Pilot scale fed-batch fermentation in a closed loop mixed reactor for the biotransformation of crude glycerol into ethanol and hydrogen by Escherichia coli MG1655

Glycerol is a low-cost carbon source that can be used to produce chemicals like ethanol or hydrogen (H2). In the work described here, the biotransformation of crude glycerol, obtained from a biodiesel production process, into ethanol and H2 by Escherichia coli MG1655 was studied for batch and fed-batch operating modes. No difference was found between the use of crude glycerol rather than food-grade glycerol as the main carbon source. Three concentrations of crude glycerol were studied for fed-batch experiments under constant and exponential feeding regimes. No nutrients were added during the feeding step and a crude glycerol-water solution was fed into the reactor. The exponential feeding regime with 37.7 g L−1 of crude glycerol in the feed gave the best overall results, with 100% of fed crude glycerol consumed, a final ethanol concentration of 7.58 ± 1.52 g L−1 and an H2 yield of 0.56 mol mol−1 of fed crude glycerol. The process was studied on a pilot scale (working volume: 200 L) in a closed loop mixed reactor, giving an ethanol concentration of 8.5 ± 1.70 g L−1, thus indicating that scale-up of the process is possible. Fed-batch mode under an exponential feeding regime is a promising strategy to increase ethanol and H2 production and crude glycerol utilization given that previous studies concerning the biotransformation of glycerol to ethanol and H2 by Escherichia coli have mainly been performed in batch mode. Hydrodynamic characterization of the reactors was performed to establish conditions that would allow an approach to a complete mixing regime in all experiments.