Self-catalyzed in situ transesterification of Mucor circinelloides lipids from waste cooking oil for sustainable biodiesel production

To address the economic and environmental limitations of conventional biodiesel production, this study developed an integrated, self-catalyzed process using the oleaginous fungus Mucor circinelloides. The methanol-tolerant mutant JLW5, generated through atmospheric and room-temperature plasma (ARTP) mutagenesis, was cultivated on waste cooking oil and optimized for lipid accumulation, enabling endogenous-lipase-mediated (“self-catalyzed”) in situ transesterification. Under optimized culture conditions, JLW5 cultivated on 30 g/L waste cooking oil and 70 g/L bacterial peptone achieved 75 ± 1.6 % lipid content (dry cell weight) and 334 ± 16 U/g lipase activity after 60 h. The lipid profile was dominated by high proportions of saturated and monounsaturated fatty acids, which are suitable for biodiesel production. Biodiesel was directly produced from dried biomass via self-catalyzed in situ transesterification in a solvent- and catalyst-free system. Optimal reaction conditions included ultrasonic pretreatment for 40 min, a methanol-to-oil ratio of 4:1, and 40 % water content at 40 °C, resulting in an 85 ± 1.2 % FAME yield. This integrated strategy eliminates lipid extraction and chemical catalysts, simplifies downstream processing, and provides an economically viable and environmentally friendly route for converting waste cooking oil into biodiesel.