Second and Third Generation Biofuel Sources: A Comparative Review of Benefits, Challenges, and Conversion Technologies

Background: Second and third-generation biofuels have been thoroughly researched as sustainable and renewable alternatives to fossil fuels, although their large-scale deployment is limited by techno-economic and environmental concerns and inconsistent assessments in different studies. Recent advancements call for a critical review and investigation of the field. Objectives: This review aims to compare the second and third generation feedstocks for biofuel conversion technologies, their techno-economic feasibility, environmental performance and trade-offs in the related processes. Methods: We used 36 open-access papers that were published recently (2020-2025) from various databases to focus on our objective for this paper review. An analysis of papers was done to gather useful information for comparative analysis. Findings: The analysis revealed that 2nd generation biofuels are constrained by pretreatment severity and enzymatic hydrolysis costs, whereas 3rd generation systems are plagued by energy intensive cultivation, harvesting and dewatering. Although microalgae exhibit higher productivity than lignocellulosic feedstocks, their net energy balance and production costs make it unfavourable, without co-product valorization and renewable energy use. Life- cycle assessments also demonstrate variable environmental benefits related to site conditions and environmental burden shifting. Significance: Unlike previous reviews that focus on a feedstock yield or a conversion technique and its efficiency, this review integrates techno-economic analysis and environmental aspects across different generations, identifying the limitations that exist, and proposes an economically feasible and environmentally safe biofuel development pathway. Keywords: Second Generation Biofuel, Third Generation Biofuel, Biofuel Feedstocks, Biofuel Conversion Technologies, Life- cycle assessment, Techno-economic analysis