Int. Journal of Renewable Energy Development 7 (2) 2018: 93-100
P a g e | 93

Contents list available at IJRED website

Int. Journal of Renewable Energy Development (IJRED)
Journal homepage: http://ejournal.undip.ac.id/index.php/ijred
Research Article

Effect of Hydraulic Retention Time on Biogas Production from
Cow Dung in A Semi Continuous Anaerobic Digester
Agus Haryanto*, Sugeng Triyono, Nugroho Hargo Wicaksono
Department of Agricultural Engineering, Faculty of Agriculture, the University of Lampung, Indonesia

ABSTRACT. The efficiency of biogas production in semi-continuous anaerobic digester is influenced by several factors, among other is
loading rate. This research aimed at determining the effect of hydraulic retention time (HRT) on the biogas yield. Experiment was
conducted using lab scale self-designed anaerobic digester of 36-L capacity with substrate of a mixture of fresh cow dung and water at a
ratio of 1:1. Experiment was run with substrate initial amount of 25 L and five treatment variations of HRT, namely 1.31 gVS/L/d (P1),
2.47 gVS/L/d (P2), 3.82 gVS/L/d (P3), 5.35 gVS/L/d (P4) and 6.67 gVS/L/d (P5). Digester performance including pH, temperature, and
biogas yield was measured every day. After stable condition was achieved, biogas composition was analyzed using a gas chromatograph.
A 10-day moving average analysis of biogas production was performed to compare biogas yield of each treatment. Results showed that
digesters run quite well with average pH of 6.8-7.0 and average daily temperature 28.7-29.1. The best biogas productivity (77.32 L/kg
VSremoval) was found in P1 treatment (organic loading rate of 1.31 g/L/d) with biogas yield of 7.23 L/d. With methane content of 57.23%
treatment P1 also produce the highest methane yield. Biogas production showed a stable rate after the day of 44. Modified Gompertz
kinetic equation is suitable to model daily biogas yield as a function of digestion time.
Keywords: biogas, yield, cow dung, loading rate, semi-continuous digester, Gompertz kinetic model.
Article History: Received March 24th 2018; Received in revised form June 2nd 2018; Accepted June 16th 2018; Available online
How to Cite This Article: Haryanto, A., Triyono, S., and Wicaksono, N.H. (2018) Effect of Loading Rate on Biogas Production from Cow Dung
in A Semi Continuous Anaerobic Digester. Int. Journal of Renewable Energy Development, 7(2), 93-100.
https://doi.org/10.14710/ijred.7.2.93-100

1. Introduction
Along with economic growth, the energy need of
Indonesia also increases. During period of 2000-2015, the
final energy consumption in Indonesia (including
biomass) grew from 777.9 million to 1,040.7 million of
barrel oil equivalent with an average annual growth of
2.65% (MEMR, 2016). The growth is projected to increase
into 4,3% under base scenario or into 5,1% under high
scenario (Sugiyono et al., 2016). Primary energy supply
in Indonesia was dominated by fossil fuels with a total of
75.35% including oil (31.49%), coal (24.28%), gas
(19.04%) (MEMR, 2016).
On the other side, Indonesia is bestowed with
enormous sources of biomass that can be explored as
renewable energy. Biomass resource has a potential of
32,654 MWe, but only 1,626 MW (off grid) and 91.1 MW
(on grid) have been developed so far. Important biomass
sources include a great number of solid and liquid wastes
from agricultural, agro-industry, and livestock activities.
Livestock in Indonesia is increasingly growing and by
2016 the number was: dairy cattle (534,000), beef cattle
(16,093,000), buffalo (1,386,000), goat (19,608,000), sheep
(18,066,000), pig (8,114,000), horse (438,000), duck
(45,321,960), native chiken (298,673,000), layer chiken
*

(162,051,000), and broiler chicken (1,592,669,000)
(Ditjenak, 2016). Dung or feces excreted from livestocks
can be utilized to produce biogas through anaerobic
digestion process.
Anaerobic digestion is a promising way to convert
agriculture waste into energy (biogas) especially in
developing countries. Regarding socio-economic features
of villagers in less developed countries, the biogas is the
right option in meeting both energy and environmental
problems (Kabir et al., 2013).
Biogas not only alleviates energy shortage in rural
areas but also effectively reduces the environmental risk
associated with agricultural waste management (Song et
al., 2014). Various appliances can be fuelled by biogas
with cooking offering an application suitable for
deployment in developing countries. Other applications
include the use of biogas as fuel for heating, lighting or
power generation. In addition, slurry digestate can be
utilized as good compost.
Small scale biogas installations systems allow energy
generation on site, thereby eliminating the energy need
for intensive transportation (Naik et al., 2014). Smallscale biogas plants with no agitation and heating devices
are most feasible because of convenience in management

