Lignocellulosic biomass for bioethanol: Insight into the advanced pretreatment and fermentation approaches

The global energy demand and need for sustainable sources are expected to rise in the coming years. The second-generation bioethanol production from lignocellulosic biomass (LB) can sustain the energy demand. Thus, this review comprehensively discussed the suitable feedstock selection and different pretreatment progress (including mechanical/thermal, biological, chemical, and physical-chemical) for LB in recent years. The effect of engineered and immobilized microbial strains on biomass conversion to bioethanol is also elaborated. The sugarcane bagasse, switchgrass, cheery wood, and corn cobs (>40 % cellulose content) are considered to be potential and promising LB for bioethanol generation. The application of pretreatments (such as extrusion, steam explosion combined with mild acids, mild thermo-alkaline, green liquor, and surfactants combined with a steam explosion) increased sugar conversion and bioethanol production. The use of genetically engineered yeast along with microbial immobilization offered a full utilization of pentoses and hexoses that enhanced the bioethanol yield. Bioethanol production is comparatively effective at a laboratory scale. However, extensive research is still required to develop a cost-effective process and complete biomass utilization.