IJERD – International Journal of Environmental and Rural Development (2022) 13-1

Research article
erd

Performance Assessment of Simple Covered Lagoon
I
Digester in Large-scale Pig
Farm in Cambodia
7de
CHAN MAKARA MEANn
Biogas Technology and Information Center,
Royal University of Agriculture, Phnom Penh,t

Cambodia
Email: meanmakara321@gmail.com 4.
7
Biogas Technology and Information Center / Faculty of Agricultural Engineering,
2

LYHOUR HIN*Royal University of Agriculture, Phnom Penh, CambodiawoBiogas Technology and Information Center/ Faculty of Agricultural Engineering,
Royal University of Agriculture, Phnomr Penh, Cambodiads
DYNA THENG

LYTOUR LOR

Biogas Technology and Information Center / Faculty of Agricultural Engineering,
Royal University of Agriculture, Phnom Penh, Cambodia

MAKARA LAY
Biogas Technology and Information Center, Royal University of Agriculture, Phnom Penh,
Cambodia / Department of Science and Technology, Linköping University, Norrköping, Sweden

BART FREDERIKS
Biogas Technology and Information Center, Royal University of Agriculture, Phnom Penh,
Cambodia
Received 31 December 2021

Accepted 22 April 2022(*Corresponding Author)

Abstract Simple covered lagoons are used to treat wastewater from commercial pig farms
in Cambodia into biogas. The electricity is generated from biogas using a generator.
However, high level of H2S corrodes or breaks down the generator. This study aims todesulfurize biogas with commercial ferrous oxide pellets (Fe2O3). The effects ofdesulfurization system on biogas production, electricity generation, and CO2 reduction are
discussed. The results show that H2S was reduced from 2,000 ppm before treatment toaround 50 ppm after treatment. CH4 (57.7 ± 8.76%) and CO2 (24.7 ± 2.67%) contents were
not affected by desulfurization. O2 content was changed from 0.3 to 4.8%. High O2 level
was a sign of pipe leakage, lowering CH4 and eventually electricity production. The
increase of O2 level decreased CH4, thus lowering generator performance. Actual electrical
output power produced from biogas was 368.5 ± 29.3 kW, with loading rates of 57.6 ±
4.6% and generator efficiency of 26.8 ± 1.7%. Estimated amounts of 22,818 tCO2equ werereduced by the biogas system. The desulfurization system was highly effective in H2S
removal without affecting biogas quality. For the long-term biogas systems in Cambodia,
local-made desulfurization systems should be tested and compared with imported products.
Keywords biogas, CO2 reduction, simple covered lagoon, CH4, desulfurization,
electricity generation

INTRODUCTION
Globally, the energy sector that covers electricity, heat, and transport contributes to 73.2% of GHG
emissions, whereas livestock accounts for 14.5% (Quinton, 2019). To produce one kWh ofⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2022) 13-1

electricity, 0.657 kg CO2 is produced. Meanwhile, a fattening pig ready for slaughter produces
448.3 kg CO2 (Philippe and Nicks, 2015).
To tackle these issues, zero-emissions in all sectors are discussed in the 26th United Nations
Climate Change Conference of the Parties (COP26) held in Glasgow, Scotland, with its intended
achievements to keep global warming below 1.5oC this century, specifically targeting CH4
reduction (UNEP, 2021). According to IPCC (2014), CH4 is 28 more potent than CO2 regarding the
100-year global warming potential, so letting it into the atmosphere is much more harmful to theenvironment. Climate change mitigation in livestock production can be done by anaerobic
digestion (AD) technology (Achinas et al., 2017).
In Cambodia, commercial pig farms have increased due to their ability to control theenvironment necessary for fast pig growth and effective disease prevention (MAFF, 2019). In those
farms, evaporative cooling systems are used to maintain temperatures of 25 to 27oC inside thebarns (Thanapongtharm et al., 2018). In consequence, electricity consumption is an average of 30
kWh per head (Putmai et al., 2020). Daily wastewater generated from sows, fatteners, and piglets is
64, 24, and 20 m3 head-1, respectively (Kulpredarat, 2016). It has been reported that the pig farmwith fattening pigs above 3000 heads have a potential to produce biogas through AD technology.
A common AD type used to treat wastewater from commercial pig farms in Cambodia is a
simple covered lagoon digester, with 44 units reported in 2019 (NBP, 2019). They are preferred
due to its low-cost construction, easy operation (Rahman and Borhan, 2012) and its suitability for
wastewater that contains 0.5 - 2% of dry matter (DM). Hin et al. (2021) found that wastewaterfrom pig farms in Cambodia contains 0.9% DM.
Biogas is a gas mixture that contains CH4 (60 - 70%), CO2 (30 - 40%), and other traceelements (Okoro and Sun, 2019; Safferman et al., 2007). CH4 is the only source of energy to
produce heat and electricity for farm use. Nevertheless, biogas contains high hydrogen sulfide(H2S) concentration up to 3,500 ppm (Hin et al., 2021; Dumont, 2015). H2S is corrosive to theengine and toxic to humans. H2S level must be limited to 200-500 ppm for generator operation(Rodrighez et al., 2014). Generally, H2S removal can be done physically by regulated air injection(Hines et al., 2019), chemically by application of sodium hydroxide (NaOH), potassium hydroxide(KOH), or Ferrous oxide (Fe2O3) (Zulkeflia et al., 2016), or biologically by the use of biofilters(Barbusiński and Kalemba, 2016). However, proper desulfurization techniques are little known in
Cambodia, especially for large-scale biogas systems. The study aims (1) to compare biogas quality
before and after being treated with ferrous oxide (Fe2O3) fed in a Chinese commercial
desulfurization system, (2) to determine the working capacity of the biogas generator, and (3) toevaluate biogas production, electricity production, the generator efficiency, and CO2 reduction
equivalence.
MATERIALS AND METHOD
Materials
The tools used in this study included A biogas 5000 analyser, supplied by Geotech, UK and Hioki
PW3365-20-01/5000 power logger (Hin et al., 2021).

