Algae in Circular Bioeconomy: Valorization of Algal Biomass Using Pyrolysis, Hydrothermal Liquefaction, and Gasification Techniques

The transition toward a circular bioeconomy necessitates sustainable resource utilization, waste valorization, and renewable energy production. Algal biomass has emerged as a promising feedstock due to its rapid growth rate, ability to thrive in nonarable lands and wastewaters, and high biochemical composition, making it an ideal candidate for biofuel and biochemical production. However, to fully harness its potential, efficient conversion technologies must be implemented. This chapter explores the utilization of algal biomass through thermochemical conversion techniques, including pyrolysis, hydrothermal liquefaction (HTL), and gasification. The chapter provides a comparative assessment of these techniques based on their process parameters, product yields, environmental impact, and economic feasibility. Additionally, it highlights the role of algal biomass valorization in advancing a sustainable bioeconomy by integrating with existing biorefineries and reducing dependency on fossil-based resources. At the same time, this upgradation holds great promise; several technical, economic, and regulatory challenges remain, including high production costs, feedstock variability, and scalability issues. The chapter concludes by discussing potential future advancements in process intensification, biorefinery approaches, and policy frameworks that could facilitate the commercialization of algal biofuels and chemicals. Overall, the integration of algal biomass conversion into the circular bioeconomy presents a viable pathway toward sustainable energy and resource management.