Heterogeneous solid acid catalysts for sustainable biodiesel production from wastewater-derived sludge: A systematic and critical review

This comprehensive review has systematically examined the use of heterogeneous solid acid catalysts in producing biodiesel from wastewater-derived sludge using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology. It highlighted the composition and characteristics of wastewater-derived sludge, presenting both the opportunities and challenges associated with its use as a feedstock for biodiesel production. Various types of catalysts were discussed, with a detailed exploration of heterogeneous solid acid catalysts, including zeolites, hetero-polyacid (HPA), mixed metal oxides, and sulphonic acid group catalysts. The advantages and limitations of these catalysts were critically analyzed, providing a balanced view of their potential for industrial applications. The application section delved into the catalytic transesterification reaction, mechanisms of biodiesel production, and effects of catalyst loading on the yield. Performance metrics, such as catalytic activity, stability, recyclability, cost-effectiveness, and environmental impact, were thoroughly evaluated, offering a clear understanding of the efficacy of these catalysts. The synthesis and characterization techniques were also reviewed, shedding light on the latest preparation methods and characterization techniques. Recent advances in catalyst development were presented, showcasing the innovative strides made in enhancing catalyst performance. The environmental and economic implications of using solid acid catalysts for biodiesel production were assessed, emphasizing the importance of sustainability and financial viability.