Varying nutrient concentrations impact ethanol production during fermentation of cellulosic sugars from mixed feedstock

Bio-based production of fuels and chemicals is typically based on a single feedstock input. Processes that can accept multiple feedstocks will help circumvent feedstock availability and diversity issues in certain geographical areas and thereby reduce the risk associated with feedstock supply to a biorefinery. This presentation is an account of ethanol fermentation process performed on cellulosic hydrolysates obtained from mixed feedstocks (corn stover, energy cane, and switchgrass) treated with 3 different pretreatment technologies (acid, alkali, and ionic liquids). SAS JMP was used to design experiments for the pretreatment tests, which were followed by enzymatic hydrolysis at 10 mg/g glucan to produce cellulosic sugars. Fermentation of these sugars was performed in shake-flasks with S. cerevisiae. Ethanol yields varied from 40% to 90% for the 36 hydrolysates tested. Apart from demonstrating fermentability of sugars, this study was also geared to identifying the least amount of nutrients (e.g. yeast extract and peptone) required for hydrolysate fermentation. Gallery^TM (ThermoFischer Scientific, MA) was used to measure concentrations of phosphate, magnesium, and nitrate throughout the fermentation process. Initial observations indicate that fermentation can proceed with half the nutrients suggested in standard sources. Reducing nutrient requirements in fermentation process has the potential to improve overall process economics and thereby biofuel cost. In the future, we will perform an integrated process with fermentation at 300L scale followed by downstream recovery studies.