Palm oil mills with wet milling process are accounted for major
production of palm oil in Malaysia, Indonesia and Thailand. Besides the
main product “crude palm oil”, the mills generate many by-products and
liquid wastes which may have a significant impact on the environment if
they are not dealt with properly. One ton of fresh fruit bunches (FFB)
composed of 230-250 kg of empty fruit bunch (EFB), 130-150 kg of fiber,
60-65 kg of shell and 55-60 kg of kernel and 160-200 kg of crude oil. EFB
are bulk solid residues and its use as a fuel for boiler is constrained
by its high moisture content and low heating value (<10 MJ/kg dry EFB).
Utilization of the EFB as substrate for mushroom cultivation and for the
production of particle board should be given first priority. In addition,
EFB could be used as organic fertilizer and mulching material. Palm fibers
are used mainly as fuel for boilers (heating value of <5 MJ/kg
dry fibers). Other applications of palm fibers include the use as substrate
for enzymatic saccharification of or for animal feed. Although palm shell
can be used as boiler fuel with heating value of 17 MJ/kg, it causes the
black smoke. Alternative use for the production of activated carbon is
preferable. Decanter cake can be used as a fertilizer or soil conditioner.
Palm oil mill effluent (POME) is the mixture of high polluted effluent
(from sterilizer and oil room) and low polluted effluent (steam condensate,
cooling water, boiler discharge and sanitary effluent). To minimize overall
treatment cost, the different wastewater streams should be collected and
treated separately. Oil separated from the wastewater stream by gravity
type oil separators is recommended which will contribute to improve production
yield and minimize the organic loading for the subsequent biological treatment
system. The most appropriate secondary treatment for POME is biological
digestion in which the combination of anaerobic and aerobic ponds is used
presently. Closed anaerobic system should be used for energy conservation.
Application of biologically treated POME for irrigation has been carried
out by some palm oil mills having their own plantation nearby. The POME
dosage should be based on the fertilizer requirement of plants. Spillage
of POME into ground water or into surface water must be avoided. If these
wastes are properly managed as described above, the palm oil mill will
become an environmental friendly industry.
paper concerns with the aspects of palm oil production including liquid
and solid by-products/residues and wastewater and possible air emission
to the atmosphere. Besides the main products “crude palm oil and palm kernel
oil”, the mills generate by-products and liquid wastes which may have a
significant impact on the environment if they are not dealt with
properly. The paper promotes closed concepts for utilization and disposal
regarding the complex of all environmental media of this branch of industry.
The relationship between oil palm plantation, palm oil mill and the environment
is shown in Figure 1.
At present the oil palm (Elacis quieensis) plantation using the
tanera variety which provides the highest oil content in the fruits of
the Fresh Fruit Bunch (FFB) with 21% oil. About 120 Kg/t FFB are nuts including
kernels 60 Kg/t FFB (5% of FFB) which contain about 30% oil ~ 30 Kg/t FFB.
If the average production of a medium size palm oil mill is 25 t FFB/h
(or 400t/d and 150,000 t/y) and FFB 5 tons per acre per year are harvested,
the average oil palm growing area per palm oil mill should be 30,000 acres
(50 trees/acre). Good agricultural practices are needed to get high yield
of fruits and oil content. Normally oil palm requires fertilizer differently
at different stages (Table 1). The transport of the harvested FFB from
the plantation to the mill is mostly organised by the farmers and done
with open lorries. Normally the oil mills are situated in the neighborhood
of the plantations. The average distance to the mill is about 30-50 Km.
Anyway the transportation time is about one day.
Table 1 Fertilizer demand for oil palm trees (4)
||Fertilizer demand (g / tree / year)
||Fertilizer demand (Kg / acre / year)
Standard palm oil extraction processes
There are 3 ways to extract the oil from the fruits of oil palm.
