(47d) Broth Rheology and Ethanol Yield for a Zymomonas Mobilis Fermentation with High Substrate Loading

To reduce the cost of ethanol distillation of fermentation broths, a high initial glucose concentration is desired. However, increases in substrate concentration typically reduce the ethanol yield due to insufficient mass and heat transfer. In addition, different operating temperatures are required to optimize enzymatic hydrolysis (50°C) and fermentation (30°C).

To overcome the incompatible temperatures, saccharification following fermentation (SFF) was employed at high solids concentrations (10 to 20 percents). The rheological parameters, such as the power law coefficients, were correlated with the broth biomass concentration.

Experimental results are presented for a high-solids ethanol fermentation using Solka Floc as the model feedstock. A recombinant strain of Zymomonas mobilis (39679:pZB4L) was used in saccharification following the fermentation (SFF) process varying both the initial concentration of Solka Floc and enzyme dosage. Compared with the traditional SSF process at high solids loading, this process produced a higher ethanol yield. The viscosities observed were in range of 0.0418 to 0.0144, 0.233 to 0.0348 and 0.292 to 0.0447 paschal-seconds for shear rates up to 100s-1 at 10, 15, and 20 percent initial solids (w/v), respectively. These results are required for the simulation and optimization of full-scale bioethanol processes.