Corresponding author: agus.haryanto@fp.unila.ac.id

© IJRED – ISSN: 2252-4940, July 15th 2018 All rights reserved

Citation: Haryanto, A., Triyono, S., and Wicaksono, N.H. (2018) Effect of Loading Rate on Biogas Production from Cow Dung in A Semi Continuous Anaerobic Digester. Int.
Journal of Renewable Energy Development, 7(2), 93-100, doi.org/10.14710/ijred.7.2.93-100

P a g e | 94
and maintenance (Song et al., 2014). In addition, the
operation and maintenance of household bio-digesters
are easier, and their environmental and economic
performances are superior compared to those of medium
and large scale. Household biogas digesters are suitable
for undeveloped regions where the rural residents live far
apart from each other (Song et al., 2014). Under correct
and proper construction of the feeding process, small
scale biogas digester is able to supply sufficient energy to
the people but also provide digestate that can be used
efficiently as fertilizer on the farm, replacing chemical
nitrogen and phosphorus (Luo et al., 2016). Recently
Haryanto et al. (2017) reported that a family scale biogas
digester with five cows potentially provides annual
economic benefit of 111.6 USD and reduce greenhouse
gas emission by 2674.8 kg CO2 equivalent. Family size
biogas technologies play a significant role to fulfil energy
need in some countries such as China (Chen et al., 2014),
India (Singh & Sooch, 2004), Nepal (Barnhart, 2014),
Bangladesh (Khan et al., 2014), and Vietnam (Nguyen,
2011).
Anaerobic digesters can be classified in mainly three
types based on the feeding strategy, namely batch, semicontinuous and continuous modes. In semi-continuous
system, the digester is periodically loaded with substrate
according to a specific rate (Aboudi et al., 2015). Most
family scale biogas digesters developed in Indonesia use
cowdung as substrate with semi continuous loading
mode. This is caused by a fact that cowdung is excreted
intermittently in such a limited amount. The quantity of
manure excreted by an adult cow is 5.8% (wet basis) of
its weight (ASAE, 2003). Normally, adult cows will
defecate up to 16 times and urinate up to nine times a
day (Aland et al., 2002). Therefore, the cowdung has to be
collected first prior to its introduction into the biogas
digester.
Biogas digester performance is affected by many
factors, among others are microbial population, acidity
(pH), carbon-to-nitrogen mass ratio (C/N ratio), operating
temperature, substrate particle size, organic loading
rate, hydraulic retention time, total solids content, and
reactor configuration (batch or continuous, single or two
stage) (Naik et al., 2014). The process tends to fail if one
or more of the environmental factors changes suddenly.
Loading rate is a very important factor because it affects
the stability of the anaerobic digestion and the biogas
production rates. Because volatile solids represent the
portion of organic-material of solids that can be digested,
then organic loading rate (OLR) indicates the amount of
volatile solids to be fed into the digester each day
(Babaee & Shayegan, 2011). Optimum organic loading
rate is required to maximize biogas production; otherwise
the productivity will be low. The purpose of this study
was to investigate the effect of loading rate on the biogas
yield produced from cow dung using semi continuous
digester. The suitability of modified Gompertz kinetic
equation is also discussed. Implication of the results is
important in designing family scale cowdung biogas
digesters.
2. Materials and Methods
2.1. Digester configuration
Biogas production was carried out using lab scale selfdesigned 36-L semi continuous anaerobic digester. Five

digesters each of 25 litres working volume were set up for
this experiment. The digester vessels were made of two
5-gallon transparent plastic drinking water containers as
depicted in Figure 1. The two containers were cut at their
bottom and then combined by using fiber resin and let it
to dry for 24 hours.

