Charcoal adsorption of wood hydrolysates for improving their fermentability: Influence of the operational conditions

Xylose solutions, obtained by acid hydrolysis of Eucalyptus wood, were subjected to treatments with charcoal to remove lignin-derived compounds that can exert an inhibitory effect on subsequent fermentation stages. The effects of three operational variables (hydrolysate concentration, hydrolysate:charcoal ratio and adsorption time) on the concentrations of xylose, acetic acid and phenolics were considered. Additional experiments were performed with hydrolysates concentrated to a third of the initial volume to evaluate the effects of temperature, pH and hydrolysate:charcoal ratio (using a broader range of ratios) on the adsorption process. Raw and charcoal-treated hydrolysates were used as fermentation media for xylitol production by the yeast Debaryomyces hansenii. Treatments with a hydrolysate:charcoal ratio of 205 g/g were sufficient for fermentation to occur; a higher charge of adsorbent did not result in significant improvements.