In this work, a proposed pilot plant has been designed to produce 1 ton h(-1) biodiesel (BD) from waste/used vegetable oil using enzymatic approach. Complete material and energy balances were carried out using Excel spreadsheets, and detailed equipment sizing were determined. Immobilized lipase (Novozyme 435) is used as a catalyst in a packed bed bioreactor. The effluent of the reactor is passed though a Liquid-liquid extractor to separate the BD from other components. This is followed by a flash dram and a vacuum distillation column for further purification of the product. In addition, an economic feasibility of this process was assessed. The amount of feed streams of waste oil, methanol and tert-butanol required were found to be 1138, 130 and 7.6 kg h(-1), respectively. The main units in the proposed plant were designed and the economic feasibility of the process was assessed. It was found that the total capital investment required is about US$ 620,000, which will be paid back within four years of operation. (C) 2010 Elsevier Ltd. All rights reserved.