1. Dry process :
have to be separated from FFB and are direct heated to stop enzymatic reaction
and to evaporate the moisture. After that the fruits are crushed by screw
press to get the crude oil. This oil is the mixture of pericarp oil and
kernel oil. The palm cake after extraction is used as animal feed. There
is no liquid waste from this process.
2. Frying process :
The FFB are fried in oil under vacuum and the fruits and bunches are
pressed to get the kernel oil.
Wet process :
This process is characterized by steaming the whole FFB in order
to inactivate the natural enzymes and loosen the fruits off the bunch and
soften the mesocarp, resulting in easier extraction of oil.
In Thailand there are 6,000 acres of plantation area and yield
3,000,000 tons of FFB. There are 18 mills using wet process which account
for 75-80% of palm oil production. The flow diagram of the standard wet
process is shown in Figure 2.
The processing steps of the standard wet process
1. Arrival and storage of FFB
Soon after harvesting, the FFB must be brought to the mill as
quickly as possible to avoid fatty acids production by natural enzymes
in the mesocarp. The FFB are unloaded on a ramp and put into containers
of 2.5-3.0 tons each.
Sterilisation of the FFB is done batchwise in an autoclave of
20-30 t FFB capacity (7-10 containers) with the application of live steam
at 120-1300C about 1 h (total time of 2 h). The steam condensate or steriliger
condensate is the wastewater generated at this step (0.15-0.18 m3 Kg/t
3. Bunch stripping
The containers with the sterilised bunches are empty into a rotary
drum thresher where the fruits are separated from the bunch stalk. This
processing step generates the empty fruit bunches (EFB) at 230-250 Kg /t
The separated fruits are carried into digesters and mechanically
threated into mash. No residue occurs in this step.
Oil extraction and handling of solid wastes
The oily mash is fed into a continuous screw press system. The extracted
oil phase is collected and is discharged to the purification section. The
remained press cake is transported to a separation system consisting of
air classifiers and cyclones for drying and separation of nuts and fibers.
Kernels are recovered from nuts in the crackers. The oil is also extracted
from kernels by screw press to get palm kernel oil. Fibers and shells are
solid residues generated during oil extraction, with the wolds of 145 and
60 Kg/t FFB, respectively.
6. Oil purification
To improve oil clarification, hot water
is added to the raw oil and passed through a vibrating screen to separate
large size solids. The oil after sieving still contains small size solids
6.2 Separation of suspended solids
The conventional procedure to separate
oil from water and suspended solids is the settling tank method. The system
is heated by steams. The oil floating on the top is collected by a funnel
then sent to crude oil tank.
6.3 Treatment of settling tank underflow
The settling tank underflow is collected
in the sludge tank and subsequently treated to recover oil. In order to
protect the equipment in the subsequent process steps against clogging,
the bottom sludge is pre-cleaned by means of microstainer/hydrocyclone
of desander. The desarders are cleaned by discharging the accumulated solids
to the drain, followed by the injection of fresh water. Desander wastewater
is normally around 5 L/t FFB
The pre-cleaned sludge is collected
in a buffer tank and then pumped to a two-phase centrifuge (separator)
or a three-phase centrifuge (decanter) for oil recovery. To improve oil
separation by the separator it is common practice to add water during centrifugation.
Therefore the separator process will generate more wastewater than the
decanter process with the quantify of 750 and 300 Kg/t FFB, respectively.
The amount of decanter cake is 12 Kg/t FFB. The recovered crude oil is
pumped to the settling tank.
6.5 Separation of fine suspended solids
The crude oil from the settling tank
combined with recovered oil from the sludge tank is about 160-200 Kg/t
FFB. The final oil purification step is also done by centrifugation to
remove fine suspended solids. The low suspended solids content in the crude
oil generates not large volumes of solid residues.
