2021 Aleya DBO aceite de palma

Environmental Technology & Innovation 21 (2021) 101258
Contents lists available at ScienceDirect
Environmental Technology & Innovation
journal homepage: www.elsevier.com/locate/eti
A brief review on biochemical oxygen demand (BOD)
treatment methods for palm oil mill effluents (POME)
∗
Nur Aleya Lokman a , Ahmad Muhsin Ithnin a , , Wira Jazair Yahya a ,
Muhammad Ali Yuzir b
a
Vehicle System Engineering, Malaysia-Japan International Institute of Teknologi (MJIIT), Universiti Teknologi Malaysia, Jalan
Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia
b
Department of Environmental Engineering and Green Technology, Malaysia-Japan International Institute of Technology (MJIIT),
Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur 54100, Malaysia
article
info
Article history:
Received 27 August 2020
Received in revised form 5 November 2020
Accepted 15 November 2020
Available online 21 November 2020
Keywords:
Palm oil mill effluents (POME)
Biochemical oxygen demand (BOD)
treatment
Wastewater
a b s t r a c t
Numerous issues pertaining to palm oil mill effluents (POME), such as the release of high
level of biochemical oxygen demand (BOD) and other pollutants into the environment,
have brought major public concern. Hence, Department of Environment (DOE) has
implemented stricter laws on the final discharge of POME, whereby BOD must be less
than 20 mg L−1 . Addressing that, the recent types of treatment methods to reduce BOD
were briefly reviewed in this article. A lower value of BOD can be achieved by improving
both biological and physiochemical treatment methods for POME. The palm oil industry
has also recently combined the existing treatment and biogas capture technology to
create an integrated system to reduce BOD effectively, and at the same time, make full
use of the valuable by-products, such as methane gas, as part of the effort to realise the
idea of zero discharge waste. In conclusion, based on the previous studies, of whether
in small or large scale, it is recommended to include information of BOD reduction for
future research guidelines, which can be used to address related palm oil waste discharge
issues for better environmental quality.
© 2020 Elsevier B.V. All rights reserved.
Contents
1.
2.
3.
4.
Introduction...............................................................................................................................................................................................
Physical and chemical properties of POME...........................................................................................................................................
Current BOD discharge limit in South East Asia (Malaysia, Thailand, and Indonesia) ....................................................................
POME treatment Processes......................................................................................................................................................................
4.1.
Biological treatment of POME ....................................................................................................................................................
4.1.1.
Anaerobic ponding treatment process.......................................................................................................................
4.1.2.
Aerobic treatment process ..........................................................................................................................................
4.1.3.
Biogas capture system/hybrid system .......................................................................................................................
4.2.
Physicochemical treatment.........................................................................................................................................................
4.2.1.
Electrocoagulation ........................................................................................................................................................
4.2.2.
Adsorption.....................................................................................................................................................................
4.2.3.
Coagulation/flocculation ..............................................................................................................................................
∗ Corresponding author.
E-mail addresses: [email protected] (N.A. Lokman), [email protected] (A.M. Ithnin), [email protected] (W.J. Yahya),
[email protected] (M.A. Yuzir).
https://doi.org/10.1016/j.eti.2020.101258
2352-1864/© 2020 Elsevier B.V. All rights reserved.
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N.A. Lokman, A.M. Ithnin, W.J. Yahya et al.
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6.
Environmental Technology & Innovation 21 (2021) 101258
4.2.4.
Advanced oxidation process (AOP) ............................................................................................................................
4.2.5.
Membrane separation/filtration treatment ...............................................................................................................
4.3.
Phytoremediation.........................................................................................................................................................................
BOD treatment method for POME: At a glance....................................................................................................................................
Conclusion and future development ......................................................................................................................................................
Declaration of competing interest..........................................................................................................................................................
Acknowledgement ....................................................................................................................................................................................
References .................................................................................................................................................................................................
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1. Introduction
Oil palm or scientifically known as Elaeis guineensis is originated from West Africa, which then widely spreads to
Malaysia, Indonesia, and Thailand. Compared to other plants, oil palm is one of the reasonably interchangeable agricultural
products that are generated from crude palm oil (CPO) (Nambiappan et al., 2018). Besides that, palm oil is one of the
main commodities among the third world countries in South East Asia. Recently, the utilisation of palm oil worldwide
has extensively improved and it is dominated by Malaysia and Indonesia in South East Asia. Recently, 28% of world palm
oil production is coming from Malaysia and 33% for world exports. If taken into account of other oils & fats produced in
the country, Malaysia accounts for 9.5% and 19.7% of the world’s total production and exports of oils and fats. As one of
the biggest producers and exporters of palm oil and palm oil products, Malaysia is responsible in fulfilling the growing
global demand for oils and fats sustainably (Malaysian Palm Oil Council (MPOC), 2020). Besides that, the increasing global
demand for palm oil, Thailand, Colombia, Nigeria, Papua New Guinea, Ecuador and Ghana are also gradually emerge as
palm oil contributors (Kuss et al., 2015).
Based on the medium growth projection case of the United Nations, the global population will reach 9.5 billion before
year 2050 (Chen et al., 2016). Hence, the generation of food should also increase proportionally to the growth of the
human population. Furthermore, the global demand for fats and oils is projected to increase up to 360 million tonnes by
2043 (Basiron, 2013). Based on the above projection reports, it is assumed that the generation of palm oil would further
increase in numbers along with the global needs of lipid consumption. Each ton of CPO production will generate about
2.5–3.0 m3 of POME (Hasanudin et al., 2015). Thus, substantial amounts of CPO and POME would be produced before
2043. Fig. 1 depicts the global palm oil production on 2017 (Iskandar et al., 2018).
The disposal of POME waste is one of the main financial issues faced by the citizens and industries, as the processing
of CPO into its final products poses major environmental issues. Untreated POME is also one of the top priority cases of
environmental issues. For instance, POME is a wastewater that is easily dissolve, and the released of suspended particles
generated a high volume of extremely contaminating waste products and odours after degradation process of organic
material by the microbes (Zaied et al., 2020). Besides that, the breakdown process is relatively complex (Khalid et al.,
2019). Besides that, oil and grease layer (O&G) in POME affects the biological activity in treatment process where oil film
is created around the microorganism in suspended matter and wastewater. This caused the dissolved oxygen (DO) levels
in the water to be reduced. In addition, oxygen molecules are hard to be oxidative for microbial on hydrocarbon molecules
(El-Gawad, 2014). As a result, the quality of water is poor due to the high levels of biochemical oxygen demand (BOD) and
chemical oxygen demand (COD) (Chan and Chong, 2018). Hence, these environmental problems have propelled various
studies to come up with numerous new ideas to produce a demandable final product from POME, which reduces the
value of final discharge treatment and generation price. In particular, 1 litre of POME can produce between 27 m3 and
29 m3 of biogas (Harsono et al., 2014). As for the palm oil factories, solid wastes, such as fruit fibre, are normally utilised
for power generation. The access to different types of energy sources from the mills helps to minimise the operation and
discharge treatment costs, while they seek an alternative to the use of fossil fuel in the treatment plant. It was estimated
the earnings of producing electricity using biogas in Malaysia are worth up to RM 4 million annually (Chin et al., 2013). In
2017 alone, 453 palm oil mills in West Malaysia and 208 palm oil mills in East Malaysia have been in operation (Malaysian
Palm Oil Board [Mpob], 2012).
In order to develop Malaysia as an environmentally friendly country, the Malaysian Department of Environment
(DOE) has enforced stricter laws on the final discharge of POME where the permitted discharge value of BOD is reduced
from 100 mg L−1 to 20 mg L−1 in East Malaysia (Bello and Raman, 2017; Tabassum et al., 2015). This should also be
promptly enforced in West Malaysia given the lack of treatment technologies and the restricted area for the ponding
treatment system. Thus, a systematic and practicable POME treatment methods must be prioritised to ensure that the
permitted discharge value of BOD can be attained (Chan and Chong, 2018). Table 1 below presents the standard discharge
requirements of POME by DOE.
To date, the recent POME treatment methods especially in reducing BOD have not been reviewed. Thus, the main
objectives of this article were to review the recent methods to treat POME in terms of BOD reduction and to introduce the newest, contemporary techniques, including conventional treatment, alternative treatment, and even hybrid
treatment. This is because BOD is one of the significant parameter that was used to measure the level of pollution.
With that, this review was expected to yield improved interpretation on a number of POME treatment technologies and
potential techniques that can address the environmental problems of POME discharge, especially on the renewable biogas
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N.A. Lokman, A.M. Ithnin, W.J. Yahya et al.
Environmental Technology & Innovation 21 (2021) 101258
Fig. 1. Global palm oil generation in 2017.
Source: (Iskandar et al., 2018).
Table 1
Standard discharge requirements of POME by DOE.
Parameters
Standard discharge limit
(DOE, 1982)
Current standard discharge limit
(DOE, 2015)
COD (mg L−1 )
BOD (mg L−1 )
pH
Temperature (◦ C)
Colour (ADMI)
Total suspended solids (TSS) (mg L−1 )
Total nitrogen (mg L−1 )
Ammoniacal nitrogen (mg L−1 )
Total volatile solids (TVS) (mg L−1 )
Oil and grease (OG) (mg L−1 )
Manganese (mg L−1 )
Zinc (mg L−1 )
Copper (mg L−1 )
Iron (mg L−1 )
Phosphorus (mg L−1 )
Potassium (mg L−1 )
Magnesium (mg L−1 )
Boron (mg L−1 )
Calcium (mg L−1 )
Chromium (mg L−1 )
100
100
5.0–9.0
45
200
400
200
NA
NA
50
10
10
10
50
NA
NA
NA
NA
NA
NA
NA
20
5.0–9.0
45
100
200
150
NA
NA
5
10
10
10
50
NA
NA
NA
NA
NA
NA
Notes: There is no standard discharge for COD after 1984; ADMI denotes American Dye Manufacturers Institute; NA
denotes not available (Zainal et al., 2017).
production. For instance, dark fermentation process (via integrated thermophilic continuous stirred tank reactor (CSTR)
and mesophilic microbial electrolysis cell (MECs)) and co-digestion process (via oxidisation by hydrogen peroxide (OHP))
have been significantly increased the renewable biogas production (Krishnan et al., 2019; Zaied et al., 2019).
