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

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 H 2 yields were reported as 0.13 mmolH 2 /mmolCO for mixed cultures, and the pure culture reached 2.5 fold higher yield (0.44 mmolH 2 /mmolCO). Bench-scale bioreactor with a custom-design micro sparger was successfully run for 7 days (highest 0.25 mmolH 2 /mmol CO). This is the first report in the literature with local isolates to demonstrate the optimization of H 2 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. • Locally isolated mixed and pure culture strains of thermophilic CO fermenting bacteria were comparatively evaluated. • Box-Behnken Statistical Experimental Design was employed with the operational and media based independent parameters. • Optimization of the cultures were carried out on two different designs. • A bench scale bioreactor was operated in both cultures with a custom-designed microsparger. • Highest H 2 production was observed in pure cultures, with a yield of 0.44 mmol H 2 /mmol CO. [ABSTRACT FROM AUTHOR]