Enrichment of activity sludge allowed to select a suitable microbial mixed culture able to grow on crude glycerol as the only carbon source, using a very simple synthetic medium without any extra nutrient supplements. Following to statistical optimisation, the selected pool was able to effectively convert crude glycerol into H2 and ethanol, both at a near¬stoichiometric yield. Subsequently, upscale tests were performed to validate the statistical model, and fed¬batch tests, in non¬sterile conditions, led to a three¬fold increase of ethanol production, thus reaching 26g/L, while producing up to 9L of H2. These results were obtained without the use of vitamin¬ and trace element solution, tryptone or yeast extract. Based on these findings it seems feasible to totally exclude the use of any synthetic medium for glycerol fermentation, through the co ¬fermentation with other waste/residual (organic) compounds, i.e. proteins and carbohydrates derived from the microalgae. In this way it might be possible to link 3rd generation biodiesel with H2 and ethanol production, while avoiding the competition with food feedstock and agricultural land use. Moreover, the valorisation of crude glycerol (converted into high¬ value products) might contribute to enhance the economic viability of microalgae feedstock and biofuels, which are, at the moment, still too costly to be commercialized.

Proceedings of the 20th European Biomass Conference and Exhibition, 18-22 June 2012, Milan, Italy, pp. 713-716