A comprehensive review of bioethanol production from diverse feedstocks: Current advancements and economic perspectives

Bioethanol is attracting increasing attention as a sustainable alternative to fossil fuels. Depending on the feedstock, it is classified into four generations. First-generation bioethanol, sourced from food crops, has higher feedstock costs but lower processing costs; however, it may lead to food scarcity. Second-generation bioethanol uses low-cost lignocellulosic feedstocks and can be adopted widely. However, despite the technological development in second-generation bioethanol, cost of processing is still high, making second-generation bioethanol uncompetitive with gasoline. Third-generation bioethanol primarily relies on algae, while fourth-generation bioethanol uses genetically modified algae to enhance bioethanol yield. Current bioethanol production mainly comes from the first-generation route, while second-generation bioethanol is slowly taking off. Third- and fourthgeneration bioethanol production is still in the lab and pilot stages. This review critically discusses and summarizes recent advancements in all four generations of bioethanol production. It highlights significant findings regarding different raw materials, processing methods, process parameters, and microorganisms involved. Further, the paper delves into the economic viability and current deployment status of various bioethanol production routes by summarizing the techno-economic analysis done and some of the commissioned plants, along with their technology readiness level. The current challenges associated with different routes are outlined while offering insights into future perspectives.