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Chemosphere 59 (2005) 1575–1581
www.elsevier.com/locate/chemosphere
Baseline study of methane emission from open digestingtanks of palm oil mill effluent treatment
Shahrakbah Yacob a,b,*, Mohd Ali Hassan b, Yoshihito Shirai a,Minato Wakisaka a, Sunderaj Subash c
a Department of Biological Functions and Engineering, Graduate School of Life Science and Systems Engineering,
Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu, Fukuoka 808-0196, Japanb Department of Bioprocess Technology, Faculty of Biotechnology and Biomolecular Sciences,
Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysiac Felda Palm Industries Sdn. Bhd., Balai Felda, Jalan Gurney Satu, 54000 Kuala Lumpur, Malaysia
Received 17 May 2004; received in revised form 5 November 2004; accepted 17 November 2004
Abstract
Anthropogenic release of greenhouse gases, especially CO2 and CH4 has been recognized as one of the main causes
of global warming. Several measures under the Kyoto Protocol 1997 have been drawn up to reduce the greenhouse
gases emission. One of the measures is Clean Development Mechanisms (CDM) that was created to enable developed
countries to cooperate with developing countries in emission reduction activities. In Malaysia, palm oil industry par-
ticularly from palm oil mill effluent (POME) anaerobic treatment has been identified as an important source of
CH4. However, there is no study to quantify the actual CH4 emission from the commercial scale wastewater treatment
facility. Hence, this paper shall address the CH4 emission from the open digesting tanks in Felda Serting Hilir Palm Oil
Mill. CH4 emission pattern was recorded for 52 weeks from 3600 m3 open digesting tanks. The findings indicated that
the CH4 content was between 13.5% and 49.0% which was lower than the value of 65% reported earlier. The biogas flow
rate ranged between 0.8 l min�1 m�2 and 9.8 l min�1 m�2. Total CH4 emission per open digesting tank was
518.9 kg day�1. Relationships between CH4 emission and total carbon removal and POME discharged were also dis-
cussed. Fluctuation of biogas production was observed throughout the studies as a result of seasonal oil palm cropping,
mill activities, variation of POME quality and quantity discharged from the mill. Thus only through long-term field
measurement CH4 emission can be accurately estimated.
� 2004 Elsevier Ltd. All rights reserved.
Keywords: Greenhouse gases (GHG); Methane (CH4); Palm oil mill effluent (POME); Anaerobic open digesting tank
0045-6535/$ - see front matter � 2004 Elsevier Ltd. All rights reserv
doi:10.1016/j.chemosphere.2004.11.040
* Corresponding author. Address: Department of Biopro-
cess Technology, Faculty of Biotechnology and Biomolecular
Sciences, Universiti Putra Malaysia, 43400 UPM Serdang,
Selangor, Malaysia. Tel.: +60 3 89468414; fax: +60 3 89430913.
E-mail address: [email protected] (S. Yacob).
1. Introduction
Climate change attributed to the greenhouse gases
(GHG) emissions has been at the forefront of current re-
search in the past decade. These efforts were clearly sta-
ted by Kyoto Protocol with the objective of reducing the
GHG emissions by 2008–2012 (Brown et al., 1998).
ed.
1576 S. Yacob et al. / Chemosphere 59 (2005) 1575–1581
Numerous publications have been published concerning
the effects on climate change, sources and sinks of GHG,
factors and mechanisms that affect the GHG emissions
and controlling strategies for GHG emissions (Bogner
et al., 1995; Sonesson et al., 2000; Avnimelech and
Shechter, 2001; El-Fadel et al., 2001; Le Mer and Roger,
2001; Gonzlez-Gil et al., 2002).
Despite being a developing and carbon sink country,
Malaysia to a certain extent also contributes to the
GHG emission. One of the major sources of GHG in
Malaysia is from the palm oil mill wastewater treatment
system. Briefly, palm oil industry is the highest grossing
crop which was the third largest contributor to Malaysia
Gross Domestic Product at 8% last year. In 2003, the total
income from the palm oil based products export generated
more thanUS$6 billion comprising half of the world palm
oil production. Palm oil is extracted from the mesocarp of
the fruitlets while palm kernel oil is obtained from the ker-
nel. In the process of producing palm oil, a considerable
amount of water is needed (Agamuthu, 1995), leading to
the generation of large volumes of wastewater also known
as palm oil mill effluent (POME).
