Hydrothermal liquefaction: A promising technology for renewable energy and environmental clean-up applications

Hydrothermal liquefaction (HTL) has emerged as an effective thermochemical technology that sustainably converts wet biomass into biocrude, which is the most significant precursor for renewable energy applications such as sustainable aviation fuel (SAF). It has also been deployed for addressing environmental challenges such as removing hazardous contaminants. The ultimate aim of this review is to provide a comprehensive overview of the state-of-the-art HTL research, focusing on its potential applications in biocrude and environmental remediation. The review covers various biomass feedstocks, process parameters, and other aid-in methods underlying HTL. Key findings from recent studies are discussed, highlighting the efficiency of HTL in producing biocrude oil, higher heating value, and energy recovery. Likewise, the advantages and disadvantages of integrating HTL and anaerobic digestion with respect to addressing downstream waste are explored. The current studies and limitations of biocrude-based SAF have been updated. Furthermore, the review summarises the critical role of HTL in removing environmental pollutants (e.g., PFAS, microplastic, bioactive/organic contaminants, and heavy metals). Finally, a discussion of the challenges (e.g., the variability and inconsistency of the feedstock, process optimisation, biocrude quality, etc.) and future prospects for HTL technology, emphasising its role in promoting sustainable and clean energy solutions, will be concluded. • The HTL biocrude yield and energy recovery with various feedstocks are reviewed. • The benefits of the integration of HTL with anaerobic digestion are discussed. • HTL sustainable aviation fuel and current commercialisation barriers are explained. • Eliminating hazardous contaminants (e.g., PFAS) using HTL is examined. • The performance of engine tests using upgraded biocrude is reviewed.