Fig. 1 Geotech biogas 5000 (left) and Hioki PW3365-20-01/5000 power logger (right)Ⓒ ISERD

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Methods
The research was conducted from January to August 2021 in a large-scale pig farm that raised
38,000 fattening pigs and 3,100 sows under cooling evaporative systems in Sihanoukville Province,
Cambodia. The farm used a full biogas system: a simple covered lagoon digester (76,000 m3
volume), a biogas desulfurization system fed with 2,400 kg of Fe2O3, a flow meter with maximum
flow rate of 500 Nm3 biogas, two 640-kW second-hand biogas generators, and a flare used to burnexcess biogas. The desulfurization rate was 0.5 kg Fe2O3 per 1 Nm3 biogas.
The biogas 5000 analyser was used to measure biogas quality before and after being treatedthrough the desulfurization system filled with Fe2O3 at blowing pressure of 5.6 kPa. Due to travel
restriction inside the farm, the data were recorded once a month for 7 consecutive months. Eachtime, measurements were made three times to obtain average values. The power logger was
attached to the generator wiring for 3 hours at a time of data collection to measure actual output
power produced from biogas. However, actual output power could be measured only with the posttreated biogas because there was only one outlet pipe connecting the biogas desulfurization system
to the generator.
Data Sampling
The collected data were CH4 (%), CO2 (%), H2S (ppm), and O2 (%). Hourly biogas flow (Nm3 h-1)
and biogas temperature (oC) were also recorded by using the flow meter that exists in the system.
Additionally, four formulas were used in this study as follows. In formula one, CO2 reduction
equivalent (tCO2 equ.) by avoidance of CH4 emission equals CH4-to-CO2 equivalent x CH4 density
x Annual CH4 production, while CO2 reduction by avoidance of grid electricity equals electricityto-CO2 equivalent x annual electricity demand met by methane production. CH4-to-CO2 equivalentis 28, and electricity-to-CO2 equivalent is 0.657 kg CO2 per kWh (Hin et al., 2021). In formula
three, Electrical loading rate (%) equals output power divided by the rated power. Formula four isthe generator efficiency (%) which was calculated by dividing the output power by the powerchemically produced through the internal combustion of biogas. Net caloric value (NCV) of biogas
with 60% CH4 is equal to 20 MJ Nm-3. Thus, the chemical power (kW) produced by biogas
combustion is equal to hourly biogas consumption by the generator multiplied by NCV and divided
by 360.
Data Analysis and Interpretation
Data were analyzed using the R studio version 4.1.1. Paired sample t-test was employed to compare
the biogas quality before and after desulfurization. A simple linear regression was used to identify
relationship between CH4 and O2. A contour plot was used to determine the effects of biogas flow
and CH4 concentration on active output power produced from the generator. Descriptive statistics
were utilized to depict generator performance, biogas generation, and CO2 reduction.
RESULTS AND DISCUSSION
Biogas Quality
Biogas quality before and after desulfurization system was compared (Fig. 2). Differences in H2S
were detected (P < 0.001; Fig. 2a) and it was reduced from 2,061 ± 138.9 ppm before treatment to50.1 ± 10.2 ppm after treatment. However, one month after the utilization of Fe2O3, H2S rose to
more than 200 ppm. The pre-treated H2S level is similar from previous studies (Dumont, 2015) and(Hin et al., 2021). On the other hands, CH4 and CO2 was 57.7 ± 8.76% and 24.7 ± 2.67%,
respectively and was not affected by desulfurization (Fig. 2b). These values were lower, whencompared to the literature by Safferman et al. (2007) for pig manure in Europe and by Hin et al.
(2021) for pig manure in Cambodia and by Wongsapai et al. (2008) in Thailand. Low CH4 and CO2Ⓒ ISERD

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values tends to be affected by the atmospheric air that penetrated into the system through pipelines
or the edges of the lagoon plastic cover sheet.
Relationship of CH4 with O2 and Average Load with Biogas Flow and CH4
We studied the relationship between CH4 and O2 to determine why CH4 content was relatively low,
as seen in Fig. 2b. Fig. 3a shows that CH4 decreased with the increase of O2 (P < 0.001; R2 = 0.92).
When O2 increases by 1%, CH4 decreases by 4.64%. Normally, O2 level in raw biogas is low. A
recommended level of O2 entering the lagoon should be in the range of 0.3-3% (Hines et al., 2015).
So, its high content in this study may signify air penetration into the system, which can be throughthe pipelines, water traps, or the edges of the lagoon plastic cover sheet. In case leakage is found at
the lagoon, high O2 inhibits methanogenic activities because CH4 is strictly produced underanaerobic conditions (Botheju and Bakke, 2011). The result of this study is similar to that
conducted by Hin et al. (2021). Thus, proper detection is required to inspect pipelines, water traps,
and the covered lagoon.