It was estimated that an average of 32 million tonnes
of POME per year was produced in the 1990s (Ma, 1999),
with average values of 25000 mg l�1 biochemical oxygen
demand (BOD) and 50000 mg l�1 chemical oxygen de-
mand (COD). The main practice of treating POME is
by using ponding and/or open digesting tank systems.
As cited by Ma et al. (1999), the end product of the
anaerobic digestion of POME is a mixture of biogas
(65% CH4, 35% CO2 and traces of H2S) from laboratory
studies and approximately 28 m3 of biogas can be ob-
tained from 1 tonne of POME (Quah and Gillies,
1984). Unfortunately, these gases are being released into
the atmosphere and could have detrimental effects to the
environment. At present, there is no available data on the
GHG emission from the actual waste treatment system.
Therefore this paper will discuss the CH4 emission pat-
tern based on CH4 composition and flow rate from the
commercial anaerobic open digesting tanks. The research
study also demonstrates the influence of mill�s operationand oil palm seasonal cropping on the CH4 emission. It
is anticipated that the information generated from this
study will be used as a guideline in establishing more real-
istic baseline of GHG emission for the palm oil industry.
2. Site descriptions and methods for monitoring
2.1. Serting Hilir Palm Oil Mill
The mill is located in the state of Negeri Sembilan
which approximately 200 km from Kuala Lumpur,
Malaysia. It is owned by the Felda Palm Industries
Sdn. Bhd. (subsidiary of Felda, the largest palm oil
based company in Malaysia). It has the capacity to pro-
cess fresh fruit bunch (FFB) at 54 tonnes h�1. The mill
was commissioned in 1986 to receive and process the
FFB from Felda plantations and its surrounding areas.
To cater for the POME generated from the oil extraction
process, the mill is equipped with an extensive wastewa-
ter treatment facility which occupies 75% of the total
mill land area. The wastewater treatment facility com-
prises of few processes, an anaerobic, facultative anaero-
bic and aerobic (algae) stages.
2.2. Open digesting tank system
The measurement of CH4 emission rate was deter-
mined at the anaerobic treatment using two out of the
six open digesting tanks. The observation was done for
52 weeks to ensure substantial data is collected to indi-
cate the role of seasonal cropping and other factors.
Each digesting tank has the capacity of 3600 m3 of
POME with a hydraulic retention time of 20 days. The
dimension of the open digesting tank is 19.5 m ·12.2 m (diameter · height). The tank was designed to
treat 180 m3 day�1 of raw POME and an equal volume
of treated POME is displaced using gravity flow into
the facultative anaerobic ponds.
2.3. CH4 measurement from open digesting tanks
The biogas produced was collected using a static col-
lection chamber with a surface area of 0.7 m2 and con-
nected to a tube for biogas sampling and detection. In
each open digesting tank a duplicate of static collection
chamber provided a second sampling point. The biogas
flow rate was recorded using a wet gas meter (OSK
14608, Shinagawa Seiki Co.) with a flow rate capacity
of 2 l h�1 to 600 l h�1, while the CH4 gas composition
was determined using gas analyzer (XP-314A, Shin-Cos-
mos Electrics Co. Ltd) plugged to the tubing.
2.4. Chemical oxygen demand (COD)
POME samples were collected daily from the inlet
and outlet of the open digesting tanks to determine the
total carbon removal. COD was measured using the
Standard Methods for the Examination of Water and
Wastewater (APHA, 1992). At the same time the CH4
emission pattern was recorded as described in the previ-
ous section. Correlation between the CH4 and total car-
bon removal was established and plotted.
3. Results
3.1. CH4 emission composition and rate
The average CH4 composition recorded was approx-
imately 36.0%, ranging from 13.5% up to 49.0% (Fig. 1).