Fig. 1 Lab scale self-designed 36-L semi continuous digester

2.2. Feedstock
Substrate used to produce biogas was fresh cowdung
collected from the Department of Animal Husbandry, the
University of Lampung. In order to have a maximum
biogas yield, fresh cow dung was diluted with tap water
at a ratio of 1:1 (Abubakar & Ismail, 2012; Ituen et al.,
2007). Fresh cow dung was analyzed for its moisture
content, total solid (TS), volatile solid (VS), ash, carbon
(C), and nitrogen (N) content. Same analysis for TS and
VS was also performed for spent slurry. Table 1 presents
results of the analysis.
2.3. Treatment
Initially, 25 L of the diluted cowdung was loaded into
the digester. The digester was refilled at five different
loading rates as presented in Table 2. The table also
provides the respected organic loading rate (OLR) and
hydraulic residence time (HRT).
Table 1
Characteristic of fresh cow dung.
Characteristic

Average Value

Water content (% wb)
Total solid, TS (% wb)
Ash (%TS)
Volatile solid, VS (% TS)
C
N
C/N ratio

80.12
19.88
30.58
69.42
39.87
1.42
28.1

Table 2
Loading rate variations and their corresponding OLR and HRT
P3
P4
P5
Treatment
P1
P2
TS (%)
VS (%TS)
Loading Rate
(L/day)
OLR (g/L/d)
HRT (d)

9.19
71.38
0.5

9.10
70.44
1.0

9.21
69.07
1.5

9.10
73.45
2.0

9.16
72.53
2.5

1.31
50.0

2.47
25.0

3.82
16.7

5.35
12.5

6.67
10.0

© IJRED – ISSN: 2252-4940, July 15th 2018, All rights reserved

Int. Journal of Renewable Energy Development 7 (2) 2018: 93-100
P a g e | 95

The moisture content of samples was obtained by sun
drying followed by oven-drying (Memmert type UM 500)
at 105°C for 24 hours. Volatile solid was determined by
burning the sample in a muffle furnace (Barnstead
International model FB1310M-33) at 550°C for at least
two hours. Sample was also sent to Soil Science Lab. to
determine the C and N content.
Important processing parameters include pH,
temperature (digester and ambient), and biogas
production (P). The pH was measured daily for fresh
(inlet) and spent (outlet) substrate using portable digital
pH-meter (PHMETER, PH_009(I)). Digester efficiency
was evaluated from VS removal (VSr), that is part of VS
removed during anaerobic digestion process and is
calculated based on Koch (2015):

é
ù
VSr (%) = 1 - VS out (1 - VS in ) ´ 100
ê
ú
ë VSin (1 - VS out ) û

(L/gVSr)

35.0
30.0

29.1

28.7

28.8

28.8

28.8

28.7

P1

P2

P3

P4

P5

Ambient

25.0
20.0

15.0
10.0
5.0

0.0

(1)

Fig. 2 Average daily digester temperature for different
treatment and ambient air temperature.

Ambient as well as digester temperatures were
monitored daily three times (morning, noon, and
afternoon) using digital thermocouple (Digi Sense, Cole
Parmer, model No. 93410-00) equipped with K-type wire.
Biogas production was measured daily using water
displacement method. Observation was recorded for 55
days, by which time the digestion process was expected to
already stable and the digesters were operating in
practically steady conditions. After stable condition was
achieved, biogas composition was analyzed using gas
chromatography (Shimadzu GC 2014) with thermal
conductivity detector (TCD) and 4 m length of shincarbon column. Helium gas was used as carrier gas with
flow rate 40 ml/min. Biogas yield (Y) was calculated from
biogas production (P) at stable condition by using:
Y = P/VSr

temperature. As seen in Figure 3, daily digester and
ambient temperatures were presented separately for
morning, noon, and afternoon. The digester temperatures
were low during morning time and then increased during
noon and afternoon. The same pattern was observed for
ambient air.

