Hydrothermal processing for plastic waste valorisation: Technical pathways, environmental performance, and prospects for commercialisation

Hydrothermal processing (HTP) is a promising solution to the global plastic waste crisis, integrating waste reduction, hazard mitigation, and resource recovery to advance the circular economy. Operating under high-temperature and high-pressure aqueous conditions, HTP transforms plastics into value-added products such as hydrochar, bio-oil, organic acids, and syngas. Different types of HTP technologies provide great potential for plastic waste valorisation, with several companies working to commercialise HTP plants fully; however, despite many advancements, HTP faces significant barriers to large-scale adoption, including high energy demand, complex system design, and economic feasibility concerns. This study highlights the environmental benefits of HTP, including reduced reliance on virgin resources and enhanced waste valorisation. Transparent communication among researchers, industry stakeholders, policy makers, and the public, supported by pilot demonstrations and cost-efficient strategies, is essential for broader societal acceptance of HTP systems. Enhancing energy efficiency through water recycling streams and process optimisation may enhance the economic costs associated with HTP systems. Furthermore, government support via subsidies and carbon credits will improve HTP’s viability as a large-scale plastic waste solution, bridging the gap between laboratory success and commercial adoption. • HTP offers cleaner plastic waste solutions compared to current methods. • HTP produces fuels and chemicals that support the circular economy. • HTC and HTL yield up to 72 % hydrochar, 80 % bio-oil from plastics. • HTD and HTG can degrade 95–98 % of plastics under ideal conditions. • High costs and poor standardisation hinder HTP scale-up globally.