2. Physical and chemical properties of POME
POME can be described as a semi-liquid, brown mixture of waste product. It has water-soluble components of palm
fruit, different kinds of lipids and carbohydrates, and compounds that consist of nitrogen and organic compounds with
acidic properties and nutrients (Kuss et al., 2015). The nutrients in POME consists of nitrogen (N), phosphorus (P),
potassium (K), magnesium (Mg), and calcium (Ca), which are crucial nutrient elements for plant growth (Muhrizal et al.,
2006). Other properties of POME include high in temperature, pH of below 7, and rich in organic substances that reflect
high level of BOD, resulting in the generation of highly polluted domestic wastewater. BOD is widely used as an indication
of organic quality or the degree of organic pollution in water. A higher BOD value indicates poorer water quality, and vice
versa. Generally, the microbial population increases proportionally to the amount of available food. In this case, fishes and
other aquatic life forms would not survive in an environment that lacks oxygen. This is due to the higher consumption
rate of dissolved oxygen (DO) by microbial action, compared to the dissolve rate of atmospheric oxygen in the water. High
BOD also implies raw or untreated POME, which often exists in the range of 25 000 mg L−1 or higher. Although POME
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N.A. Lokman, A.M. Ithnin, W.J. Yahya et al.
Environmental Technology & Innovation 21 (2021) 101258
Table 2
Properties of raw POME.
Parameters
References
(Nasrullah et al., 2017)
(Loh et al., 2017a,b)
(Bala et al., 2015)
(Nwoko and Ogunyemi, 2010)
(Vijayaraghavan et al., 2007)
COD
BOD
TSS
O&G
pH
25 000
15,600
20,000
2 000
3.6
50 347
21 060
54 748
7213
4.5
75 900
34 393
14 467
191
4.7
70 000
30 100
28 900
10 540
4.5
13 452
16 307
11 978
–
3.5
All parameter are in unit of mg L−1 except pH (no unit).
is not poisonous, it emits bad odour, which can be a nuisance to the people who reside in areas near the palm oil mill
(Chan and Chong, 2018).
Generally, the pH of POME is low (approximately pH 4.5) due to the generation of organic acids during the fermentation
process; hence, it can be utilised as organic and inorganic compounds (Din et al., 2006). POME can also be applied
as fertiliser or animal feed substitute due to its non-toxic nature and fertilising characteristics in terms of providing
sufficient mineral requirements. Besides that, the level of aluminium (Al) in POME is high compared to chicken manure
and composted sawdust.
Besides that, the decomposition of lignocellulosic materials significantly increases the colour intensity of the final
discharge of POME (Tan et al., 2014). Thus, the authority has set up the standard discharge of colour intensity to 500
American Dye Manufacturers Institute (ADMI) (Bello and Raman, 2017). The high content of lignin and other organic
substances in POME increases its colour intensity up to the point where it cannot simply be treated via conventional
treatment. Residual oil is also another main issue since most of the palm oil millers have failed to meet the standard
discharge requirements (Kamyab et al., 2018). Table 2 below shows the properties of raw POME.
3. Current BOD discharge limit in South East Asia (Malaysia, Thailand, and Indonesia)
In order to create a greener and environmentally friendly country, the DOE in Malaysia has gazetted stricter laws on
the standard discharge requirements, particularly the permitted discharge value of BOD, which is reduced to 20 mg L−1
in East Malaysia (Bello and Raman, 2017; Tabassum et al., 2015). Accordingly, systematic treatment technologies must be
developed to ensure that the effluents can be discharged according to the gazetted laws (Chan and Chong, 2018).
Meanwhile, from the total CPO production of 28.9 million m3 tonnes, approximately 21.35 million m3 tonnes of POME
were produced from Indonesian palm oil mills back in 2014 (Dotro et al., 2017). Nevertheless, many palm oil mills are
not able to abide by the wastewater discharge limits, resulting in a significant increase in the number of polluted rivers
(Chan and Chong, 2018). In addition, the generation of approximately 9.12 million kg of BOD was expected daily if the
POME is discharged without prior purification. Otherwise, if each citizen is assumed to produce 14.6 kg annually, the BOD
value will nearly reach to waste produced by 45.6 million people in Indonesia (Paramitadevi and Rahmatullah, 2017).
Back in 2008, almost 1 544 000 tonnes of CPO were generated in Thailand, of which about 50% of this figure was
utilised domestically. Another 25% of the generated amount of CPO was converted to biodiesel for domestic fuel blends.
The remaining 285 000 tonnes (25%) of CPO were exported to Asia and Europe. In addition, the crushing mills in Thailand
have discharged more than 5 million m3 of POME during the process of extracting CPO, which contains very high organic
content (Tantitham et al., 2009). However, in the same year (2008), the amount of BOD produced was approximately
1.108 million tonnes if the untreated POME were discharged into the environment. By estimating each individual in
Thailand produces 14.6 kg of BOD annually (Doorn et al., 2006), this pollution load is equivalent to waste generated
by 75 million citizen, which is about thrice of the population of Malaysia (Ahmad and Chan, 2009). Table 3 shows the
overall environment quality restriction on POME by Malaysia, Thailand and Indonesia.
4. POME treatment Processes
4.1. Biological treatment of POME
Anaerobic treatment, aerobic treatment, and facultative ponds are examples of biological treatment. These environmentally friendly treatment processes are favoured means to treat POME. A group of microorganism consumes POME
due to its high organic content. Therefore, anaerobic digestion that produces methane gas has significant potential. By
applying the appropriate analysis and environmental control, biological treatment can easily treat most effluents that
contain biodegradable constituents with the ratio of BOD and COD of 0.5 and above (Zaher and Hammam, 2014). Multistage degradation of organic matters consists of hydrolysis, acidogenesis, acetogenesis, and methanogenesis, which are
part of anaerobic digestion. The action of a group of microorganisms in these treatment processes produces methane
and carbon dioxide (Bajpai, 2017). Additionally, acid-forming bacteria is found to be responsible for the conversion of
fresh POME into volatile fatty acids (VFAs) before its transformation into methane and carbon dioxide through anaerobic
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N.A. Lokman, A.M. Ithnin, W.J. Yahya et al.
Environmental Technology & Innovation 21 (2021) 101258
Table 3
Standard discharge limits of POME by Malaysia, Indonesia and Thailand.
Source: Iskandar et al. (2018).
Parameters
pH
BOD
COD
Total Solid
Suspended solid (SS)
O&G
Ammoniacal Nitrogen
Total Nitrogen
References
Malaysia
Indonesia
Thailand
5.0–9.0
100, 20 (Sabah and Sarawak)
–
–
400
50
10
10
6.0–9.0
100
350
0
250
25
–
50
5.5–9.0
20
120
3000
50
5
–
100
All parameter are in unit of mg L−1 except pH (no unit).
Fig. 2. Typical configuration of ponding treatment system for POME.
Source: (Zainal et al., 2017).
digestion process (Wong et al., 2013). Biogas such as bio methane and bio hydrogen are produced via rapid breakdown
process of organic substances from POME (Adekunle and Okolie, 2015). Furthermore, the integration of biogas system and
the current POME treatment potentially reduces the BOD value to a range of between 50 mg L−1 and 100 mg L−1 and
COD value to a range of between 1400 mg L−1 and 12 000 mg L−1 (Loh et al., 2017a,b). The following subsections discuss
the principal processes used in the biological treatment of wastewater.
4.1.1. Anaerobic ponding treatment process
Generally, wastewater with low level of BOD (less than 300 mg L−1 ) can be treated effectively using the aerobic
system, while wastewater with high level of BOD (more than 300 mg L−1 ) can be treated using the anaerobic system
(Daud et al., 2018). Thus, considering the high concentration of organic matters in POME, anaerobic digestion should be
considered as the main POME treatment process. According to Harsono et al. (2014), almost half of the palm oil factories
employ anaerobic lagoon to treat POME whereas the other half of these factories use different types of anaerobic digesters
(Harsono et al., 2014). Fig. 2 presents the diverse functions of ponds that are made up of earthen structures (Zainal et al.,
2017).
The anaerobic system was also found to deliver the best performance in treating POME due to the organic characteristics of POME (Choong et al., 2018). Therefore, during the earlier phase in the palm oil mill industry, the conventional
techniques, particularly ponding system, is often utilised to treat POME. Anaerobic ponds are commonly used by the
palm oil millers when the available space for POME treatment is limited. The anaerobic pond for the treatment system
was found to reduce the levels of COD (100–1725 mg L−1 ), BOD (100–610 mg L−1 ), and ammoniacal nitrogen (100–200
mg L−1 ) to a certain range accordingly (Zainal et al., 2017). Nevertheless, the open ponding system requires extensive
space. Besides that, the implementation of this system may cause negative environmental impact, such as the production
of liquor and release of methane, resulting in depleting the ozone layer and produce greenhouse gas (GHG) (Hosseini and
Wahid, 2015). Besides that, the total hydraulic retention time (HRT) needed for anaerobic ponds, is long, ranging from 45
to 60 days (Othman et al., 2014).
A standard lagoon system that comprised of seven ponds was established in a palm oil factory, which revealed the
following findings: (1) the effluents at the second pond had a high level of POME since it was the first receiver; (2)
the fourth pond (Anaerobic 2), fifth pond (Facultative), and seventh pond (Algae 1) recorded high BOD values; (3) the
implementation of adsorption process by sunlight treated POME at the second, fourth, fifth, and seventh ponds, which
proved zeolite as an effective adsorbent due to its high removal efficiency; (4) the percentages of turbidity (80.5%), COD
(54.5%), and BOD (78.0%) removal were the highest in the second pond (Ismail et al., 2013).
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N.A. Lokman, A.M. Ithnin, W.J. Yahya et al.
Environmental Technology & Innovation 21 (2021) 101258
Fig. 3. Schematic diagram of trickling filter.
Source: (Abdullah et al., 2013).
