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.

Keywords: Algae biofuel; Biofilm; Microbial ecology; Mixed-community; Phormidium kuetzingianum.

Fig. 1

Photobioreactor microbial community composition based on 16S rRNA gene amplicon sequencing. The figure shows relative abundance and taxonomic assignments of the most abundant populations (>2% per lake average abundance) for duplicate photobioreactors inoculated with a Deer Lake, b Goodenough Lake, c Last Chance Lake and d Probe Lake mats at 0, 58, 85, 98 and 128 days. Eukaryotic algae sequences are based on BLAST identification of sequence reads identified as chloroplasts

Fig. 2

Productivity of mixed-community phototrophic biofilms grown at pH 10, 0.5 M carbonates under red (a, open circle), white (b, open square) and blue (c, inverted triangle) light shown as oxygen production, volumetric (d) and surface areal (e) productivities

Fig. 3

Photobioreactor microbial community composition based on 16S rRNA gene amplicon sequencing and fluorescence microscopy. The figure shows relative abundance and taxonomic assignments of the most abundant populations (>1% relative abundance) for photobioreactors illuminated with red (a), blue (b), and white (c) light, during 77 days. Fluorescence microscopy images of biomass from the red light (d) showing the dominance of a cyanobacterium closely related to Phormidium and blue light (e) showing the dominance of a diatom closely related to Nitzschia. Eukaryotic algae sequences are based on BLAST identification of sequence reads identified as chloroplasts

Fig. 4

Productivity of a mixed-community biofilm grown at pH 9.0, 0.5 M bicarbonate illuminated with red light as a function of oxygen production (a) volumetric (b) and surface areal (c) productivity. d Relative abundance and taxonomic affiliations of abundant populations (>1% relative abundance) based on 16S rRNA gene sequencing on day 20. Eukaryotic algae sequences are based on BLAST identification of sequence reads identified as chloroplasts