Fig. 2 Comparison of H2S (a) and CH4 and CO2 (b) before and after desulfurization(Mean ± SD; N = 21)
Paired sample t-test was used for the analysis. Different alphabetic letters denote significant differences atthe error level of 0.05, and NS means non-significance.

Fig. 3 Relationship between CH4 and O2 (a), and determination of average load
as a function of biogas flow and CH4 (b)The low CH4 reduces the biogas generator performance. Figure 3b indicates an average load
as a function of hourly biogas consumption and CH4 content. With the same biogas flow rate, low
CH4 content reduces the amounts of electrical power produced. To maintain the same electrical
power produced with low CH4, unusual high biogas flow rates were recorded, which leads to theⒸ ISERD

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overuse of daily produced biogas. In contrast, CH4 content of 60 - 65% gives better generator
performance and reduce the hourly biogas consumption at the same output power.
Specific Biogas Characteristics for Generator Operation
Fed into the generator, the biogas was pushed by an electrical blower at 5.6 ± 0.5 kPa. Its
temperature averaged 37.0 ± 5.1oC, rated best for biogas production (Babaei and Shayegan, 2020).
Biogas system produced 4,478 Nm3 day-1, but the actual daily biogas consumption was 4,862 ±
64.6 Nm3 day-1 (Table 2). Therefore, the amount of biogas consumption was 8.6% greater than the
biogas production.
Table 1 Biogas production, electricity consumption, and CO2 reduction equivalent
Description
Biogas temperature
Estimated daily biogas production
Recorded daily biogas consumption
Biogas flow rate
Actual generator power
Specific biogas consumption
Actual output power
Chemical power produced by biogas
combustion
Loading rate
Genset efficiency
CO2 reduction equivalent
CO2 reduction equivalent per head

Unit
o
C
Nm3 day-1
Nm3 day-1
Nm3 h-1kW
Nm3 kWh-1
kW

Mean ± SD
37.0 ± 5.1
4,478
4,862 ± 64.6
237.6 ± 29.6
640
0.64 ± 0.08
368.5 ± 29.3

kW

1365.9 ± 174.9%%
tCO2equ yr-1
tCO2equ yr-1 head-1

57.6 ± 4.6
26.8 ± 1.7
22,8180.56

In Table 1, the generator was a 640-kW biogas generator, and actual electrical output power
produced from biogas was 368.5 ± 29.3 kW, so the loading rate of the generator was estimated at
57.6 ± 4.6% of its full capacity. With the hourly biogas flow rate of 237.6 ± 29.6 Nm3 h-1, thetheoretical electrical power generated from biogas was estimated at 1365.9 ± 174.9 kW. Therefore,
the generator efficiency was 26.8 ± 1.7%, and it was higher than the study by De Souza et al.
(2016) and Jeong et al. (2009). The specific biogas consumption in this study was 0.64 ± 0.08 Nm3
kWh-1, which was lower than that studied by De Souza et al. (2016), whose finding was 0.76 m3
kWh-1.
CO2 Reduction Equivalent
Using the biogas system reduces the enormous amounts of CO2 and CH4 emissions. In this study,
the CO2 reduction equivalent was estimated at 22,818 tCO2equ yr-1, or 0.56 tCO2equ yr-1 head-1.
CO2 reduction was lower than that studied by Hin et al. (2021). However, it was higher than
Peerapong and Limmeechokchai (2017), whose founding was 0.47 tCO2eq yr-1 head-1 and for Thai
pig farms. The difference in CO2 emission reduction tends to link with estimated daily manure
production.
CONCLUSION
The use of desulfurization system greatly reduced H2S, but did not affect CH4 and CO2 contents.
Biogas quality was undermined by higher O2 levels in it. With low biogas quality, actual electrical
power produced from biogas was also low. However, considerable amounts of CO2 can be cut withthis biogas system. The limitations of this study are that the biogas generator performance could be
evaluated only with already treated biogas because it is the actual farm operation and altering thesystem or reconnecting raw biogas pipes to the generator are very costly. Further research will

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improve biogas quality with locally made desulfurization systems and prolong the age of iron oxidepellet use to reduce labor and increase system operation efficiency.
ACKNOWLEDGEMENTS
The study was made possible thanks to the project “Reduction of Greenhouse Gas Emission
through Promotion of Commercial Biogas Plant in Cambodia” implemented by United Nations
Industrial Development Organization (UNIDO) that not only provided funding, but also
continuously assisted in strengthening the research team. Many thanks may also go to the farmowner that allowed for a long-term experiment.
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