Evaluation of dilute acid pretreatment on cashew apple bagasse for ethanol and xylitol production

• Dilute acid pretreatment on cashew apple bagasse (CAB) to solubilize hemicellulose.
• Achievement of the hemicellulose and cellulose-derived sugars from CAB.
• Hydrolyzate was used as a fermentation medium for ethanol and xylitol production.
• Concentrations of the inhibitors in hydrolyzate cause no toxicity to yeasts.

Pretreatment conditions such as the concentration of sulfuric acid added, solid concentration and the contact time were studied to maximize the yields from the bagasse. The best condition for dilute acid pretreatment was obtained when using 0.6 mol/L H2SO4 for 15 min at 121 °C. At this pretreatment condition, no detectable quantities of furfural or hydroxymethyl furfural were observed in the hydrolyzate fraction after treatment with Ca(OH)2. Scanning electron microscopy imaging showed the physical structural changes of cashew apple bagasse when it was pretreated with dilute sulfuric acid. Dilute-sulfuric acid pretreatment of CAB released hemicellulose-derived sugars to the liquid and these carbohydrates can be used to ethanol and xylitol production. An ethanol concentration of 10.0 g/L was obtained after 4 h of fermentation by Saccharomyces cerevisiae in agitated Flasks, with a yield of 0.49 g/gglucose and a productivity of 1.43  g/(L h) In a 4 L bench-scale bioreactor using S. cerevisiae, the maximum ethanol concentration obtained was 9.59 ± 1.74 g/L, and the maximum productivity obtained was 1.22 ± 0.06  g/(L h) Kluyveromyces marxianus CCA 510 produced ethanol and xylitol, reaching a concentration of 11.89 ± 0.34 g/L and 6.76 ± 0.28 g/L, respectively, at 96 h.