Evaluating the potential purification and upgrade of household use biogas using biochar based adsorption technology

Abstract

The increasing global energy demand and the environmental impacts of fossil fuel consumption have necessitated the adoption of sustainable and environmentally friendly energy alternatives. Biogas, generated through the anaerobic digestion of organic materials such as agricultural waste, animal manure, and municipal waste, offers a viable renewable energy source. However, raw biogas contains impurities such as hydrogen sulfide (H₂S), carbon dioxide (CO₂), moisture, and trace gases that lower its calorific value, corrode system components, and pose operational and environmental risks. This study evaluated the effectiveness of biochar-based adsorption technology in purifying household-use biogas, with emphasis on the removal of H₂S and CO₂. Biochar produced from maize cobs via controlled pyrolysis was selected due to its high surface area, porosity, and functional groups favorable for gas adsorption. The research was conducted at Makerere University Agricultural Research Institute Kabanyolo (MUARIK). A laboratory-scale biodigester was constructed to generate raw biogas. Biochar was produced and characterized, after which a filter system packed with the biochar was designed and tested. Gas samples were collected before and after filtration and analyzed using a gas analyzer to determine concentrations of methane (CH₄), carbon dioxide (CO₂), carbon monoxide (CO), and hydrogen sulfide (H₂S). The performance of the biochar filter was assessed based on impurity removal efficiency, adsorption capacity, breakthrough time, and reusability. The results showed a significant reduction in H₂S and CO₂ concentrations—averaging 85% and 78% removal, respectively—resulting in improved biogas quality suitable for domestic applications. The biochar demonstrated adequate breakthrough times and maintained considerable adsorption capacity after regeneration, confirming its potential for reuse. These findings affirm the viability of using locally available agricultural waste to produce cost-effective biochar for biogas purification. The study contributes valuable insights for the development of decentralized, low-cost biogas upgrading systems in rural and resource-constrained communities, supporting broader access to clean and sustainable energy.