Metals addition for enhanced hydrogen, acetic and butyric acids production from cellulosic substrates by Clostridium butyricum

Highlights: • Hydrothermally pretreatment of SCB was suitable for producing H₂ by C. butyricum. • H₂ production was favored in the presence of 25 μM Fe. • Butyric acid was predominated for cellulose and glucose assays. • When no metal was added to the medium the production of H₂ and organic acids dropped. The influence of Fe (Iron), Ni (Nickel) and Se (Selene), important cofactors for hydrogenase (hyd), was evaluated in the bioproduction of H₂, volatile organic acids (VOA) and alcohols using Clostridium butyricum as inoculum and 5 g/L of cellulose, glucose or sugarcane bagasse (SCB) in batch reactors at 37 °C. Conditions A (25 μM Fe), B (25 μM Fe + 1 μM Ni), C (25 μM Fe + 1 μM Ni + 1 μM Se) and D (with no metal addition) using cellulose and glucose were performed to optimize the culture medium. H₂ production was favored in condition A being around 16 mmol/L and 6 mmol/L for glucose and cellulose, respectively. The predominance of butyric acid was observed in all experimental series with cellulose and glucose. On the other hand, acetic acid was predominant in the SCB assay. The presence of other bacteria in SCB may have contributed to the change in the route of the final metabolites. The results suggested the possibility of improving H₂ and OA production by C. butyricum supplementing the medium with Fe using SCB as substrate source.