Moisture-Driven CO2 Direct Air Capture and Delivery for Cultivating Cyanobacteria

Area of Science:

• Biotechnology
• Chemical Engineering
• Environmental Science

Background:

• Carbon dioxide (CO2) capture from ambient air is crucial for mitigating climate change.
• Cyanobacteria cultivation offers a sustainable platform for biofuel and valuable co-product generation.

Purpose of the Study:

• To develop and demonstrate a passive CO2 capture system for enhanced cyanobacteria cultivation.
• To evaluate the long-term performance and economic viability of the CO2 capture system in a pilot-scale biorefinery.

Main Methods:

• Development of a solid sorbent system for passive CO2 capture and release in an alkaline medium.
• Cultivation of Synechocystis sp. PCC 6803 in flasks, bench-scale, and a pilot-scale outdoor raceway pond (840 L) over 300 days.
• Assessment of sorbent performance, degradation factors (nitrate binding, biofouling, UV damage), and potential restoration methods.

Main Results:

• Sorbent CO2-release capacity and kinetics were reduced by nitrate binding and biofouling, but partially restored with a wash protocol.
• Long-term outdoor use led to sorbent mechanical failure and loss of functional groups, likely due to UV damage.
• Preliminary techno-economic analysis indicated potential biorefinery viability for biofuel production if sorbent performance is maintained.

Conclusions:

• The developed passive CO2 capture system shows promise for cyanobacteria cultivation but faces challenges with sorbent durability and performance over time.
• Strategies to mitigate sorbent degradation and improve longevity are necessary for large-scale implementation.
• Biorefining, integrating biofuel production with high-value co-product extraction (protein, phycocyanin), presents a potentially viable economic model.