Enhancement of biodiesel synthesis over highly active CaO derived from natural white bivalve clam shell

White bivalve clam shell (WBCS), a good source of calcium carbonate collected from sea shore was subjected to calcination–hydration–dehydration treatment to obtain CaO with high activity. The performance of the newly obtained CaO from the calcination–hydration–dehydration treatment of WBCS and commercial CaO was tested for their catalytic activity via transesterification of waste frying oil (WFO). The results showed that the methyl ester conversion for the commercial CaO was 67.57% whereas it was 94.25% for the CaO obtained from calcination–hydration–dehydration treatment of WBCS at a 7 wt.% catalyst (based on oil weight), methanol to oil ratio of 12:1, reaction temperature of 65 °C and reaction time of 1 h.