0
10
20
30
40
50
60
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51
Week of sampling
CH
4 co
nten
t (%
)
0
5
10
15
20
Bio
gas
flow
rate
(l p
er m
in p
er m
)2
Methane (%) Biogas Flowrate
Fig. 1. Biogas emission pattern over 52 weeks of observation.
S. Yacob et al. / Chemosphere 59 (2005) 1575–1581 1577
Over the period of 52 weeks the average was marginally
higher than data collected in the preliminary study car-
ried out in October 2001 (Shirai et al., 2003). No other
gases such as CO2 and H2S were chemically determined.
This is because of insignificant concentration of H2S
(<2000 ppm) and assuming that the remaining biogas
was mainly CO2. It has been established that CH4 and
CO2 are the main gases produced from POME anaero-
bic biodegradation (Ma, 1999). From Fig. 1, the flow
rate of biogas was negatively correlated to the CH4 com-
position. As evident in week 21 (November 2002) until
week 25 (December 2002) the flow rate dropped from
9.8 l min�1 m�2 to the lowest of 0.9 l min�1 m�2 while
the CH4 composition increased up to 49.0%. Vice versa
from week 44 (April 2003) until week 50 (June 2003),
significant increased in biogas flow rate coupled with
the sudden declined in CH4 composition. These phe-
nomenons were also demonstrated through out the 52-
week observation with minor troughs. An average of
5.4 l min�1 m�2 biogas flow rate was recorded in this
study.
3.2. Total CH4 emission from open digesting tanks
Based on the data collection over 52 weeks, the CH4
emission from the open digesting tanks was influenced
by the activities of the palm oil mill and the seasonal
cropping (Fig. 2a). Commencement of low crop season
in November 2002 was marked by lower volumetric dis-
charge of POME, and coupled with a decline in CH4
emission. The lower emissions continued until May
2003, before increased FFB, POME discharge and
CH4 emission were observed. During this period, a
long year-end public holiday closed the palm oil mill
for a few days, further reducing emissions. In general
1 tonne of POME will be generated from every 2 tonnes
of FFB processed from the mill. As shown in details
in Fig. 2b, the lowest CH4 emission per tank was
recorded in week 25 and week 38 at 0.64 tonne
week�1 and 0.62 tonne week�1 respectively. The decline
in FFB processed was coupled by a decrease in CH4
emission.
An average of 518.9 kg day�1 per tank of CH4 was
emitted from the mill. With a total of 273 days of oper-
ation and six open digesting tanks, it is estimated from
July 2002 until June 2003, 849 tonnes of CH4 was re-
leased to the atmosphere (Table 1).
3.3. Relationship between CH4 emission rate, COD
removal and POME discharged
A correlation between CH4 emission rate and total
COD removal was found and plotted in Fig. 3. An aver-
age of 0.109 kg of CH4 was emitted from a kilogram of
carbon removed. During this observation an average
COD of raw POME was 43288 ± 1924 mg l�1 while
the treated POME was 8327 ± 2049 mg l�1. Based on
these figures the open digesting tank system was able
to remove 34.9 kg of COD per 1 m3 of POME. This indi-
cates approximately 80.7% of COD was removed before
the treated POME being channeled into the facultative
ponds for further treatment. At the facultative ponds,
0
5000
10000
15000
20000
25000
30000
35000
Jul-02 Aug-02 Sep-02 Oct-02 Nov-02 Dec-02 Jan-03 Feb-03 Mar-03 Apr-03 May-03 Jun-03
Week of sampling
FFB
& P
OM
E (
tonn
e pe
r m
th)
0
20
40
60
80
100
120
140
CH
4 (t
onne
per
mth
)
FFB POME Methane
Low crop season
Year-end public holidays
0
100
200
300
400
500
600
700
800
900
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51
Week of sampling
POM
E (
tonn
e pe
r w
eek)
0
5
10
15
20
CH
4 (t
onne
per
wee
k)
POME Methane
(a)
(b)
Fig. 2. (a) Monthly profiles of CH4 emission over the production of FFB and POME. (b) Weekly CH4 emission and amount of POME
discharged.
