.
-
Disposal
of the middle (light) liquid fraction over a Subsoil
Infiltration Field (SIF) located 50m from the Phase
Separation Tank.
-
Periodical
removal of the settled sludge from the PST and
burial in deep (anaerobic) pits, near the Subsoil
Infiltration Field (SIF).
-
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.
-
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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