387 PAL & KACHHWAHA: WASTE COOKING OIL Journal of Scientific & Industrial Research Vol. 72, June 2013, pp. 387-392 *Author for correspondence E-mail: sskachhawaha@rediffmail.com Waste cooking oil: a promising feedstock for biodiesel production through power ultrasound and hydrodynamic cavitation Amit Pal and * Surendra S. Kachhwaha Department of Mechanical Engineering, Delhi Technological University, Bawana Road, Delhi, India * Department of Mechanical Engineering, School of Technology, Pandit Deendayal Petreoleum University, Gandhinagar, Gujarat, India Received 24 July 2012; revised 03 December 2012; accepted 30 April 2013 The present research work deals with the details of development of laboratory test rigs for power ultrasound and hydrodynamic cavitation test rigs for conversion of WCO into biodiesel in comparison to conventional mechanical stirring. Results show that cavitation techniques can be successfully applied to transesterification reactions, to achieve more than 90% yield of the product for molar ratio 4.5:1 with minimum catalyst percentage of 0.5% and appears to be rapid and effective compared to the mechanical stirring method, for preparing alkyl esters from triglycerides. Introduction Diesel fuel plays an important role in the industrial economy of developing countries, particularly in transport of industrial and agricultural goods, etc. Economic growth is always accompanied by commensurate increase in the transport activities 1 . Majority of the world