Overview of glycerol as a carbon source in the hydrogen production process

The novelty of the current work considers the characteristic of the fermentability of glycerol by PNS bacterium R. capsulatus. Hydrogen production using glycerol as a carbon source was verified. Therefore, green hydrogen was provided by several biological routes, including an agroindustrial co-product (glycerol) use. Rhodobacter capsulatus, Rhodospirillum rubrum, a co-culture of both, and the fermentative bacteria Enterobacter cloacae, besides a microbial consortium, were used. Experiments were carried out in 50-mL and 1500-mL bioreactors, in which the hydrogen productivity, hydrogen yield, cell density, pH, glycerol, and organic acids were monitored. The findings shown Rhodobacter capsulatus strain at an initial inoculum density of 1.2 g/L presented applicable results for hydrogen productivity (18.3 mmol H2/L day) and yield (5.2 mol H2/mol consumed glycerol) using glycerol (10 g/L) as a carbon source. Biomass density reached almost 4 g/L, while pH varied from 6.8 to 5.5 during glycerol adding. The metabolites formed were mainly butyric acid (3.2 g/L), in R. capsulatus culture, and lactic acid (2.3 g/L) and propionic acid (6.5 g/L), in R. rubrum culture.