Dark fermentative hydrogen production from hydrolyzed sugar beet pulp improved by iron addition.

This study evaluated the impact of three different iron compounds (Fe2O3, FeSO4, FeCl3) on hydrogen production via mesophilic dark fermentation (DF) of hydrolyzed sugar beet pulp (SBP). In batch tests, the maximum hydrogen yield of over 200 dm3H2/kgVS was achieved with the addition of 0.1 gFe2O3/dm3, which was twice greater than the control. In semi-continuous experiments, the highest hydrogen production of 52.11 dm3H2/kgVS combined with 19.4 dm3CH4/kgVS methane yield was obtained at a dose of 1 gFe2O3/dm3. Acetic, lactic and caproic acids were the main metabolic products of DF. Microbiological studies showed some balance between hydrogen producing microorganisms from the order Clostridiales and lactic acid producers (LAB) affiliated with the orders Lactobacillales and Coriobacteriales. Moreover, the presence of methanogens affiliated to the genera Methanobrevibacter and Methanosphaera was also documented. An interesting finding was the appearance of rare bacteria from the genus Caproiciproducens, which was responsible for increased caproic acid production.