Biorefinery for efficient xanthan gum, ethanol, and biogas production from potato crop residues

Abstract

Potato crop residues (PCR), as a naturally abundant source of lignocellulosic biomass, were used for the microbial production of xanthan gum and biofuels in the frame of two different biorefining scenarios. To enhance production yields, organosolv pretreatments with 50 and 75% (vv−1) ethanol at 120, 140, and 180 °C, in the presence or absence of (1% ww−1) H2SO4 (as a catalyst), were used before enzymatic hydrolysis. The hydrolysate of the pretreated PCR was microbially fermented to xanthan gum and ethanol through scenarios 1 and 2, respectively. Moreover, the stillages (waste residues) of both scenarios were anaerobically digested to produce biomethane. The maximum glucose yield of 74.6% was achieved after the catalytic pretreatment of PCR with 50% ethanol at 180 °C, while the yield from the untreated PCR was only 34.8%. Xanthan gum and ethanol yield from the untreated PCR were only 6.2 g xanthan gum per 100 g substrate and 27.5%, respectively. After the pretreatment at the optimum conditions, the highest xanthan gum (12.5 g per 100 g substrate) and ethanol (56.1%) yields were obtained. Moreover, the greatest biomethane yield of 196.0 mL g−1 volatile solids was obtained from the liquid fraction of organosolv pretreatment at 180 °C with 50% ethanol, in the absence of the catalyst. Overall, the highest obtained energy was 66.7 and 147.7 L gasoline equivalent per ton of PCR for scenarios 1 and 2, respectively. Scenario 1 provided an economic potential of $ 280.7, which was higher than that of the second scenario ($ 107.4).