Used edible oils generally recycled as animal feed or used as a raw material for lubricant and paints and the rest discharged into the environment (Watanabe et al., 2001). To eliminate environment and human health risk caused by waste oils/fats (Chen et al., 2006) and to lower biodiesel production cost, usage of waste oils/fats for biodiesel production is recommended (Watanabe et al., 2001). Waste cooking oil, animal fats, yellow grease, brown grease and waste from vegetable oil refining industries are major sources of waste oil for biodiesel production (Huynh et al., 2011). Waste oils are rich in high percentage of FFA and high water content, so lipase — mediated transesterification is a promising method for production of biodiesel with high yields (Huynh et al., 2011). Novozym 435 is capable of converting used olive oils (Sanchez and Vasudevan, 2006). Novozym 435 is capable of converting used olive oils in to biodiesel (Sanchez and Vasudevan 2006).

Algae Oils

Usage of algae oil for biodiesel production has considerable interest because of their availability costs compared to edible oils and animal fats. High photosyn­thetic rate, rapid growth rate, and high productivity make algae a good renewable source for oil/fats. High lipid content (20—40%), tolerance to water, and smaller land usage up to 132 times less compared to terrestrial oil crops make them more prominent choice for oil source (Karatay and Donmez, 2011). Usage of algae oil could reduce the food scarcity problem caused by bio­energy crops (Mata et al., 2010). However, technological development is needed to improve the microalgae oil extraction processes.

CHOICE OF ENZYME

Lipases from bacteria and fungi are the most commonly used for transesterification. In general at re­action temperatures 30—50 °C, the best enzymes will show conversions above 90%. Catalytic reaction time, alcohol type and enzyme condition (free enzyme or immobilized) are also the crucial parameters for select­ing enzyme (Table 8.3). Immobilized Pseudomonas cepacia lipases converts the jatropha oil into FAME in 8 h with ethanol; for the same free enzyme, it took 90 h for trans- esterifying soybean oil with methanol.