As the world strives for global carbon neutrality, the need for innovative negative emission technologies (NET) becomes increasingly important in the fight against climate change. The production and storage of hydrochar, a coal-like material formed by hydrothermal carbonisation (HTC) of fresh biomass, has the potential to sequester significant amounts of CO2.
We were commissioned by a leading Swiss retail company to conduct a feasibility study to investigate potential hydrochar storage sites in Switzerland. In our study we show that the most feasible way to store hydrochar in large quantities (1 mio. m3) in Switzerland would be a surface landfill. Existing underground structures (e.g. abandoned mines) are not suitable for storing hydrochar because they do not meet the volumetric, technical and geological requirements for safe storage.
We commissioned laboratory analyses that revealed previously unknown material properties of the hydrochar produced by our commissioner. The results show that total organic carbon in the solid fraction and ammonium and dissolved organic carbon in the leachate are significantly above the permitted limit values for waste deposition in a landfill defined by the Swiss waste ordinance. However, the other chemical parameters measured (elements and heavy metals) do not exceed the thresholds. In addition, our study reveals that the legal situation for hydrochar storage in Switzerland is unclear and needs further discussion and regulations by cantonal and federal authorities.
We propose that the material properties of hydrochar to be fine-tuned (i.e. optimised) further to ensure safe storage. Furthermore, we recommend to carry out a pilot study for testing the hydrochar storage in a landfill under real conditions.