A Comprehensive Review of Feedstocks as Sustainable Substrates for Next-Generation Biofuels

With the rise in global population, industrialization, and economic expansion, the persistent overconsumption of conventional fossil fuels has resulted in the depletion of fossil fuel reserves. This has fuelled the need to investigate and boost scientific research efforts on sustainable and renewable bioenergy feedstock. A substitute that can minimize reliance on nonrenewable energy resources while also lowering greenhouse gas emissions. In this context, biofuels have received a great deal of interest in recent years as a prospective substitute for conventional fossil fuels. The prime reason behind this is the feedstock utilized in their synthesis. The feedstocks employed here are environmentally safe, nontoxic, and emit little to no pollution. These feedstocks are classified into four generations: first, second, third, and fourth. Food crops and lignocellulosic biomass and waste constitute first- and second-generation feedstocks. The third- and fourth-generation feedstock is microalgae. This paper provides a comprehensive overview of feedstocks utilized to produce biofuels, including the various pre-treatment methods, strategies, and techno-economic analysis in order to pave the way for next-generation biofuels. It also covers the advantages, drawbacks, challenges, and current developments.