Biodiesel, one of the alternative energy supplies from sustainable sources, is attracting great attention to replace conventional fossil fuels. Waste oil, including oil from ditches, waste cooking oil, and leftover oil in the oil factory, is considered as raw materials for biodiesel production. A pilot plant with a capacity of 30 metric tonnes of crude biodiesel per day has been built to optimize process conditions for esterification of the waste oil using polyferric sulphate catalysts in a stirred tank. The optimized process conditions are: 1.5-2.0 wt% catalyst, methanol vapor at a molar ratio of 1.5 to the waste oil, and reaction temperature at 100-110 degrees C. The conversion of waste oil to fatty acid methyl esters was above 98% for most batches. Refined biodiesel was obtained in a yield of 93%, and the main properties of biodiesel from waste oil in this process are comparable to the international standards.