The valorization of glycerol: Economic assessment of an innovative process for the bioconversion of crude glycerol into ethanol and hydrogen

The worldwide energy demand has been continuously increasing, thus requesting more sustainable alternatives to the rapidly depleting fossil fuels. Therefore, biofuels such as hydrogen, bioethanol and biodiesel are gaining more importance as a renewable and pollution-free solution, which might give a significant contribution to the future energy mix. In recent years, the exponential growth of biodiesel production has led to a glycerol glut, however, according to some authors, crude glycerol might represent a suitable, abundant and low-priced feedstock for fermentation technologies. In this study we performed an energetic and economic assessment of an innovative process, which is under development in our lab, for the bioconversion of crude glycerol into ethanol and hydrogen. Ongoing experiments showed the possibility to reach at least 26 g/L of ethanol, together with 9 L of hydrogen, in non-sterile conditions and without nutrient supplements. Since kinetics and ethanol concentration need to be further improved, we performed this study with a view to evaluate the possibility of reaching economic viability. Results showed that with 26 g/L of ethanol and a retention time as high as 120 h, the calculated energy cost would be about 0.019 €/kW hth and 0.057 €/kW hel, considering the contribution of both, hydrogen and bioethanol. Moreover, bioethanol cost would be as low as 0.21 €/L, even without taking into account the possible hydrogen revenues. These results are very promising and suggest that the process has reasonable chances to achieve economic viability, thus deserving further attention. The procedure followed in this work provided a realistic and concrete target to pursue in the future lab experiments, in order to bring this technology closer to the market.

► Innovative process for highly efficient joint ethanol and H2 production from crude glycerol.
► No need for pretreatment, nutrient supplementation, nor sterilization.
► Energetic and economic assessment to evaluate the possibility to reach economic viability.
► Bioethanol production cost as low as 0.21 €/L.
► Major bottleneck is not the downstream processing but the cost of large-sized reactor.