6.6 Drying and cooling
After centrifugation the
crude oil still contains water which is removed by a vacuum evaporation
system. Subsequently, the dried crude oil is kept in storage tanks before
selling to an oil refinery. Residues of the drying step is cooling water
with the quantify of ~ 300 Kg/t FFB
Characteristics of residues
The entire palm oil milling process does not use any chemicals as a
processing aid. Therefore, all substances found in the products, by-products
and residues are originated from oil palm. The main residues are EFB, fibers,
shells, decanter cake and wastewater. The nutrient contents of these residues
are shown in Table 2.
Table 2 Average nutrient contents in the residues of palm
* Kg/t dry residue for solids, Kg/m3 for POME
||Kg /t FFB**
|After final oil trap
|After anaerobic treatment
|After full biological treatment
** To be verified by additional measurements
Process Integrated Pollution Prevention and Control Strategy (IPPCS)
In order to manage the production process efficiently, the IPPCS must
be applied such as improve production technology, minimize residues and
utilize residues as by-product. IPPCS will help to save resources and energy
and reduce environmental pollution.
1. Improvement in production technology
1.1 Plantation management
- improve the oil yield of oil palm
- management of plantation
1.2 Quality of raw material
- co-operation between the plantations
and the palm oil mills
2. Prevention of oil loss in the production process
- reuse of condensate
- improve process control and equipment maintenance
- improve oil extraction process
- improve oil separation process
3. Utilization of solid residues
3.1 Empty fruit bunches (EFB)
3.1.1 Return to plantation
The EFB may be used
as covering material, organic fertilizer and soil conditioner in the plantation.
However, EFB utilization rate is limited by its potassium content. Therefore,
as given in Table 3 only 0.2-2.0 t EFB can be used per acre per year. However,
exact figures concerning the actual availability of EFB as substrate to
the palm trees have not yet been developed and need further investigation.
Table 3. Average annual application of EFB for oil palm plantation
||EFB applications (ton/ acre / year)
Substrate for mushroom cultivation
EFB could be used
directly as a substrate for mushroom cultivation. At present many farmers
use EFB to grown straw mushroom.
3.1.3 Fuel for boiler
The use of EFB as
a fuel for boiler is constrained by its high moisture content and low heating
value (calorific value of dried EFB ? 10 MJ/Kg). In addition, there are
better solid residues available as fuel source at the mills such as dried
fibers and shells.
3.1.4 Incineration to recover ash
Incineration of EFB
to reduce its volume and to recover the ash has a great disadvantage of
generating excessive air pollution. This method should not be applied because
of the wastage of valuable carbon material, which can be useful for soil
Picture 2: Fibers
Picture 4: Shells
Around 15% of the FFB are palm fibers. They
are used mainly as fuel for boiler (calorific value of dried fibers ? 5
MJ/Kg). Other use is an addition in animal feed. Adding 5-6% NaOH or urea
and allowing 2-3 weeks fermentation can improve its quality.
Shells can be used as boiler fuel (calorific
value of 17 MJ/Kg). However, fibers are more than enough to be used as
fuel for boiler. Therefore, the shells are often accumulating in the mill.
Another possible use of shells is the production of charcoal and activated
carbon which should need further investigation.
3.4 Decanter cake
For mill using decanter to separate
oil from sludge, the generated decanter cake can be used as soil conditioner
and fertilizer like EFB. The acceptable annual soil application can be
calculated using Table 1 and 2.
4. Utilization of liquid residue
4.1 Low suspended solids (SS) wastewater
During palm oil extraction process there
are many wastewater streams that contained very low SS. At the steam turbine,
there was cooling water of 1 m3/h and at the oil drying step there was
3 m3/h of vacuum condensate. These wastewater can be reused in any step
in the mill.
4.2 Steriliser condensate
Normally the steriliser condensate go
is directly into the final oil trap. The steriliser condensate contains
~ 1% oil which can be recycled into the process at digester, screw
press or settling tank. The reuse of cooling water and condensate will
reduce the amount of both water consumption and wastewater for treatment.
