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CO-PYROLYSIS OF CASSAVA PEELS, RICE HUSKS, AND PLASTIC WASTE FOR BIO-OIL IN RURAL NIGERIA

CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Nigeria is the world’s largest producer of cassava (Manihot esculenta), with annual production exceeding 60 million metric tonnes in recent years, far surpassing other major producers in Africa and globally. This positions the country as a dominant player in cassava cultivation and processing. However, processing generates substantial agricultural residues, particularly cassava peels, which constitute a significant portion of the root mass, often estimated at 10 to 20 percent or more depending on processing methods. These peels are typically discarded, leading to millions of tonnes of waste annually that contribute to environmental degradation when left to rot or openly burned. Similarly, Nigeria ranks among Africa’s top rice producers, generating large volumes of rice husks (approximately 20 to 22 percent of paddy weight) as a by-product. These husks are frequently underutilized, burned in open fields, or used inefficiently for low-value applications, releasing greenhouse gases and particulate matter.

Compounding these agricultural wastes is the growing challenge of plastic waste. Nigeria generates an estimated 2.5 million tonnes of plastic waste annually, much of it from single-use items such as water sachets, packaging, and consumer goods prevalent in both urban and rural areas. In rural communities, where formal waste collection infrastructure is virtually absent, plastics are often dumped indiscriminately, burned, or littered into waterways, exacerbating flooding, soil contamination, and microplastic pollution.

These waste streams, cassava peels, rice husks, and plastics represent not only environmental liabilities but also untapped feedstocks for waste-to-energy technologies. Pyrolysis, a thermochemical conversion process involving the thermal decomposition of organic materials in an oxygen-limited or oxygen-free environment (typically 400 to 600°C), offers a viable pathway to valorize these wastes into bio-oil (a liquid fuel precursor), syngas, and biochar. Bio-oil can serve as a renewable substitute for fossil-derived fuels in cooking, heating, electricity generation, or as a feedstock for further refining into transportation fuels.

Co-pyrolysis, the simultaneous pyrolysis of biomass (such as cassava peels and rice husks) with plastics provides synergistic advantages over mono-feedstock pyrolysis. Lignocellulosic biomass like cassava peels and rice husks yields oxygen-rich bio-oils characterized by high acidity, instability, water content, and lower heating values, limiting direct applications. Plastics (e.g., polyethylene, polypropylene, or polystyrene) decompose into hydrocarbon-rich volatiles with high hydrogen content. During co-pyrolysis, hydrogen radicals from plastics interact with oxygenated radicals from biomass, promoting deoxygenation reactions, reducing acidity, and enhancing the yield and quality of bio-oil (higher calorific value, greater hydrocarbon content, and improved stability).

Recent scholarly investigations confirm these benefits in contexts relevant to Nigeria. For instance, Adeboye et al. (2021) optimized the co-pyrolysis of cassava peels with polystyrene using response surface methodology in a fixed-bed reactor, demonstrating enhanced pyrolysis oil yields and improved fuel properties through synergistic interactions. Similarly, Anaga et al. (2023) produced high-grade bio-oil from the co-pyrolysis of rice husks with low-density polyethylene (LDPE) and polyethylene terephthalate (PET), with the resulting liquid fuel exhibiting properties comparable to commercial diesel. Egbosiuba et al. (2022) further highlighted the potential of cassava peels through catalyzed pyrolysis, achieving bio-oils with favorable higher heating values (up to 42.68 MJ/kg under optimized conditions) and noting the feedstock’s high volatile matter content as advantageous for liquid product formation.

In rural Nigeria, where energy poverty remains acute many households depend on traditional biomass (firewood) or kerosene, leading to deforestation, indoor air pollution, and health issues this technology aligns with sustainable development priorities. Small-scale, locally fabricated fixed-bed or auger reactors could be deployed using abundant local wastes, fostering decentralized energy production, reducing reliance on imported fuels, and creating income opportunities through bio-oil sales, biochar utilization in agriculture (as a soil amendment), or small enterprises. Studies on biomass-plastic co-pyrolysis underscore its potential for circular economy models in resource-constrained settings, with synergistic effects lowering activation energies and improving overall process efficiency.

This study explores the co-pyrolysis of cassava peels, rice husks, and plastic waste specifically for bio-oil production, tailored to the realities of rural Nigeria, where these materials are plentiful and waste management systems are underdeveloped.

1.2 Statement of the Problem
Rural Nigeria faces interconnected crises encompassing energy insecurity, unmanaged agricultural waste accumulation, and severe plastic pollution. Cassava peels and rice husks are frequently discarded in uncontrolled heaps or subjected to open combustion, releasing methane, carbon dioxide, and other pollutants while contaminating soil and water resources. Plastic waste, predominantly consisting of low-value single-use items, overwhelms informal disposal systems due to the near-total absence of formal waste collection services in rural regions. This results in obstructed drainage systems, recurrent flooding, soil and water contamination with microplastics, and toxic emissions from unregulated burning practices.

