Enhanced bioethanol production from cellulosic feedstocks by a modified bioreactor

Lignocellulose was converted to reducing sugars using saccharification enzymes from cocultivated Trichoderma ressei and Aspergillus niger, and then bioethanol was produced using reducing sugars as the nutrients for Zymomonas mobilis in an immobilization system. The cocultivated T. ressei and A. niger exhibits enzymatically synergistic effects after 96 h of cultivation, which enables a production rate of reducing sugar of 1.29 g/L and a conversion rate of cellulose of 23.3%. Also, an 18% total inoculum concentration and a 1/1 inoculation ratio of T. ressei to A. niger obtains a production rate of reducing sugar of 2.57 g/L and a conversion rate of cellulose of 46.3%. The co-immobilization cultivation results showed that using polyurethane as a carrier could optimize total saccharification enzyme activity at an inoculum ratio of 1/1 and a total inoculum concentration of 6.5×10⁶ spores/mL. Based on the observed results, a bioreactor was further modified to enhance bioethanol production. The strains A. niger, T. reesei, and Z. mobilis were co-cultivated with a co-immobilization cultivation system. It was found that, after 24 h of cultivation, the production of bioethanol reached 0.56 g/L and the conversion rate of reducing sugar reached 11.2% using carboxymethylcellulose (CMC) substrates. The experimental results revealed the enhanced bioethanol production using the modified bioreactor. However, further studies are highly desired to determine how to prevent multi-stage failure of reducing volume of the culture medium.