Average Temperature (oC)

2.3. Analysis and Calculation

(2)

3. Results and Discussion
3.1. Process temperature and pH
Figure 2 showed average daily temperatures of the
five treatments as well as the ambient temperature
averaged over 53 days observation. It was revealed that
the temperature was almost same among the five
treatments (ranging from 28.7 to 29.1 oC). This meant
that the digester working at mesophilic zone. Based on
working temperature, anaerobic digestion process is
classified into psychrophilic (10–20 oC), mesophilic (20–
40 oC), and thermophilic (40–60 oC) (Salam et al., 2015;
de Mes et al., 2003). Digester temperatures, however,
were slightly higher than the ambient. This was caused
by a fact that some processes during anaerobic digestion
are classified as endothermic, and the others are
exothermic. But overall, anaerobic digestion process is
very slightly exothermic reaction that producing heat (de
Mes et al., 2003). However, the digesters or reactors were
quite small with no such insulation that the heat
produced during digestion process was easily transferred
to the environment. As a consequence, the temperature
of the digesters was just little higher than or in balance
with environment or ambient temperature. Daily
digester temperatures were affected by ambient

Figure 4 showed daily pH values of the five different
treatments for 55 days observation. It can be seen that
the average pH values were slightly differ, between 6.8–
7.0 with the maximum values between 7.5–7.8 and the
minimum values of 5.8–6.4.
Biogas is produced during biological process involving
a group of bacteria working in an anaerobic condition.
The interaction of several factors affects the performance
of biogas process. Temperature and pH are among the
important factors. The bacteria optimally work at a
certain pH range. Methanogenic bacteria work effectively
at the pH range of 6.5 to 8. Hydrolysis and acidogenis
stages optimally go on at a pH range between 5.5 and 6.5
(Sibiya et al., 2014). Anaerobic degradation processes
meet the requirement for both activities and cell growth
of anaerobic microorganisms at the acidity of 5.5–8.5
(Abbasi et al., 2012).
Stafford (1982) reported the effects of pH upon
methane production from anaerobic digestion of dairy
cattle manure maintained at pH levels of 7.6, 7.0, 6.0,
5.5, and 5.0. Active digestion was achieved at all pH
levels except for pH 5.0. Biogas and methane production
was highest at pH of 7.0. In our experiment, the pH
value of fresh substrate was in the range of 6.5 – 7.7. The
pH was observed changing overtime but the value was
close to the initial. This implied that the system was well
buffered. Although there were some decreases in the pH,
but overall, the values were still in the good range for
biogas process. The values also indicated that biogas
process was in good condition for all treatments.
3.2. VS removal
Anaerobic digestion process involves consortium of
microorganisms that make use organic components
within the substrate as building blocks. Therefore,
efficiency of an anaerobic digestion system can be
evaluated from the value of VS removal, which is a
measure of anaerobic digestion system ability in
decomposing organic material. For the purpose of
evaluating the effect of organic loading rate on the
process efficiency, VS reduction and biogas yield were
both taken into account as the indicators to assess the
reactor performance and efficiency of each loading rate.

© IJRED – ISSN: 2252-4940, July 15th 2018 All rights reserved

Citation: Haryanto, A., Triyono, S., and Wicaksono, N.H. (2018) Effect of Loading Rate on Biogas Production from Cow Dung in A Semi Continuous Anaerobic Digester. Int.
Journal of Renewable Energy Development, 7(2), 93-100, doi.org/10.14710/ijred.7.2.93-100

Temperature (oC)

35
15

Temperature (oC)

Temperature (oC)

Temperature (oC)

35

Temperature (oC)

P a g e | 96

30

25
20

30
10

25
5
20
0
35
0
15

30
10
25
5
20
0
35 0
15

7.13
6.75
6.79
6.82
6.65
7.09
6.66
6.92
7.63
Series1
7.25
Series2
7.52
Series3 7.2
7.15
7.75
6.89
6.86
7.32
Series1
5
10
7.31
Series2
7.22
Series3 6.8
6.7
7.76
7.05
7.01
Series1 6.86
5
10
7.34
Series2

30
10

6.47
7.04
6.54
7.31
6.51
7.22
6.67
6.78
6.91
7.77
6.95
7.38
7.65
7.1
7.66
7.4
6.8
15
6.94
6.83
7.33
6.94
7.78
7.24
7.22
7.38
15
7.8

6.9
7.64
6.59
6.64
7.09
6.8
7.8
7.13
6.95
7.59
7.86
7.39
7.9
7.53
7.51
7.71
7.3
20
7.08
7.09
6.87
7.48
7.32
7.69
6.87
7.91
20
7.74

6.82
7.16
6.51
7.06
6.92
6.99
7.31
7.49
6.98
7.55
7.72
7.75
7.39
7.19
7.43
7.78
7.13
257.45
7.22
7.16
7.97
7.78
7.3
7.73
7.35
25
7.91