4.1.2. Aerobic treatment process
In the presence of oxygen, aerobic biological treatment process remains widely utilised in treating organic wastewater
and preventing the accumulation of organic matters from the initial clarified and biologically treated effluents. By using
heterotrophic bacteria, biodegradable organic substances are hydrolysed and transformed into carbon dioxide, water,
and active biomass (Dotro et al., 2017). However, the aerobic treatment process is rarely used to treat raw POME that
has high level of organic load. Due to its high organic load, it can be rather challenging for this treatment process to
deliver optimal efficiency in terms of technical and economic sense. Furthermore, an unprocessed POME attains a ratio
of 100:3:0.8 (BOD:N:P) under aerobic condition, which is considered malnutrition, as the most optimum ratio would be
100:5:1 (Metcalf, 2003). In addition, aerobic treatment requires high energy aeration to degrade the organic matter in
POME (Bala et al., 2014)
Najafpour et al. (2005) applied fungi S. cerevisiae in a rotating biological contractor (RBC) to treat effluents, which
revealed that the removal efficiency of BOD was about 91% (POME volumetric flow rate was 1.1 × 10−3 m3 h−1 ) and the
HRT in the batch experiment was 55 h (Najafpour et al., 2005). Meanwhile, Abdullah et al. (2013) assessed the efficiency of
trickling filter (Fig. 3) as a prototype of aerobic attached-growth system to treat POME, which revealed successful removal
of BOD and COD (of about 90%) at hydraulic loading rate (HLR) lower than 1 m3 m−2 d−1 (Abdullah et al., 2013). The study
further revealed two main factors that contributed to the successful removal of BOD and COD: (1) the sedimentation of
POME substances and addition of coagulants eliminate the organic matter on the filter; (2) the breakdown of water of
non-diffusible organics into soluble substrates was limited. Nevertheless, the study also highlighted that the reduction
of BOD and COD are inversely proportional to hydraulic loading due to the constraints of hydrolysis of non-diffusible
organics into soluble substrates.
On the other hand, the implementation of aerobic oxidation was performed on anaerobically treated POME and
diluted, unprocessed POME which successfully eliminated 93% of BOD for the former POME sample and 82% for the
latter POME sample with HRT of 2.5 days. This study proved that the first technique used to treat POME, specifically
anaerobic treatment, significantly reduced the level of BOD due to the effective breakdown of organic matters under
aerobic condition (Vijayaraghavan and Ahmad, 2006).
Sequencing batch reactor (SBR) is recently utilised as the succeeding form of activated sludge process given its ability
to remove BOD and suspended solids (SS) (Ahmed et al., 2015). For instance, Chan et al. (Chan et al., 2010) applied SBR
to treat anaerobically digested POME via maturation pond, which successfully reduced COD (95%–96%), BOD (97%–98%),
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 4. Methane gas capture and application trend.
Source: (Loh et al., 2017a,b).
and TSS (98%–99%) (Chan et al., 2010). The study further examined the percentages of COD and BOD removal under the
thermophilic state, which recorded almost 72% and 76%, respectively (Chan et al., 2011). Following that, they found out
that the aerobic treatment generates higher quality effluents under the mesophilic state compared to the thermophilic
state. By optimising mixed liquor suspended solids (MLSS) (to 27 kg m−3 ), OLR (to 2.5 kg COD m−3 d−1 ), and HRT (to
120 min), the effectiveness of aerobic treatment was upgraded via thermophilic state, as COD was successfully reduced
by 86%; BOD was successfully reduced by 87%; TSS was successfully reduced by 89%.
4.1.3. Biogas capture system/hybrid system
Most industrial players in the palm oil industry pay more attention to applying maintainable technologies, such
as methane capture or composting technology, towards zero waste discharge. The purposes of such techniques are to
minimise the emission of GHG and reduce air pollution. Thus, the integration of biogas system and a conventional
treatment ensures that BOD are within the permissible range (Loh et al., 2017a,b). In Malaysia, the biogas capture system,
which is conducted under the Palm Oil National Key Economic Area (NKEA), aims to improve the gross national income
(GNI) before the end of 2019 (MPOB, 2017). By preventing the release of methane gas from the open ponding batch
system, the release of harmful GHG can be reduced via methane prevention to produce electrical power and fertilisers
(Krishnan et al., 2017). Additionally, methane gas and other recycled organic materials can be used to incorporate with
the existing treatment processes that do not produce any waste for the palm oil industry. In this case, the main objective
for conducting the appropriate treatment process is to discharge the effluents according to the standard discharge limits
that are set by the authority.
Generally, the purpose of the captured methane gas from POME in terms of its uses differs from one mill to another.
Methane gas can be transformed into beneficial and renewable energy source, such as for heat, electricity, or even both
(Loh et al., 2014). In Malaysia, methane gas is mostly used for the production of steam heat and electricity or to power
up downstream business projects. Fig. 4 shows the different types of feasible uses of the captured methane gas for the
completed plants from 1984 to 2016. In particular, 14% of the total number of plants (n = 92) initiated the methane gas
captures system in the palm oil mill biomass boilers; 28% produced renewable electricity from the captured biogas; 56%
did not use but blaze the biogas; 2% applied biogas for thermal energy generation to power up the boilers and chillers of
the palm oil refinery (Loh et al., 2017a,b). Overall, about half of the biogas captured served to produce energy whereas
the remaining half involved flaring the gas.
At a glance, there are many successful and reliable locally developed and foreign biogas capture technologies that are
commercially adopted, such as closed anaerobic reactor equipped with continuous flow stirred tank reactors (CSTR) by
Novaviro–Keck Seng (Tong, 2011). This particular technology is able to remove BOD of between 250 mg L−1 and 500 mg
L−1 . Smart & Green Sdn. Bhd also uses CSTR to treat POME. It was reported that the BOD of final discharge was 350 mg/L
(Haji et al., 2010). Konzen Clean Energy Sdn. Bhd also applied the same technology and reported BOD reduction from
80% to 90% (Kervyn and Conil, 2011). Furthermore, there is also the methane fermentation system that engages with
specific microorganisms, which is developed by Malaysia Palm Oil Board (MPOB) and Biogas Environmental Engineering
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 5. Experimental set-up of UMAS.
Source: (Abdurahman, 2017).
(BEE) Sdn.Bhd (Lian et al., 2011). It was reported that the system managed to reduce 50 mg L−1 to 270 mg L−1 of BOD
for the final discharge. Besides that, MPOB and Ronser Bio-Tech Sdn Bhd provided a hybrid plug-flow system of UASB
and expanded granular sludge bed (EGSB) to treat POME (Loh et al., 2013). In particular, the final discharge of BOD was
800–1000 mg L−1 after the sample went through the digester tank.
Besides that, one of the examples of biogas capture reactor treatment system is the ultrasonic-membrane anaerobic
system (UMAS), which is a cost-effective design and simultaneously makes use of methane gas from the biomethanation
process. For instance, a prior study fed the POME into an anaerobic reactor at pH 1.75 and temperature of between 30 ◦ C
and 35 ◦ C for five hours before the obtained samples were permeated to examine the values of COD, BOD and TSS, which
revealed that COD and BOD were successfully reduced at 66.06% and 96.88%, respectively, and 94.24% of TSS was removed
at HRT of 10 days with the efficiency of methane gas generation at 83.61% (Abdurahman, 2017). As shown in Fig. 5, the
biogas was successfully obtained from the top of 200 litre of the reactor using a designated syringe.
Besides that, Shafie et al. (2016) applied UMAS to treat POME and found that the removal efficiency of BOD was not
quite good (66%) on permeate, considering that the operation of UMAS in an optimal condition is able to reduce BOD
value to 174 mg L−1 (almost the standard limit for effluents under the Environmental Quality Act 1974). The study further
implied that UMAS needs to operate within five hours per day for one week to achieve maximum removal efficiency of
COD and BOD (Shafie et al., 2016).
Meanwhile, moving bed biofilm reactor (MBBR) was applied in another study to treat different POME samples: (1)
Sample A, which was an influent that was originated from the palm oil factory, underwent the secondary treatment in a
stabilisation pond and tertiary treatment in a maturation pond; (2) Samples B, C, and D, which were obtained from the
palm oil mill, underwent the secondary treatment in a stabilisation pond and tertiary treatment that incorporated MBBR.
The study revealed the following results: (1) the BOD of Sample A exceeded 100 mg/L (not within the discharge limit of
BOD); (2) the BOD of Samples B, C, and D ranged between 21.6 mg L−1 and 54.6 mg L−1 (within the discharge limit of
BOD); (3) the reduction of BOD for Sample A ranged between 6.41% and 21.65%; (4) the reduction of BOD for Sample B
ranged between 35.58% and 55.44%; (5) the reduction of BOD for Sample C ranged between 17.55% and 43.06%; (6) the
reduction of BOD for Sample D was the highest, which ranged from 56.18% to 65.49% (AmbokUpek and Othman, 2016).
One of the disadvantages of MBBR is it requires a longer start-up period (Kawan et al., 2016).
Referring to Fig. 6, another prior study utilised up flow anaerobic sludge blanket-hollow centred packed bed (UASBHCPB) to reduce the operational issues of POME anaerobic treatment under the thermophilic condition within 36 days
(Poh and Chong, 2014). The removal efficiency of COD and BOD at almost 90%, the removal efficiency of SS at 80%,
the generation of methane gas at 60% were achieved at OLR of 27.65 g L−1 d−1 , mixed liquor volatile suspended solids
(MLVSS) concentration of 14.7 g L−1 , and retention time of two days (Poh and Chong, 2014). Nevertheless, the drawback
of UASB-HCPB is it is expensive compared to existing system (Chan et al., 2015).
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 6. Design of UASB-HCPB reactor.
Source: (Poh and Chong, 2014).
Low concentration of influent can be effectively treated with the attached growth anaerobic fluidised bed reactor
(AFBR). Almost 100% of bed growth can be reached through high up flow liquid velocity and short HRT (Moharram et al.,
2016). The AFBR depends on the natural properties of support substances (Shete, 2013). The inverse flow fluidised reactor
also shows good stability when weight is applied (Wang et al., 2015). Small porous fluidised media further demonstrates
high level of biomass in the reactor, which reduces the retention time. Shorter retention time (6 h), improved methane
gas production, and ability to reduce the organic substance suggested that fluidised bed are more advantageous than
anaerobic filter (AF) in treating POME (Poh and Chong, 2009).