4.3 Wastewater from oil room
The main wastewater from the palm oil
extraction by wet process is the wastewater from oil room after separator
or decanter. This stream of wastewater combined with sterilizer condensate
and cooling water are called palm oil mill effluent (POME). The characteristics
of POME from four palm oil mills are shown in Table 4.
Table 4 Average pollution load in wastewater from 4 palm oil mills
a – using only decanter
b – using separator and decanter
c – using only separator
Application of biologically treated POME for irrigation is a method
used by many palm oil mills. The application as fertilizer has to be carried
out carefully, as overdose will result in nutrient imbalance and lead to
undesirable chemical reactions in the soil. Prolonged inadequate utilization
of POME may cause the accumulation of magnesium and inhibit the availability
of potassium. The POME dosage should be based on the fertilizer requirement
of the plants and not on the permissible hydraulic loading rate of the
soil. Spillage of POME into ground water or into surface water must be
avoided. The amount of POME to be applied under good agricultural practices
is given in Table 5. It indicated shat the utilization of POME is limited
by the potassium (or magnesium) value. Therefore, only 1.2-18 m3 POME can
be used per acre per year for an oil palm plantation. It can be concluded
that biological treatment has no signifcant influence on the permissible
amount of POME for proper fertilizer. The feasibility utilization of POME
must be analysed and tested for practical application. Investigations in
Malaysia show that POME used in an oil palm plantation increased the yield
by 13 %. Some palm oil mills in Thailand also applied POME in the plantation
and found that growth of palm trees and oil yield are increased.
Table 5 Average annual application of POME for oil palm plantation
||POME application (m3/acre/year)
Treatment of wastewater from palm oil mill
1. Primary wastewater treatment
1.1 Segregation of wastewater streams
As shown in the schematic process flow diagram in Figure 2, a palm
oil mill has the following effluent streams:
1.1.1 high polluted effluent : effluent from steriliser and oil room
1.1.2 low polluted effluent : steam condensate and cooling water
and boiler house discharge.
1.2.3 Sanitary effluent: wastewater from toilet and canteen.
In order to minimise overall treatment cost the different wastewater
steams should be collected and treated separately. The highly polluted
wastewater streams from a palm oil mill have different suspended solid
contents which influence the effectiveness of the pretreatment system.
The steriliger condensate and oil leakage should be collected separately
from oil room effluent.
1.2 Oil separation
In order to recover the oil from wastewater, the different wastewater
streams should be treated separately in gravity type oil separators. The
oil removal by means of gravity separator will improve the production yield
and minimise the organic loading for the subsequent biological treatment
1.2.1 Low suspended solids wastewater
Since the oil in this
type of wastewater is mainly in the free form, oil could be easily removed
in gravity type oil separators. The pretreated wastewater could be reused
in the mill which may be during digesting and pressing.
1.2.2 High suspended solids wastewater
This stream mainly
comes from centrifuge in the oil room. Since this wastewater is generated
by separation equipment with high accelerating force, further oil removal
by gravity separation is marginal. However, installation of oil trap is
recommended mainly as safety device in case of accidental oil discharge.
2. Secondary wastewater treatment
The most appropriate secondary treatment method for palm oil mill wastewater
is biological digestion. Since this wastewater is composed of mainly organic
substances and absent of toxic substances. At present, biological treatment
systems operated in palm oil mills use a combination of anaerobic and aerobic
treatment methods. However, only limited information is available on design
2.1 Effluent cooling
The optimum temperature for anaerobic treatment is 37C but the
palm oil mill effluent has a temperature in the range 75-90C. A cooling
step is required prior to biological treatment. The cooling pond shape
has to be designed carefully. The depth of the pond should not exceed 1.5
m otherwise the cooling efficiency will decrease. The hydraulic retention
time of the cooling pond should be at least 1 day. Despite the high initial
temperature of the effluent, biological decomposition of palm oil mill
wastewater already starts in the cooling pond. This normally leads to acidifying
process and odor-generating substrates are released resulting in bad smell.
Control of pH (at about 7.0-7.5) is important to avoid this problem.
