During anaerobic digestion of manure in CSTR biogas reactors, less than half of the organic material is degraded to methane and carbon dioxide. The remaining organic material, mainly lignocellulose, is only slowly degraded in anaerobic environments and leaves the reactor almost unattached. Liquefaction is a transformation process whereby solid biomass are converted into liquid products under high pressure and high temperature.

Anaerobic degradation of liquefied manure (LM) was examined in both batch and continuous cultures. The main objective of the work was to determine the optimal parameters for anaerobic degradation of LM. The continuous experiments also examined the biodegradation of specific chemical components of the LM using GC/MS analysis.

The batch experiments shows that liquefied manure (LM) is degraded most efficiently when low concentrations (1-5% LM) are added to manure, whereas a significant inhibition occurs when higher concentrations (> 25% LM) are added. The results from the CSTR experiments confirm the results from the batch experiments.

The GC/MS analysis shows that LM is composed of a broad range of organic compounds, of which many are toxic. The results shows further a large potential for anaerobic degradation of some toxic compounds and, thereby, gives further knowledge of the potential of combining liquefaction and anaerobic digestion.