Investigation and Optimization of CO2 Uptake

Climate change caused by the accumulation of CO₂ in the atmosphere has emphasized the need for effective CO₂ mitigation strategies. Microalgae are fast-growing photoautotrophic microorganisms that use light energy to take up and fix CO₂, producing biomass with inherent value and applicability in fields like agriculture, nutrition, and bioenergy. The fact that wastewater can be used to support microalgal growth presents the opportunity to achieve the “triple benefit” of integrated CO₂ capture, wastewater remediation, and value-added biomass production. While microalgal cultivation has conventionally utilized monocultures growing in suspension, microalgae in nature largely exhibit sessile growth in mixed-species biofilms with close associations to other microorganisms. Considering one of the tenets of microbial community ecology is that species diversity promotes productivity, the use of mixed, non-axenic phototrophic biofilms in algal biotechnologies can present a new paradigm which harnesses natural phototrophic microbial ecosystems and the ecological and physiological advantages that they offer. The research presented herein set out to expand our understanding of mixed phototrophic biofilms. A key interest was the CO₂ uptake performance of these biofilms under conditions that are relevant for the integration of CO₂ mitigation, wastewater treatment, and biomass production via photosynthetic growth. A novel CO₂ sequestration monitoring system (CSMS) was developed to track real-time CO₂ uptake by phototrophic biofilms, which demonstrated good sensitivity in detecting changes in uptake rate brought about by varying environmental and cultivation conditions. It was also shown that the presence and concentration of organic carbon sources significantly impacted biofilm carbon capture and led to observable longitudinal partitioning of heterotrophic and autotrophic growth. The system was further used to evaluate the impact of nitrogen starvation, a common algal biomass optimization strategy, on biofilm CO₂ uptake. Starvation appeared to promote sloughing of biofilm biomass and coincided with a steady, near linear decrease in CO₂ uptake rate. These insights contribute to an improved understanding of phototrophic biofilms and represent an important step toward large-scale biofilm-based CO₂ mitigation.