Abstract
Microalgae offer a simple and sustainable way to capture carbon dioxide (CO2 ) from industrial emissions while producing valuable biomass for fuels, feed and other bioproducts. In this review, we summarize recent progress in designing and improving closed-loop microalgae systems that capture CO2 and recycle nutrients and energy. We compare several industrial pilot projects around the world to show which designs work best at scale and highlight remaining hurdles. To organize these challenges, we introduce a Barrier-Impact Matrix that maps technical, economic and regulatory obstacles alongside potential solutions. Finally, we discuss how to get more value from the harvested biomass and how life cycle assessments (LCAs) can guide future improvements.