Trends and advances in sustainable bioethanol production technologies from first to fourth generation: A critical review

By the end of 2050, the world population is anticipated to reach 10 billion, which will change the perception of energy utilization. In recent years, the reliance on fossil fuels has shifted towards alternative energy sources. Over the past few years, there has been a profound emphasis on converting biomass into ethanol fuel, recognized as the most environmentally friendly liquid fuel as an alternative to fossil fuels. Bioethanol production from biomass offers a solution to decrease reliance on crude oil consumption while mitigating environmental pollution. This review's main objective is to examine the trends and advances in bioethanol production technologies involved in all four generations of bioethanol. Based on raw materials, the methods for the manufacturing of bioethanol are categorized into four generations. The first generation (1G) is the most prevalent bioethanol production, centered chiefly on glucose fermentation made from cereals by common yeast strains. The energy balance of conflict and food security are both negatively impacted by this generation. In order to balance food and fuel dichotomy, second-generation (2G) bioethanol uses biological processing of (ligno) cellulosic feedstock. However, pretreatment and hydrolysis are required, which makes these processes more costly than the first generation. Third-generation (3G) bioethanol uses photosynthetic microbes to obtain renewable fuel, which primarily entails the processing of algal raw material to manufacture the bioethanol. At the same time, algae's metabolic engineering of algae for bioethanol production from photoautotrophs falls within the fourth generation (4G). This review has covered recent technological advancements and notable obstacles in bioethanol production methods and is underscored alongside a glimpse into future prospects.