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World Applied Sciences Journal 35 (3): 344-351, 2017
ISSN 1818-4952
© IDOSI Publications, 2017
DOI: 10.5829/idosi.wasj.2017.344.351
Comparison of Biogas Productionfrom Macroalgae Eucheuma cottonii
in Anaerobic Degradation under Different Salinity Conditions
Mujizat Kawaroe, 2Salundik, 1Rhojim Wahyudi and 1,4Dea Fauzia Lestari
Department of Marine Science and Technology, Faculty of Fisheries and
Marine Science Bogor Agricultural University, Dramaga, Bogor, Indonesia
Department of Animal Productions and Technology, Faculty of Animal Science,
Bogor Agricultural University, Dramaga, Bogor, Indonesia
Surfactant and Bioenergy Research Center (SBRC),
Bogor Agricultural University, Baranangsiang, Bogor, Indonesia
Center for Environmental Research, Bogor Agricultural University, Dramaga, Bogor, Indonesia
Abstract: Eucheuma cottonii (E.cottonii) is one of the most widely cultivated macroalgae species in Indonesian
marine culture. Some of the harvested biomass has been rejected for utilization by industry, however its
utilization as a feedstock for biogas production is deemed as a feasible alternative use. In the present study,
the chemical characteristics of the substrates, acclimatization process of the anaerobic digestion inoculum and
biogas production from E. cottonii at different salinity levels (0 and 29 ppt) were analyzed using the batch
method. Biogas production was carried out in a 30L digester made of fiber with an additional modification
gauge. The lignin content, carbohydrate content and C/N ratio were 2.77±0.083%, 63.89±1.162% and 23.13,
respectively. Generally, the pH ranges during acclimatization were lower than batch process. The range for
0 ppt digester were 5.9-7.2 in acclimatization and 7-7.8 in batch process, in other hand the range for 29 ppt
digester were 6.1-7.3 in acclimatization and 7.1-8 in batch process. The highest daily biogas production on 0 ppt
digester was 2.54 mLg 1VS and in 29 ppt digester was 2.05 mLg 1VS. These productions were not significantly
different between two treatments. Cumulative biogas and methane volume of 0 ppt treatment were higher than
29 ppt.
Key words: Keywords
Eucheuma cottonii
South of Sulawesi Province. This area has the same
characteristics as coastal areas in Indonesia, but has less
electricity and freshwater availability. Therefore, the
challenge is how to convert the rejected macroalgae into
biogas without a fresh water mixture and washing before
anaerobic degradation process. Previous research was
conducted by Kawaroe et al. [1] in the laboratory using
fresh water to wash and mix with the substrate to reduce
the sand and mud contents of the substrate.Due to fresh
water limitations in the field, the washing and mixing
process used local seawater in that area.
Biogas is produced from anaerobic degradation
by methane-producing bacteria [2,3,4], Gram-negative
basil bacteria [5], or Gram-positive bacteria [6].
Eucheuma cottonii (E. cottonii) is a cultivated
macroalgae species that grows in Indonesia and it is used
as an export commodity. Sometimes the harvest product
does not qualify as food grade export criteria because of
its low quality, then will be rejected. The rejected product
opens an opportunity to develop alternative biogas
energy from biomass. This product can be collected and
stored for biogas source especially in coastal areas where
biogas can be utilized by fishermen for electricity and
household necessities.
One of the most famous cultivation areas of
E. cottonii is PuntondoVillage in the Takalar Region,
Corresponding Author: Mujizat Kawaroe, Department of Marine Science and Technology,
Faculty of Fisheriesand Marine Science Bogor Agricultural University, Dramaga, Bogor, Indonesia.
World Appl. Sci. J., 35 (3): 344-351, 2017
The biodegradation process is divided into four
stages: hydrolysis, acidogenesis, acetogenesis and
methanogenesis [3]. The lignin content is one of the most
influential factors in the biodegradation process. Lignin is
composed of heterogeneous and complex carbohydrates
and is, like cellulose, a component of the cell wall in
plants; lignin is difficult for bacteria to decompose [7].
The lignin content in macroalgae is relatively lower (15% w) than that in terrestrial plants (15-20%) [8, 9, 10]
and according to Kawaroe et al. [13] lignin content in
E. cottonii is 0.85%. In addition, E. cottonii biomass
contains 35.6-78.3% carbohydrate [11,12]. Therefore, this
biomass has good potential as a substrate for anaerobic
biodegradation and biogas production [13].
