Mary Ann Franden, Heidi M. Pilath, Ali Mohagheghi, Philip T. Pienkos, and Min Zhang. National Bioenergy Center, NREL, 1617 Cole Blvd, MS3323, Golden, CO 80401
From a process economics consideration, one of the biggest challenges involves achieving high sugar yields while ensuring that the sugar streams generated are less toxic to fermentation organisms in order to achieve higher ethanol yields. To obtain higher monomeric xylose yields from biomass pretreatments with less loss to sugar degradation products in diluted acid hydrolysis, lower severity pretreatment conditions using a solids loading at 30% (w/w) in the horizontal pretreatment reactor were tested. To characterize the toxicity profiles of the hydrolysates generated under these low severity pretreatment conditions we evaluated 37 corn stover hydrolysate samples containing a range of monomeric and oligomeric xylose contents as well as furfural and acetic acid concentrations. Using high-throughput growth assays and mini-fermentations, we examined both growth and fermentation profiles using Zymomonas mobilis 8b and identified key compounds which contribute towards the majority of toxicity present in these hydrolysates. This method has shown to be effective for evaluating toxicity of hydrolysates produced from different conditions which provides critical feedback for selecting and optimizing the pretreatment process for biomass to ethanol conversion.
