Circular bioeconomy approaches for sustainability and carbon mitigation in microalgal biorefinery

Circular bioeconomy was defined as “the sustainable and resource-efficient valorization of biomass in integrated multioutput production chains (biorefineries) while also making use of the residues and wastes and optimizing the value of biomass over time via cascading.” This definition represents the stark difference between the current fossil fuel-based linear economy, the concept of which is take, make, and waste. This kind of resource utilization has multifold effects on the economy and environment: sustainability of the energy resources, energy and food insecurity, high greenhouse gas emissions and global climate change, and incessant waste disposal issues. Microalgae has tremendous potential as a sustainable feedstock in a biorefinery and can play diverse roles in a circular economy. Microalgal biorefineries can be developed by incorporating key circular bioeconomy concepts such as sustainability, cascading use, and waste hierarchy. Microalgal carbon dioxide tolerance and the ability of microalgae to recover finite nutrients such as nitrogen and phosphorus from wastewaters are highly relevant to wastewater bioremediation and concomitant microalgal biomass generation. The beneficial components present in microalgal biomass such as lipids, carbohydrates, pigments, and antioxidants can be extracted sequentially from the biomass, emphasizing the cascading use of biomass. Spent microalgal biomass is also considered a valuable organic carbon-based feedstock. This chapter provides comprehensive information on the potential of microalgae in carbon mitigation and waste valorization. The valuable components of microalgal biomass and their multifarious applications are discussed in detail. The circular bioeconomy perspective is discussed in detail with future research perspectives for the realization of sustainable microalgal biorefinery.