Abstract
The effects of temperature (35 and 55°C) and straw–manure mixtures (90, 75, 50, and 0% straw) on methane (CH4) production were studied using laboratory-scale fermentors. Batch fermentations showed that the ultimate CH4 yield (B0) of straw–manure mixtures was directly proportional to the relative proportion and B0 of the individual components. Also, hammer or ball milling did not increase the B0 of straw. Kinetic analysis showed that fermentation stress occurred when the straw content of straw–manure mixtures was higher than 40% at 35°C, or higher than 75% at 55°C. This fermentation stress was observed to occur when the free ammonia concentration was below 10 g/m3.