As shown in Fig. 7, laboratory scale of AFBR was conducted at optimum temperature using diluted POME as substrate
(Ahmed and Idris, 2006). In particular, the start-up of this reactor was 17 days and the sand used was first seeded. The
AFBR successfully eliminated a great amount of organic substances at smaller HRT and the percentage of BOD and TSS
removal were between 64% and 91% and 68% and 89%, respectively. Additionally, the study used fungi Saccharomyces
cerevisiae biofuel as assisting substances on FBR to treat POME. After five days of study, BOD (92%), COD (95%), total
Kjeldahl nitrogen (TKN) (85%), SS (94%), volatile suspended solids (VSS) (95%), and turbidity (90%) were further removed
with the retention time of half a day (Al-Mamun and Idris, 2010). However, the disadvantage of AFBR is microorganisms
that are highly in turbulent state are willingly attached to the reactor bed.
Coulter and others pioneered the promotion of the basic idea of AF, but Young and McCarty were the ones who
demonstrated an up flow anaerobic filter (UAF) to treat alcoholic liquor wastewater (Tauseef et al., 2013). This filter
was conducted in laboratory scale to treat POME (Vijayaraghavan and Ahmad, 2006). However, the use of an operational
AF reportedly has clogging issue (Lee et al., 2016).
Referring to Fig. 8, UAF can be carried out in two types of conditions, namely the mesophilic condition and thermophilic
condition. High or medium concentration of influents can be treated with thermophilic anaerobic filters, especially POME
with high concentration of organic substances (Daud et al., 2018). Thermophilic POME influent produces much greater
yields, as compared to mesophilic POME influent (Fajar et al., 2018). Through the use of UAF, optimum performance in
reducing organic substances can be achieved where almost 97% of BOD and 94% of COD were successfully removed in
a study by Mustapha et al. (2003). Nevertheless, the drawback of UAF is it needs continuous maintenance to achieve
desirable product (Choi et al., 2013).
Furthermore, POME treatment pilot plant with zero discharge was installed at Kilang Kelapa Sawit (KKS) Labu, Sime
Darby. This plant is equipped with a complex concrete tank for pre-treatment and aerobic or clarifier system, followed by
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 7. AFBR lab scale (not to scale).
Source: (Al-Mamun and Idris, 2010).
Fig. 8. Up flow anaerobic filters (UAF).
Source: (Mustapha et al., 2003).
a biological treatment system and a series of ultrafiltration (UF) and reverse osmosis (RO) used for reclamation (Tabassum
et al., 2015). As shown in Fig. 9, the advanced anaerobic expanded granular sludge bed (AnaEG) system involves several
main phases, namely pre-treatment, biological treatment, and membrane separation. The first phase serves to recover all
impurities in POME. Meanwhile, the second phase generates biogas and ensures the BOD of the effluents remains under
20 mg L−1 . Membrane separation is the third and final phase where wastewater is purified and free from impurities. The
treated waste is retrieved as modified organic fertiliser that is rich in nitrogen, phosphorus, and potassium (NPK) (Loh
et al., 2013). Tabassum et al. (2015) reported that BOD of the treated POME remained under 20 mg L−1 at a consistency of
80% after the biotechnical aerobic process (BioAX) phase. Most of the good grade biogas comprise methane, of between 65%
and 70% (Loh et al., 2013). Overall, this treatment process requires a total of nine days, which is lower than the duration
required by other conventional treatment processes. Most importantly, this treatment ensures zero GHG emission.
Chan et al. (2012) then developed a new integrated anaerobic–aerobic bioreactor (IAAB) (Fig. 10). Back in 2009, it
was conducted in a small scale with a volume of 60 m3 , followed by its expansion to a 1.8 L IAAB in 2012 and a 3000
L pilot plant scale at Havys Oil Mill in 2015 (Lim, 2018). The IAAB is one huge reactor that involves anaerobic, aerobic,
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 9. AnaEG and BioAX integrated system for POME treatment.
Source: (Loh et al., 2013).
Fig. 10. Schematic diagram of IAAB.
Source: (Chan et al., 2012).
and sedimentation compartments. The final effluents from the settling compartment recorded BOD of 20 mg L−1 . Finally,
in a stable state condition, the removal efficiency of COD, BOD, and TSS recorded almost 99% OLR of 10.5 g COD L−1 d−1 ,
where methane production of 0.24 L CH4 g−1 COD was eliminated.
On the other hand, in order to optimise the deposition process, Aznury et al. (2018) used a batch system by converting
the digester into a pyramid-shaped sedimentation tank (Fig. 11). The fermentation tank was fabricated into a beam-shaped
to produce biogas. During the initial process, POME in the first digester tank went through sedimentation with a flow rate
of 6 L min−1 for one day. Following that, POME in the second digester tank that was added with active microbial seed was
fermented to generate biogas. At the end of the fermentation process, POME was streamed to the third digester tank for
the water treatment phase before the release of final discharge into the water stream. The obtained results revealed that
the final discharge of POME recorded COD of 100 mg L−1 and BOD of 30.9 mg L−1 . 30% of methane gas was produced from
its initial concentration. The generated methane gas during the fermentation time of 10 days, 20 days, and 30 days were
9.82% mol, 15.8 mol %, 33.19% mol, respectively (Aznury et al., 2018). Table 4 below shows the advantages, disadvantages
and BOD removal of various BOD treatment methods for POME.
Based on the discussed biological treatments, it can be said that most of the above treatment carried out anaerobic
digestion (AD) process. However, wastes generated from AD process are still too strong to be discharge into the water
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 11. Fabrication of a truncated pyramid beam digester.
Source: (Aznury et al., 2018).
stream. This is due existence of organic matters such as suspended solids that caused the high level of BOD in POME.
Thus, physicochemical treatment such as coagulation, flocculation and membrane separation technique must be carried
out to make sure the BOD of POME is low so that the discharge requirement can be achieved.
4.2. Physicochemical treatment
Although there are different types of biological treatment, certain processes may not deliver the required results
with respect to the minimum requirements that are set by the authority (Ahmed et al., 2015). Apart from biological
treatment processes, physicochemical treatment processes or also known as polishing techniques are alternative means
to treat POME. Basically, physicochemical treatment processes separate the colloidal particles that transform the physical
properties of the substances (Liew et al., 2014). Nonetheless, these processes may not be fully reliable given the high
capital investment, operating cost, and maintenance cost involved. Moreover, this tertiary treatment must be integrated
with other treatment means to achieve the final discharge limits that are set by the authority (Zainal et al., 2017).
4.2.1. Electrocoagulation
Electrocoagulation (EC) is recently proved as one of the successful technologies that can treat different kinds of
wastewater generated from factories. EC also promotes the removal of contaminants in a shorter amount of time.
Additionally, the treatment process is rather straightforward without the need for any chemical substance during the
treatment. The process generates a small amount of pollutants with respect to the final discharge limits. The EC process
has been extensively applied as pre-treatment and post-treatment steps in biological treatment for POME (Sontaya et al.,
2013). The effect of EC on the removal of particulate BOD in a major constituent of municipal wastewater was shown to
depend on the removal efficiency of TSS. The highest removal efficiency of particulate BOD was around 99% at the current
of 0.8 A and contact time of 5 min (Bukhari, 2008). EC was implemented in a prior study to treat POME in bench scale
using sodium chloride (NaCl) as the electrolyte and aluminium (Al) as electrodes, which revealed significant results on
the removal efficiency of COD and BOD before and after EC at 95% confidence level. On average, the initial value of COD
(36 800 mg L−1 ) before EC was reduced to 25 600 mg L−1 (removal percentage of 30%) whereas the value of BOD was
reduced from 23 400 mg L−1 to 14 400 mg L−1 (removal percentage of 38%) (Agustin et al., 2008).
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Table 4
The advantages, disadvantages and BOD removal of various biological BOD treatment methods for POME.
Treatment method
Advantages
Disadvantages
BOD removal efficiency
(%);
BOD final reading (mg
L−1 ; ppm)
References
Anaerobic ponding
-Low costs involved
-Straightforward
-Easy handling of the
process
-Require extensive area
-Production of liquor
and release of methane,
produce greenhouse gas
-Long HRT
100–610 mg L−1
(Zainal et al., 2017)
(Rupani et al., 2010)
(Othman et al., 2014)
Standard anaerobic
lagoon system
-Energy used is
minimum
-Sludge can be recovered
and used fertiliser
Issues related to solid
accumulation at the
bottom
78%
(Ismail et al., 2013)
Rotating biological
contractor (RBC)
-No sludge return
-Low energy
requirement
- Good separation
between the solid and
liquid
-Low pathogen removal
- Shaft bearings and
mechanical drive units
require frequent
maintenance
91%
(Najafpour et al., 2005)
Aerobic attached-growth
system
-No formation of
pollution-causing gases
-Poor separation
between treated
wastewater and biomass
- High energy for
aeration needed to
degrade organic content
in wastewater
90%
(Abdullah et al., 2013)
Aerobic oxidation on
anaerobically treated
POME
-Reduces coliforms,
pathogens and fats
- Lesser sludge
respiration rate
-Often used as a
secondary treatment
process
- Poor separation
between treated
wastewater and biomass
93%
(Vijayaraghavan and
Ahmad, 2006)
Sequencing batch reactor
(SBR)
-Generate less pollution
-High rate of digestion
and stability
-Performance depends
on the reactor geometry
-At high OLR, the
efficiency of reactor are
low
97–98%
72% (thermophilic)
87% (mesophilic)
(Chan et al., 2010)
(Chan et al., 2011)
Continuous flow stirred
tank reactors (CSTR)
-Increase contact area of
wastewater with
biomass via mixing
-higher methane
generation compared to
conventional
-biomass retention is
reduced
-generation of methane
at high treatment
volume is less efficient
250–500 mg L−1
350 mg L−1
90%
50–270 mg L−1
(Tong, 2011)
(Haji et al., 2010)
(Kervyn and Conil, 2011)
(Lian et al., 2011)
Hybrid plug-flow system
(UASB and EGSB)
-Improve contact area
between substrate and
biomass
-Able to treat high
strength wastewater at
thermophilic and
mesophilic condition
-Long start up period
-Foaming and sludge
floatation ant high OLR
800–1000 mg L−1
(Loh et al., 2013)
(continued on next page)
As shown in Fig. 12, an experiment on designing the electrode based on different types of electrode orientation,
arrangement, and materials was conducted in a prior study, which specifically involved vertical electrode orientation,
monopolar series (MP-S) arrangement, and steel wool for the electrochemical build-up. The selection of these electrode
orientation, arrangement, and materials was based on the highest removal efficiency of various parameters involved
(Nasrullah et al., 2018). By applying electrode in a vertical orientation, the removal efficiency of COD, BOD, and SS recorded
57%, 53%, and 51%, respectively. Meanwhile, by applying MP-S arrangement, the removal efficiency of COD, BOD, and SS
recorded 65%, 62%, and 60%, respectively. The percentages of COD (74%), BOD (70%), and SS (66%) removal were higher
when steel wool was used as electrode (Nasrullah et al., 2018). Hence, the study further utilised electrocoagulation process
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Environmental Technology & Innovation 21 (2021) 101258
Table 4 (continued).
