Orange peel pretreatment in a novel lab-scale direct steam-injection apparatus for ethanol production

• A novel lab-scale direct steam-injection apparatus was used to produce ethanol from orange peel waste.
• The main inhibitor concentrations after acid-catalysed steam-explosion (ACSE) were <1.5 g L−1.
• ACSE (180 °C; 150 s) and conventional enzymatic saccharification resulted in 56% of glucose yield.
• Repeated batch fermentations resulted in ethanol yield (0.495 g g−1) and productivity (4.85 g L−1 h−1).

Orange peel waste (OPW) was converted into ethanol by consecutive acid-catalysed steam-explosion (ACSE), enzymatic saccharification and fermentation with Saccharomyces cerevisiae F15. The first step was performed in the presence of 0.5% (volume fraction) sulphuric acid at a solid loading of 160 g L−1 using a novel laboratory-scale Direct Steam-Injection Apparatus under different reaction temperatures and times. ACSE at 200 °C for 90 s (or 180 °C for 150 s) yielded the highest solubilization of pectin (∼73%) and a positive effect on the subsequent enzymatic hydrolysis step, that was carried out at 50 °C with an enzyme loading of 6 FPU g−1 cellulose. OPW, pretreated at 180 °C for 150 s, yielded the highest glucose solubilisation degree (∼56%) at the end of the saccharification step, and the maximum ethanol yield coefficient (∼0.495 g g−1) and productivity (4.85 g L−1 h−1) at the end of the 3rd repeated fermentation batch in shaken-flasks.