THE INTERNATIONAL JOURNAL OF SCIENCE & TECHNOLEDGE ISSN 2321 – 919X www.theijst.

com

THE INTERNATIONAL JOURNAL OF

SCIENCE & TECHNOLEDGE

Biogas: An Alternative Source of Energy for

Developing Economy
Akinnate, Felix Akindele
Lecturer, Department of Integrated Science,
Adeyemi Federal University of Education, Ondo, Nigeria
Olabode, Olubusuyi Oladele
Lecturer, Department of Integrated Science,
Adeyemi Federal University of Education, Ondo, Nigeria
Akinyosoye, Favour Moyo
Lecturer, Department of Integrated Science,
Adeyemi Federal University of Education, Ondo, Nigeria

Abstract:
There is an increase in energy demand due to increased population, leading to high waste generation, deforestation,
and global warming. The world's reserves of fossil fuel that has resulted in an increase in energy price cannot be
allowed to be depleted. There is a need to look more into economic biogas production, which can serve as an
alternative source of energy. Biogas is now preferred because of its environmentally friendly, renewable, clean, cheap,
high quality, and versatile fuel, which uses feedstocks. This paper looks more into the processes of production of
biogas using the waste of plant-based materials that are typically rich in different polysaccharides that are generated
from local farm production of plants and animals in rural Nigeria. Four main steps in biogas production are
emphasized, and various factors that affect biogas production are stated. Various ways of manipulating these factors
for maximal biogas production were suggested. One of the main challenges in biogas production is the high cost of
biodigester, which is taken care of in the paper through a low-cost construction of an alternative biogas digester that
serves effectively from used materials. Economic production of biogas is given a probable investment, as described in
this work.

Keywords: Biogas, biodigester, fossil fuel, feedstock, slurry

1. Introduction
One of the major challenges in the world today is the depletion of reserved fossil fuels, which is a cause of the
increase in energy prices (Schnürer, 2016). There is an increase in energy demand due to the increased population,
leading to high waste generation, deforestation and global warming (Biodun et al., 2021). Energy is a very important factor
in any nation (Forgács, 2012). In a developing country like Nigeria, there is a corresponding increase in energy
consumption demand (Aluko, 2018). A nation like Nigeria has an installed capacity of 12,522MW at the moment. However,
it is operating at a capacity of 3,879MW while the estimated energy need is placed between 98,000MW and 160,000MW,
leaving behind a huge generation gap (Sambo et al., 2012). As part of efforts to bridge the energy gap, the country has been
investing in constructing various dams and even solar energy projects and exploiting other resources and potentials such
as natural gas, coal, and nuclear power. However, these are not currently being utilized due to a lack of proper
technologies and/or political will (Aluko, 2018).
It has been suggested that Nigeria's energy demands can be met sustainably via the use of renewable energy, such as
biogas (Adewuyi, 2020). Anika et al. (2019) reported that the use of renewable energy is highly advantageous because the
sources of energy are readily available, cheap and do not require elaborate technology and importantly, the fuel generated
is environmentally friendly. Renewable resources for energy production are becoming more important because the
burning of fossil fuels leads to the release of CO2, a gas that is implicated in global warming (Samantha, 2020). The problem
of global warming can be partly circumvented by the production of biogas from plants or waste materials in a biological
process (Busic et al., 2018).
Biogas is a flammable, smokeless, hygienic, colorless, odorless gas, but with odour when not desulfurized. It has an
energy content of 37.3 MJ/m3, explosion limits of 6–12% in air, ignition temperature of 650–750°C, specific gravity of
0.847–1.004, and calorific value of 4740–7500 kcal/Nm3 (Ali et al., 2013). Biogas is an environmentally-friendly,
renewable, clean, cheap, high-quality, and versatile fuel that is generated in digesters filled with feedstock. It is considered
an alternative green energy resource and can be utilized for different energy services like heat, combined heat and power,
or as car fuel (Ngan et al., 2020).

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2. Process of Biogas Production

Biogas is a combustible anaerobically generated gas consequent upon the activities of a consortium of anaerobic
microbes decomposing organic wastes such as solid wastes, fruit wastes, industrial effluent, cattle manure and discarded
vegetables (Njogu et al., 2015). Biogas is formed when organic material, such as food waste or manure, is degraded by
microorganisms in the absence of oxygen, the so-called anaerobic (oxygen-free) degradation or digestion. This process
differs from composting, which is also a bio-degradation process, where aerobic conditions (i.e., oxygen) are required for
the organisms to grow and work (Schnurer & Jarvis, 2018).
Abbasi et al. (2012) reported that during this process, complex organic matter such as protein, fats, and
carbohydrate polymers (cellulose and starch) are first hydrolyzed into monomers like amino acids, long-chain fatty acids,
and sugars. These monomers are then fermented to form volatile fatty acids (lactic, propionic, and butyric acids) during
acidogenesis (second step). In the third step (acetogenesis), bacteria consume these volatile fatty acids and generate acetic
acid, carbon dioxide (CO2), and hydrogen (H2). Finally, methanogenic organisms consume acetate, H2, and some of the CO2
to produce methane (CH4) (Haryanto et al., 2018).

