Hydrothermal treatment: A green leap forward in solid fuel production from waste biomass and plastics

In a bid to address the growing concerns over waste management and environmental sustainability, researchers from Tohoku University have delved into the potential of hydrothermal treatment for transforming waste biomass and plastics into solid fuels. The study, led by Qingxin Zheng and Masaru Watanabe, provides a critical review of the current state and future prospects of hydrothermal technology in waste conversion.

The review article, titled "Production of solid fuels by hydrothermal treatment of wastes of biomass, plastic, and biomass/plastic mixtures: A review," outlines the chemical and physical peculiarities of water under hydrothermal conditions, which make it an ideal medium for waste conversion. The authors discuss the mechanisms of hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL), and hydrothermal gasification (HTG), highlighting their effectiveness in processing a variety of biomass and plastic wastes.

The study emphasizes that hydrothermal treatment not only offers a green alternative to traditional waste disposal methods but also presents an opportunity for carbon reduction and the achievement of carbon neutrality. The authors report that hydrothermal carbonization results in the production of solid fuels, or hydrochar, from biomass waste, while plastic waste can be converted into liquid chemicals or oil-based products through hydrothermal liquefaction. Furthermore, hydrothermal gasification at higher temperatures can generate combustible syngas.

The review also underscores the importance of understanding the reaction mechanisms under hydrothermal conditions, the synergistic effects when combining hydrothermal treatment with other technologies, the potential of catalytic hydrothermal technology, and the need for establishing large-scale applications for solid waste treatment.

In their conclusions, the authors suggest that hydrothermal technology holds significant promise for the treatment of biomass and plastic waste, offering a sustainable and adjustable process with diverse materials and flexible combinations. They envision that biomass/plastic mixtures may be more competitive as a source for producing solid fuels through hydrothermal treatment, given their potential to improve combustion efficiency and energy density.