Waste Biorefinery Concept for Production of Value-Added Products Through Hydrothermal Liquefaction Pathway: A Critical Review and Outlook

Increasing urbanization has led to reliance on fossil fuels, a higher production of waste, and rising greenhouse gas emissions. Sustainable waste management and value-added renewable bioproducts from wet biowaste could be achieved in a biorefinery via a hydrothermal liquefaction (HTL) pathway. Waste biomass is a significant feedstock for potential valorization technologies and is already the single largest source of renewable energy in the United States. HTL’s key advantage over other conversion methods is its ability to directly convert high moisture and nonlipid feedstocks into biocrude at high efficiency. The high biocrude yield with ample carbon and energy content can be upgraded to a wide range of value-added bioproducts, including fuels, chemicals, polymers, and asphaltenes. In this work, a comprehensive review was conducted for this paradigm-shift pathway covering HTL feedstocks, process parameters, biocrude yield and quality, biocrude upgrading and potential bioproducts, and sustainability metrics. Gaps in knowledge were identified, providing a future direction for research to promote waste biorefineries in a circular economy. © 2025 Elsevier B.V., All rights reserved.