This research was focused on different salinity of
mixture water for anaerobic degradation. There were two
salinity compared in the process, 0 ppt (fresh water) and
29 ppt (seawater). The observations concerned on
chemical characteristic of E. cottonii as a substrate,
acclimatization process of the inoculum and substrate and
biogas production of rejected E. cottonii under different
salinity conditions (0 ppt and 29 ppt).
material reduced the inhibition factor in the anaerobic
degradation process [14,15], while the starter inoculum
was derived from a manure and water mixture (1:2) with
different salinity levels (0 ppt and 29 ppt).Water is an
important element for biological process on biogas
production. The composition should be sufficient to
support degradation activity. In this research the
composition of water was more than manure itself.
The foods of cow were dry weeds, these food condition
determine the type of the manure (texture and solidity).
The manure was compact and needed much water to make
perfect dissolved substrate.
The substrate and starter were acclimatized as an
inoculum in as much as 24 L of a working volume of the
digester. The purpose of acclimatization was to adapt the
bacteria to the macroalgae substrate to produce highquality biogas. The inoculum was observed until it
reached a neutral pH and produced biogas. Next, 1.2 L of
the substrate per day was loaded in each digester under
different salinity conditions, followed by releasing the
same amount of slurry. The loading volume was
determined by multiplying the loading rate of 0.5 kg
CODL 1day 1 by the working volume of the digester and
then dividing by the chemical oxygen demand (COD)
value of the macroalgae substrate used. During
acclimatization, the inoculum was stirred and analyzed by
measuring the pH, temperature, salinity and biogas
production every day. The biogas composition was
analyzed once per week.
Research Location: The research was conducted from
September 2014 to April 2015 at Puntondo Village, Takalar
Region, South of Sulawesi Province. Macroalgae
samples were taken from the rejected product of the
harvest. The samples were then analyzed at the Chemical
Oceanography and Animal Science Laboratory of
Hasanudin University and Police Forensic Laboratory of
Makassar. Fresh manure source was taken from cattle
resident farm around research site in Puntondo.During the
anaerobic process, two digesters with a 30 L capacity
made from fiber that were equipped with two tanks as the
substrate input (inlet) and sludge output (outlet) were
used. The digesters could be easily moved and had a
modified gauge for biogas production sampling. The gas
volume was determined by water displacement from a onegallon water tank connected to the experimental digester
using the batch method.
Anaerobic Biodegradation Using Batch Method:
The process of anaerobic biodegradation was started by
removing half of the slurry volume on digesters (12 L) and
then by adding the same amount of substrate under
different salinity conditions to each digester. The
substrate contained 4 kg of E. cottonii and 8 L of water
(0 ppt and 29 ppt). The substrate input was loaded once
and stirred every day gently. The mixing helped to
homogenize substrate and we should keep anaerobic
condition inside digester. The design of digester is also
important to make anaerobic condition during biogas
production process. The position of inlet and outlet
should be equal with upper past of main digester. The
substrate in inlet and slurry in outlet will cover the holes
of main digester to make sure there is no air comes in and
out of digester.The pH, temperature, salinity, biogas and
methane production volume were measured every day,
while the biogas composition and COD were measured
once per week.
Substrate and Inoculum Preparation: The substrate was
prepared by soaking macroalgae under water with
different salinity conditions. In the first reactor, macroalga
was mix with fresh water (0 ppt). While in the second
reactor, macroalga was mix with saline water (29ppt).
Both are in the ratio 1:2. The leaching and dilution of raw
World Appl. Sci. J., 35 (3): 344-351, 2017
Data Analysis: The rejected substrate of E. cottonii was
cleaned from mud and sand and then, the blend was used
in the juice form. The water, ash, carbohydrates, lipid,
protein and nitrogen contents were analyzed [16]; the
lignin content was measured according to Van Soest [17]
and the total organic carbon content was measured
according toWalkey and Black [18]. A refractometer,
digital pH meter and thermometer measured the salinity,
pH and temperature, respectively. The biogas volume was
calculated by measuring the water volume removed from
the gallon tank. The biogas sample was accumulated in a
plastic sample bag and was then analyzed in a laboratory
by gas chromatography. The substrate sample was also
collected to measure the COD and then, it was analyzed
[19]. ANOVA General Linear Model analyzed data
statistically using Minitab version 14 to compare 0 ppt
and 29 ppt treatment.
Table 1: Proximate analysis of Eucheuma cottonii.
Euchema cottonii
Water content (%)
Ash content (%)
Lipid (%)
Carbohydrate (%)*
Protein (%)
Lignin (%)
Total Organic Carbon (%)
Nitrogen (%)
C/N rasio
* by difference
inhibition occurred when the lipid content was greater
than 30% under anaerobic degradation. On the other
hand, high protein content in the substrate is not
recommended because of the high risk of inhibition
by ammonia [26, 27, 28]. The carbohydrate content
of E. cottonii in Indonesia commonly ranges between
35.6-78.3% [11]. Its polysaccharide content are composed
to carbohydrates, such as floridian starch and
xylenes, which are easily decomposed by bacteria [29]
and they potentially produce biogas by anaerobic
degradation [30].
