From biogas to biomethane: Evaluating the role of microalgae in sustainable energy production – A review

Abstract

Methane, predominantly derived from fossil resources, is a highly utilised energy source due to its high energy density. However, the rapid consumption of fossil fuels has precipitated anthropogenic climate change and resource depletion, compelling the necessity for a transition towards sustainable and climate-compatible energy sources. This review examines biogas upgrading technologies, encompassing physical, chemical, and biological methods, with a particular focus on photosynthetic CO₂ fixation to enhance methane purity and meet biomethane purity standards. Biological processes, in particular those utilising microalgae, demonstrate considerable potential for CO₂ sequestration and have the capacity to reduce emissions while simultaneously generating valuable byproducts. The review investigates key process parameters, including pH, liquid-to-gas (L/G) ratio, temperature, and gas retention time (GRT), along with the removal efficiency of CO₂. The mass transfer of CO₂ and the role of microorganisms are also examined. Furthermore, biological, and chemical/physical upgrading technologies are economically and ecologically compared.