IIT Guwahati’s Two-Stage CO₂ Capture Boosts Microalgal Biofuel Efficiency

IIT Guwahati research paves way for efficient CO₂ capture, microalgal biofuel production

Guwahati, August 13

Microalgae capture CO₂ while producing biomass that can be converted into renewable fuels such as biodiesel, as well as other useful bioenergy products.

However, past research has shown that prolonged exposure to high CO₂ concentrations can deplete nutrients and reduce photosynthetic performance.

To address this, the IIT Guwahati research team, led by Prof. Kaustubha Mohanty, Professor, Department of Chemical Engineering, IIT Guwahati, along with his research scholar, Deepesh Singh Chauhan, developed a two-stage process.

This includes: In the first stage, the research team grew microalgal culture under 15% CO₂, where the higher carbon availability promoted rapid growth. The research team observed that prolonged exposure to 15% CO₂ in the initial stage resulted in acidification and reduced algae growth rate.

In the second stage, the team reduced the CO₂ concentration to 5%, and calcium and phosphorus were added to stabilise the environment and improve biomass aggregation. This reduction in CO₂ concentration helped restore the pH balance and maintain photosynthetic activity. Additionally, calcium supplements included in the process promoted self-flocculation of the microalgal cells.

The findings of this research have been published in the prestigious Renewable Energy journal.By conducting this experiment in a 2-litre bubble-column photobioreactor, the team was able to record microalgae progress.

The findings included 25.7% higher biomass production, 35.4% higher CO₂ fixation, 1.86 times higher lipid productivity, a 37.65% improvement in total intracellular bioenergy efficiency, and a higher energy value of the resulting biomass.

Highlighting the impact of the research, Prof. Kaustubha Mohanty said, "This research paves the way for more effective industrial CO₂ capture, where industrial flue gas can be used as a continuous source of CO₂. The research also addresses one of the most commercially relevant aspects of CO₂ capture, i.e., reducing downstream separation energy, a major cost component of microalgal biorefineries. Its most immediate pathway to impact would be as a pilot-scale technology for CO₂-rich industrial exhaust streams and integrated microalgal biorefineries."

Another important feature of the developed process is its ability for auto-sedimentation of the microalgal biomass.

The research team found that the addition of calcium promoted cell aggregation, allowing the algal cells to form compact flocks, which increased the biomass recovery efficiency by 98.46%.

Additionally, the biodiesel derived from the developed microalgae was found to comply with biodiesel standards in India, the United States, and Europe.

Speaking about the triple-action feature of the developed process and its by-product, Deepesh Singh Chauhan said, "The findings demonstrate the potential of integrating CO₂ capture, microalgal biomass production, renewable bioenergy generation and low-energy biomass recovery within a single cultivation framework."

The study concludes that the two-stage nutrient-assisted CO₂ modulation strategy provides a promising pathway towards microalgal biorefineries, particularly by addressing two important challenges simultaneously: maintaining efficient carbon fixation during prolonged cultivation and reducing the energy requirements associated with biomass harvesting.

— ANI