3. Composition of Biogas
Biogas has a composition consisting of methane (CH4), carbon dioxide (CO2), Nitrogen(N2), hydrogen (H2), water
vapour, oxygen (O2), hydrogen sulphide (H2S) and ammonia (NH3) (Rakican, 2007) as presented in table 1.
Biogas is produced after organic materials (plant and animal products) are broken down by bacteria in an oxygen-
free environment, a process called anaerobic digestion. Biogas systems use anaerobic digestion to recycle these organic
materials, turning them into biogas, which contains both energy (gas) and valuable soil products (liquids and solids)
(Tanigawa, 2017), as presented in figure 1.

Biogas Composition Typical Analysis (%/Volume)

Methane 55–65
Carbon dioxide (CO2) 35–45
Nitrogen (N2) 0–3
Hydrogen (H2) 0–1
Hydrogen sulfide (H2S) 0–1
Oxygen (O2) 0–2
Ammonia (NH3) 0–1
Table 1: Approximate Percentage of Biogas Components
Source: Lebuhn Et Al, (2015)

Figure 1: Anaerobic Digestion Process

Sources: Tanigawa, 2017

Awe et al. (2017) stated that biogas is a valuable renewable energy and also a secondary energy carrier produced
from biodegradable organic materials via anaerobic digestion. It can be used as a fuel or as a starting material for the
production of chemicals, hydrogen and/or synthesis gas, etc. Biogas is produced spontaneously in environments where
organic material accumulates with little or no oxygen present, for example, in wetlands and rice paddies, on the seabed, or
in the stomachs of ruminants (Schnürer & Jarvis, 2017). Methane (CH4) is the most important component of biogas
because it has the highest energy density among the biogas components. Therefore, high CH4 content of biogas is desirable
(Ngan et al., 2020). Anaerobic digestion involves the use of microbes for biological oxidation and reduction of organic
carbon to its most oxidized state (CO2) and reduced form (CH4) (Obileke et al., 2020).
It has been known for several centuries that combustible gas is generated when organic waste is allowed to rot in
huge piles. For example, in the seventeenth century, Van Helmont recorded that decaying organic material produced
flammable gases (Abbasi et al., 2012). Biogas was first identified 600 years ago as a product of decomposing organic

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matter, and in 1884, Louis Pasteur investigated animal waste, suggesting it as an appropriate fuel for the lighting of street
lamps (Korbag et al., 2020).
The process of production of biogas being used for energy generation has been in place since the second half of
the 19th century. It started with small reactors to provide gas for cooking and heating for individual households, farms, or
villages in Asia and Africa and then increasingly commercialized to large-scale systems, mainly in Europe (Schnürer &
Jarvis, 2017).
Biogas production is an established process in which there is little information available on the microorganisms
involved in using different wastes. Thus, understanding the microorganisms' activity and the factors that can influence
biogas composition are crucial to maximize fermentation performance and reduce process costs (Nettmann et al., 2010). A
complex microbiological process is behind the efficient production of biogas and different species of microorganisms that
work closely together need to be active for biogas to be formed. Microorganisms need access to an appropriate nutrient
medium, i.e., a substrate (Kushkevych et al., 2017).
With access to a substrate, microorganisms can metabolize, build up new cells (anabolism) and produce energy
(catabolism) for their growth. The organic waste treated in the biogas process represents the substrate for various
microorganisms (Schnürer & Jarvis, 2017).
Methane, which is the end product of a biogas process, is also a microbial waste product. In addition to the
substrate, the microorganisms require suitable environmental conditions in order to thrive and function. Examples of
important environmental factors for growth are: temperature, pH, oxygen content, and salt concentration. Different
organisms have different requirements for these environmental factors in order to be able to grow optimally (Schnürer &
Jarvis, 2018).

4. Steps in Biogas Production

The production of biogas involves four main steps: hydrolysis, acidogenesis, acetogenesis, and methanogenesis.
The microbes convert the substrates into CH4, CO2 and other gases (Schnürer, 2016) as presented in figures 2 and 3. The
microorganisms involved in the process mainly belong to the Bacteria and Archaea domains, with some fungi also taking
action in the hydrolysis step. The consortium of microbes involved breaks large macromolecules into their simpler organic
components and subsequently converts them into methane (Schnürer, 2016).

