Recent Progresses and Future Perspective of Biogas-Upgrading Techniques

Abstract

Biogas is a promising renewable energy source that is produced by anaerobic digestion of organic waste and is mainly made up of carbon dioxide (CO₂) and methane (CH₄). However, its direct application is limited due to the presence of impurities such as CO₂, hydrogen sulfide (H₂S), water vapor, and trace gases (hydrogen sulfide, hydrogen, ammonia, nitrogen, oxygen, siloxanes, and carbon monoxide) that reduce its calorific value and cause operational issues. Their presence is undesirable since it lowers the calorific value of biogas and causes a number of issues with machine performance. Therefore, throughout the process of converting biogas into biomethane, multi-stage technologies for their removal are employed. This review provides a comprehensive overview of recent advances and future directions in biogas-upgrading technologies. Conventional physicochemical methods such as water scrubbing, chemical absorption, pressure swing adsorption (PSA), membrane separation, and cryogenic techniques are critically discussed with respect to efficiency, energy consumption, operational complexity, and cost. Furthermore, emerging biological upgrading technologies, including in situ and ex situ hydrogenotrophic methanation, and microalgae-based CO₂ fixation have been highlighted. These biological methods offer eco-friendly and cost-effective alternatives by converting CO₂ into CH₄ under mild conditions, although their scalability and integration into existing infrastructure remain under exploration. The review highlights technological challenges, comparative performances, and research gaps, offering insights into integrated and hybrid approaches that combine physicochemical and biological pathways for optimal biogas purification. This work serves as a reference for researchers and practitioners seeking sustainable and efficient biogas-upgrading solutions for grid injection, transportation fuel, and decentralized energy systems. The readers will learn about the scientific and technological obstacles to biogas technology advancement from this review.