Hydrothermal Carbonization for Nutrient and Energy Recovery
Summary
Hydrothermal carbonization (HTC) is a thermochemical process that converts wet biomass under moderate temperature and pressure into a carbon-rich solid (hydrochar), an aqueous phase containing solubilised nutrients, and a gas fraction. This technology offers dual benefits of energy densification and nutrient recovery, addressing global challenges in waste management, renewable energy supply and sustainable agriculture. By retaining nitrogen, phosphorus and other essential elements within the hydrochar and process water, HTC facilitates the production of slow-release fertilisers and soil amendments, while repurposing the solid fraction as a low-emission fuel or adsorbent for contaminant removal. Key parameters such as reaction temperature, residence time, feedstock composition and pH can be tuned to optimise hydrochar yield, nutrient speciation and energy content. Recent advances have broadened the range of feedstocks to include agricultural residues, manure, sludge and microalgae, thereby creating a versatile platform for circular resource recovery.
Research from Nature Portfolio
Recent work has demonstrated that reaction conditions strongly influence the physicochemical properties and sorption capacity of microalgae-derived hydrochar. Systematic variation of temperature, residence time and initial pH revealed that higher temperatures yield larger surface areas, while milder conditions and neutral pH preserve functional groups that promote cationic dye adsorption. These findings highlight the potential to tailor hydrochar for nutrient retention and pollutant capture, offering pathways to integrate wastewater treatment with resource recovery in a single process.
Hydrothermal Carbonization for Nutrient and Energy Recovery publication trend
The graph below shows the total number of articles in hydrothermal carbonization for nutrient and energy recovery across all publications each year (not limited to Nature Index journals).
Technical terms
Hydrothermal carbonization (HTC): A wet thermochemical process that converts biomass into hydrochar under moderate temperature (180–260 °C) and autogenous pressure.
Hydrochar: The carbon-rich solid product of HTC, characterised by porous structure, functional surface groups and nutrient-binding capacity.
Process water (aqueous phase): The liquid fraction from HTC containing dissolved organic compounds, nitrogenous and phosphorous species, and potential phytotoxins.
Slow-release fertiliser: A material that gradually supplies essential nutrients to plants, reducing leaching and improving nutrient use efficiency.
Phytotoxicity: The toxic effect of substances on plant germination and growth, often due to organic acids or residual compounds in hydrochar or process water.
References
- Hydrothermal carbonization of wet biomass from nitrogen and phosphorus approach: A review. Renewable Energy (2021).
- Influence of hydrothermal carbonization conditions on the porosity, functionality, and sorption properties of microalgae hydrochars. Scientific Reports (2023).
- Influence of lipid extraction and processing conditions on hydrothermal conversion of microalgae feedstocks – Effect on hydrochar composition, secondary char formation and phytotoxicity. Chemical Engineering Journal (2022).
- Speciation of Main Nutrients (N/P/K) in Hydrochars Produced from the Hydrothermal Carbonization of Swine Manure under Different Reaction Temperatures. Materials (2021).
- The Influence of pH on the Combustion Properties of Bio-Coal Following Hydrothermal Treatment of Swine Manure. Energies (2020).
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