A review on bioethanol production: first generation to fourth generation

Abstract The supply of energy to all the sectors is difficult nowadays due to increase of its demand and depletion of fossil fuels. Fossil fuels have to be replaced by an alternative energy sources due to creation of ill environment by fossil fuels. Bioethanol has developed as one of the leading renewable fuels with through generations. In the first-generation, Bioethanol is produced from food crops like corn or sugarcane, however it faced numerous obstacles such as food security and land competition. In the second-generation, bioethanol derived from lignocellulosic biomass to replace the first-generation feed stocks. This, unfortunately, also faced the same challenge. Feedstock recalcitrance, high processing costs, and limited commercial viability. Third-generation bioethanol, based on engineered microbial or algal systems, represent a more sustainable pathway with lower land use and higher yields, though it still faces constrains in the form of high energy inputs and the need for advanced bioreactor design. Fourth generation bioethanol addresses the issues of all three generations of bioethanol production. The main findings of these processes include genetic engineering of microbial strains, improved enzymatic hydrolysis, and integrated bio refinery concepts that enhance efficiency and reduce waste. Technologically, Bioethanol advances highlight the optimization challenges between conversion efficiency, resource availability, and cost-effectiveness. Environmentally, adoption of Bioethanol paves the way to reduced greenhouse gas emissions, increased circular use of biomass, and reduced dependence on fossil fuels.