1578 S. Yacob et al. / Chemosphere 59 (2005) 1575–1581
CH4 emission was still being observed (visual assessment
through bubbling activities). However the volumetric
flow rate was significantly low and cannot be detected
by the wet gas meter.
As shown in Fig. 4, for every tonne of POME trea-
ted, an average of 5.5 kg of CH4 was emitted from the
open digesting tanks. Based on this ratio and total
POME discharged (July 2002–June 2003), it was
estimated that 864 tonnes of CH4 is emitted from the
anaerobic treatment. This value is not far from the ac-
tual CH4 measured during the 52 weeks observation
(Table 1).
4. Discussion
From this study we found out that the CH4 compo-
sition under normal operation of the open digesting
tanks was significantly lower than what was reported
earlier by Ma et al. (1999) which was 65%. Lower CH4
composition and ratio between biogas emission and
amount of POME discharged were largely attributed
to the lack of operational control and high tendency
of O2 contamination in the open digesting tanks, thereby
reducing the anaerobic degradation efficiency. On the
other hand, fully controlled reaction inside the closed
Table 1
Estimation of CH4 emission from July 2002 until June 2003
Total FFB processed 291790 tonnes
Total POME discharged 157035 tonnes
Average CH4 emission rate (per tank) 518.9 kg day�1
Average CH4 composition 36%
No. of days processed 273 days
Approximate CH4 emitted from
six open digesting tanks
849 tonnes
Approximate CO2 emitted from
six open digesting tanks
4672 tonnes
Total CO2 equivalent emitted from
Serting Hilir Palm Oil Milla21652 tonnes
a CH4 is 20 times global warming potential for 100 year
more than CO2 (Milich, 1999).
S. Yacob et al. / Chemosphere 59 (2005) 1575–1581 1579
bioreactor and completely anaerobic condition was
achieved by Ma et al. (1999). In this study, the data
was derived from a commercial open digesting tanks
which governed by factors such as seasonal fluctuations,
quality and quantity of POME and activities of mill.
Hence, measurement of CH4 emission from commercial
activities should be carried out in situ as to prevent any
over estimation of CH4 release into the atmosphere.
We postulated that there is a transfer of O2 from the
atmosphere into the effluent through three main mecha-
nisms. Firstly, O2 can be introduced when fresh POME
is being pumped into the tank causing vigorous mixing
of the effluent. Secondly, slow mixing of effluent through
rising of biogas bubbles and minor eruption of biogas.
These conditions reduce the anaerobic level in the diges-
0
200
400
600
800
1000
1200
1400
4000 4500 5000 5500 60
Total carbon rem
CH
4 em
issi
on (
kg p
er d
ay)
Fig. 3. Relationship between CH4 emi
ter. The third mechanism is the low concentration of
hydrogen in the POME that has escaped into the atmo-
sphere (under the open digesting tank operation).
Hence, the hydrogen is not available for hydrogen-utiliz-
ing homoacetogens and hydrogen-utilizing methanogens
to produce acetate and methane (Lay et al., 1998). There
is also a possibility that the CH4 generated from the
anaerobic process was consumed by methanotrophic
microorganisms as reported in the landfill research by
Bogner et al. (1995).
Attempts to evaluate the affect of seasonal cropping
of oil palm to the biogas flow rate or methane emission
was shown in the second part of the study. Significant
reduction in CH4 emission rate was observed from Octo-
ber 2002 until May 2003 when the amount of POME
discharged declined. This is a normal condition, as the
oil palm will experience low cropping season for
6 months before increasing its production for the next
6 months. Occasional public holidays and closure of
the mill also have an affect on the CH4 emission as no
POME will be loaded into the open digesting tanks.
