(Zahari et al. 2012). The juice is then used as fermentation
feedstock to produce bioethanol, succinic acid, lactic acid
and bioplastic.
A study done by Wanrosli et al. (2007) found that OPF
shows an excellent strength property that is comparable to
hardwoods after the chemical pulping process. It has
potential as reinforcement pulp in newsprint production
using softwood thermo-mechanical fibres (Wanrosli et al.
2007).
2.3.3 Oil Palm Trunk (OPT)
Oil palm trunk and fronds obtained from oil palm growing
on plantations are abundantly available during the replanting
period which is approximately in every 25 years. It is a
non-wood monocotyledonous species that consist of vascular bundles and parenchyma cells rich in fibres, tracheid,
vessels parenchyma and ray parenchyma cells which are
different from hardwoods and softwoods (Sulaiman et al.
2012). It contains the highest amount of starch and total
sugar (generally cellulose and hemicellulose) with the concentration varied depending on the position along the trunk
(Ramle 2015). According to Yamada et al. (2010), OPT
contains a large quantity of sap that is almost 70% from the
whole trunk weight, where the total sugar content in the sap
after storage of 30 days is comparable to sugar cane juice.
The glucose, sucrose, fructose and galactose content are able
to be fermented by industrial bacterial activities making OPT
a potential precursor material for bioethanol production
(Yamada et al. 2010).
In addition, OPT has a high mechanical strength that is
exploited for the production of binderless particleboard,
laminated board, plywood, fibreboard and furniture. Compared to the old trunk, the young trunk has greater
mechanical and physical properties which contribute to a
higher quality final product (Sekaran 2019).
2.3.4 Palm Kernel Shells (PKS)
Palm kernel shells are the remaining shell portions after the
kernel nut is extracted following the crushing process in the oil
mill (Hashim et al. 2012). Its fibrous nature makes it easy to
handle in large quantity from the production line to the
end-user. The moisture content in PKS is between 11 and 13%
which is low compared to other palm oil biomass residues. It
contains residues of palm oil that contributes to a higher
heating value compared to average lignocellulosic biomass.
An experimental study by Uche Paul, John (Uche Paul 2015)
discovered that the PKS has a calorific value of 23,605 kJ/kg,
while the palm fibre and EFB has a value of 14,512 kJ/kg and
17,855 kJ/kg, respectively. Therefore, PKS has potential as a
good solid fuel material that will combust more effectively as
well as being sustainable (Uche Paul 2015). In addition, PKS
produced from mill operation is generally uniform in size that
makes handling easy and it has low biological activity due to
its low moisture content (Ikumapayi et al. 2019). The PKS has
been characterized for its excellent bioenergy generation as
biochar, bio-oil and biogas production (Ikumapayi et al.
2019). A study by Oti et al. (2015) stated that PKS is a potential
partial substitute for cement and lightweight aggregate as
crushed PKS is hard and able to physically bond with the
hydrated cement paste. Table 2 summarizes the potential
usage of solid wastes from oil palm.
2.4 Current Oil Palm Waste Management
2.4.1 Ponding System
A common method for treating POME is the open ponding
system that uses mostly biological treatment methods such
as acidification, anaerobic, facultative and aerobic degradation (Loh et al. 2013). Syahin et al. (2020) summarized the
advantages and limitations of various ponding systems for
POME treatment. The ponding system is considered a simple technology with low operating cost and low maintenance. However, a huge land area and long HRT are
required. In addition, the final discharge still has a high
residual COD and BOD, implying an inefficient treatment
system (Zhang et al. 2008).
2.4.2 Solid Fuels and Mulching
Palm pressed fibre and shell produced by the oil mills are
normally used as burning materials or solid fuels for steam
boilers. The calorific value of dried fibres is about 5 MJ/kg
(Embrandiri 2015). Boiler operation is needed to generate
steam to operate turbines for electricity generation. Energy
generated from these two solid fuels is more than sufficient
to power up the palm oil mill (Zafar 2019). In contrast to
shells and fibres, EFB is usually returned to the plantations
as mulch to control weed growth, prevent erosion and
maintain soil moisture. Application of EFB as a solid fuel is
limited due to its high moisture content of up to 70%.
2.5 Alternative Green Technology
2.5.1 Anaerobic Digestion (AD) System
Anaerobic digestion can be defined as an engineered
methanogenic decomposition of organic matter by various
species of anaerobic microorganisms in the absence of
oxygen (Nour et al. 2013). Most palm oil mills in Malaysia
employ an AD process as the primary treatment of POME
due to its high concentration of organic content (Nour et al.
2013). During the AD process, organic content in POME is
converted into methane, carbon dioxide and water through a
series of processes. Since no aeration is required, low energy
is consumed during the AD process. Furthermore, the
methane gas produced is valuable as an alternative energy
Palm Oil Industry—Processes, By-Product ...