Treatment method
Advantages
Disadvantages
BOD removal efficiency
(%);
BOD final reading (mg
L−1 ; ppm)
References
Ultrasonic-membrane
anaerobic system
(UMAS)
-Remove high BOD
within short HRT
-High substrate removal
efficiency
-Membrane fouling
-High cost of membrane
96.88%
66%
(Abdurahman, 2017)
(Shafie et al., 2016)
Moving bed biofilm
reactor (MBBR)
-Improved resilience to
load and flow variation
-Improved nitrification
-Requires a longer
start-up period
- Fixed film media tends
to wash out of the
systems over time
Sample A
(6.41%–21.65%)
Sample B
(35.58%–55.44%)
Sample C
(17.55%–43.06%)
Sample D
(56.18%–65.49%)
(AmbokUpek and
Othman, 2016)
(Kawan et al., 2016)
Up flow anaerobic sludge
blanket-hollow centred
packed bed (UASB-HCPB)
-High BOD removal at
short HRT
-High methane
generation
-Expensive compared to
existing system
90%
(Poh and Chong, 2014)
Anaerobic fluidised bed
reactor (AFBR)
-Able to operate at high
OLR at short HRT
-Low sludge generation
-Able to tolerate with
shock load
-Microorganisms that are
highly in turbulent state
are willingly attached to
the reactor bed
64%–91%
92% (with fungi
Saccharomyces cerevisiae)
(Al-Mamun and Idris,
2010)
Up flow anaerobic filter
(UAF)
-High biomass
concentration retained in
the packing
-Able to performance at
high volume of loads
-Filter clogging
-Needs continuous
maintenance to achieve
desirable product
97%
(Bodkhe, 2008)
(Mustapha et al., 2003)
(Choi et al., 2013)
Advanced Anaerobic
Expanded Granular
Sludge Bed (AnaEG)
system
-Lower power
consumption
-Lower sludge
production
-Tolerance to high
organic loads
-Kinetics highly
dependent to the
temperature of the
effluent
-Slow operation without
the help of acclimated
inoculum
<20 mg L−1
(Tabassum et al., 2015)
Integrated
anaerobic–aerobic
bioreactor (IAAB)
-Good stability
-pH adjustment is not
required
-Able to treat POME at
high OLR and shorter
HRT
-Poor separation
between treated
wastewater and biomass
99% (<70 mg L−1 )
(Chan et al., 2012)
Pyramid-shaped
sedimentation batch
system
- Able to handle high
OLR
-Reliable and energy
efficient
- Need large treatment
area
- Issues related to solid
accumulation at the
bottom
30.9 mg L−1
(Aznury et al., 2018)
using high current intensity to treat the effluents, which reported that 85% of COD, 83% of BOD, and 84% TSS were
successfully reduced within 50 min. By implementing the optimum operating parameters, the electrocoagulation process
managed to eliminate COD, BOD, and SS up to 95%, 94%, and 96%, respectively. The experimental results proved that the
use of high current intensity in EC delivered effective treatment at a lower reaction time (Nasrullah et al., 2019). Despite
of all the high removal efficiencies, the drawback of EC is it consumes high electricity in POME treatment as it gives high
impact on the operating costs (Moussa et al., 2017).
4.2.2. Adsorption
POME consists of a large amount of oil and grease (OG). Hence, it is a significant challenge to remove oily droplets in
POME during the treatment process. Therefore, numerous tertiary treatment processes have been implemented to address
this type of problem (Florence et al., 2009). Among these treatment processes, adsorption is one of the environmentally
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Fig. 12. Electrocoagulation experimental setup and its electrode design in terms of electrode orientation, arrangement, and materials.
Source: (Nasrullah et al., 2018).
friendly means to treat wastewater (Ahmed et al., 2015). Adsorption treatment using citrus peel, chitosan, activated
carbon (AC), barley waste, fly ash, zeolite, and aluminium phyllosilicate clay or organo-clay were often used to remove
OG, such as high-density metal wastewater (Shavandi et al., 2012a,b). In addition, different types of adsorbents, such
as wood sawdust, garlic peel, and palm kernel fibre are proposed for wastewater treatment (Adegoke and Bello, 2015).
In particular, adsorption has been used in POME to remove residual oil (Jahi et al., 2015), SS, and high-density metal
(Shavandi et al., 2012a,b). However, adsorption needs additional treatment because it has no specific scalability studies
have been performed (Wahi et al., 2017).
Meanwhile, another study used modified banana peel or specifically banana peel activated carbon (BPAC) as an
adsorbent in a biological treatment process for POME, which reported that colour, TSS, COD, and BOD were successfully
reduced by 95.96%, 100%, 100%, and 97.41%, respectively, at pH 2 within 30 h (Mohammed and Chong, 2014). Besides that,
Igwe et al. (2010) examined the effectiveness of POME treatment using boiler fly ash as an adsorbent, which revealed that
the adsorption of BOD, colour, and TSS increased proportionally to the weight of boiler fly ash. The apparent energy for
the adsorption of BOD, colour, and TSS were 1.25 kJ mol−1 , 0.58 kJ mol−1 , and 0.97 kJ mol−1 , respectively (Igwe et al.,
2010). This demonstrated that the adsorption occurs via physio sorption. On the other hand, another study utilised mango
pit as a coagulant and fly ash as an adsorbent in the coagulation–flocculation process (Asadullah and Rathnasiri, 2015),
which recorded removal efficiency of BOD at about 94%. In other words, adsorption can also be incorporated into certain
tertiary treatment processes for POME. The capability of adsorption process in removing pollutants is potentially high;
thus, the combination of adsorption and other treatment techniques would enhance the performance rate of the treatment
process (Asadullah and Rathnasiri, 2015). On the other hand, adsorption was implemented as a pre-treatment process in
another study, which successfully removed 63.23% of BOD, before the pre-treated POME sample was further treated using
ultrafiltration (UF) membrane system, resulting in a good quality POME sample (Azmi and Yunos, 2014).
As the improvement of tertiary treatment technologies has gained growing research interest, more studies have begun
to identify effective, novel types of adsorbent. For instance, the use of oil palm biomass (OPB) for the bio-adsorption
process. Several prior studies were conducted to treat POME samples from pond using palm-based bio-adsorbent.
Specifically, POME was initially mixed up with the bio-adsorbent with a known dosage of between 0.5 g L−1 and 300
g L−1 and mixing rate of between 20 revolutions per minute (rpm) and 150 rpm. The duration of adsorption was
recorded between 0.5 h and 24 h in the batch treatment system. The implementation of this system using this particular
bio-adsorbent revealed removal efficiency of BOD at 88% (Ibrahim et al., 2017; Wafti et al., 2017).
Meanwhile, the pyrolysis of banana and orange peels was conducted under various temperatures from 400 ◦ C to 500 ◦ C,
which produced between 30.7 wt % and 47.7 wt % yield of dark biochar that was then tested as an adsorbent in POME
treatment (Lam et al., 2018). The successful reduction of almost 57% of BOD, COD, TSS, and OG (within the discharge
limits) proved the effectiveness of biochar as an adsorbent in POME treatment. In another study, a double insulated
carbonisation–activation reactor (using low cement castable), where its internal space was protected with stainless steel
plated and fibreglass jacketed heat insulation layer (for better heat transfer to the bed of material in reactor), was applied,
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 13. Experimental set-up to generate metallic AC.
Source: (Liew et al., 2019).
which successfully increased the surface area of activated carbon (AC) from 305 ± 10.2 m2 g−1 to 935 ± 36.7 m2 g−1 and
gave a high generation of 30% within the retention time of seven hours through the carbonisation of oil palm kernel shell
(OPKS) at 400 ◦ C. After that, steam activation was further implemented at the temperature of between 500 ◦ C and 1
000 ◦ C in the same reactor, with steam flow rate of between 12.80 L min−1 and 18.17 L min−1 , which reaffirmed the
effectiveness of AC as a bio adsorbent for POME treatment through the high percentage of TSS (90%), COD (68%), colour
(97%), and BOD (83%) removal (Zainal et al., 2018).
On the other hand, the integration of a microbial fuel cell (MFC) and AC powder adsorption has been assessed. To
date, the removal of BOD using MFC adsorption hybrid system with adsorbent commercial activated carbon (CAC) remains
inadequately explored, which propelled by Tee et al. (2016) to test this treatment system in removing BOD, which later
revealed the removal efficiency of 93.1 ± 0.5% for POME and 16 mg L−1 for the BOD. On the other hand, the removal
efficiency of 85 ± 0.5% was reported for the implementation of the adsorption system only (Tee et al., 2016).
