Biochar from digestate (Foto: ATB)
Biochar from digestate (Foto: ATB)

Solid and liquid organic residual materials can also be treated with thermo-chemical processes to obtain substrates rich in energy and charged with carbon: biochar. Beside its use as solid fuel biochar offers the opportunity for carbon sequestration. As soil additive it allows a sustainable increase of growth capacity of poor agricultural soils. Biochar can be produced via different processes. The traditional way to produce charcoal is Pyrolysis.

Materials with high water content such as almost all organic waste materials have to be dried before the Pyrolysis treatment, which demands a high energy input. A to date little known process but promising solution is offered by the process of hydro thermal carbonising (HTC). For the conversion the presence of water, pressure of up to 50 bar and temperatures of only 180 – 250°C are required. Within the project APECS, funded by BMBF, the HTC processes will be substantially investigated. The project is focussed on the application of digestate of the biogas production. For the investigation of HTC processes reactors from 100 ml until 20 l are used in the ATB biochar lab.

First results showed that digestate can be converted very well into biochar via HTC. Biochar from solid and liquid organic residual materials contain higher hydrogen content and own a higher energy density but a lower active surface (max. 12 m²/g) in comparison to biochar from the reference material cellulose. The artificially produced biochar needs to be compatible for soils and has to improve the soil quality sustainable.

This was investigated by an international research project funded by the Leibniz-Association to assess the added value from biochar utilization as a soil additive.

Contact: Dr. Judy Libra    

Video: production of biochar as soil improving material form biogan waste materials  

Biochar laboratory 

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Leibniz-Institut für Agrartechnik und Bioökonomie e.V.
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