Biogas Purification, Upgrading and Utilization: Focusing on Biological Systems

Biogas, a renewable energy source generated by organic matter degradation without oxygen, consists primarily of CH4 (45–75%) and CO2 (20–50%), along with minor components like O2, H2S, N2, NH3, H2, volatile methyl siloxanes (VMSs), and volatile organic compounds (VOCs). While conventional physicochemical methods have been used for biogas purification, biological technologies have emerged due to their cost-effectiveness and eco-friendliness. The chapter provides an overview of biological systems for biogas purification and upgrading. It covers in-situ desulfurization through microaeration and aerobic and anoxic ex-situ desulfurization techniques within different bioreactor configurations such as fixed-bed (biofilters, biotrickling filters) and suspended biomass (CSTR, gas-lift, bubble column, bioscrubber). The chapter also addresses the removal of poorly biodegradable volatile methyl siloxanes (VMSs) and volatile organic compounds (VOCs), known for causing combustion-related deposit formation and emission of toxic compounds during combustion, respectively. Biogas upgrading has gained momentum, producing high CH4 concentration effluent (biomethane) comparable to natural gas. Various upgrading technologies exist, including physical and chemical methods and biological approaches. Among biological options, microalgae and hydrogenotrophic archaea are prominent for biogas upgrading, utilizing photobioreactors for CO2 assimilation and hydrogenotrophic methanogens for CO2 and H2 conversion. The implementation of biological techniques can reduce investment and operational costs compared to physicochemical methods, promoting sustainable integration of upgraded biogas into the energy mix. The chapter concludes by outlining future research directions for biological biogas purification and upgrading.