Abstract:
The main contaminants in biogas namely carbon dioxide, hydrogen sulfide, and siloxanes limit its application especially in engines by reducing energy density and causing corrosion on machine parts. Furthermore, the carbon dioxide in biogas contributes highly to global warming. Therefore, biogas should be upgraded to increase its safe application. Most commercial methods of biogas cleaning are expensive for small and medium scale digesters. There is no review documentation detailing the usage of natural materials in the purification of biogas. The aim of the current study was to systematically and critically review recent developments in the applications of natural materials in the purification and upgrade of biogas. Documented literature indicate that the low-cost natural adsorbents have potential in purification of biogas. The adsorption capacity of biogas contaminants for most materials can be enhanced by physical and chemical activation. The two mechanisms through which these material eliminate carbon dioxide in biogas namely surface adsorption and wet carbonation process have been discussed. In addition, the study looked at the factors that affect the removal of carbon dioxide from biogas using natural materials. The adsorption capacity of biogas contaminants for different natural and modified materials were reviewed. Furthermore, a summary of the merits and demerits of different natural adsorbents for biogas purification is presented. Future studies should investigate the methane loss during upgrading process using low-cost adsorbents. Comparative investigations of the process cost-effectiveness of using natural materials to upgrade biogas should be carried out to determine their suitability against the commercial processes.