Bio‑hydrogen and VFA production from steel mill gases using pure and mixed bacterial cultures

A major source of CO2 emissions is the flaring of steel mill gas. This work demonstrated the enrichment of carboxydotrophic bacteria for converting steel mill gas into volatile fatty acids and H2, via gas fermentation. Several combinations of pure and mixed anaerobic cultures were used as inoculum in 0.5-L reactors, operated at 30 and 60 °C. The process was then scaled up in a 4-L membrane bioreactor, operated for 20 days, at 48 °C. The results showed that the enriched microbiomes can oxidize CO completely to produce H2/H+ which is subsequently used to fix the CO2. At 30 °C, a mixture of acetate, isobutyrate and propionate was obtained while H2 and acetate were the main products at 60 °C. The highest CO conversion and H2 production rate observed in the membrane bioreactor were 29 and 28 mL/LR/h, respectively. The taxonomic diversity of the bacterial community increased and the dominant species was Pseudomonas. [Display omitted] •Steel mill gas was converted into bio-H2 from enriched mixed bacterial culture.•VFAs were produced via in situ hydrogenation of CO2.•The type of bio-product was affected by the fermentation temperature.•Enrichment of mixed cultures led to higher conversion/production rates.•The dominant species shifted from Defluviitoga tunisiensis to Pseudomonas.