Biohydrogen production by Thermotoga maritima from a simplified medium exclusively composed of onion and natural seawater

Abstract

Biohydrogen production by the anaerobic hyperthermophilic and halophilic bacterium, Thermotoga maritima (TM), was conducted using a mixture of Onion Waste Juice (OWJ) and seawater (SW). The highest production of biohydrogen (H2) with OWJ, as the exclusive source of carbon and energy, was obtained for an optimum volume of 50% (v/v), with the highest overall productivity of biohydrogen (15.6 mM/h) and a maximum yield of 2.6 ($\mathrm{mol}_{\mathrm{H}_{2}}/\mathrm{mol}_{\mathrm{Hexose}}$). This was mainly due to the presence of organosulfur compounds and the natural presence of ammonium contained in OWJ. The addition of inorganic nitrogen and iron sources in the mixture of SW and OWJ has improved biohydrogen production, achieving productivity yield (23.0 mM/h for 3.2 $\mathrm{mol}_{\mathrm{H}_{2}}/\mathrm{mol}_{\mathrm{Hexose}}$) close to the maximum obtained for TM. Above 600 mL, the high concentration of substrate ($>$30 gCOD/L) led the metabolism to deviate towards lactate production at the expense of H2 production. A fed-batch culture with the sequential addition of concentrated OWJ mixed with only sea salt was investigated for the prevention of substrate-associated growth inhibition by controlling the nutrient supply. The total cumulative biohydrogen produced was about 300 mM after 30 h of incubation.

Keywords

• Bioreactor
• Biohydrogen
• Onion waste juice
• Seawater
• Dark fermentation
• <i>Thermotoga maritima</i>
• Hyperthermophilic
• Bioreactor