The lignin content in E. cottonii was reported to be
2.77±0.083%, which is categorized as a low content (<7%),
simplifying the degradation of raw materials [13,15,31,32]
such as polysaccharides, cellulose and hemicelluloses by
bacteria[2,24,33] to produce high methane. A high content
of lignin (>15%) can inhibit biodegradation [10,34].
The C/N ratio value was 23.13, which is categorized
as a normal and balanced range for anaerobic
biodegradation, whose optimum C/N ratio is 20-30 [35, 36,
37]. According to Wu et al. [38] and Wang et al .[39], the
balanced condition will increase methane production
11-16 times and produce low concentrations of total
ammonium nitrogen (TAN) and free ammonia.Low C/N
ratios can promote the increasing of ammonia
concentrations because nitrogen is released and
accumulated in the form of ammonia, exceeding the
concentration required to inhibit microbial growth and
anaerobic degradation. In the same way, high C/N ratios
can increase the growth of the methanogen population
because its protein requirements are met; thus, there is no
reaction with the residual carbon content of the substrate
and less biogas is produced[1,37].
Chemical Characteristics of E. cottonii: The water
content of E. cottonii was 16.3±12:23%. A high water
content of the substrate enhances the growth of
microorganisms under degradation [20]. The ash content
was 14.39±0.035% (Table 1). According to Matanjun et al.
[21] this species has a fairly high ash content.The ash
consisting of several major minerals, such as sodium,
potassium, calcium and magnesium. Minerals such as
calcium and magnesium are needed to improve the growth
of microbes and have a positive impact on the granulation
and sodium role in the formation of ATP and NADH [22].
Chen et al. [14] and Soto et al. [23] reported that the
medium concentration encourages microbial growth in
anaerobic digesters, but excessive concentrations can
diminish the growth, causing inhibition or toxicity.
According to Chen et al. [14], the optimum
concentration of Ca2+ and Na+ ions for methane
synthesis from acetate was found to be 200 mgL 1
and 230 mgL 1respectively, whereas a concentration of
8,000 mgL 1of either ion inhibited the process.
The organic content consists of lipids, carbohydrates
and proteins of macroalgae, whichare hydrolyzed by
microorganisms in order to produce methane [24]. This
species has the highest levels of carbohydrates
(63.89%± 1,162), with 0.01±1.30% of lipids and 5.33%±0.01
of proteins. The lipid content is within the range of
most macroalgae (1-3%) [21]. Cirne et al. [25] reported
that no inhibition of methane production occurs if the
lipid concentration is greater than 18%; however,
Inoculum and Substrate Acclimatization Process:
The acclimatization process for the inoculum was
indicated by a stable or neutral pH value in the digester.
Both treatments had a different day to reach stable pH.
World Appl. Sci. J., 35 (3): 344-351, 2017
The increases in the pH value in both the digesters
showed effective anaerobic degradation and that
the bacteria adapted to the substrate. According to
Igoni et al. [42], the anaerobic process works well when
the pH levels are between 6 and 8. Substrate should be
continually loaded to acclimate and adapt manure
bacteria to the macroalgae substrate under different
salinity conditions. The pH was non- significantly
different between 0 ppt and 29 ppt digester on
acclimatization process. The pH range in 0 ppt digester
was 5.9-7.2, while in 29 ppt digester was 6.1-7.3. On the
other hand there was a significant difference on pH
fluctuation in time between starting and ending time of
acclimatization process.
During acclimatization
production of biogas was 13.75mLg 1VS in 0 ppt digester
and 4.72mLg 1 VS in 29 ppt digester (Fig. 2). While the
cumulative methane volume were 7.94 mLg 1 VS in 0 ppt
digester and 2.38 mLg 1VS in 29 ppt digester. There were
significantly different of cumulative biogas and methane
production between 0 ppt and 29 ppt digester. Both
cumulative volume in the 29 ppt digester was found to be
less than that that of the 0 ppt digester due to the
adaptation process of the microorganisms to the salinity
levels. High salinity can inhibit anaerobic activity and
produce a low methane content [43]. According to Chen
et al. [14], inoculum and substrate adaptation are required
to maintain the microorganism viability from inhibitors,
such as salinity in the digester. Increasing the pH and
biogas production
showed that there was a
successful acclimation process. The optimum pH level for
acidogenic bacteria is 5-6.5, while the optimum pH level
for methanogen bacteria is 6.5-8.0 [44].