Figure 2: Anaerobic Degradation of Carbohydrate, Lipids and Proteins and the Phyla
Commonly Reported to Be Involved in Different Steps
Sources: Koumiss & Angelika, 2018

The initial step is performed by hydrolytic bacteria, and possibly also fungi, that convert polymers
(polysaccharides, lipids, proteins, etc.) into soluble monomers (LCFA, glycerol, amino acids, sugars, etc) (Kazda et al.,
2014). This first stage is very important because large organic molecules are simply too large to be directly absorbed and
used by microorganisms as a substrate/food source and in this stage, sugars, fats and proteins are converted into smaller
organic compounds such as amino acids, simple sugars, fatty acids and some alcohols (Schnürer, 2016).
The monomers resulting from the different hydrolysis reactions are further oxidised mainly through various
fermentation reactions through the Embden–Meyerhof–Parnas (EMP) or Enter–Doudoroff (ED) pathways. The
biochemical pathways of sugar oxidation are diverse, but in most cases, they end up with pyruvate as a key intermediate.
In the next step, pyruvate can be used as an internal electron acceptor for re-oxidation of NADH, resulting in the
production of C2–C6 products such as acetate, propionate, butyrate, lactate, valerate, caproate and to some extent
hydrogen/formate (Worm et al., 2014). Acidogenic bacteria convert monomers obtained during the hydrolysis stage into
volatile fatty acids (VFAs) with high carbon numbers, such as butyrate, propionate, and alcohols in addition to CO2, H2, and
acetate (Cibis et al., 2016).

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During acetogenesis, the products formed in hydrolysis/acidogenesis are further converted by a group of bacteria
called acetogens, generating acetate, H2, and CO2 as main products. During this process, various electron acceptors can be
used, including CO2, nitrate, sulfate, and protons, with the latter being most important in the biogas process (Ragsdale &
Pierce, 2008). For the third reaction stage, acetogenic bacteria convert VFAs into acetate (Da Silva., 2017). Acetogens can
also directly use products from hydrolysis, such as sugars and amino acids (Drake et al., 2008), or oxidize pyruvate, which
is a common intermediate in anaerobic degradation reactions to acetate (Worm et al., 2010).
Methanogenesis is the final stage of the biogas process. In this stage, methane and carbon dioxide (biogas) are
formed by various methane-producing microorganisms called methanogens. The most important substrates for these
organisms are hydrogen gas, carbon dioxide, and acetate, which are formed during anaerobic oxidation (Costa & Leigh,
2014).
Methanogens are divided into two main groups depending on the substrate they utilize: hydrogenotrophs and
methylotrophs.

Figure 3: (A) Methylotroph Process of Methanogenesis,

(B) Hydrogenotroph Process of Methanogenesis
Sources: Schnurer, 2016

5. Factors That Affect Biogas Production

The growth and metabolism of anaerobic microorganisms are essentially impacted by physical and chemical
conditions such as temperature, pH value, nutrient supply, mixing intensity, and the additional presence of inhibitors
(Schnürer & Jarvis, 2018), as presented in figure 4.

Figure 4: Expression of Factors Affecting Biogas Production

Source: Schnürer and Jarvis, 2018

6. Substrates for Biogas Production

To achieve a stable and efficient biogas production process, the material added to digesters must have a good
balance of both macro- and micronutrients (Angelidaki et al., 2011). The material added to a biogas process is a substrate
(food) for the microbes and its properties have a major influence on process stability and efficiency (Schnürer & Jarvis,
2018). Biogas can be produced from different biodegradable materials such as agricultural wastes, which include: animal
manure, crop residues (wheat straw) and energy crops (grass, maize, etc.). Municipality waste includes sewage and
organic fractions of Municipal Solid Waste (MSW) and organic industrial and commercial waste such as
beverage/food/tobacco processing waste, slaughterhouse/ rending waste and dairy waste (Schnürer & Jarvis, 2018).

6.1. Agricultural Waste

Agricultural waste emanates from different agricultural activities. They include animal waste and lignocellulosic
biomass, usually in the form of crop residue, forest residue and energy crop (Nwokolo et al., 2020). Biogas production
from different agricultural wastes through anaerobic digestion has increased worldwide due to not being competitive with
food supply and being environmentally friendly. Furthermore, this method presents other advantages that contribute to

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reducing pollution produced by organic waste, decreasing waste as garbage, and becoming value-added products
(Martinez-Gutierrez1, 2018).

6.2. Animal Waste

Animal waste is a renewable and cost-effective substrate for the production of biogas through anaerobic digestion.
If not properly handled and disposed of, this organic waste poses a threat to the environment because of its high
concentration of nitrogen and phosphorus. In addition, the presence of pathogens, antibiotics, heavy metals and
microorganisms in animal waste can contaminate water bodies, air and soil (Abdeshahian, 2016). Animal wastes identified
as a viable substrate for biogas production are manure derived from cattle, pigs, sheep, goats and poultry.