Meanwhile, Fig. 13 shows an experimental set-up that integrated microwave vacuum pyrolysis and sodium–potassium
hydroxide (NaOH–KOH) activation to generate a highly porous AC from palm kernel shell (PKS) that was successfully
upgraded into metallic AC through the integration of nickel (Ni) and aluminium (Al) atoms (Al/AC and Ni/AC) to treat
POME. After three days of treatment, the metallic AC removed 85% of BOD and 89% of COD compared to the standard AC
(Liew et al., 2019).
Meanwhile, activated sludge was implemented in another study to examine the efficiency of the aerobic operating
condition on the anaerobically treated POME sample based on the food to microorganism ratio (F/M ratio) of 0.3 kg BOD
kg−1 MLVSS d−1 , which revealed the most suitable medium for initial pH (6.5 ± 0.1), HRT (48 h), organic load rate (OLR;
650 ± 20 mg L−1 ), initial (MLVSS; 2000 ± 200 mg L−1 ), solids residence time (SRT; 10 days), and molasses concentration
(50 mg L−1 ) with the removal efficiency of COD of between 62% and 68% and BOD of between 60% and 65% in the effluents
(Wun et al., 2017).
4.2.3. Coagulation/flocculation
In addition, tertiary treatment processes that use coagulants and flocculants are physicochemical treatment processes
that add chemical substances into POME to separate colloidal particles. The added chemical substances change the physical
state of POME to form particle or floc that exists in a form of uncertain stability. Despite the introduction of numerous
tertiary treatment processes, a large scale of chemicals are still required (Mohd-Salleh et al., 2019) and residual element
from the coagulant water pollution is liberated by coagulation and flocculation (Keeley et al., 2014). For instance, the
combination of microbubble flotation and coagulation techniques was conducted in a prior study to treat anaerobically
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treated effluents using polyaluminium chloride (PAC) as a coagulant (that was added into POME), which revealed removal
efficiency of BOD at 77% with bubbling period of 12.5 min and flow rate of 19.8 L min−1 (Poh et al., 2014).
Furthermore, Hossain et al. (2019) studied the performance of ferrous sulphate heptahydrate (FeSO4 .7H2 O) waste from
titanium oxide industry in removing BOD, COD, and TSS from POME. Jar tests were carried out by applying different
coagulant doses (1–5 g L−1 ), pH (2–10), and temperature (40–80 ◦ C) as a function of treatment time ranging from 5 to
90 min. Results show that the FeSO4 .7H2 O waste have removal efficiency of 70% COD, over 80% BOD, and over 85% TSS in
a single stage coagulation treatment. The coagulation adsorption mechanisms for the removal of COD, BOD, and TSS from
POME were carried out based on Brunauer–Emmett–Teller (BET), Freundlich, and Langmuir isotherm models. The removal
of COD, BOD, and TSS from POME was best described by the Freundlich isotherm model, which mean that coagulation
adsorption happened in a multilayer formation with non-uniform distribution of adsorbed particles (Hossain et al., 2019).
Besides that, King et al. (2019) have treated POME by using ultrasound cavitation (US), coagulation treatment (natural
coagulant chitosan and synthetic coagulant ferric chloride (FeCl3 ) and AC as adsorbent. As a result, the eventual hybrid
treatment of US, FeCl3 coagulation and AC adsorption in series removed BOD5 89.7%, COD 88.1%, colour 99.9% and TSS
99.5% respectively. The final effluent concentration of the treated POME was in the standard discharge limit complied by
DOE (King et al., 2019).
4.2.4. Advanced oxidation process (AOP)
Advanced oxidation process (AOP) is a technique that uses the high strength and reactive neutral form of hydroxide
ion (OH− ). This treatment process can reduce organic matters of below 2.8 eV (Deng and Zhao, 2015). Some of the
most used techniques of AOP included UV (ultraviolet) radiation/titanium dioxide, UV radiation/hydrogen peroxide,
and ozone (Mohd Fadzil et al., 2013). Accordingly, photochemical process occurs by breaking down the UV light,
UV radiation/titanium dioxide, UV radiation/hydrogen peroxide whereas non-photochemical process occurs through
ozonation and Fenton process (Carra et al., 2016). The reaction between hydrogen peroxide solution and ferrous iron
catalyst in the Fenton process is known as Fenton’s reagent, which helps to reduce organic contaminants through chemical
oxidation, as the solution produces hydroxyl radicals (Saeed et al., 2015). However, further POME treatment is needed to
achieve higher removal efficiencies (Saeed et al., 2016). In one of the prior studies, POME was treated via UV-responsive
zinc oxide (ZnO), which successfully reduced half of COD after the sample was irradiated with UV for 4 h; at the end of
the experiment, the removal efficiency of COD and BOD recorded 87.78% and 74.10%, respectively (Ng and Cheng, 2015).
Meanwhile, cavitation is a pressure-related process that takes place when the local pressure decreases under the vapour
pressure according to the liquid temperature (Tao et al., 2016). Nonetheless, sonochemical oxidation and hydrodynamic
cavitation are the only processes identified to treat wastewater efficiently. For instance, sonochemical oxidation was said
to have high-frequency waves that can treat effluents (Parthasarathy et al., 2016) and rapid change of pressure (Wang
and Xu, 2012). In one of the prior studies, POME was treated using sonochemical oxidation, specifically the ultrasound
horn system, with AC as the adsorbent within 30 min (Fig. 14), which successfully removed 100% of COD and BOD
(Parthasarathy et al., 2016).
Referring to Fig. 15, cylindrical column immobilised photocatalytic reactor (CCIPR) was designed to conduct photooxidative reduction of pre-treated POME in a cylindrical glass photo reactor (UV/TiO2 (titanium oxide) system), where
the outer surface was covered with TiO2 whereas the UV source was located inside the glass tube, which successfully
reduced COD (to 17 mg L−1 ) and BOD (to 52 mg L−1 ) (Alhaji et al., 2018).
Haji Alhaji et al. (2017) also study the degradation of COD, BOD and colour present in POME using UV/TiO2 system. A
Statistical tool called face-centred central composite design has been run through response surface methodology (RSM)
by the use of design expert software to model and optimise the photo degradation process. The three models developed
for the three pollutants are non-significant as revealed from the Prob > F values of 0.0584 for COD, 0.0612 for BOD
and 0.4239 for colour and this confirms that proposed models fit the experimental data. The optimum conditions for
the three parameters are 5.50 for initial pH, 4.84 mg for catalyst dosage and 42.86 min for time and the percentage
removal of the COD, BOD, and colour are within the range of 59.43–96.81%, 48.05–102.68% and 60.63–94.29% respectively.
Regression analysis obtained through analysis of variance provided significant quadratic polynomial with the coefficient
of determination R2 = 0.9646, 0.9496 and 0.9223 for COD, BOD, and colour removal respectively (Haji Alhaji et al., 2017).
Ng and Cheng (2016) treated the effluent via photo-polishing of POME with a concomitant production of CH4 -lean
biogas over UV/(Zinc oxide) ZnO photo catalysis system. The photoreaction results showed that the optimum ZnO loading
for POME photo mineralisation was 1.0 g L−1 , with about 50% of COD removal after just 4 h of UV irradiation. It is found
that all the photo mineralisation kinetics can be modelled to the first-order reaction order, with specific reaction rates
(k) ranging from 1.022 × 10−3 to 3.118 × 10−3 min−1 . The maximum amount of gaseous generated, viz. 36,172 µmol of
CO2 and 333 µmol of methane were produced at this optimum loading. Significantly, the organic removal efficiency was
further enhanced when the UV exposure was prolonged to 22 h, attaining final readings of 44 ppm, 26 ppm and 20 mg
L−1 , respectively, for COD, BOD and OG (Ng and Cheng, 2016).
The idea of generating syngas from POME through catalytic steam transformation pathway is recently introduced,
as highlighted in several prior studies. For instance, Ng et al. (2018) applied catalytic steam reforming process to
convert POME syngas by applying 20 wt%Ni/80wt%Al2 O3 catalyst, which demonstrated a good rate of crystallinity and
purification This particular catalyst was created through the wet-impregnation process. The study further concluded
higher percentages of COD and BOD removal when the temperature increases, and vice versa, based on the following
results where the highest percentage of BOD removal (99.52%;160 ppm) was achieved at 1173 K (899.85 ◦ C), compared
to the obtained percentage of BOD removal (88.21%; 1980 ppm) at 723 K (449.85 ◦ C). However, the drawback of this
system was carbon easily deposited on the catalyst’s surface and high power consumption.
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 14. Experimental setup of POME treatment using ultrasound horn system.
Source: (Parthasarathy et al., 2016).
Fig. 15. Fabrication of CCIPR.
Source: (Alhaji et al., 2018).
4.2.5. Membrane separation/filtration treatment
Membrane
separation is a technique that removes a substantial amount of chemicals and microorganisms in
wastewater (Nqombolo et al., 2018). Numerous membrane separation processes have been used to treat wastewater,
18
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 16. Process flow diagram of the experimental set-up of membrane technology (UF and RO).
Source: (Azmi et al., 2012).
such as ultrafiltration (UF), reverse osmosis (RO), and ‘‘loose RO’’ (Liang et al., 2014). The pre-treatment of POME using
membrane increases its permeability in relation to COD, BOD, TSS, and colour. The use of membrane separation to treat
POME was extensively explored in prior studies and showed significant, high removal efficiency (Khulbe and Matsuura,
2018). Nonetheless, membrane fouling and high cost maintenance are one of the drawbacks from membrane separation
(Huang et al., 2018) . For instance, as shown in Fig. 16, UF and RO were combined to treat POME and the obtained results
were positive, where the removal efficiency of turbidity and BOD were almost 99.0% and 98.9%, respectively, and the final
discharge of effluents appeared to be purified with the appearance of lucent water (Azmi et al., 2012).
Meanwhile, UF blended cellulose acetate (CA) and polyethersulfone (PES) membranes were used in another study to
treat POME. In this study, the bovine serum albumin (BSA) solution was added into POME to test the efficiency of CA and
PES membranes, which revealed that 54.77% of BOD was successfully removed (Idris and Ahmad, 2011). The study further
tested the ability of PES membrane by designing hollow fibres using several lithium halides, specifically lithium chloride
(LiCl), lithium bromide (LiBr), and lithium fluoride (LiF) additives, which reported that the use of 3 wt% LiBr showed the
greatest achievement by reducing 96.7%, 53.12%, and 76.7% of turbidity, COD, and BOD, respectively (Idris et al., 2010).
