Strategies for Reducing Supplemental Medium Cost in Bioethanol Production from Waste House Wood Hydrolysate by Ethanologenic Escherichia coli: Inoculum Size Increase and Coculture with Saccharomyces cerevisiae

In this paper, we report a simultaneous realization of both efficient ethanol production and saving medium nutrient (corn steep liquor [CSL]) during bioethanol fermentation of overliming-treated hydrolysate of waste house wood (WHW) using ethanologenic Escherichia coli KO11. In cultivation using WHW hydrolysate supplemented with 4% (v/v) CSL and 0.2 g-dry cell weight (DCW)/l E. coli KO11 cells, the overall ethanol yield reached 84% of the theoretical value at 61 h. When we conducted the cultivation with 1% CSL to reduce the supplemental medium cost, the overall ethanol yield remained in the range of 66–72% even at 90 h. We proposed two alternative methods for increasing the overall yield even with 1% CSL. The first method involved increasing the inoculum size of E. coli KO11 up to 0.8 g-DCW/l, where 83% of the overall yield was attained at 60 h of cultivation. The second method involved the coculture of 0.2 g-DCW/l E. coli KO11 together with 0.02 g-DCW/l of Saccharomyces cerevisiae TJ1, and the overall yield reached 81% at 47 h of cultivation.