Development and optimization of a fermentation process for the production of 2,3-butanediol

The Ph.D. project aims to develop and optimize the fermentative production of diols from biowastes. In particular 2,3-butanediol (2,3-BDO), a promising platform chemical from which valuable derivatives can be produced. The biotechnological production of 2,3-BDO has been mainly studied with pathogenic bacteria by using pure sugars. However, the pathogenicity of such microorganisms, the high cost of sugars, and the not optimized fermentation conditions make this process not industrially competitive. During the first year, the microorganism Bacillus licheniformis ATCC-9789 was selected and its capability to ferment different sugars commonly occurring in biomass hydrolysates and biowastes was assessed. The selected microorganism is able to ferment hexoses and sucrose into 2,3-BDO. Furthermore, cheese whey could be potentially partially converted in 2,3-BDO, and molasses as well represent an interesting feedstock to produce 2,3-BDO with the selected strain. Since 2,3-BDO is produced preferentially under microaerobic conditions, the second year activities have been focused on the optimization of the oxygen supply conditions in batch fermentation mode using glucose as substrate. Experimentally, the application of a statistical design of the experiment allowed the identification of an optimal stirring/aeration combination, and the identification of a range of oxygen transfer rate values inside which the fermentation performances are maximized. The possibility of producing 2,3-BDO at high concentration and productivity was evaluated carrying out fed-batch experiments. Since complex media and the optimal oxygen supply conditions are both mandatory to obtain the best performances, different feed and oxygen supply strategies, were assayed. Another activity focused on the evaluation of alternative media instead of the complex media. Flasks and bioreactor experiments have been carried out using a mineral media, and meat and bone meal, whereas ,molasses and glucose were used as carbon sources. In conclusion, animal flour and molasses seem to be suitable alternatives to the commercial substrates to produce 2,3-butanediol.