Life cycle assessment of hydrochar produced from wood waste for agricultural applications

The growing need to address soil degradation and climate change requires sustainable approaches for managing agricultural biomass waste. Orchard wood residues are commonly disposed of by burning or composting, which contributes to greenhouse gas emissions and environmental risks. Hydrothermal carbonization (HTC) offers a promising alternative by converting biomass into hydrochar that can be used as a soil amendment while potentially reducing carbon emissions. In this study, apple tree pruning residues were converted into hydrochar via HTC at 180 °C and 250 °C. The environmental performance of HTC was evaluated using life cycle assessment (LCA) and compared with conventional composting scenarios. The LCA results demonstrate that HTC yields negative net greenhouse gas emissions (−0.797 to −0.819 kg CO 2 -eq per kg hydrochar), highlighting its carbon-negative potential, while composting results in positive emissions (2.212–2.675 kg CO 2 -eq). Process water recirculation further increased hydrochar yield by up to 9.3% at 180 °C and 3.3% at 250 °C, while lowering ecosystem burdens through a reduction in freshwater demand and minimizing carbon loss, thereby improving the overall environmental performance of HTC. Although hydrochar scenarios show higher impacts on categories such as water consumption and ecotoxicity compared to composting, the climate benefits strongly outweigh these trade-offs. The Monte Carlo analysis validates the reliability of negative emission results amid various uncertainties, indicating that 250 °C HTC exhibits marginally enhanced sequestration potential, albeit with increased variability.