IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Research articleerd

Production and Quality of Biogas from Pilot Biodigesters
using Cow Manure
LYTOUR LOR*
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia
Email: llytour@rua.edu.kh

MACHITO MIHARA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan

BUNTHAN NGO
Royal University of Agriculture, Phnom Penh, Cambodia

LYHOUR HIN
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

DYNA THENG
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

CHANMAKARA MEAN
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

BART FREDERIKS
United Nations Industrial Development Organization, Vienna, Austria
Received 30 January 2020

Accepted 30 November 2020(*Corresponding Author)

Abstract Biogas systems are being applied at commercial pig farms and at starch processing
plants to manage their wastes and produce biogas for generating electricity or heat for on-siteuse. The installation numbers are increasing in Cambodia. The data on potential biogas
production quantity from different feedstocks as well as on biogas quality are required todesign the biogas systems. The purposes of this study was to determine biogas production
and biogas quality from dairy cow manure produced in pilot digesters, and to analyze thevariation in biogas production and quality during the year of 2019 and 2020. Pilot biodigesters were installed at the Biogas Technology and Information Center, a research unit
located in the Royal University of Agriculture, to obtain these data, since it is easier to do theexperiments with the pilot digesters than that with commercial ones. The experiments wereconducted during the year of 2019. In the experiments, 3 identical floating drum bio-digesters
were used. Each bio-digester has 1 m3 of volume and has been supplied mixture of 5-10 kg
of fresh manure from dairy cattle with 5-10 liters of water every day. The daily biogas
production quantity was recorded using a gas flow meter attached to the outlet of each biodigester; also the gas quality, such as methane, carbon dioxide, oxygen, and hydrogen sulfide
was measured using a portable biogas analyzer. The average rate of biogas production wasaround 37 liters of biogas per kg of wet manure. Average percentage of methane was around52%, and average concentration of hydrogen sulfide varied from around 390 ppm to 604 ppm.
These two parameters are the main indicators of biogas quality.
Keywords biogas, floating drum digester, cow manure, methane, hydrogen sulfide

INTRODUCTION
Global warming is the worldwide concern which is caused by greenhouse gas emissions. InCambodia, methane is a major greenhouse gas from animal production. Ministry of EnvironmentⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2020) 11-2(2002) projected that methane emission from domestic livestock would be 545 Gg in 2020 compared
to 303 Gg from rice production, 2 Gg from grassland burning, and 5 Gg from agricultural residueburning.
Recently in Cambodia, animal production has increased in all kinds of animals, especiallycommercial farms. In 2017, there were 83 commercial cattle farms, 653 pig farms with total numberof cattle and pig 20,363 heads, and 742,771 heads, respectively (MAFF, 2018a). According to Prakas
no. 549 of the Ministry of Agriculture, Forestry and Fisheries issued on December 12, 2018, allcommercial animal farms are required to manage their waste properly, especially using biogas
systems (MAFF, 2018)
Currently, some commercial farms and agro-processing plants have already installed biogas
plants to treat their waste and convert biogas to electricity for use on farms. To design biogas systems,
data on potential biogas production and quality from various feedstocks are required. These data are
available in other countries but not in Cambodia. To obtain these data in local condition, the use ofpilot digester is more appropriate since it is difficult to do on commercial biogas systems.
OBJECTIVE
The objectives of this study were (1) to determine biogas production and quality from dairy cow
manure by pilot digesters and (2) to analyze the variation in biogas production and quality during theyear of 2019 and 2020.
METHODOLOGY
Experimental Procedure
The experiment was conducted in 2019 and early 2020. Fresh cow manure was collected from dairy
cattle farm located on the campus of the Royal University of Agriculture. The ratio of manure towater was 1:1 to bring down the percentage of DM to around 10% in the mixture (Farouk et al.,2017). The mixture was thoroughly mixed and solid pieces of grass were removed before feeding
into the digesters to avoid sludge build up in the digesters. Daily manure used was 5kg/day or
10kg/day (fresh manure). At the beginning feeding rate of 5kg/day was used to start up the digester
and then was increased to 10kg/day. Ground water was used to mix with the manure.
Table 1 Amount of feedstock and water used
Digester

Mass of Water(liter)
5 to 10Mix Ratio

RemarkDigester 1

Mass of Feedstock(kg)
5 to 10

1:1- 25 February to 11 March 2019,8kg/day of cow manure used- 12 March to 29 July 2019, 10kg/day ofcow manure used
- 30 July 2019 to 31 January 2020,5kg/day of cow manure used

