Thermobarical pretreatment of cattle waste for biomethanation

The influence of thermobarical treatment on digestibility of cattle manure was investigated in lab-scale experiments. Therefore, solid cattle manure, liquid cattle manure and mixtures of these from different origins were treated in a closed vessel at temperatures of 140, 160, 180, 200 and 220°C for 5 minutes respectively. The pressure was that of the water vapor pressure at the respective temperature. Methane yield could be increased significantly (up to 58% at a temperature of 180°C) by thermobarical pretreatment. Higher treatment temperatures led to a decrease in methane yield compared to untreated material. This effect is caused by the formation of inhibitors and indigestible substances. An extended analysis of the data obtained via batch anaerobic digestion tests demonstrates a correlation between formation rate and methane yield in the acceleration phase predeterminating the methane yield at the end of the batch test after 30 days. A regression of the values from this correlation resulted in the findings of 164°C as optimum and 115°C as minimum treatment temperature.