Enhancing CO2 Fixation in Microalgal Systems: Mechanistic Insights and Bioreactor Strategies
Zhongliang Sun, Chenmei Bo, Shuonan Cao, Liqin Sun
Abstract
Microalgae are small, single-celled, or simple multicellular organisms that contain Chlorophyll a, allowing them to efficiently convert CO2 and water into organic matter through photosynthesis. They are valuable in producing a range of products such as biofuels, food, pharmaceuticals, and cosmetics, making them economically and environmentally significant. Currently, CO2 is delivered to microalgae cultivation systems mainly through aeration with CO2-enriched gases. However, this method demonstrates limited CO2 absorption efficiency (13–20%), which reduces carbon utilization effectiveness and significantly increases carbon-source expenditure. To overcome these challenges, innovative CO2 supplementation technologies have been introduced, raising CO2 utilization rates to over 50%, accelerating microalgae growth, and reducing cultivation costs. This review first categorizes CO2 supplementation technologies used in photobioreactor systems, focusing on different mechanisms for enhancing CO2 mass transfer. It then evaluates the effectiveness of these technologies and explores their potential for scaling up. Among these strategies, membrane-based CO2 delivery systems and the incorporation of CO2 absorption enhancers have shown the highest efficiency in boosting CO2 mass transfer and microalgae productivity. Future efforts should focus on integrating these methods into large-scale photobioreactor systems to optimize cost-effective, sustainable production.