7. Plant/Crop Residue
Plant-based materials, such as fruit, grains, vegetables, and root crops, are typically rich in different
polysaccharides, which are chains of sugars linked in linear chains (cellulose and starch) or branched chains
(hemicellulose, pectin, and glycogen). In the plant cell wall, hemicellulose, cellulose, and lignin are associated in the form of
lignocellulose (Sánchez & Cardon, 2008). Energy crops and crop residues represent an important source of biomass that
can serve as a substrate for biogas production, among which are energy crops, but the grass is considered a more suitable
feedstock; hence, its availability is not limited to season change (Gerin et al., 2008).

8. Biogas Digester Schematic Diagram and Part Functions

Figure 5
Source: Nwankwo et al., 2017

Item Name of Part Function

A Container of choice size Serve as biodigester where anaerobic digestion occurs
1 Waste inlet Grinded waste (domestic waste, cow dung and any other
agricultural waste)
2 Waste inlet valve Closes the waste inlet pipe
3 Waste pipe Guides the waste into the digester. It goes 75 to 90% into
the digester
4 Water+Manure (cow Substrate and medium for anaerobic digestion
dung) + Waste
5 Slurry outlet Slurry is discharged from this outlet and can be used as
liquid fertilizer.
6 Cleaning pipe Slurry emptied through this valve when cleaning is
required
7 Gas outlet Biogas produced leaves the digester via this outlet into a
tyre tube that serves as a storage
8 3-way gas valve For directing biogas produced into either tyre tube and
from tube to the burner. The gas flow is controlled by the
valve knob.
9 Extra slurry hole For removal of slurry in case the slurry outlet pipe is
blocked.
B Tyre tube Serve as a gas storage unit.
10 Gas outlet (to tyre) Biogas from biodigester flow into the tyre tube for storage.
The flow is controlled by a three-way valve.
11 Gas outlet (to burner) Biogas is directed to Bunsen burner from the tyre tube.
The flow is controlled by a three-way valve.
Table 2: List and Functions of Materials Required to Build a Local Digester
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Establishment construction of a biogas plant will be of great advantage to the teeming population of the nation of
Nigeria, most especially the low and medium-level citizens who cannot afford cooking and kerosene due to the high cost. It
is a project that converts organic waste into cooking gas, which causes a nuisance in the environment. The biogas
generated will replace traditional energy sources like firewood, which is one of the factors contributing to deforestation.
Biogas is one of the current successful alternative energy. It is very economical and eco-friendly because the
materials required for the production of biogas are readily available abundantly. Materials like cow dung, piggery waste
and poultry droppings are giving farmers problems to eradicate. Plant waste after harvest can also serve as material for
biogas production and all these are readily available in our farms. Kitchen waste, domestic waste, and human excreta can
serve as materials for biogas production. Biogas production will reduce the nation's dependence on fossil fuel, which is
getting depleted as a non-renewable source of energy, and also can be a means of reducing the emission of greenhouse
gases and other toxic emissions coming from our farms. This reduces the harmful effects of methane on the environment.
The accumulation of waste materials in a particular space in our farms, which most times contaminate our surface and
underground waters and have toxic effects on the human population, will be minimized. The use of biogas will help to save
time in cooking while at the same time reducing the dirtiness of utensils because using biogas does not generate smoke.
One of the major challenges of farming is the availability of fertilizer for plant production. Slurry from biogas plants is a
very good liquid fertilizer for crop production, especially vegetables. The use of liquid fertilizer in farms will reduce the
cost of production because the huge amount of money spent on fertilizers will be reduced. The use of biogas as a source of
energy in most African countries is not pronounced or popular because of a lack of awareness, and the technology is not
clear to rural people despite the simplicity of the construction of a biodigester. On the part of the government, a lack of
political commitment and policies that encourage the use of biogas is standing in the way of the popularity of biogas
technology. Many European and Asian countries, most especially India, are using biogas as alternative sources of energy,
and many of their rural dwellers depend on the use of biogas for cooking and lighting. The commitment of the government
to biogas technology in Nigeria will save costs on the purchase of fossil fuels and reserve our depleting fossil fuel. The
technology will also help increase food production due to the availability of liquid fertilizer from the slurry of biodigesters.
The major constraint of biogas technology is the high cost of the initial investment in the construction of a biodigester due
to the high level of poverty among our rural dwellers.

Figure 6

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47 Vol 11 Issue 10 DOI No.: 10.24940/theijst/2023/v11/i10/ST2310-009 October, 2023