Reconsidering the potential of direct microalgal biomass utilization as end-products: A review

Microalgae can rapidly sequester carbon dioxide (CO2) and convert it into various marketable products. Thus, these photosynthetic microorganisms have gained substantial attention as prospective biological platforms for the practical reduction of CO2 and establishing renewable and sustainable supply chains. However, conventional biomass applications to which attention has been directed, such as a feedstock for biodiesel production, are only achievable through cumbersome downstream processes, including extraction, fractionation, separation, and refinement. These stereotypical biomass utilization strategies have increased concerns regarding economic, energetic, and environmental viability. As a promising alternative, utilization of whole microalgal biomass as end-products has emerged because it can directly provide various beneficial commodities through a streamlined production route only consisting of harvesting and drying processes. The process review in this study clearly shows the energy and CO2 reduction efficiencies of this strategy compared with other traditional production routes. Despite the high potential, this application strategy has been overlooked because of the limited commercialized examples and the broad use of established methods. Recently, many applications have been suggested, and their practicality has been thoroughly verified according to the main biochemical constituents, namely carbohydrates, proteins, and lipids. Raw microalgal biomass produced by a potentially carbon-negative and net-energy-positive process can be employed as-is in an extensive range of fields that cover most human needs, including nutritious foods and feeds with bioactive functions, cosmetics, thermoplastic materials, and fuels for direct combustion. Thus, this comprehensive review aims to provide an opportunity to reconsider the potential and practicality of whole microalgal biomass utilization strategies.