A review of major trends, opportunities, and technical challenges in biodiesel production from waste sources

As the world addresses the increasing demand for sustainable energy solutions, biodiesel has surfaced as a viable alternative to conventional fossil fuels. The expansion of biodiesel feedstock plantations, particularly palm oil in tropical regions, can lead to deforestation, loss of biodiversity, and significant carbon emissions from the destruction of carbon-rich ecosystems. That is why this article focuses on biodiesel production from waste sources in order to maintain balance in the ecosystem. This review paper discusses the global energy landscape and the need for renewable and environmentally friendly alternatives. It explores the various waste sources in depth that are investigated for biodiesel production, comprising waste cooking oil, animal fats, algae, and other organic residues. Each feedstock is analyzed for its viability, challenges, and economic feasibility in biodiesel production. A critical assessment of different biodiesel production methods, such as transesterification, pyrolysis, thermochemical conversion, anaerobic digestion, thermal cracking, hydro-treating and enzymatic processes, is presented, highlighting the key factors influencing their efficiency and scalability. Recent developments to enhance waste-derived biodiesel production’s sustainability and economic viability to meet UN Sustainable Development Goals are also highlighted. Furthermore, the environmental impact of biodiesel, including greenhouse gas emissions and land use, is discussed to provide a holistic understanding of its ecological footprint. The biodiesel from waste sources can significantly increase the brake thermal efficiency of the engine along with a substantial decrease in emissions like CO and HC. However, the NOx and CO₂ emissions are increased with the application of biodiesel from waste sources. The CO₂ and NOx emissions can be reduced by exhaust gas recirculation and selective catalytic reduction techniques. The paper also addresses regulatory frameworks and standards governing biodiesel production from waste sources, emphasizing the need for harmonized policies to encourage widespread adoption. The paper concludes by outlining future research directions and potential breakthroughs that could further enhance biodiesel production’s effectiveness, sustainability, and scalability from waste sources. Waste Cooking Oil (WCO) and animal fats are currently the most economically feasible options for biodiesel production due to their low cost and established collection and processing infrastructure. Algae present high potential but require technological advancements and cost reductions to become economically viable. This review aims to assist researchers, policymakers, and industry stakeholders in advancing the utilization of waste materials for biodiesel production, promoting a more sustainable energy landscape.