Purification of Biogas Using Low-cost Locally Available Materials for Off-grid Power Applications

Upgrading biogas is essential to increase its calorific value and expand its applications, primarily in power and rural electrification uses. Raw biogas is typically 50–70 % methane (CH₄), with some carbon dioxide (CsO₂), hydrogen sulfide (H₂S), and water vapour that lowers energy efficiency and leads to system parts corrosion. Although efficient, conventional purification methods such as water scrubbing, chemical adsorption, and pressure swing adsorption remain costly and technically demanding for small-scale or rural use. Five cheap locally available materials that could be used for biogas purification were screened in this study: zeolite, iron ore, charcoal, potash, and clay. The materials were tested individually and in mixtures, and commercial-grade adsorbent (soda lime and silica gel) served as control. Portable biogas analyzer was utilized in determining the composition of gas before and after purification to determine CO₂, H₂S, and H₂O removal efficiency. The findings confirmed the efficiency of zeolite and potash in CO₂ removal, with maximum efficiency being 6.72 % for potash. Iron ore eliminated over 80 % of H₂S, confirming its high desulfurizing capacity. Charcoal adsorbed CO₂ and H₂S at the same time, concentrating methane to 76.2 %. Clay was ineffective alone but worked synergistically in mixed-material systems. With all five materials together, methane concentration increased from 69 % to 82.37 %, very close to the industrial control value of 88.46 %. These results reaffirm that indigenous adsorbents offer a practical, low-cost alternative to industrial purifiers and hold great promise for decentralized biogas upgrading, rural electrification, clean waste management, and climate-resilient access to energy.