Document Type : Research Paper
Swedish Centre for Resource Recovery, University of Borås, SE 501 90, Borås, Sweden
The economic viability of the 2nd generation bioethanol production process cannot rely on a single product but on a biorefinery built around it. In this work, ethanol and fungal biomass (animal feed) were produced from acid-pretreated wheat straw slurry under an innovative simultaneous saccharification, fermentation, and filtration (SSFF) strategy. A membrane unit separated the solids from the liquid and the latter was converted to biomass or to both biomass and ethanol in the fermentation reactor containing Rhizopus sp. pellets. Biomass yields of up to 0.34 g/g based on the consumed monomeric sugars and acetic acid were achieved. A surplus of glucose in the feed resulted in ethanol production and reduced the biomass yield, whereas limiting glucose concentrations resulted in higher consumption of xylose and acetic acid. The specific growth rate, in the range of 0.013-0.015/h, did not appear to be influenced by the composition of the carbon source. Under anaerobic conditions, an ethanol yield of 0.40 g/g was obtained. The present strategy benefits from the easier separation of the biomass from the medium and the fungus ability to assimilate carbon residuals in comparison with when yeast is used. More specifically, it allows in-situ separation of insoluble solids leading to the production of pure fungal biomass as a value-added product.
- Economically viable production of 2nd generation bioethanol cannot rely on a single product.
- SSFF can be used for production of ethanol and biomass from wheat straw.
- Glucose present in the feed controlled the assimilation of xylose and acetic acid.
- The fungal growth rate was found not to be influenced by the feed composition.
- Rhizopus biomass yields of up 0.34 g/g and ethanol yields of 0.40 g/g were obtained.