On the other hand, another study examined two phases of treatment, where the use of AC powder in both chemical
treatment and adsorption was performed in the first phase as a pre-treatment process whereas the integration of UF and
RO was conducted in the second phase for the membrane separation treatment (Ahmad et al., 2003). This experiment
revealed that the removal efficiency of turbidity at 97.9%, COD at 56.0%, and BOD at 71.0% were obtained in the first
phase, which also removed the membrane contamination, resulting in the breakdown of flux. As for the final phase, the
removal efficiency of turbidity at 100%, COD at 98.8%, and BOD at 99.4% were obtained under a neutral condition. Fig. 17
shows the flow diagram in POME treatment.
Referring to Fig. 18, the membrane filtration process that used UF membrane and hollow fibre membrane configuration
that was made using PES material was conducted in another study, which revealed that the overall efficiency of treatment
was achieved through the ponding system. BOD (97.4%), COD (89.77%), SS (93.94%), TKN (94.40%), ammoniacal nitrogen
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Environmental Technology & Innovation 21 (2021) 101258
Fig. 17. POME treatment technique.
Source: (Ahmad et al., 2003).
Fig. 18. Membrane filtration process.
Source: (Nik Sulaiman and Chea,
2013).
content (97.98%), colour (96.53%), and turbidity (79.71%) demonstrated significant reduction (Nik Sulaiman and Chea,
2013).
The development of membrane has been continuously improved based on the enhanced understanding of previous
filtration mechanisms; hence, membrane bioreactor (MBR) system has become a feasible option to treat wastewater. Moro
(2010) conducted an experiment using the MBR system in two phases, namely anaerobic submerged MBR combined with
biogas capture and aerobic submerged MBR, which demonstrated removal efficiency of BOD at 99% (Moro, 2010).
Additionally, Azmi et al. (2012) applied a sandwich membrane by implementing sand-filtration and chitosan-based
coagulation–flocculation process and reported removal efficiency of BOD at 95%. In 2014, another study also made use of
UF membrane to treat POME, but the process was integrated with adsorption as pre-treatment using flat sheet regenerated
cellulose (RC) (Azmi and Yunos, 2014). In particular, adsorption technique was first implemented before the use of UF to
remove any residual or in other words, to prevent further membrane contamination on the surface. The removal efficiency
of BOD was reported at 63.23% (Azmi and Yunos, 2014).
Besides that, epoxidised natural rubber/polyvinyl chloride/microcrystalline cellulose (ENR/PVC/MCC) composite membranes were used to treat POME, where the loadings of MCC were set at 0 w/w%, 5 w/w%, 10 w/w%, and 15 w/w%. The
addition of MCC loads raised the hydroxyl peak of the membranes in the Fourier-transform infrared spectroscopy (FTIR)
spectrum to demonstrate the increase in membrane hydrophilicity. The function of MCC was to serve as a pore-forming
agent since the ENR/PVC/10% MCC offered maximum water flux and well-spread pores. The levels of COD, BOD, and TSS
were reduced to 99.9%, 70.3%, and 16.9%, respectively, during the initial phase of treatment (Arman Alim and Othaman,
2018).
To optimise the process of RO membrane treatment, Said et al. (2017) applied RSM to study the factors that affect the
removal of 3 parameters which were POME concentration, pH and trans membrane pressure (TMP). At the end, based on
the response surface and contour plots, it can be observed that the optimums of parameter removal are achieved when
the concentration of POME was 10.05%, pH of POME was 3.0 and the TMP was 0.50 kPa. The final values of COD, BOD and
colour were 29.974 mg L−1 , 24.33 mg L−1 and 11.76 platinum-cobalt Scale (Pt/Co), respectively (Said et al., 2017).
Hadi et al. (2019) assessed the effluent polishing plant using a UF membrane installed at a palm oil mill for the
treatment of POME. The performance was assessed based on the palm oil mill activity, ponding system and polishing
plant. Characteristic of the incoming and treated effluent, dissolved oxygen (DO) in the aeration ponds and the effluent
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Environmental Technology & Innovation 21 (2021) 101258
Table 5
The advantages, disadvantages and BOD removal of various physicochemical treatment methods for POME.
Treatment method
Advantages
Disadvantages
BOD removal efficiency
(%);
BOD final reading (mg
L−1 ; ppm)
References
Electrocoagulation
-Removal of
contaminants in a
shorter time
- Straightforward process
- Reduce heavy metals
and phenolic compound
-Consumes high current
intensity
-High operating cost
38%
53% (electrode in vertical
orientation)
62% (MP-S arrangement)
70% (Steel wood type
electrode)
83% (At high current
intensity)
94% (Optimum operating
parameters)
(Agustin et al., 2008)
(Nasrullah et al., 2018)
(Nasrullah et al., 2019)
Adsorption
-High removal of
residual oil
-High proficiency
-Relatively less costly
material
- No specific scalability
studies have been
performed
-Performance depend
upon sorbent
97.41% (BPAC)
94% (Mango pit)
63.23% (Pre-treated)
88% (OPB)
57.0% (Dark biochar)
83% (Activated carbon,
(AC))
85 ± 0.5% (CAC)
93.1 ± 0.5% (MFC+AC)
85% (Metallic AC)
60%-65% (Activated
sludge)
(Mohammed and Chong,
2014)
(Asadullah and
Rathnasiri, 2015)
(Azmi and Yunos, 2014)
(Ibrahim et al., 2017;
Wafti et al., 2017)
(Lam et al., 2018)
(Zainal et al., 2018)
(Tee et al., 2016)
(Liew et al., 2019)
(Wun et al., 2017)
Coagulation/Flocculation
-Low cost
-High TSS removal
-Natural coagulant are
biodegradable and not
dangerous to
environment
-Eliminates only
suspended solid (SS) and
residual oil
-Inorganic coagulant are
sensitive to pH change
77.0% ((PAC as a
coagulant)
> 80% (FeSO4 .7H2 O
waste)
89.7% (Hybrid treatment
of US, FeCl3 coagulation
and AC adsorption)
(Poh and Chong, 2014)
(Hossain et al., 2019)
(King et al., 2019)
Advanced oxidation
process (AOP)
-Catalyst can be recycled
-No potential production
of bromated by product
-No sludge generation
-pH adjustment will
increase operating cost
-UV light penetration
can be disturbed by
turbidity
-Energy and cost
intensive processes
-If the catalyst is added
as a slurry, separation
step is needed
74.10% (UV-responsive
ZnO)
100% (ultrasound horn
system with AC)
52 mg L−1 (UV/TiO2
system)
48.05–102.68% (UV/TiO2
system via face-centred
central composite
design)
26 ppm (UV/ZnO
photo-catalysis)
Catalytic steam
reforming (20
wt%Ni/80wt%Al2 O3
catalyst)
99.52% (899.85 ◦ C)
88.21% (449.85 ◦ C)
(Ng and Cheng, 2015)
(Parthasarathy et al.,
2016)
(Alhaji et al., 2018)
(Haji Alhaji et al., 2017)
(Ng and Cheng, 2016)
(Ng et al., 2018)
(continued on next page)
flow rate of the treatment plant have been determined. Due to low process throughput at the mill, the polishing plant
operated at only 60% of its designed capacity. Treatment of effluent showed reduction of BOD from 39.3 ± 5.8 to 6.1 ± 3.8
mg O2 dm−3 (80%–94% BOD removal efficiency) (Hadi et al., 2019). Table 5 shows the advantages, disadvantages and BOD
removal of various physicochemical treatment methods for POME.
Based on the above discussed treatment, it can be said that physicochemical treatment of POME is crucial for effluent
to be discharge into the water stream. As we know, high BOD is caused by high content of organic matters and suspended
solids in POME. Thus, by implementing one of the treatments such as membrane separation technique, suspended solids
can be filtered out and BOD of the final discharge is low.
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Environmental Technology & Innovation 21 (2021) 101258
Table 5 (continued).
Treatment method
Advantages
Disadvantages
BOD removal efficiency
(%);
BOD final reading (mg
L−1 ; ppm)
References
Membrane
separation/Filtration
treatment
-Less chemical utilisation
-Less solid waste
generated
-High elimination of TSS
from POME
-Good quality of water
output and achieved
‘zero
discharge’ concept
-Membrane fouling and
degradation
-High cost maintenance
-High pressure is needed
during operation
-Chemicals in needed to
clean the membrane so
that the maximum
performance of the
membrane can be
achieved
-
98.9% (UF+RO)
54.77% (CA+PES material)
76.7% (PES material with
3wt% LiBr)
99.4% (UF+RO)
97.4% (UF+ PES material)
99% (Anaerobic and
aerobic submerged MBR)
95% (Sandwich
membrane)
63.23% (UF + flat sheet
regenerated cellulose
adsorbent)
70.3% (ENR/PVC/MCC
composite membranes)
24.33 mg L−1 (RO
membrane treatment via
RSM)
80%–94% (UF membrane)
(Azmi et al., 2012)
(Idris and Ahmad, 2011)
(Idris et al., 2010)
(Ahmad et al., 2003)
(Nik Sulaiman and Chea,
2013)
(Moro, 2010)
(Azmi et al., 2012)
(Azmi and Yunos, 2014)
(Arman Alim and
Othaman, 2018)
(Said et al., 2017)
(Hadi et al., 2019)
4.3. Phytoremediation
Phytoremediation is a combined term of a Greek word, Phyto (defined as plant) and Latin word, remedium (defined as
correct or remove an evil). Chaney introduced the idea of phytoremediation (Chaney, 1983). Essentially, phytoremediation
is an environmentally friendly approach that uses green plants, soil, and related microorganisms to remove pollutants. This
green technology is a relatively recent technology in the field of research over the past two decades (since the 1990s) with
relatively low capital, operational cost, and maintenance cost, as compared to other remediation options in wastewater
treatment (Ali et al., 2013; Farraji, 2014). Aquatic plant species, such as water hyacinth (Eichhornia crassipes), water lettuce
(Pistia stratiotes), and vetiver grass, were often used in phytoremediation treatment research for POME, either with diluted
samples or pre-treated samples. The main issues for using industrial effluent samples, such as POME, are the high content
of organic matters and suspended solids. Thus, phytoremediation is often used as a polishing method of treatment,
especially for POME (Md Sa’at and Qamaruz Zamana, 2017). Nevertheless, the disadvantage of phytoremediation is it
depends on climatic and hydrologic changes, where it limits the growth rate of plants used (O’Connor et al., 2019).