Fig. 1: Daily biogas production in different salinity
(0 ppt and 29 ppt) during acclimatization process.
Anaerobic Degradation Using the Batch Method:
Biogas production during the acclimatization process
showed that the macroalgae substrate could be degraded
and adapted to different salinity conditions (0 ppt and
29 ppt). The biogas volume increased after substrate
loading until the 57th day and then decreased until the 71st
day, similar to that in methane production. The production
of biogas was fluctuated during anaerobic process,
but there was non-significantly difference between the
treatments. The highest production on 0 ppt digester
was 2.54 mL g 1VS and in 29 ppt digester was 2.05 mL
g 1VS. Constant conditions until the 71st day were caused
by decreasing the amount of substrate degraded by
bacteria and by reducing the amount of biogas
Fig. 2: Cumulative biogas volume, methane volume and
pH during acclimatization process.(A) Salinity at
0 ppt. (B) Salinity at 29 ppt.
The 0 ppt digester was stabilized on the day 20th in
the pH range of 5.9 to 7.2. Biogas production at 0 ppt
digester started on the day 7th, with as much as
0.004mLg 1VS, while the 29 ppt digester was established
on the day 27th in the pH range of 6.1 to 7.3 and started
producing biogas on day 8th with as much as 0.02mLg 1VS
(Fig. 1). According to Bruhn et al.[15] and Demirbas [40],
high salinity levels can retard the anaerobic process. The
depletion of the pH value indicates acidification or
organic acid accumulation in the digester [41].
World Appl. Sci. J., 35 (3): 344-351, 2017
Fig. 3: Daily biogas volume in different salinity digester
during batch system.
Fig. 5: Chemical oxygen demand and cumulative
methane volume from E. cottoniidegradation.(A)
Salinity at 0 ppt. (B) Salinity at 29 ppt.
process. According to Chen et al. [14], microorganisms or
degrading bacteria can maintain viability at certain
concentrations, exceeding the inhibition concentration of
factors after they have adapted and produced a higher
volume of methane. Additionally, polymerase chain
reaction-denaturing gradient gel electrophoresis (PCRDGGE) analysis conducted by Zhang et al. [46] and
Patil et al. [47] showed a change in the bacterial
community interaction and that of archaea under high
salinity concentrations and that their interaction can
intensify anaerobic degradation.
The increases in biogas production were influenced
by the low lignin content and high carbohydrate
content.The low lignin content assists bacteria in the
degradation to organic material and then in the production
of high biogas and methane contents [2,13,15,31].
The high carbohydrate content in macroalgae species
also affects biogas production. MacroalgaeE. cottonii
contains polysaccharides and cellulose [21], which can be
easily decomposed by bacteria [29,48].
Fig. 4: Cumulative biogas volume, methane volume and
pH during batch method.(A) Salinity at 0 ppt. (B)
Salinity at 29 ppt.
The cumulative biogas and methane volumes in the
0 ppt digester were 91.94mL g 1VS and 81.62mLg 1VS,
respectively, higher than those with a 29 ppt salinity,
whose volumes were 91.12mLg 1VS and 73.40mLg 1VS,
respectively (Fig. 4). Both cumulative biogas and methane
volume were significantly different between 0 ppt and
29 ppt. This difference was caused by the salinity
concentration level, which inhibits bacterial activity[43].
Otherwise, the difference in this range would be not
significant because bacteria would not have adapted to
the salinity level (29 ppt) during the acclimatization
World Appl. Sci. J., 35 (3): 344-351, 2017
The pH value tends to be variable from the 1st until
the day 50th and then, it remains constant until the day
71st (Fig. 4). This fluctuation indicates the degradation
process of organic material, while the constant value is
caused by the substrate reduction inside the digester.
The pH range in both digesters was 6.9-7.7 and 7.0-8.0.
These values are categorized as conditions for anaerobic
degradation. According to Igoni et al. [42], the optimum
pH range for anaerobic biodegradation is 6-8.
Chemical oxygen demand (COD) is an indicator for
oxygen requirement in organic material oxidation
contained in the substrate. This value can also determine
the methane production volume from anaerobic
degradation. A COD reduction occurred from the initial
day until the last day of the batch method (Fig. 5). The
range value of COD removal in the 0 ppt digester was
3.45-6.17 gL 1, while in the other digester was 3.055.17gL 1. The removal was significantly different
between two different salinity levels. There was a
negative correlation between the COD and cumulative
methane production. COD reduction was related to
anaerobic degradation activity in breaking down organic
materials become methane gas.
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