Conventional waste management approaches, such as landfilling or uncontrolled incineration, prove environmentally unsustainable and economically impractical in low-resource rural contexts. Heavy reliance on fossil fuels and traditional biomass exacerbates deforestation, indoor air pollution associated with respiratory illnesses and constrains socio-economic development. While individual pyrolysis of biomass or plastics has garnered limited attention, integrated co-pyrolysis of these locally abundant waste materials cassava peels, rice husks, and plastics remains insufficiently explored for rural Nigerian applications. Existing research, including studies by Adeboye et al. (2021) and Anaga et al. (2023), indicates technical viability but lacks comprehensive evaluation of context-specific feasibility, scalability, and socio-economic integration within rural communities. Targeted research is urgently required to address this gap and harness the potential of these waste streams for renewable energy production while mitigating environmental degradation.

1.3 Objectives of the Study

The primary objective of this study is to investigate the co-pyrolysis of cassava peels, rice husks, and plastic waste as a sustainable strategy for bio-oil production and waste valorization in rural Nigeria.

Specific objectives are to:

1. Analyze the generation rates, physico-chemical characteristics, and prevailing management practices of cassava peels, rice husks, and plastic waste in selected rural Nigerian contexts.
2. Examine the fundamental principles, reaction mechanisms, and synergistic advantages of co-pyrolysis over individual pyrolysis in enhancing bio-oil yield, quality, and stability, drawing on recent experimental evidence.
3. Evaluate the technical, economic, and environmental feasibility of small-scale co-pyrolysis systems suitable for deployment in rural settings, including reactor design considerations and product utilization pathways.
4. Identify key barriers, enablers, and policy recommendations for the adoption and scaling of co-pyrolysis technology within rural energy and waste management frameworks.

1.4 Research Questions

1. What are the estimated quantities, characteristics, and disposal challenges associated with cassava peels, rice husks, and plastic waste in rural Nigerian communities?
2. In what ways does co-pyrolysis of these feedstocks influence bio-oil yield, chemical composition, and fuel properties relative to mono-pyrolysis, as evidenced by recent studies?
3. What specific synergistic interactions occur among cassava peels, rice husks, and plastic waste during co-pyrolysis, and how can they be optimized?
4. What are the primary technical, economic, social, and institutional barriers to, and opportunities for, implementing co-pyrolysis systems in rural Nigeria?

1.5 Significance of the Study

This research advances sustainable development by proposing an integrated circular economy approach to waste management and renewable energy in rural Nigeria. By converting abundant local wastes into bio-oil and biochar, it could alleviate energy poverty, reduce environmental pollution (including greenhouse gas emissions and plastic leakage), support climate change mitigation, and stimulate rural economies through value-added products and job creation in collection, processing, and utilization. The findings will contribute to the limited body of Nigeria-specific literature on biomass-plastic co-pyrolysis (building on works such as Adeboye et al., 2021; Anaga et al., 2023; Egbosiuba et al., 2022) and inform policymakers, researchers, NGOs, and entrepreneurs on scalable, low-cost technologies aligned with national renewable energy targets and Sustainable Development Goals (SDGs 7, 12, and 13).

1.6 Scope of the Study

This chapter provides a literature-based conceptual foundation, emphasizing waste profiles in rural Nigeria (with illustrative reference to high-production areas), principles of co-pyrolysis, and its relevance to bio-oil production. The study draws on recent scholarly works but is conceptual in this introductory phase; experimental validation, detailed process optimization, and field assessments fall beyond the current scope.

1.7 Definition of Key Terms

• Co-pyrolysis: The simultaneous thermal decomposition of two or more feedstocks (here, lignocellulosic biomass and plastics) in an inert atmosphere to produce enhanced yields of bio-oil, syngas, and char through synergistic radical interactions.
• Bio-oil: The condensable liquid fraction from pyrolysis, comprising a complex mixture of oxygenated and hydrocarbon compounds, suitable as a renewable fuel or chemical platform after upgrading.
• Cassava peels: The outer skin and associated residues from cassava root processing, rich in cellulose, hemicellulose, and starch.
• Rice husks: The silica-rich outer covering of rice grains, a major agricultural by-product with high ash content.
• Plastic waste: Discarded synthetic polymers (e.g., PE, PP, PS, PET) from packaging and daily use, serving as a hydrogen-rich co-feedstock in pyrolysis.

References

Adeboye, B. Z., Adewole, B. Z., & others. (2021). Optimization and modeling of process parameters on the yield of enhanced pyrolysis oil during co-pyrolysis of cassava peel with polystyrene. Environmental Challenges, 5, 100347. https://doi.org/10.1016/j.envc.2021.100347

Adewole, B. Z., Adeboye, B. Z., & others. (2021). Co-pyrolysis of cassava peel with synthetic polymers: Thermal and kinetic behaviors. Waste Disposal & Sustainable Energy, 3, 1–12. https://doi.org/10.1007/s42768-021-00085-w

Anaga, E. S., Oji, A. A., & Okwonna, O. O. (2023). Bio-oil production from co-pyrolysis of rice husk and plastic waste. EQA – International Journal of Environmental Quality, 54, 27–35. https://doi.org/10.6092/issn.2281-4485/16454

Egbosiuba, T. C., & others. (2022). Biochar and bio-oil fuel properties from nickel nanoparticles assisted pyrolysis of cassava peel. Heliyon, 8(8), e10140. https://doi.org/10.1016/j.heliyon.2022.e10140