Combining hydrothermal carbonization (HTC) and biogas production

Biogas production by anaerobic digestion (AD) has attracted growing interest all over the world. However, how to store and make use of the resulting digestates is still problematic. Digestates from livestock manure usually contain pathogens that can cause health risks when these digestates are applied as fertilizer without sterilization. In addition, transportation costs and seasonal demand of digestates add to the difficulty of disposal. Due to the incomplete conversion of lignocellulosic feedstocks in AD and the high water content of resulting digestates, hydrothermal carbonization (HTC) has proven particularly suitable for processing of the digestates.

Hydrothermal carbonization is defined as a thermochemical transformation process for low value, wet biomass to a solid product termed as hydrochar. Hydrochar is a coal-like powder that can be used as a soil amendment and energy production.

In this project, the resulting digestates will be hydrothermally carbonized into carbon-rich and stable, lignite-like hydrochar through various conditions and catalysts. The hydrochar addition during anaerobic digestion and the anaerobic digestion of process water have been investigated in previous projects; however, little is known about the degradation of phytotoxic compounds of fresh hydrochar and the waste water during anaerobic digestion. Therefore, the effect of integrating hydrochar and process water into anaerobic digestion is also interesting to understand. Another goal is to identify the economic feasibility and energy efficiency of the overall processes under respective conditions.

The anaerobic digestion experiments will be performed in cooperation with the State Institute of Agricultural Engineering and Bioenergy at the University of Hohenheim, and a part of the experiments and analyses will be carried out at the Karlsruhe Institute of Technology.