(257b) Effect of Inhibitors in Corn Stover Hydrolysate On Fermentation of Glucose and Xylose by Zymomonas Mobilis

One of the biggest challenges is to achieve high sugar yields resulting from pretreatment and enzymatic saccharification of biomass while ensuring that the sugar streams generated are not overly toxic to fermentation organisms in order to achieve higher ethanol yields in fermentation at process concentrations. Biomass pretreatment is necessary to reduce the recalcitrance of lignocellulosic feedstocks to enzymatic saccharification and to allow the liberation of soluble sugars from plant cell wall carbohydrates, but pretreatment can also release a number of undesirable compounds into the hydrolyzate that can inhibit the growth and ethanol productivity of fermentation organisms. Inhibitors vary in range and amount depending on the feedstock, pretreatment methods and process conditions. We conducted systematic studies by 1) developing a quantitative, high throughput biological growth assay using an automated turbidometer to obtain the inhibitory kinetics for individual compounds (aldehydes, organic and inorganic acids along with various cations and alcohols) on growth of Z. mobilis 8b in glucose and xylose as well as in real hydrolyzates, 2) investigating the toxicity basis of the corn stover hydrolysates, and 3) examining the impact of the conditioning process on cell growth and fermentation through analysis of chemical composition of the conditioned hydrolyzates with detailed chemical identification and quantitation of potential inhibitory compounds. Research findings from these studies will be presented.