CO2 Biofixation by Microalgae

Rising temperatures and heavy emissions of greenhouse gases have prompted many efforts to cut those emissions and clean up pollutants. Among the options, the most promising are using less, recovering value from waste, and treating waste with living systems. Within that last group, research points to microalgae as a strong way to capture carbon dioxide. Through photosynthesis, these organisms can absorb large amounts of CO2.

Microalgae also serve industries such as food production, fertilizer manufacturing and biofuel. To sequester carbon effectively, the algae must be grown under carefully chosen conditions for temperature, nutrients, pH and light. Growers typically house them in enclosed vessels called photobioreactors, which often run in continuous mode. Closed systems of this kind limit contamination, improve the transfer of CO2 and make the process easier to manage.

Controlling such a system goes beyond the usual adjustments of pH and temperature, because biomass, substrates and by-products must also be regulated. This requires building a model of the system and estimating its parameters, using estimators to reconstruct variables that cannot be measured online, and applying a control law that keeps conditions optimal despite modeling errors and disturbances such as changing pH, temperature, light and biofilm growth.