A Comprehensive Economic Feasibility of Biogas Production from Co-digestion of Sisal Processing Waste and Cow Manure: A Case of Kilifi Sisal Plantation

Abstract

This paper evaluates the economic feasibility of biogas production and operational challenges at the Kilifi Sisal Plantation, focusing on substrates such as cow manure, sisal pulp, mango waste, and sisal bole. The research provides a cost-benefit analysis, revealing cow manure, costing KES 258 per ton, as the most cost-effective substrate, followed by Sisal Pulp from KPL at KES 139.8 per ton. Mango waste and sisal bole, with costs of KES 670 per ton and KES 3661 per ton, present higher financial barriers respectively. The Kilifi biogas plant utilizes a fixed-dome system, producing approximately 395 m³ of biogas daily from cow dung and sisal pulp. While the system generated KES 312,000 over 10 years from energy savings and fertilizer production, the plant faces key challenges, including the inability to meet the 250KW grid connection capacity, which leads to unsold excess electricity, and high operational costs amounting to KES 3,187,254 annually. The small-scale biodigester's Net Present Value (NPV) is KES 2,301.14, and the Payback Period (PBP) is approximately 6.3 years. To enhance profitability, the study recommends optimizing feedstock management, expanding the plant's grid connection capacity to meet national requirements, and investing in technological upgrades, such as automating the feeding system and improving energy efficiency. Additionally, the study recommends regular maintenance and training, implementation of wastewater recycling, and undertaking lifecycle and economic assessment in order to identify cost-saving opportunities and the plant's long-term sustainability.