SPO

There is an ever growing demand for alternative sources of petroleum-based fuel due to the depletion of the world’s petroleum reserves and the increasing environmental concerns. Biodiesel, a renewable biofuel, can be used in any compression ignition engine without the need for modification. Therefore it has recently been considered as the best diesel substitute. Vegetable oils are renewable in nature, and can be produced on a large scale and environmentally friendly. These features make them promising feedstocks for biodiesel production. Vegetable oils include edible and non-edible oils. More than 95 % of biodiesel production feedstocks come from edible oils since they are produced in many regions in large quantities (Gui et al. [7]). Used or waste cooking oil is not suitable for human consumption but is a feedstock for biodiesel production. Its usage significantly reduces the cost of biodiesel production. Since the cost of raw materials accounts for about 60–80 % of the total cost of biodiesel production, choosing a right feedstock is very important (Singh and Sing [9], Gui et al. [7]). Recovery of waste vegetable oil (WVO) plays an essential role in both the environmental and economic sustainability of biodiesel. A total of 108 billion liters of WVO is estimated to be generated annually worldwide, but still, out of this quantity only 6 billion liters are collected and used in biodiesel production (Albiyobir [3]). In addition to the economical savings, collecting WVO also benefits the environment by decreasing the contamination of rivers, lakes or oceans. WVO along with waste animal fat is an ecotoxic agent, and accounts for 25 % of waste water pollution. One liter of WVO poured down the drain can contaminate one million liters of water and cause serious damage to the ecological lif