Digester 2Digester 3

10101010

1:1
1:1

Three floating drum biodigesters of identical design were used, see Fig. 1. This design was
selected because it would ease the modification of the digester for various experiments. It is equippedwith two sampling pipes on the sides of the digester from which substrate can be extracted foranalysis. Each biodigester has a total volume of 1m3. The hydraulic retention time was around 47
days, which depends on daily feeding rate of 5 kg or 10 kg, to ensure complete anaerobic digestionof the feedstock.
The duration of data collection was shown in Table 2. Digester 1 was started up in December
2018 and started to produce stable biogas in February 2019 and the daily biogas production wasrecorded. It took longer than 1 month before the digester started to produce biogas. After the low
biogas production was observed for Digester 1, it was opened in September 2019 to make sure thatⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2020) 11-2there was no sludge building up in the digester. The digester 1 was restarted up again and began
producing biogas in October 2019. Digester 2 and Digester 3 was completed the construction andstarted up in July 2019. During long holidays such as Cambodian New Year in April and Pchum Ben
in September and Water Festival in November, data was not collected daily.

(a)

(b)
Fig. 1 Drawing of the pilot digester (a) side view (b) top view
From July to early August 2019, the biogas composition was measured once every two weeks.
It was done daily since late August 2019 when the air injection experiment was conducted onDigester 2 to remove H2S.
Daily biogas production was measured by using gas counter which was attached to the outlet
end of the pipe. To avoid direct emission of methane into the atmosphere, it was burned by using abiogas stove after passing through the gas counter.
For the quality of the biogas produced, contents of methane, carbon dioxide, oxygen, andhydrogen sulfide were measured using a portable gas analyzer. The gas analyzer, Geotech Biogas
5000, was regularly calibrated to ensure its accuracy in measuring. At the beginning, the biogas
quality was measured weekly. Later on, it was measured daily since there was a need to test hydrogensulfide removal using air injection into gas holder of the digesters. The content of hydrogen sulfide
before and after the air injection need to be measured daily.
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IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Table 2 Duration of Data Collection
DigesterDigester 1

Duration of data collection
February 2019 to January 2020

Digester 2
Digester 3

July 2019 to January 2020
July 2019 to January 2020

Remark-In September 2019, the digester was opened since thelow biogas production was observed. After new startup,the digester started produce biogas in October 2019.
-24 February to 11 March 2019, 8kg of manure per day

RESULTS AND DISCUSSION
Production of Biogas
During the monitoring, the average daily biogas production of digester 1, digester 2, and digester 3
were 238 L/day, 426 L/day, and 371 L/day, respectively. The average daily biogas production of thedigester 1 was the lowest since it was fed mostly only 5 kg of cow manure per day. The average dailybiogas production of digester 1 was only 71 L/day in February 2019. At that time, it was thebeginning of biogas production after it was started up in December 2018. The daily biogas productionof digester 1 and digester 2 were similar. The two digesters were constructed at the same time andfed 10 kg of cow manure daily. The fluctuation of average biogas production in each month may
have been caused by quality of animal feed and weather conditions. Matos et al. (2017) reported thatbiogas production potential from dairy cattle manure raised under organic production system is lowerthan that of the conventional one which supplement commercial feed in the animal diet. Daily biogas
production is higher in summer than in winter as reported by Choudhury et al. (2019) during
evaluation of hydrogen sulfide scrubbing systems on two US dairy farms.
Table 3 Average daily biogas production of each digester (L/day)Digester 1
MonthJan-19
Feb-19Mar-19Apr-19
May-19Jun-19Jul-19Aug-19Sep-19Oct-19
Nov-19Dec-19Jan-20
Average

Digester 2

Avg(L/day)Min(L/day)

Max(L/day)

Std(L/day)

71
159
290
253
250
251
192

55
67
251
184
152
178
13390
223
512
300
302
316
596

15
4277
25
34
33
92

411
199
179
204
223

175
66
24
98

652
549
367
350

133
123
80
71

Digester 3

Avg(L/day)Min(L/day)Max(L/day)Std(L/day)Avg(L/day)Min(L/day)Max(Lday)

Std(L/day)