Therefore lesser organic matter to be converted into
CH4. As shown in Table 1, a total of 157035 tonnes of
POME was discharged from July 2002 until June 2003
whereas the full potential of six open digesting tanks is
295000 tonnes. This indicates when the amount of
POME discharged is below 1080 tonnes day�1 not all
the open digesting tanks will be fed daily or fed at lower
feeding rate (<180 m3 day�1). This in turn reduces the
loading rates for anaerobic process and hence prolongs
the retention of POME in the digester. Long public
00 6500 7000 7500 8000
oved (kg per day)
ssion and total carbon removed.
0
1
2
3
4
5
6
7
8
9
10
200 300 400 500 600 700 800 900
POME (tonne per day)
CH
4 (t
onne
per
day
)
Fig. 4. Relationship between CH4 emission and POME discharged.
1580 S. Yacob et al. / Chemosphere 59 (2005) 1575–1581
holidays as observed in weeks 25 and 26 also have an ef-
fect on the biogas production pattern. This may explain
the decline in the CH4 emission rate.
Other reasons for the fluctuation of emission include
the quality and quantity of POME discharged from the
mill. Upon discharge from the mill, POME is in the form
of highly concentrated dark brown colloidal slurry of
water, oil and fine cellulosic materials from sterilisation
and clarification stages. The final POME would include
hydrocyclone washing and cleaning up processes in the
mill (Agamuthu, 1995). Therefore, the chemical proper-
ties of POME vary widely and depend on the operation
and quality control of individual mill. Our COD results
also support this statement as the POME COD may
vary from 41200 mg l�1 up to 47800 mg l�1 (data not
shown). This may influence the characteristics of POME
discharged from the mill. From Figs. 2a and 4, it can be
seen that the amount of CH4 emitted is a function of
POME discharged from the mill. We also have estab-
lished the ratio between amount of POME discharged
and CH4 emission which is for every tonne of POME,
5.5 kg of CH4 will be emitted. The calculated amount
of CH4 from the ratio is slightly higher than the actual
emission measurement for 52 weeks.
In line with the commencement of Kyoto Protocol in
2008 until 2012, this study provides valuable informa-
tion in establishing the GHG emission particularly in
the palm oil industry. Using the CDM as a platform,
the developed nations would be able to partner with
developing nations in the effort of reducing GHG. Few
technologies are currently being developed and opti-
mized to reduce the GHG emission. Among them are
the utilization CH4 as a renewable energy to generate
electricity, production of organic acids and biodegrad-
able plastic from POME (Hassan et al., 1997; Noraini
et al., 1999). It is expected that through the integration
of such technologies into the POME wastewater treat-
ment system could lead to a substantial GHG reduction.
Additional income could be generated by the production
of value-added products such as electricity, organic acids
and biodegradable plastic. On top of that the project will
generate Certified Emission Reduction (CER) for sale or
export. Then this CER can be used for developed na-
tions commitments to mitigate their GHG emissions.
The palm oil industry can derive new economic, devel-
opment and environment benefits through the imple-
mentation of CDM projects.
5. Conclusion
Results indicated that an average of 36.0% and
5.4 l min�1 m�2 of CH4 composition ad biogas flow rate
respectively was recorded under normal mill operation.
While CH4 could be emitted at 518.9 kg day�1 from
one open digesting tank. A correlation was also estab-
lished between CH4 emission and COD where 0.109 kg
of CH4 for every kilogram of COD removed. While
for every tonne of POME discharged, an average of
5.5 kg of CH4 will be emitted from the anaerobic treat-
ment. The results presented herein indicate that a long-
term observation is crucial to determine the CH4
S. Yacob et al. / Chemosphere 59 (2005) 1575–1581 1581
emission as it is severely governed by the seasonal crop-
ping of oil palm. Secondly, mill�s activities will also influ-
ence the quality and quantity of POME discharged
which in turn affect the anaerobic process. Therefore,
CH4 emission estimation should be based on field mea-
surement and the method used in this study can be used
as a guideline for future baseline study in the other palm
oil mills.
Acknowledgments
The project was sponsored by Kyushu Institute of
Technology, Japan. The authors would like to thank
the management of Serting Hilir Palm Oil Mill for their
cooperation throughout the study.
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