As shown in Fig. 2 , the gas production rate was between 140–
250 NmL/d in phase 2 and between 300–760 NmL/d in phase 3.
The gas production rate could be considered as approximately
the carbon dioxide production rate due to carbon dioxide took
the proportion of more than 99%. The carbon dioxide increased
from phase 2 to phase 3, which was in accordance with the conver-sion of fermentation type from coexistence of homofermentation
and heterofermentation to heterofermentation.