467
466
375
453
409
390
423
426

417
158
104
276
146
126
227

523
544
500
599
494
497
719

38
68
99
70
73
107
108

428
354
375
416
302
306
415
371

200
123
104
259
227
176
299

517
501
500
579
419
429
664

125
101
99
80
52
76
79

Fig. 2 Average daily biogas production per kg of wet manure (L/kg)Ⓒ ISERD95

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Average daily biogas productions per kg of wet manure were 33 L/kg, 42 L/kg, and 36 L/kg indigester 1, digester 2, and digester 3, respectively; see Fig. 2. The mean biogas production of the threedigesters was 37 L/kg of fresh manure. After opening for checking in August 2019, the digester wasrestarted and began to produce biogas in early October 2019. In October 2019, the rate of biogas
production was highest, around 80 L/kg of wet manure, due to the change of feedstock from cow to pig
manure which yield higher biogas production rate from the same mass. Aremu and Agarry (2012)
reported a little higher biogas production from pig manure than cow manure in Lithuania. Matulaitis(2015) found higher methane content in biogas produced from pig manure than from cattle one.
Quality of Biogas
Table 4 Biogas composition
Digester 1Digester 2Digester 3MonthCH4(%)

CO2(%)O2(%)

H2S(ppm)

Bal(%)

CH4(%)

CO2(%)O2(%)

H2S(ppm)

Bal(%)

CH4(%)

CO2(%)O2(%)

H2S(ppm)Bal(%)

Jul-19

48.8

35.0

1.1

410.5

14.6

50.7

35.3

0.3

446.5

13.8

50.9

35.6

0.2

503.0

13.4

Aug-19

48.2

36.2

0.6

410.0

14.6

51.2

38.3

0.3

273.1

10.1

51.3

38.6

0.3

265.4

10.1

51.1

41.6

0.4

115.6

6.1

51.1

41.6

0.4

115.6

6.1

Sep-19Oct-19

51.9

38.4

0.1

751.7

9.7

49.4

40.2

0.2

169.7

10.2

49.0

39.0

2.0

242.6

9.9

Nov-19

52.5

39.3

0.1

692.4

8.1

50.0

40.6

0.1

299.6

9.3

50.4

41.3

0.1

584.6

8.2

Dec-19

55.4

42.2

0.2

722.0

2.2

54.9

41.9

0.1

740.3

3.1

54.6

41.3

0.0

936.1

2.3

Jan-20

54.3

43.3

0.1

637.5

2.8

53.2

42.4

0.2

693.3

4.2

53.8

43.3

0.1

897.5

2.7

Average

51.8

39.1

0.4

604.0

8.7

51.5

40.0

0.2

391.2

8.1

51.6

40.1

0.4

506.4

7.5

The average percentage of methane in digester 1, digester 2, and digester 3 were 51.8%, 51.5%,
and 51.6% respectively; see Table 4. Abubakar and Ismail (2012) reported that average methane inbiogas from cow dung from slaughterhouse in Malaysia was 47% which is similar to these results.
Choudhury et al. (2019) reported average methane content of 64.1±0.2% in biogas of US dairy farms.
Methane content fluctuates according to digester conditions and quality of feedstock. Average
percentages of carbon dioxide in the three digesters were around 40%, while average percentage ofoxygen was less than 1%. The average hydrogen sulfide varied from around 390 ppm to 604 ppm.
The average highest concentration of 936.1 ppm was in the digester 3 in December 2019. Meanhydrogen sulfide in biogas from dairy farms in the US was 450±42 ppm (Choudhury et al., 2019). It
is suitable for use with gas heating boiler and combined heat and power (CHP) systems (Allegue andHinge, 2014; Petersson and Wellinger, 2009). To use with engine, it is recommended that hydrogensulfide should be reduced to 100 ppm to 250 ppm (Bioclean, 2020).
CONCLUSION
The average daily biogas production of the pilot digesters, each with 1m 3 working volume, varied
from 223 L/day to 426 L/day when feeding with 5 kg to 10 kg of cow manure per day and mixed
with water using 1:1 ratio. The average rate of daily biogas production was around 37 L/kg of wetcow manure.
The biogas contained on average 51.6% methane, 39.7% carbon dioxide, 0.3% oxygen, 500ppm
hydrogen sulfide, and other gases was around 8.1%. Average percentage of methane was lower thanthe one reported in US dairy farms, which was around 64%. However it was similar to the one in
Malaysia which was around 47%. The average hydrogen sulfide varied from around 390 ppm to 604
ppm. It is suitable to use with gas heating boiler and combined heat and power (CHP) systems.
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However, it is not suitable to use with gas engine without pre-treatment system which is used toreduce hydrogen sulfide concentration in the biogas to 100 ppm to 250 ppm.
ACKNOWLEDGEMENT
This paper is made possible by funding from U IDO through the project entitled “Reduction ofGHG emission through promotion of commercial biogas plants”, which is jointly implemented by
the Ministry of Environment (MOE), the Ministry of Agriculture, Forestry and Fisheries (MAFF)
and UNIDO with financial support from the Global Environment Facility (GEF).
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