Series3

6.34
6.05
6.98
6.9
7.12
7.06
6.83
7.57
7.55
7.57
7.33
7.68
7.94
7.87
7.11
7.01
7.8
307.74
7.71
7.08
7.08
7.08
7.36
7.2
7.65
30
7.25
7.2

27
30.8
30.1
30.3
31.5
32.1
32.6P5: HRT 10; LR 2.5 L/d
31.7
30
31.2
33.5
28.5
30.2
30.5
32.2 P4: HRT 12.5; LR 2.0 L/d
26.8
31.7
35 29.6 40
45
50
29
30.4
29.3
27.1
28.2 P3: HRT 16.7; LR 1.5 L/d
29
31.5
35
40
45
50
30.6
29.9

25
5

55

55

P2: HRT 25; LR 1.0 L/d

20
0
35 0
15

5 Series1 10

15

20

25

30

35

40

45

50

55

Series2
Series3

30
10

25
5

P1: HRT 50; LR 0.5 L/d
20
0
40
15

0

10

Afternoon

15

20

25

15

20

25

30

35

40

30

35

40

30

35

40

45

50

55

45

50

55

45

50

55

Morning

35
10

Noon

30

Temperature (oC)

5

5
25

0
20

0

5

10

Morning

15

Day

Ambient

Noon
10

Afternoon

5
0
0

5

10

15

20

25

Day
Fig. 3 Daily temperatures of the digesters and ambient (separated from morning, noon, and afternoon)

© IJRED – ISSN: 2252-4940, July 15th 2018, All rights reserved

Int. Journal of Renewable Energy Development 7 (2) 2018: 93-100
P a g e | 97

Fig. 4 Daily pH values of the anaerobic digestion process (small figure in the centre is average pH value during 53-day measurements)

start up, transition, and stable periods. The figure shows
that acclimatization period goes on for 11 days.
120.0
100.0

VS removal

Figure 5 showed the relationship of organic loading rate
and VS removal. Elevating loading rate has resulted in
slightly increase of VS removal. But at an organic
loading rate of higher than 5.35 g VS/L/d, there was a
tendency of VS removal to decrease. The digester
efficiency (in term of VS removal) was almost same in the
range of 42.1% to 46.4%. Babaee & Shayegan (2011)
reported that at an OLR range of 1.4-2.75 gVS/L.d, VS
removal decrease with increasing OLR. On the other
hand, Gomez (2010) reported at an OLR range of 3.4-5.0
gVS/L.d, an increase in organic matter biodegradation
was observed with increasing the OLR.

80.0
60.0

40.0
VS removal (%)

20.0

VS removal (gram)

0.0
0.0

3.3. Biogas Yield

Start up Period

Average Biogas Yield (liter)

2.0

3.0

4.0

5.0

6.0

7.0

Organic Loading Rate (g VS/L.d)

By using a 10-day moving average, the daily biogas
yield is presented in Figure 6. In Figure 6, we can
differentiate three regions, namely acclimatization or

8

1.0

Fig. 5 Effect of loading rate on VS removal

Transition Period

Stable Period

7

P5

6

P4

5

P3

4

P2

3

P1

2
1
0
0

2

4

6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54

Day
Fig. 6 The growth of daily biogas yield using 10-days moving average (solid circles represent the day where biogas can be burnt)

© IJRED – ISSN: 2252-4940, July 15th 2018 All rights reserved

Citation: Haryanto, A., Triyono, S., and Wicaksono, N.H. (2018) Effect of Loading Rate on Biogas Production from Cow Dung in A Semi Continuous Anaerobic Digester. Int.
Journal of Renewable Energy Development, 7(2), 93-100, doi.org/10.14710/ijred.7.2.93-100

P a g e | 98

200

100

9

90

8

80

7

70

6

60

5

50

4

40

3

30

2

20

1

10

0

Biogas Productivity (L/g VSr)

10

0
0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Organic Loading Rate (gVS/L/d)
Biogas Yield

Biogas Productivity

Fig. 8 Effect of organic loading rate on daily biogas yield and
biogas productivity

3.4. Biogas Kinetic

180
160

Cumulative Biogas Production (L)

This also implies that the decomposition process was not
completed yet. Figure 8 also further strengthens the
conclusion that treatment P1 with organic loading rate of
1.31 g VSL/d is the best for biogas production with biogas
productivity of 77.32 L/kg VS removal. Jha et al. (2012)
reported higher productivity (358 LCH4/kgVS removal).
This means that there is a challenge to improve the
biogas productivity, for instance by applying agitation or
other mechanical treatments.

