Subcritical Water Pretreatment for the Efficient Valorization of Sorghum Distillery Residue for the Biorefinery Platform

Abstract

The depletion of fossil fuels is resulting in an increased energy crisis, which is leading the paradigm shift towards alternative energy resources to overcome the issue. Lignocellulosic biomass or agricultural residue could be utilized to produce energy fuel (bioethanol) as it can resolve the issue of energy crisis and reduce environmental pollution that occurs due to waste generation from agriculture and food industries. A huge amount of sorghum distillery residue (SDR) is produced during the Kaoliang liquor production process, which may cause environmental problems. Therefore, the SDR generated can be utilized to produce bioethanol to meet current energy demands and resolve environmental problems. Using a central composite experimental design, the SDR was subjected to hydrothermal pretreatment. The conditions selected for hydrothermal pretreatment are 155 °C, 170 °C, and 185 °C for 10, 30, and 50 min, respectively. Based on the analysis, 150 °C for 30 min conditions for SDR hydrothermal pretreatment were selected as no dehydration product (Furfural and HMF) was detected in the liquid phase. Therefore, the pretreated slurry obtained using hydrothermal pretreatment at 150 °C for 30 min was subjected to enzymatic hydrolysis at 5% solid loading and 15 FPU/gds. The saccharification yield obtained at 72 h was 75.05 ± 0.5%, and 5.33 g/L glucose concentration. This non-conventional way of enzymatic hydrolysis eliminates the separation and detoxification process, favoring the concept of an economical and easy operational strategy in terms of biorefinery.