Establishment and assessment of a novel bioethanol and efficient biogas coupling fermentation system integrated with the pretreatment of a cellulolytic microbial consortium

A novel bioethanol and biogas coupling fermentation system integrated with the pretreatment of a cellulolytic microbial consortium was proposed to treat cassava distillage. In the present study, 8 batches of ethanol fermentation integrated with 7 batches of biogas fermentation were successively proceeded. The recycled water after two-stage of anaerobic digestion was reused for raw material mixing in the later 7 batches of ethanol fermentation, whereas only tap water was used in the first batch. It was found the ethanol yield, starch utilization ratio, fermentation time can be kept steady at about 12.6%(v/v), 90% and 48 h respectively during the recycling process, which were very close to those of the conventional process using tap water. The organic substrates, volatile fatty acids, total and ammonia nitrogen reached steady states after 2-5 batches of recycling, while the total ion and alkalinity revealed a little decrease tendency with the increment of the recycling batches. Further, the total methane yield and methane producing velocity of each recycling batch in the proposed coupling system could reach 180-206 L and 40-45 L CH4 L−1 d−1 (litres of methane generate per litre of reactor volume per day) respectively, which was 16.1-32.9% and 25-40.6% higher than those of the original one. In addition, the total mass yield obtained by the combination in the proposed coupling system was 317 g ethanol plus 68.7 g methane/kg cassava, and 8.3% higher energy was generated compared with the original system. In conclusion, the insertion of a biological pretreatment step into the proposed coupling system revealed obvious superiorities and applicable potential.