An overview of microdiesel - A sustainable future source of renewable energy

Microdiesel obtained from microbes using renewable materials as carbon sources is an important alternative to petroleum diesel. This review provides information related to microdiesel production using various carbon sources; i.e. carbon dioxide, C2, saccharides, and lignocellulose. Microbes can accumulate different contents of fatty acids in the form of triacylglycerol (TAG). Not all microbes store fatty acids and utilize a broad range of substrates as carbon sources, and vice versa. Microbes can be engineered to consume various carbon sources, and accumulate increased amounts of fatty acids with different composition. The properties of microdiesel depend on its fatty acid profile, which in turn determines its efficacy. The structural features of the fatty acids, such as carbon chain length, branching and degree of unsaturation, affect the physiochemical properties of the biodiesel (cetane number (CN), oxidation stability (OS), iodine value (IV), cold flow properties, density and kinematic viscosity). Fatty acid methyl ester (FAME) profiles can be used to evaluate the key properties of biodiesel, i.e. the stability of the oil used. The overview presented herein concludes that microdiesel production using non-feed carbon sources and genetically engineered microbes shows much promise.