In order to improve effluent cooling as well as to get some adjustment
of the pH-value and to decrease the substrate concentrations in the initial
part of the treatment system, some part of the anaerobically treated effluent
can be recycled back to the inlet of the cooling pond. The optimum recycling
ratio had to be established for each individual palm oil mill by experiment
and should be between 30-70% of the wastewater flow rate. The recycling
effluent should come from the spot where highly active anaerobic biomass
is available (30-40 days retention time of the overall pond system).
2.2 Anaerobic treatment systems
These systems have significant advantages over aerobic treatment
- almost energy free operation
- only moderate impact from high organic loads.
- low surplus of sludge formation
Open anaerobic pond
The anaerobic digestion
system usually used in Thailand is the open pond system consisting of a
series of several ponds. During design and operation of the pond system
the volume requirement for collection of the settled primary sludge of
the raw POME as well as the anaerobic excess sludge have to be considered.
Sludge accumulation will result in reduction of pond volume and overall
The decision on whether or not
to use this system depends on many factors. The main factors are land price,
conditions of the surrounding area and the loss of biogas as a source of
energy must be considered as well. However, the biogas is not an important
source of energy for palm oil mill at present because the energy produced
by combustion of fiber and shell is sufficient. This may change if refinery
activities are introduced and more environmental friendly treatment is
2.2.2 Closed anaerobic digester
Palm oil mills have sufficient
supply of energy from the use of solid residues. Energy surplus and the
simplicity as well as low investment and operation cost of the opened pond
system make the closed anaerobic digester at present not applicable in
palm oil mills. Various systems of closed anaerobic reactors are available
such a completely mixed, fixed bed and upflow anaerobic sludge blanket
(UASB) reactors. To achieve operational stability in the anaerobic digester,
intense fluctuation organic loading has to be avoided. This can be achieved
by using the cooling pond as equalization tank for continuous feeding to
the anaerobic reactor.
2.3 Aerobic treatment systems
Various aerobic treatment systems for wastewater are readily available
in Thailand. The most widely applied system for palm oil mills is the aerobic
2.3.1 Aerobic pond systems
The various aerobic pond systems
which differ in the type of oxygen supply and design loading rates are
facultative ponds, oxidation ponds, aerated lagoons and polishing ponds.
The oxygen supply in most ponds is established by photosynthetic activities
of algae and plants and by adsorption of oxygen from the atmosphere except
aerated lagoons are artificially aerate. The high temperature of the pond
content does enhance the biochemical reactions resulting in more substrate
2.3.2 Activated sludge process
In the activated sludge process, oxygen is supplied intensively by aeration
and mixing. The concentration of active biomass in the aeration tank must
be controlled. The suspended biomass is separated from the treated effluent
in a final clarifier. The operation units are aeration tank, clarifier,
return sludge system and excess sludge removal and treatment system.
The example of biological treatment of palm oil mill wastewater with
combination of anaerobic ponds and aerobic ponds is shown in Table 6. The
500 tons FFB capacity palm oil mill will generated 25 m3/h of wastewater.
If the influent has the BOD5 of 30,000 mg/l and the retention of 171 days,
the effluent will have BOD5 of 100 mg/l.
The raw material for palm oil extraction is fresh fruit bunches.
If the palm oil mill is located near the oil palm plantation it will reduce
the cost of transportation and get good quality raw material. The palm
oil mill generates both solid and liquid residues. Process integrated pollution
prevention and control strategy is needed for extraction of palm oil by
improvement of production technology, prevention of oil loss and utilization
of solid and liquid residues. Proper treatment of palm oil mill effluent
in combination with utilization as liquid fertilizer will make the zero
discharge concept come to work. Then the palm oil mill will become an environmental
Thanks Deutsche Gesselschaft fur Technische Zusammenarbeit (GTZ),
Department of Industrial Works, Ministry of Industry, and Thailand Research
Fund for supporting most part, of this work.
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