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

Abstract

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.

Keywords: Dark fermentation; Hydrogen; Iron; Sugar beet pulp.