Biogas Yield (L/d)

During this period, biogas production is low and almost
constant at an average lest than one litre a day. Pandey
et al. (2013) noted that start up period takes place 1–3
weeks. Main problem during this period is creating a
balanced population, characterized by low biogas yield.
The transition period started at day 11 and finished at
around day 37 at which the stable period starts. It is
revealed that during transition period the biogas yield
gradually increases from around 0.6-0.9 to around 5-7
L/d. After stable period was achieved, biogas yield was
stable at around 6 to 7 L/d. Again, treatment P1 with
OLR of 1.33 g VS/L/d showed the best and gave the
highest biogas yield with average of 7.23 L/d. In addition
to biogas production measurement, the biogas was burnt
to simply check if the biogas contains enough methane. It
was observed that for the first three weeks the biogas
could not be combusted, implying that the methane
content was still low. In the figure, we indicated the day
at which the biogas was able to be burnt and produce
blue flame, namely day 22 for P2 and P3, day 25 (P4),
day 26 (P5), and day 27 (P1).
Figure 7 shows cumulative biogas production resulted
from different treatments. The figure reveals that
treatment P1 with OLR of 1.33 g VS/L/d give the highest
cumulative biogas production 194.4 L during 53 days of
consecutive measurement. Based on these date, we have
calculated the biogas yield and biogas productivity. The
results are presented in Figure 7. Both biogas yield and
biogas productivity tend to decrease with increase in
OLR.

From Figure 7 it is revealed that relationship of daily
biogas yield and digestion time resembles a sigmoidal
curve. One of kinetic model that is suitable to describe
this is modified Gompertz kinetic equation. This model
describes a sigmoidal growth curve contained three
unknown mathematical parameters (Syaichurrozi et al.,
2013) and is recently used by many researchers to
describe a cumulative biogas yield from a batch system
as a function of digestion time, for example Budiyono et
al. (2010), Yusuf et al., 2011), and Syaichurrozi et al.,
2013). For the case of our work (with a semi continuous
digester), modified Gompertz kinetic equation is
presented as:

P5 (LR 2.5 L/d)

140

P4 (LR 2.0 L/d)

120

P3 (LR 1.5 L/d)

100

P2 (LR 1.0 L/d)

80

P1 (LR 0.5 L/d)

60
40
20
0
0

5

10

15

20

25

30

35

40

45

50

55

Day
Fig. 7 Cumulative biogas production.

It is obvious that loading rate influences not only the
biogas yield but also biogas productivity. Previously we
have showed that the increase in loading rate has
resulted in the increase of VS removal (Figure 4). In
contrast, Figure 8 shows that by increasing loading rate
the biogas yield as well as biogas productivity decreased.
This can be understood because the higher the loading
rate (meaning the shorter HRT) the process becomes
uncomplete so that the biogas production is also low.

é
æ R ×e
öù
B(t ) = B expê- expç b (l - t ) + 1÷ú
è B
øû
ë

(3)

where B(t) is daily biogas yield (L) at any time (t), B is
biogas production potential (L), Rb is maximum biogas
production rate (L/d), and λ is lag phase (d), which is the
minimum time for the system to produce biogas.
Constants B, Rb and λ were determined using the nonlinear regression approach with the aid of the solver
function of the MS Excel ToolPak (Yusuf et al., 2011).
Table 3 shows mathematical parameters of modified
Gompertz kinetic equation resulted from our work. The
normalized error is in the range of 0.06 (6%) to 0.10
(10%), meaning that the modified Gompertz kinetic
model is adequately suitable to describe the daily biogas

© IJRED – ISSN: 2252-4940, July 15th 2018, All rights reserved

Int. Journal of Renewable Energy Development 7 (2) 2018: 93-100
P a g e | 99
yield as a function of digestion time. Based on this model,
the highest value daily biogas production potential (B) of
9.85 L is achieved at a loading rate of 2.5 L/d with
maximum production rate of 0.18 L/d and lag time of 6.44
days. Figure 9 presents the suitability of modified
Gompertz kinetic equation for daily biogas yield
produced from semi continuous digester of two loading
rates, namely 1.0 L/d and 2.5 L/d.
Table 3
Gompertz kinetic parameters of semi continuous cowdung
digester
Loading
B
Rb
λ
Normalized
Rate
Error
(L/d)
(L)
(L/d)
(d)
0.5
7.63
0.33
11.99
0.0583
1.0
9.22
0.17
5.66
0.0697
1.5
7.27
0.29
14.46
0.0864
2.0
4.63
0.16
3.34
0.1025
2.5
9.85
0.18
6.48
0.0221

