Biogas upgrading using algal-bacterial processes

Abstract

Photosynthetic biogas upgrading constitutes, to the best of our knowledge, the only biotechnology capable of simultaneously removing CO₂ and H₂S from raw biogas. Recent studies at the pilot scale confirmed the potential of algal-bacterial processes to obtain a biomethane with sufficient quality to be injected into natural gas networks. The main limitation identified in this novel biotechnology is the large land requirement for microalgae to fix all CO₂ removed from biogas, which would eventually limit its applicability to biogas design flow rates < 500 Nm³ h^− 1. Algal-bacterial photobioreactors also exhibit a high-water footprint, which can compromise the environmental sustainability of the process. The latter limitation can be overcome by coupling biogas upgrading to wastewater/digestate treatment, which would allow reducing the eutrophication impact of these wastewaters while producing a valuable algal biomass. The valorization of the algal biomass using a biorefinery approach would also contribute to the sustainability and economic viability of this technology.