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OPTIMIZATION OF BIOGAS AND BIOFERTILIZER PRODUCTION FROM MUNICIPAL AND ABATTOIR WASTE IN NIGERIAN CITIES
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Nigeria’s rapid urbanization and population growth have significantly increased the generation of municipal solid waste (MSW) and abattoir wastes in major cities such as Lagos, Abuja, Kano, and Port Harcourt. MSW in Nigerian urban centers typically contains 50–70% organic fractions (food waste, market residues, and yard trimmings), while abattoirs produce large volumes of high-moisture, nutrient-rich wastes including blood, rumen contents, intestinal wastes, manure, and slaughterhouse effluents. These wastes are often poorly managed, leading to open dumping, uncontrolled burning, or discharge into water bodies, which contributes to environmental pollution, greenhouse gas emissions, and public health risks.
Anaerobic digestion (AD) offers a sustainable solution by converting these organic wastes into biogas (primarily methane, 50–70%) for energy applications (cooking, electricity generation, or heating) and digestate as nutrient-rich biofertilizer. Biogas serves as a clean renewable energy source, while the stabilized digestate improves soil fertility, enhances crop yields, and reduces dependence on imported chemical fertilizers.
Optimization of biogas and biofertilizer production involves strategic process enhancements such as co-digestion of MSW (carbon-rich) with abattoir wastes (nitrogen- and protein-rich) to achieve an optimal carbon-to-nitrogen (C/N) ratio of 20–30:1, thereby preventing ammonia inhibition and improving methane yield. Additional strategies include substrate pretreatment (mechanical grinding, thermal, or chemical), control of operational parameters (mesophilic temperature 35–40°C, which aligns well with Nigeria’s tropical climate; pH 6.8–7.2; hydraulic retention time; and organic loading rate), use of additives or inocula, and reactor design improvements (e.g., fixed-dome or floating-drum digesters suitable for small-to-medium scale urban applications).
Recent scholarly work supports the feasibility and optimization potential in Nigerian contexts. Audu et al. (2020) conducted a multi-criteria assessment of abattoir wastes in Nigeria’s north-central region (covering sites in Abuja, Niger, and Nasarawa States) and estimated an annual biogas potential of approximately 1.667 × 10⁶ m³ from studied abattoirs, alongside 1,380 tonnes of dry biofertilizer, with significant GHG emission reductions and electricity generation capacity. Mutisi et al. (2025) demonstrated enhanced biogas production and waste stabilization through co-digestion of abattoir effluent and rumen content, highlighting improved process stability, higher methane content, and effective management of high-protein wastes common in urban slaughterhouses.
In Nigerian cities, where energy access remains inconsistent and waste management infrastructure is strained, optimized AD systems could enable decentralized or semi-centralized plants at abattoirs or waste transfer stations. This approach aligns with circular economy principles, turning waste liabilities into resources for energy security, soil health improvement, and climate mitigation.
1.2 Statement of the Problem
Nigerian cities confront significant challenges related to waste accumulation, energy poverty, and soil degradation. Municipal solid waste (MSW) and abattoir wastes are commonly disposed of in open dumpsites or landfills, resulting in uncontrolled methane emissions, a potent greenhouse gas (GHG) as well as leachate contamination of groundwater and surface water. Abattoir effluents contribute to odor pollution, pathogen dissemination, and waterway degradation, while the high protein content of slaughterhouse wastes may induce process instability such as ammonia toxicity and volatile fatty acid accumulation when subjected to anaerobic digestion (AD) without co-substrates.
Heavy dependence on fossil fuels for cooking and electricity generation, combined with reliance on costly imported chemical fertilizers, intensifies economic and environmental burdens. While AD technology has been piloted in Nigeria, many systems exhibit suboptimal performance due to inadequate feedstock blending, insufficient process monitoring, and a lack of site-specific optimization for co-digestion of municipal and abattoir wastes. Existing research provides limited insight into integrated optimization strategies tailored to the heterogeneous composition and seasonal variability of these waste streams within Nigerian urban contexts. This gap impedes scalable implementation despite established technical feasibility (Audu et al., 2020; Mutisi et al., 2025).
1.3 Objectives of the Study
The main objective is to investigate the optimization of biogas and biofertilizer production through anaerobic co-digestion of municipal solid waste and abattoir waste in Nigerian cities.
Specific objectives are to:
- Quantify the generation rates, physico-chemical characteristics, and current management practices of MSW and abattoir wastes in selected Nigerian urban centers.
- Review and analyze optimization techniques (co-digestion ratios, pretreatment methods, and operational parameters) for enhancing biogas yield, methane content, and digestate quality as biofertilizer.
- Assess the technical, economic, and environmental feasibility of optimized AD systems for urban deployment, including energy output, fertilizer value, and GHG mitigation potential.
- Identify barriers, opportunities, and policy recommendations for scaling optimized biogas and biofertilizer production in Nigerian cities.
1.4 Research Questions
- What are the quantities, characteristics, and disposal challenges of municipal solid waste and abattoir wastes in major Nigerian cities?
- How do co-digestion and other optimization strategies influence biogas yield, process stability, and biofertilizer quality compared to mono-digestion?
- What synergistic effects occur when combining MSW and abattoir wastes in anaerobic digestion, and how can key parameters (C/N ratio, temperature, pH) be optimized?
- What are the primary technical, economic, environmental, and institutional barriers to, and enablers for, implementing optimized AD systems in Nigerian urban contexts?
1.5 Significance of the Study
This research promotes sustainable urban waste management and renewable energy development in Nigeria by providing evidence-based optimization strategies for biogas and biofertilizer production. Successful implementation could reduce landfill methane emissions, generate clean energy for households and industries, improve soil fertility for urban and peri-urban agriculture, create employment in waste collection and plant operation, and support national climate and renewable energy targets. The findings will build on existing studies (Audu et al., 2020; Mutisi et al., 2025) and offer practical insights for policymakers, waste management authorities, abattoir operators, and investors toward circular economy models in Nigerian cities.
1.6 Scope of the Study
This chapter establishes the conceptual and contextual foundation through literature synthesis, focusing on waste profiles and AD optimization principles relevant to Nigerian cities. Emphasis is placed on co-digestion of MSW and abattoir wastes; experimental optimization, detailed techno-economic modeling, and field pilot studies are beyond the scope of this introductory chapter.
1.7 Definition of Key Terms
- Anaerobic Digestion (AD): Biological process in which microorganisms break down organic matter in an oxygen-free environment to produce biogas and digestate.
- Biogas: Renewable gaseous fuel primarily composed of methane (CH₄) and carbon dioxide (CO₂), generated from AD.
- Biofertilizer: Nutrient-rich, stabilized digestate from AD, used as an organic soil amendment to improve fertility and structure.
- Co-digestion: Simultaneous anaerobic digestion of two or more complementary feedstocks (e.g., MSW and abattoir waste) to enhance process performance.
- Municipal Solid Waste (MSW): Waste generated from households, markets, and commercial activities in urban areas, with high organic content in Nigeria.
- Abattoir Waste: Organic residues from slaughterhouses, including blood, rumen contents, manure, and effluents.
References
Audu, I. G., Barde, A., Yila, O. M., Onwualu, P. A., & Lawal, B. M. (2020). Exploring biogas and biofertilizer production from abattoir wastes in Nigeria using a multi-criteria assessment approach. Recycling, 5(3), 18. https://doi.org/10.3390/recycling5030018
Mutisi, C., Moreroa, T., & others. (2025). Co-digestion of abattoir effluent and rumen content for waste management and biogas production. IET Renewable Power Generation. https://doi.org/10.1049/rpg2.70123