A heterogeneous catalyst has been derived from a waste material (i.e., exoskeleton of mollusk) for transesterification of a waste feedstock (i.e., used frying oil (UFO)) for synthesis of biodiesel. The exoskeleton of mollusk shell was crushed, ground, and calcined at 900 degrees C to derive CaO as a heterogeneous catalyst. The catalyst was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray fluorescence spectroscopy (XRF), and differential thermal analysis/thermogravimetric (DT/TG) analysis. The XRD peaks observed at 2 theta = 31.80, 36.93, and 53.37 degrees were characteristic of CaO and showed high crystallinity. The FTIR absorption bands of the calcined shell were observed at 1474, 870, and 502 cm(-1), which are attributed to the vibration of CO32- molecules, and a sharp peak at 3640 cm(-1) indicated the presence of OH- stretching due to Ca(OH)(2). The XRF analysis demonstrated the Pila globosa shell to comprise 79.86% of calcium along with few minor elements (viz. Pd, I, Te, Sb, Sn, W, Al, Si, Sr, Cr, S). The (DT/TG) analysis showed the decomposition of calcium carbonate present in Pila globosa at 860 degrees C. The waste-driven substances (exoskeleton of mollusk as catalyst and UFO as feedstock) resulted in a high yield (92%) and conversion (97.8%) of biodiesel that was obtained at a 10:1 (methanol to oil) molar ratio, 4.0 wt % catalyst, at 60 +/- 0.5 degrees C in 5 h reaction. The conversion of UFO to biodiesel was determined by H-1 FT-NMR