2-67: Effect of Na+, K+, NH4+ and glycerol on the glucose/xylose co-fermentation by recombinant S. cerevisiae 424A(LNH-ST)

For large-scale industrial production of cellulosic ethanol to be feasible, it is critical to understand the impacts inhibitors which may negatively affect the fermentation. Potential inhibitors to this process include cations such as sodium, potassium, calcium, and ammonium found in the plant biomass and /or used in pH adjustment prior to and during the fermentation, and the accumulation of fermentation byproducts, such as glycerol, due to recycling of stillage. For this reason, bench-scale fermentations were conducted using Purdue recombinant glucose/xylose co-fermenting S. cerevisiae 424A (LNH-ST) to test the inhibitory effect of four cations (sodium, potassium, ammonium), and glycerol potentially found in the cellulosic ethanol process.  The tested concentration of the cations range from 0.1 M to 0.5 M and the glycerol concentration range from 10 to 30 g/L in fermentation of glucose and xylose in YEP media.  From these fermentations, it was found that glycerol and potassium were less inhibitory than ammonium and sodium.  Additionally, the impact of all inhibitors was stronger toward xylose utilization than glucose utilization.