129
feedstock to produce bioethanol, succinic acid, lactic acid
and bioplastic.
A study done by Wanrosli et al. (2007) found that OPF
shows an excellent strength property that is comparable to
hardwoods after the chemical pulping process. It has
potential as reinforcement pulp in newsprint production
using softwood thermo-mechanical fibres (Wanrosli et al.
2007).
2.3.3 Oil Palm Trunk (OPT)
Oil palm trunk and fronds obtained from oil palm growing
on plantations are abundantly available during the replanting
period which is approximately in every 25 years. It is a
non-wood monocotyledonous species that consist of vascular bundles and parenchyma cells rich in fibres, tracheid,
vessels parenchyma and ray parenchyma cells which are
different from hardwoods and softwoods (Sulaiman et al.
2012). It contains the highest amount of starch and total
sugar (generally cellulose and hemicellulose) with the concentration varied depending on the position along the trunk
(Ramle 2015). According to Yamada et al. (2010), OPT
contains a large quantity of sap that is almost 70% from the
whole trunk weight, where the total sugar content in the sap
after storage of 30 days is comparable to sugar cane juice.
The glucose, sucrose, fructose and galactose content are able
to be fermented by industrial bacterial activities making OPT
a potential precursor material for bioethanol production
(Yamada et al. 2010).
In addition, OPT has a high mechanical strength that is
exploited for the production of binderless particleboard,
laminated board, plywood, fibreboard and furniture. Compared to the old trunk, the young trunk has greater
mechanical and physical properties which contribute to a
higher quality final product (Sekaran 2019).
2.3.4 Palm Kernel Shells (PKS)
Palm kernel shells are the remaining shell portions after the
kernel nut is extracted following the crushing process in the oil
mill (Hashim et al. 2012). Its fibrous nature makes it easy to
handle in large quantity from the production line to the
end-user. The moisture content in PKS is between 11 and 13%
which is low compared to other palm oil biomass residues. It
contains residues of palm oil that contributes to a higher
heating value compared to average lignocellulosic biomass.
An experimental study by Uche Paul, John (Uche Paul 2015)
discovered that the PKS has a calorific value of 23,605 kJ/kg,
while the palm fibre and EFB has a value of 14,512 kJ/kg and
17,855 kJ/kg, respectively. Therefore, PKS has potential as a
good solid fuel material that will combust more effectively as
well as being sustainable (Uche Paul 2015). In addition, PKS
produced from mill operation is generally uniform in size that
makes handling easy and it has low biological activity due to
its low moisture content (Ikumapayi et al. 2019). The PKS has
been characterized for its excellent bioenergy generation as
biochar, bio-oil and biogas production (Ikumapayi et al.
2019). A study by Oti et al. (2015) stated that PKS is a potential
partial substitute for cement and lightweight aggregate as
crushed PKS is hard and able to physically bond with the
hydrated cement paste. Table 2 summarizes the potential
usage of solid wastes from oil palm.
2.4 Current Oil Palm Waste Management
2.4.1 Ponding System
A common method for treating POME is the open ponding
system that uses mostly biological treatment methods such
as acidification, anaerobic, facultative and aerobic degradation (Loh et al. 2013). Syahin et al. (2020) summarized the
advantages and limitations of various ponding systems for
POME treatment. The ponding system is considered a simple technology with low operating cost and low maintenance. However, a huge land area and long HRT are
required. In addition, the final discharge still has a high
residual COD and BOD, implying an inefficient treatment
system (Zhang et al. 2008).
2.4.2 Solid Fuels and Mulching
Palm pressed fibre and shell produced by the oil mills are
normally used as burning materials or solid fuels for steam
boilers. The calorific value of dried fibres is about 5 MJ/kg
(Embrandiri 2015). Boiler operation is needed to generate
steam to operate turbines for electricity generation. Energy
generated from these two solid fuels is more than sufficient
to power up the palm oil mill (Zafar 2019). In contrast to
shells and fibres, EFB is usually returned to the plantations
as mulch to control weed growth, prevent erosion and
maintain soil moisture. Application of EFB as a solid fuel is
limited due to its high moisture content of up to 70%.
2.5 Alternative Green Technology
2.5.1 Anaerobic Digestion (AD) System
Anaerobic digestion can be defined as an engineered
methanogenic decomposition of organic matter by various
species of anaerobic microorganisms in the absence of
oxygen (Nour et al. 2013). Most palm oil mills in Malaysia
employ an AD process as the primary treatment of POME
due to its high concentration of organic content (Nour et al.
2013). During the AD process, organic content in POME is
converted into methane, carbon dioxide and water through a
series of processes. Since no aeration is required, low energy
is consumed during the AD process. Furthermore, the
methane gas produced is valuable as an alternative energy
Palm Oil Industry—Processes, By-Product ...
129