Fourth-Generation Biofuels: A Comprehensive Review of Technological Progress and Challenges

The current ecological footprint and economic viability of existing biofuel production techniques render them inadequate for replacing fossil fuels and mitigating their contribution to the global greenhouse gas (GHG) emissions inventory. Metabolic engineering of algae underpins the production of fourth-generation biofuels, which are capable of fulfilling this demand. First-generation biofuels are derived from agricultural commodities such as corn and sugarcane. Second-generation biofuels utilize various forms of (ligno)cellulosic biomass. The third and fourth generations of biofuel production are characterized by “algae-to-biofuels” technologies: the former entails the processing of algal biomass for biofuel generation, while the latter focuses on the metabolic engineering of algae to produce biofuels from oxygenic photosynthetic microorganisms. This review examines the advancements, fundamental roadmaps, and policies pertinent to the future production and utilization of biofuels through advanced synthetic biology employed in fourth-generation biofuels (4G).