A comprehensive review on the sustainable valorisation of animal waste into heterogeneous catalysts for biodiesel production

The growing demand for sustainable energy alternatives has accelerated the search for cost-effective and environmentally benign catalysts in biodiesel production. This review provides a comprehensive evaluation of animal waste—including bones, shells, fats, and other organic residues—as a promising resource for developing heterogeneous catalysts used in esterification and transesterification reactions. It explores various preparation methods such as calcination, hydrothermal treatment, and acid/base modifications, with a focus on their influence on catalyst surface properties, thermal stability, and catalytic activity. In contrast to conventional catalysts, animal-waste-derived materials demonstrate high performance with feedstocks rich in free fatty acids, achieving biodiesel yields exceeding 90 % while offering strong reusability and reduced environmental burden, in other words, the sentence demonstrates that high biodiesel yields are achieved without compromising catalyst reuse or reducing the environmental impact of the process, illustrating how both can occur at the same time. A distinguishing aspect of this review is the integration of performance comparisons with traditional and nanostructured catalysts, as well as discussions on the alignment of these catalysts with circular economy strategies. The potential role of artificial intelligence in optimizing catalyst design, reaction conditions, and real-time process control is also examined. This review provides a comprehensive assessment of the use of animal waste as heterogenous catalysts for biodiesel production. It focuses on the environmental and economic benefits associated with the use of these sustainable catalysts and waste reduction.