High Lipid Yield and Efficient Biodiesel Production from Fusarium solani 102F Using Waste Eggshell as Biocatalyst

Oleaginous fungi offer a sustainable alternative to plant-based feedstocks for biodiesel production, yet their industrial potential remains limited due to high processing costs and strain-dependent performance. Here, we report that the endophytic fungus Fusarium solani 102F, isolated from a drought-tolerant legume tree in a hot–arid region, accumulates lipids and serves as a promising microbial platform for biodiesel production. Through systematic screening of nine endophytic isolates, F. solani 102F emerged as the top lipid producer with low biomass accumulation. Stepwise preliminary screening of culture conditions, including incubation time, agitation, pH, temperature, carbon and nitrogen sources, and salt, significantly increased biomass and lipid production. The highest FAME was achieved with glucose and casein as the best carbon and nitrogen sources, respectively, at 25 °C, pH 5.0, and 200 rpm shaking over seven days. Moderate salt level further boosted lipid accumulation compared with high salt level. Direct transesterification of F. solani 102F biomass yielded 15.8% FAMEs, supporting its potential as a microbial feedstock for biodiesel production. Importantly, we demonstrate that waste eggshell-derived CaO acts as a low-cost, effective heterogeneous biocatalyst for the transesterification of extracted fungal lipids from F. solani 102F, increasing biodiesel yield from 15.8% in the non-eggshell treatment to 27.02%, corresponding to a 71% relative increase. The fatty acid methyl esters resulting from transesterification with ES-derived CaO were analyzed by GC–MS, revealing a transesterified lipid profile enriched in C16–C18 monounsaturated chains, making them highly suitable for biodiesel production. This integrated approach, combining a robust fungal strain with waste eggshell-derived catalyst, provides a potential route for microbial biodiesel production, advancing circular bioeconomy strategies for renewable energy.