1. Table of content
● Introduction to Biogas
● Biogas feedstocks
● Production of Biogas
● Anaerobic Digestion
● Variables that affects the production of Biogas
● Utilization of Biogas
● Benefits of Biogas
● Challenges of Biogas
● Potential of Biogas production in Nigeria
● Biogas Production in Nigeria
2. Introduction to Biogas
Biogas is a mixture of gases produced from the breakdown of organic materials
(dead plant and animals) in an oxygen-free environment through a process called
anaerobic digestion (Sara, 2017).
Biogas production system uses the process of anaerobic digestion to recycle
organic wastes by turning them into biogas and important soil products (liquid and
solids) (Al Seadi et al, 2008).
Biogas consists primarily of methane(50-75%), CO2(30-40%) and trace amount of
other gases such as H2S, moisture and siloxanes (Al Seadi et al, 2008).
3. Biogas feedstocks
Biogas are produced from relatively inexpensive feedstocks which must be
biogenic in nature.
The feedstocks include the following:
● Food wastes
● Livestock wastes or manure
● Agricultural wastes or crop residues
● Wastewater
4. Production of Biogas
Biogas is produced by the microbial degradation of biomass in the absence of
oxygen i.e anaerobic digestion (Al Seadi et al, 2008).
Biogas is produced naturally, especially in landfills and livestock manure
management systems through anaerobic digestion (Liu et al, 2011).
However, these processes can be optimized.
5.
6. Anaerobic Digestion
Anaerobic digestion (AD) involves a series of biochemical processes by which
microbial organisms break down organic matter in the absence of oxygen (Al
Seadi et al, 2008).
Biogas installation is used in the production of biogas and digestate.
Anaerobic digestion can be divided into four categories:
● Hydrolysis
● Acidogenesis
● Acetogenesis
● Methanogenesis
7. Hydrolysis
This is a stage in anaerobic digestion where organic compounds such as
carbohydrates, proteins and fats are broken down into smaller and simple soluble
units by extracellular enzymes such as cellulases, amylases and lipases secreted
by fermentative bacteria (Clifford, 2020).
(C6H10O5)n + nH2O nC6H12O6
(R-CHNH2COOH)n + H2O nR-CHOH2COOH + nNH3
C3H5(OCOR) + 3H2O C3H5(OH)3 + 3RCOOH
8. Acidogenesis
This is a process where the products of hydrolysis are converted into organic acids by acids
forming bacteria.
The sugar and amino acids products of the hydrolysis are converted into volatile free fatty acids (
mainly acetate, propionate, butyrate), hydrogen (H2), CO2, and ammonia (lactate and alcohols may
also be produced) via fermentative reactions (Al Seadi et al, 2008).
C6H12O6 + 2H2 → 2CH3CH2COOH + 2H2O
C6H12O6 → 2CH3CH2OH + 2CO2
9. Acetogenesis
The acidogenesis intermediates are attacked by acetogenic bacteria; the products from
acetogenesis include acetic acid, CO2, and H2.
CH3CH2COO- + 3H2O → CH3COO- + H+ + HCO- + 3H2
C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2
CH3CH2OH + 2H2O → CH3COO- + 2H2 + H+
10. Methanogenesis
This is the production of methane from acetogenesis intermediate products, some
gases such as CO2 are also produced (Liu et al, 2011). Methanogenesis is carried
out by the methanogenic bacteria (Al Seadi et al, 2008). Some of the bacteria include:
● Methanobacterium
● methanobacillus
● methanococcus
● methanosarcina, etc.
11. Methanogenesis
The following are common reactions that take place during methanogenesis:
● 2CH3CH2OH + CO2 → 2CH3COOH + CH4
● CH3COOH → CH4 + CO2
● CO2 + 4H2 → CH4 + H2O
13. Variables that affect the production of biogas
These are the factors that affect the anaerobic bioconversion of processes in an
AD system. They are as follows:
● Raw materials
● Oxidation and reduction potential
● Temperature
● pH
● C/N ratio
● Inhibitors
14. Raw materials
Different raw materials have different biogas production potentials.
Source:X Liu, Z Yan and Z-B Yue. Biogas. 2011.103-104. Elsevier. Amsterdam, Netherlands
Materials Content of biogas (%)
CH4 CO2
Carbohydrates 50 50
Protein 50 50
Fat 72 28
15. Oxidation and Reduction Potential
Methanogens are strict anaerobic microorganism that can be inhibited or even
killed by trace oxygen.
Thus a low oxidation-reduction potential(ORP) is needed to maintain their
activities.
The ORP required for the methanogenesis ranges from -400 to -150 mV and −100
to 100 mV for non methanogenesis processes (Liu et al, 2011).
16. Temperature
Temperature is an important factor that significantly affects the reproduction and
activities of anaerobic microbes.
The temperature of different digesters varies between 8 and 65 °C.
Generally, biogas production increases with increase in temperature.
The highest methane production is generally achieved in the temperature range
from 35 to 40 °C under mesophilic conditions and at approximately 55 °C for
thermophilic conditions.
17. pH
The favorable pH range for anaerobic microbes is 6.8–7.5.
Methanogenic microorganisms are very sensitive to pH.
18. C/N ratio
The appropriate ratio of carbon to nitrogen (C/N) in AD process is 20–30.
Deviating from this range, the biogas production yield will decrease.
19. Inhibitors
Organic wastes and plants from livestock farms tends to contains poisonous
substances, such as disinfectants, pesticides, and heavy metals, which can inhibit
the growth, metabolism, and propagation of the anaerobes.
20. Uses of Biogas
•Power generation
•Bio fertilizer
•Bio methane
•Biogas can be used to augment conventional energy sources
21. Benefits of biogas
● Renewable energy source
● Reduced greenhouse gas emissions and global warming
● Waste reduction
● Job creation
● Digestate can be used as fertilizer
22. Challenges of Biogas
● Few technological advancement
● Biogas contain impurities
● Less suitable for dense metropolitan
23. Potential of biogas production in Nigeria
Total biochemical potential of biogas that could be generated from the biomass
feedstock is 72 billion cubic metres, from which 270 TWh of electricity could be
generated, which is enough to satisfy the annual electricity need of the Nigerian
population.
The amount of solid wastes generated in developing countries such as Nigeria
has steadily increased over the last two decades as a result of population
explosion and continuous growth of industries and agricultural practices.
Thus, the potential of biogas production in Nigeria is huge.
24. Biogas production in Nigeria
Biogas production is feasible in Nigeria because of her enormous waste. This
waste can be utilized to produce free cooking gas call biogas and wonderful
organic fertilizer.
The pioneer biogas plants are a 10m3 biogas plant constructed in 1995 by the
Sokoto energy research centre (SERC) in Zaria and a 18m3 biogas plant
constructed in 1996 at Ojokoro Ifelodun piggery farm, Lagos by the Federal
Institute of Industrial Research Oshodi (FIIRO) Lagos (Zuru et al., 1998).
25. REFERENCES
X Liu, Z Yan and Z-B Yue. Biogas. 2011. Elsevier, Amsterdam, Netherlands.
T Al Seadi, D Rutz, H Prassl, M Köttner, T Finsterwalder, S Volk, R Janssen. Biogas
Handbook. University of Southern Denmark, Denmark.
C Clifford. Anaerobic Digestion. The Pennsylvania State University, accessed 12th,
April, 2021. <https://www.e-education.psu.edu/egee439/node/727>.
Abila, N. (2012). “Biofuels development and adoption in Nigeria: Synthesis of drivers,
incentives and enablers,” Energy Policy 43, 387-395.
