Researchers at IIT Guwahati have developed a two-stage cultivation process that can simultaneously improve carbon dioxide (CO₂) capture, microalgal biomass production, biomass recovery and renewable bioenergy generation, potentially supporting more efficient algae-based biorefineries, ANI reported.
The process, developed by a team led by Professor Kaustubha Mohanty of the Department of Chemical Engineering and research scholar Deepesh Singh Chauhan, uses different CO₂ concentrations at two stages of microalgae cultivation.
In the first stage, microalgae are cultivated under 15% CO₂ to promote rapid growth. However, the researchers found that prolonged exposure to high CO₂ levels can cause acidification and slow algal growth.
The second stage reduces the CO₂ concentration to 5%, while calcium and phosphorus are added to stabilise the cultivation environment and support biomass aggregation. The lower CO₂ concentration helps restore pH balance and sustain photosynthetic activity, while calcium promotes self-flocculation of algal cells.
Experiments conducted in a 2-litre bubble-column photobioreactor showed a 25.7% increase in biomass production and a 35.4% improvement in CO₂ fixation. Lipid productivity was 1.86 times higher, while total intracellular bioenergy efficiency improved by 37.65%.
The researchers also reported a 98.46% increase in biomass recovery efficiency through calcium-assisted aggregation and auto-sedimentation. The resulting biomass had a higher energy value, while biodiesel produced from the microalgae met biodiesel standards in India, the United States and Europe.
Mohanty said the process could be adapted for industrial CO₂ capture using flue gas as a continuous carbon source. It could also help address the high energy requirement for separating and recovering microalgal biomass, which is a major cost in algae-based biorefineries.
“This research paves the way for more effective industrial CO₂ capture,” Mohanty said, adding that the technology could eventually be tested at pilot scale for CO₂-rich industrial exhaust streams and integrated microalgal biorefineries.
Chauhan said the process brings together CO₂ capture, microalgal biomass production, renewable bioenergy generation and low-energy biomass recovery in a single cultivation framework.
The findings have been published in the journal Renewable Energy. The researchers said the two-stage strategy could help address the challenges of maintaining carbon fixation during prolonged cultivation while reducing the energy needed to harvest microalgal biomass, ANI stated.
