Hydrothermal processing of microalgal biomass: Circular bio-economy perspectives for addressing food-water-energy nexus

[Display omitted] •Process, mechanisms and product portfolio for algal HTC/HTL/HTG were reviewed.•Research on HTL of algal biomass has been more focused compared to HTC/HTG.•Enviro-economic feasibility constraints to be addressed for scale-up.•Process optimization, integration and supply chain management must be emphasized.•Holistic thermochemical engineering perspectives promote food-water-energy nexus. Hydrothermal processing of microalgae is regarded as a promising technology to generate multitude of energy based and value-added products. The niche of hydrothermal technologies is still under infancy in terms of the technical discrepancies related to research and development. Thus, the present review critically surveyed the recent advancements linked to the influencing factors governing the algal hydrothermal processing in terms of the product yield and quality. The sustainability of hydrothermal technologies as a standalone method and in broader aspects of circular bio-based economy for energy and value-added platform chemicals are comprehensively discussed. Process optimization and strategic integration of technologies has been suggested to improve efficiency, with reduced energy usage and environmental impacts for addressing the energy-food-water supply chains. Within the wider economic transition and sustainability debate, the knowledge gaps identified and the research hotspots fostering future perspective solutions proposed herewith would facilitate its real-time implementation.