Lipids from yeasts and fungi: Tomorrow's source of biodiesel?

In the search for new transport fuels from renewable resources, biodiesel from microbial lipids comes into view. We have evaluated the lipid yield and energy use of a process for production of biodiesel from agricultural waste using lipid-accumulating yeast and fungi. We included different bioreactors for submerged and solid-state fermentation in our evaluation. Using existing kinetic models, we predict lipid yields on substrate between 5% and 19% (w/w), depending on the culture system. According to the same models, improvement of the yield to 25-30% (w/w) is possible, for example by genetic modification of the micro-organisms. The net energy ratio of the non-optimized systems varies between 0.8 and 2.5 MJ produced per MJ used; energy use for pre-treatment and for oxygen transfer are most important. For the optimized systems, the net energy ratio increases to 2.9-5.5 MJ produced per MJ used, which can compete very well with other biofuels such as bioethanol or algal biodiesel. This shows that, although quite some work still has to be done, microbial lipids have the potential to be tomorrow's source of biodiesel. (c) 2013 Society of Chemical Industry and John Wiley & Sons, Ltd