Hydrothermal Carbonization and Anaerobic Digestion of Organic Waste
Summary
Hydrothermal carbonization (HTC) and anaerobic digestion (AD) represent complementary thermochemical and biochemical pathways for the valorisation of wet organic residues such as sewage sludge, agricultural by-products and food waste. Under moderate temperatures (180–250 °C) and self-generated pressures, HTC converts moist biomass into a coal-like solid (hydrochar) and a nutrient-rich aqueous phase, while AD relies on microbial consortia to break down organic matter into biogas, chiefly methane and carbon dioxide, in oxygen-free reactors. By integrating these two technologies, it becomes possible to improve overall energy yields, recover nutrients, reduce greenhouse-gas emissions and minimise residual waste streams. Hydrochar can serve as a solid fuel or soil amendment, process water can be directed back to AD for enhanced biogas production, and digestate can be upgraded for further HTC treatment. This tandem approach aligns with circular-economy principles, offering decentralised or centralised biorefinery models for sustainable waste management and renewable energy generation.
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Hydrothermal Carbonization and Anaerobic Digestion of Organic Waste publication trend
The graph below shows the total number of articles in hydrothermal carbonization and anaerobic digestion of organic waste across all publications each year (not limited to Nature Index journals).
Technical terms
Hydrothermal carbonisation (HTC): A thermochemical process converting wet biomass into a carbon-rich solid under elevated temperature and pressure in water.
Hydrochar: The porous, coal-like solid product of HTC, enriched in fixed carbon and often used as fuel or soil amendment.
Anaerobic digestion (AD): A biological process in which microorganisms decompose organic matter in the absence of oxygen, producing biogas.
Digestate: The residual semi-solid effluent remaining after AD, containing undigested organics, nutrients and microbial biomass.
Process water: The aqueous fraction separated from hydrochar after HTC, rich in soluble organics and nutrients.
Supercritical water gasification (SCWG): A high-pressure process using superheated water above its critical point to convert aqueous organics into syngas.
References
- Process simulation of co-HTC of sewage sludge and food waste digestates and supercritical water gasification of aqueous effluent integrated with biogas plants. Energy (2024).
- Integration of Hydrothermal Carbonization and Anaerobic Digestion for Energy Recovery of Biomass Waste: An Overview. Energy & Fuels (2021).
- Coupling Hydrothermal Carbonization with Anaerobic Digestion for Sewage Sludge Treatment: Influence of HTC Liquor and Hydrochar on Biomethane Production. Energies (2020).
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