Conversion of straw–manure mixtures to methane at mesophilic and thermophilic temperatures

The effects of temperature (35 and 55 degrees C) and straw-manure mixtures (90, 75, 50, and 0% straw) on methane (CH(4)) production were studied using laboratory-scale fermentors. Batch fermentations showed that the ultimate CH(4) yield (B(0)) of straw-manure mixtures was directly proportional to the relative proportion and B(0) of the individual components. Also, hammer or ball milling did not increase the B(0) of straw. Kinetic analysis showed that fermentation stress occurred when the straw content of straw-manure mixtures was higher than 40% at 35 degrees C, or higher than 75% at 55 degrees C. This fermentation stress was observed to occur when the free ammonia concentration was below 10 g/m(3).