Solar-Energy-Driven Conversion of Biomass to Bioethanol: a Sustainable Approach

Betina Tabah betinatabah@gmail.com ^1,2 Indra Neel Pulidindi ^1,2 Venkateswara Rao Chitturi ⁴ Leela Mohana Reddy Arava ⁴ Alexander Varvak ^2,3 Elizabeth Foran ^2,3 Aharon Gedanken ^1,2

¹Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
²Institute for Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan, Israel
³The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
⁴Department of Mechanical Engineering, Wayne State University, Detroit, MI, USA

Bioethanol is one of the most promising transportation fuels with economic, environmental, and energy benefits. However, currently, the production methodologies and purification technologies of biofuels industry are not economical. Our study demonstrates an economically viable, energy efficient, and sustainable alternative to the state-of-the-art process for bioethanol production from biomass. We have developed a solar-thermal-energy-driven simultaneous saccharification and fermentation (SSF) process for single-step conversion of biomass to bioethanol. In the early stages, aqueous solutions of glucose, starch, or cellulose were fed into the specially designed solar reactor containing the instant baker’s yeast (Saccharomyces cerevisiae) and the necessary enzymes. The yeast (biocatalyst) was not supplemented by any other nutrient, and it was demonstrated that the same yeast and enzymes could be used for at least two months without any decrease in enzymatic activity. After obtaining very high yields (up to 91% of the theoretical yield) and excellent separation of ethanol from the fermentation broth, the methodology was successfully extended to a continuous-flow single-step conversion of marine algae Ulva rigida to bioethanol (84% of the theoretical yield). Harnessing solar thermal energy for driving the SSF reaction as well as the special design of the solar reactor that facilitates in situ separation of ethanol from the fermentation broth by evaporation–condensation process make the current method industrially appealing and adoptable for large scale production. This study explores new avenues for a decentralized power supply based on solar thermal energy. The bioethanol produced was demonstrated as a potential fuel for direct ethanol fuel cells with high current and power density values, and 65% thermodynamic efficiency. In addition, the secondary metabolite glycerol was fully reduced to the value-added product 1,3-propanediol by S. cerevisiae, which is the first example of a fungal strain converting glycerol in situ to 1,3-propanediol.