In this paper we will present a process, where the hydrolytic enzyme production, the hydrolysis of the carbohydrates and the fermentation of the resulting sugars will be performed in a single step by a multi-species consortium of industrially proven, immobilized aerobic and anaerobic microorganisms in a membrane bioreactor. Cellulolytic enzymes are produced by fungal strains in the aerobic zone of the reactor and hydrolyze the hemicellulose and cellulose to mono-sugars, which are subsequently fermented to ethanol by yeast in the anaerobic zones. The produced ethanol is pre-separated from the fermentation broth by diffusion through the membrane.
The feasibility of the concept was successfully demonstrated by producing ethanol with >85% yield by the combined action of Trichoderma reesei and Saccharomyces cerevisiae using pure cellulose as the sole carbon source. Furthermore, semi-continuous runs were performed and a steady ethanol production rate was achieved over 8 cycles of medium exchange. Whole water-only pretreated wheat straw slurries were successfully co-fermented to ethanol in the same membrane reactor by adding Pichia stipits to the consortium in order to convert the hemicellulose sugars as well.