For instance, Hamzah (2014) applied phytoremediation using single plants, such as Pistia stratoites, Leersia oryzoides,
and Ludwigia peploides, to treat the final discharge of POME, where Pistia statoites demonstrated removal efficiency of
BOD5 at 93%, COD at 30%, and NH3 -N at 82%; Lersia oryzoides demonstrated removal efficiency of BOD5 at 90%, COD at
27%, NH3 -N at 80%; Ludwigia peploide demonstrated removal efficiency of BOD5 at 93%, COD at 20%, and NH3 -N at 80%
(Hamzah, 2014). Meanwhile, another study applied phytoremediation using water hyacinth (Eichhornia crassipes) as the
aquatic macrophage treatment system (AMATS) (Redzwan, 2014). Firstly, the pre-treatment for the raw POME sample was
conducted to remove its organic load, which ensured that the sample was less harmful to water hyacinth and improved
the performance and its physical state for successful phytoremediation treatment process. As a result, water hyacinth was
found to demonstrate outstanding removal efficiency of both BOD and COD (up to 50%); the removal efficiency of BOD
and COD increased as more water hyacinths were used in the treatment process (Redzwan, 2014).
Vetiver grass (Chrysopogon zizanioides L.) belongs to the same grass family as maize, sorghum, sugarcane, and
lemongrass. Vetiver was first used for soil and water conservation purposes by the World Bank to protect the environment
for the past two decades, particularly in the field of wastewater treatment, due to its prominent morphological and
physiological characteristics and tolerance for adverse conditions (Truong, 2003). For instance, Darajeh et al. (2014) treated
low concentration POME and high concentration POME with vetiver plants in 14 days and found that vetiver plants with
full-grown root and shoots in the hydroponic conditions were able to eliminate up to 90% of BOD in low concentration
POME and 60% in high concentration POME whereas the control set (without vetiver plants) was only able to remove
15% of BOD. Following in 2016, the study was expanded to 30 vetiver grass samples for the treatment of palm oil mill
secondary effluents (POMSE), which assessed the reduction of BOD and COD using response surface methodology (RSM).
The obtained results were remarkable, where up to 96% of BOD and 94% of COD were removed within an experimental
period of four weeks—the lowest final value of BOD was 2 mg L−1 for low concentration POMSE (initial BOD was 1/4 50
mg L−1 ) using 15 vetiver slips in 13 days; the second lowest final value of BOD (initial BOD was 175 mg L−1 ) was 32 mg
L−1 for medium concentration POMSE using 30 vetiver slips in 24 days.
Hence, the potential of phytoremediation as treatment technology to reduce the amount of pollutants in POME was
demonstrated. However, reports of integrating phytoremediation in the constructed wetland treatment remain scarce.
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Environmental Technology & Innovation 21 (2021) 101258
Table 6
The removal efficiency of different plants used to treat POME.
Type of influent
Methodology
Plants
HRT
Removal efficiency
References
Final discharge POME
Phyto-remediation
using single plants
Pistia stratoites, Leersia
oryzoides, Ludwigia
peploides
Not stated
Pistia statoites BOD5 : 93%
COD: 30%
NH3 -N: 82%
Lersia oryzoides BOD5 : 90%
COD: 27%
NH3 -N: 80%
Ludwigia peploides
BOD5 : 93%
COD: 20%
NH3 -N: 80%
(Hamzah, 2014)
Raw POME
Coagulation
pre-treatment
Eichorniacrassipes
Batch-6 week
treatment
BOD: 50%
COD: 50%
(Redzwan, 2014)
Anaerobic treated pond
Hydroponic treatment
Vetiveria zizanioides
Batch-5 weeks BOD:
90% (low concentration);
60% (high concentration)
COD:
94% (low concentration);
39% (high concentration)
(Darajeh et al., 2014)
The diversity of aquatic plants in POME treatment and industrial wastewater treatment should be explored in terms of
the following recommendations proposed in a prior study (Md Sa’at and Qamaruz Zamana, 2017): (1) the use of various
aquatic plants, especially the indigenous plant species as emergent plants, such as Cyperus sp., Scirpus sp., and Canna lilies,
and as floating plants, such as Azolla sp., Ipomoea sp.; (2) the assessment on the plant uptake of nutrients according to
the plant species and mechanism of uptake; (3) the measurement of the plant growth along with the treatment applied;
(4) the use of constructed wetland that promotes biodiversity approach and complete the biosystems for wastewater
treatment; (5) the use of raw POME and introduction of pre-treatment in the system to reduce organic matters and SS.
Accordingly, Table 6 shows the removal efficiency of different plants to treat POME.
5. BOD treatment method for POME: At a glance
Based on the literature reviews, it is found out that biological treatment is mostly utilised by the oil palm miller to treat
POME due to its low costs, cheap and it is non complicated process (Marsidi, 2013), but time consuming process are one
of the main drawback of this treatment. Based on energy and economical aspect, the open ponding system requires large
land application and bring negative impact towards the. Besides that, for an effective POME treatment, the optimum
POME treatment temperature must be higher than the unprocessed POME, which commonly in between 74.85 ◦ C to
84.85 ◦ C. This is due to the heat released that can be utilised as energy, which produced a very high value by-product
(How et al., 2018). Moreover, tertiary treatment processes mostly are dependent on the main treatment due to the natural
process. Thus, tertiary process is best combined with conventional process or biogas capture system for an effective
POME treatment. Phytoremediation is well known for its environmental friendly treatment that uses green plant, soil
and related microbes to treat POME. Due to relatively low capital, operational cost and maintenance cost, researchers are
likely to focus on phytoremediation for further POME treatment (Farraji, 2014). Nevertheless, phytoremediation depends
on climatic and hydrologic changes that limit the growth rate of plant used. For biogas capture system, the disadvantage
of these technologies is palm oil millers need to invest lots of money to construct biogas plant and the complex power
production system. The methane capture process that generate valuable by-product is pondered as new innovation, thus
money spent on this latest technology might take a long time to complete and reasoned for bad investment. Furthermore,
the people working in the palm oil industries that applied loan for high investment think that the profit return process is
slow and the amount of time taken to recover the cost of an investment is long (approximately 5 years through feed-in
tariff payment) (Chin et al., 2013). As a result, many aspects must be taken to minimise the bad impact caused by the
POME before it is being discharge to the water stream, taking account the pros and cons of each treatment, so that suitable
and effective POME treatment process can be achieved.
6. Conclusion and future development
Evidently, the palm oil generation has contributed to the economic development. However, the environmental issues
that are related to the production of wastewater from the palm oil mills have gained growing public concern. Thus,
specific actions and initiatives must be implemented to ensure environmental sustainability. As the enforcement of
laws and regulations has become stricter, it has become crucial for the oil palm industry to demonstrate development
progress especially in ensuring their compliance with the standard discharge limits for the final discharge of POME. The
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Environmental Technology & Innovation 21 (2021) 101258
sustainability of palm oil industry is highly affected by the effectiveness of waste management in the industry to reduce
the environmental effects while increasing the economic benefits. For palm oil producers like Malaysia, Indonesia Thailand
and other tropical developing countries, the utilisation of matured AD-based biogas technologies in treating wastewater
is installed in the pipeline (Hosseini and Wahid, 2013). For instance, POME in Malaysia is treated via AD that generated
biogas as by-product due to the biodegradable organic matter in POME. AD is also well known and recommended for
POME treatment. Furthermore, biological treatment needs low energy to operate, no emissions of bad odour and valuable
biogas production (Loh et al., 2017a,b). Since 2016, biogas is widely used for electricity generation to enhance off-grid
or on-grid activities, while 28% of the biogas power plant in Malaysia either sell their excess energy to national grid or
utilised the self-produced energy to contribute the utility need of downstream activities (Loh et al., 2017a,b). This same
goes in Indonesia and Thailand, where these countries encouraged their local palm oil industry towards public–private
partnership with several overseas investments involved to focus on sustainable management and the demand for energy.
In addition, electricity generation from biogas from POME has increased in demand in Thailand (Hosseini and Wahid,
2013). With the increasing global palm oil production annually, issues of discharging effluents into the environment,
particularly the water stream, river, and sea, has emerged, especially of those that do not properly treat the effluents,
resulting in environmental pollution and negative consequences to the aquatic lifeforms. Despite the implementation of
numerous biological treatment processes, most of the processes used do not discharge effluents that meet the discharge
limit of BOD. Some of the existing conventional treatment processes also deliver similar unfavourable results. Thus, this
review article gave opportunity to researchers and palm oil millers to discover more on the potential of existing BOD
treatment method and implement new or integrated methods, so that the BOD levels can be achieved based on the
standard discharge requirement .
For discharging a higher quality POME, we will assume an integrated system for BOD treatment, advanced anaerobic
expanded granular sludge bed (AnaEG), as the first stage and applies membrane separation process as the second stage.
During the first stage, most of the organic wastes will be converted to biogas and high strength POME are generated
through handling of a different range of OLR at short HRT. The first stage will reduce the membrane fouling and increase
the lifespan of the membrane. In the second stage, UF membrane is used to remove the huge amount of suspended solid
whereas RO membrane is used to segregate dissolved solids. At the end of the process, crystal clear POME can be recovered
and can be discharged into the water stream with BOD level within the standard discharge requirement. Besides that, it
is also suggested to include key data on the reduction of BOD level or BOD removal efficiencies as references for future
research.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgement
The authors proudly received financial support from Takasago Thermal Engineering, Malaysia, Cost Centre No.
R.K130000.7343.4B366.
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