Optimizing biohydrogen production yields by employing locally isolated thermophilic bacteria from hot springs

Abstract

A climate-neutral economy is anticipated to rely heavily on hydrogen because it enables emission-free transportation, heating, and manufacturing operations. Biohydrogen can be produced from various kinds of biological waste making the interest high. However, the yield and efficiency of the processes are still challenging. This study applied Box-Behnken statistical experimental design to investigate the influence of temperature (oC), pH, and CO volume (mL) together with the amount of Fe+2, Zn+2, and Ni+2 to enhance biohydrogen production yields from thermophilic cultures, both mixed and pure cultures isolated from hot springs in Izmir, Türkiye. The maximum H2 yields were reported as 0.13 mmolH2/mmolCO for mixed cultures, and the pure culture reached 2.5 fold higher yield (0.44 mmolH2/mmolCO). Bench-scale bioreactor with a custom-design micro sparger was successfully run for 7 days (highest 0.25 mmolH2/mmol CO). This is the first report in the literature with local isolates to demonstrate the optimization of H2 yields with a comparative approach, and scale-up in a 2 L bench scale bioreactor. The viability of using novel thermophilic isolates as biohydrogen producers was successfully proven.