Removal of Fermentation Inhibitors Formed during Pretreatment of Biomass by Polymeric Adsorbents

Abstract

The production of aldehydes that are microbial inhibitors may occur when hexoses and pentoses in an aqueous solution are exposed to temperatures above 150 °C under acidic conditions common to acid-catalyzed lignocellulose biomass pretreatment. Concentrations greater than 0.1% of the degradation product, furfural, strongly inhibit fermentation, as was confirmed for hydrolysate that contained 0.5% (w/o) furfural. Methods of furfural removal that have been reported include sulfite or alkali addition to achieve chemical reduction, ion exchange, hydrophobic adsorption, and irreversible adsorption on activated carbon. This paper reports the removal of furfural from biomass hydrolysate by a polymeric adsorbent, XAD-4, and desorption of the furfural to regenerate the adsorbent using ethanol. Liquid chromatographic analysis showed that furfural concentrations were less than 0.01 g/L compared to the initial concentrations that were in the range of 1−5 g/L. Fermentation of the resulting biomass hydrolysate with recombinant Escherichia coli ethanologenic strain K011 confirmed that the concentration of furfural in the hydrolysate caused negligible inhibition. Fermentation of XAD-4-treated hydrolysate with E. coli K011 was nearly as rapid as the control medium that was formulated with reagent-grade sugars of the same concentration. Ethanol yields for both fermentations were 90% of theoretical. Modeling of the adsorptive properties of this styrene-based adsorbent indicates that it is suitable for on−off chromatography and could be useful in a continuous processing system for removing small amounts of aldehydes that might otherwise inhibit fermentation.