Biodiesel and biogas are two very important sources of renewable energy worldwide, and particularly in the EU countries. While biodiesel is almost exclusively used as transportation fuel, biogas is mostly used for production of electricity and heat. The application of more sophisticated purification techniques in production of pure biomethane from biogas allows its delivery to natural gas grid and its subsequent use as transportation fuel. While biogas is produced mostly from waste materials (landfills, manure, sludge from wastewater treatment, agricultural waste), biodiesel in the EU is mostly produced from rapeseed or other oil crops that are used as food, which raises the 'food or fuel' concerns. To mitigate this problem, considerable efforts have been made to use non-food feedstock for biodiesel production. These include all kinds of waste oils and fats, but recently more attention has been devoted to production of microbial oils by cultivation of microorganisms that are able to accumulate high amounts of lipids in their biomass. Promising candidates for microbial lipid production can be found among different strains of filamentous fungi, yeast, bacteria and microalgae. Feedstocks of interest are agricultural waste rich in carbohydrates as well as different lignocellulosic raw materials where some technical issues have to be resolved. In this work, recovery and purification of biodiesel and biogas are also considered.
Keywords: anaerobic digestion; biodiesel; biogas; microbial lipids; recovery and purification; transesterification.