Biologically-mediated carbon capture and utilization by microalgae towards sustainable CO2 biofixation and biomass valorization – A review

Abstract

The continuously rising emission of carbon dioxide (CO2) is a universal hazard which urgently requires collaborative action between policymakers and scientists. International treaties such as the Paris Agreement (with 196 signatories) reflect the importance of anthropogenic climate change as a truly global public concern. Towards the aim of climate recovery, the most broadly utilized CO2 reduction strategies, including carbon capture and storage (CCS); carbon capture, utilization, and storage (CCUS); and carbon capture and utilization (CCU) are reviewed herein. Of these methods, CCU shows the greatest potential by recycling captured CO2 and harnessing it as a resource to generate emissions-neutral or -negative value-added products (VAPs). Within CCU methodologies, biologically-mediated CCU (bio-CCU) by microalgae is a promising biotechnology to drastically reduce CO2 emissions. This review therefore details the mechanisms of photosynthesis to sequester CO2 and incorporate it into valuable biomolecules. Microalgal cells utilize CO2 as precursors of macromolecules, including lipids, proteins, carbohydrates, and pigments; all of which are discussed within the frame of industrial relevance and market value. The biofixation potential of microalgae is clearly demonstrated by the carbon content of the myriad VAPs they produce. Moreover, pathways towards decreasing carbon footprint (via carbon capture prior to emission to the atmosphere) and increasing carbon handprint (reducing carbon emissions by consuming CO2-neutral or -negative products) related to bio-CCU are presented herein. Finally, existing challenges and knowledge gaps are acknowledged and described, and future research needs are recommended.