9.0
LR 2.5 L/d (Experiment)

Biogas Yield (L/d)

8.0

LR 2.5 L/d (Model)

7.0

LR 1.0 L/d (Experiment)

6.0

LR 1.0 L/d (Model)

3.5. Reflection to Family Digester
Our previous work reported that family scale cowdung
biogas digester with a capacity of 3.5 to 6.0 m3 was fed
with loading rate of 80 to 150 L/d that resulted in
hydraulic retention time of 32 to 40 days. As presented in
Table 5, we have calculated that the digesters have
organic loading rate between 1.2 to 1.62 g VS/L.d which
is very closed with our best condition. This means that
the family digesters in the field were fed with a very good
loading rate. This also implies that digesters were
installed with good design so that the size complies with
feedstock availability.
Table 5
Characteristic of family scale cow dung biogas digester
Digester
A
B
C
Digester type
Plastic
Plastic
Fixed
tube
tube
dome
Digester capacity (L)
3500
4700
6000
Working volume (L)
2800
3760
4800
Loading rate (L/d)
80
80
150
HRT (d)
35
47
32
VS content (%)
5.66
5.27
5.49
OLR (g VS/L/d)
1.617
1.121
1.373

D
Fixed
dome
6000
4800
120
40
6.28
1.256

Source: Adapted from Haryanto et al. (2017)
*) working volume was assumed as 80% of digester capacity.

5.0

4. Conclusions

4.0
3.0
2.0
1.0
0.0
0

10

20

30

40

50

60

Digestion Time (d)
Fig. 9 Comparison of daily biogas yield: observation vs.
prediction using Gompertz kinetic model.

3.4. Biogas Composition
Biogas is generally used as fuel. Therefore, its value is
determined by combustible components, i.e. methane.
Good quality biogas mainly consists of methane at
around 55-70% followed by carbon dioxide around 3045%. Table 4 presents the composition of biogas. It was
revealed that the biogas comprised of fairly high
methane content (41.73 to 57.23 %) so that it was well
burnt and can be used for fuel. The table shows that
methane content decreases by increasing loading rate
with the highest value (57.23%) is given by biogas
collected from digester with OLR of 1.33 g VS/L/d).
Increasing loading rate means shortening HRT that
leading to incomplete decomposition of organic matter.
Table 4
Biogas composition.
Composition
P1
CH4
57.23
CO2
31.13
N2
11.54

P2
50.53
32.91
16.56

P3
49.82
40.43
9.75

P4
51.80
35.82
12.38

P5
41.73
39.04
19.23

Loading rate influenced biogas yield and biogas
productivity from cowdung in semi continuous digester.
Increasing loading rate resulted in the decrease in both
biogas production and biogas yield. Organic loading rate
of 1.31 g VS/L/day gave the highest biogas yield (average
7.32 L/day) and biogas productivity (77.32 L/kg VS
removal). The biogas produced from cow dung using semi
continuous digester contained fairly good methane
content up to average 57.23%. Digester efficiency, in
term of VS removal, was almost same for all treatments
and was in the range of 42.1% and 46.4%. Daily biogas
yield as a function of digestion time can be adequately
represented by modified Gompertz kinetic model.
Acknowledgments
The authors acknowledge the Directorate General of
Higher Education (DIKTI), Ministry of Research,
Technology, and Higher Education for supporting this
work under STRANAS scheme with contract number:
419/UN26/8/LPPM/2016 (June 2, 2016).
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© IJRED – ISSN: 2252-4940, July 15th 2018 All rights reserved

Citation: Haryanto, A., Triyono, S., and Wicaksono, N.H. (2018) Effect of Loading Rate on Biogas Production from Cow Dung in A Semi Continuous Anaerobic Digester. Int.
Journal of Renewable Energy Development, 7(2), 93-100, doi.org/10.14710/ijred.7.2.93-100

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