Robust, high-productivity phototrophic carbon capture at high pH and alkalinity using natural microbial communities

Abstract

Background: Bioenergy with carbon capture and storage (BECCS) has come to be seen as one of the most viable technologies to provide the negative carbon dioxide emissions needed to constrain global temperatures. In practice, algal biotechnology is the only form of BECCS that could be realized at scale without compromising food production. Current axenic algae cultivation systems lack robustness, are expensive and generally have marginal energy returns. Results: Here it is shown that microbial communities sampled from alkaline soda lakes, grown as biofilms at high pH (up to 10) and high alkalinity (up to 0.5 kmol m-3 NaHCO3 and NaCO3) display excellent (>1.0 kg m-3 day-1) and robust (>80 days) biomass productivity, at low projected overall costs. The most productive biofilms contained >100 different species and were dominated by a cyanobacterium closely related to Phormidium kuetzingianum (>60%). Conclusion: Frequent harvesting and red light were the key factors that governed the assembly of a stable and productive microbial community.