Enhancing CO Fixation in Microalgal Systems: Mechanistic Insights and Bioreactor Strategies.

Microalgae are small, single-celled, or simple multicellular organisms that contain Chlorophyll a, allowing them to efficiently convert CO 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, CO is delivered to microalgae cultivation systems mainly through aeration with CO-enriched gases. However, this method demonstrates limited CO absorption efficiency (13-20%), which reduces carbon utilization effectiveness and significantly increases carbon-source expenditure. To overcome these challenges, innovative CO supplementation technologies have been introduced, raising CO utilization rates to over 50%, accelerating microalgae growth, and reducing cultivation costs. This review first categorizes CO supplementation technologies used in photobioreactor systems, focusing on different mechanisms for enhancing CO mass transfer. It then evaluates the effectiveness of these technologies and explores their potential for scaling up. Among these strategies, membrane-based CO delivery systems and the incorporation of CO absorption enhancers have shown the highest efficiency in boosting CO mass transfer and microalgae productivity. Future efforts should focus on integrating these methods into large-scale photobioreactor systems to optimize cost-effective, sustainable production.