Enhancing bio-hydrogen production from sodium formate by hyperthermophilic archaeon, Thermococcus onnurineus NA1

Hyperthermophilic archaeon, Thermococcus onnurineus NA1 was reported to grow on formate producing hydrogen (H-2). In this study, to sustain high H-2 production rate and demonstrate the feasibility of mass production of H-2, high cell density cultivation of T. onnurineus NA1 on sodium formate was employed under optimized conditions. From batch cultures, it was observed that the salinity of medium, significantly changed by the addition of formate salt and pH-adjusting agent, crucially affected cell growth and H-2 production. With salinity carefully controlled between 3.7 and 4.6 %, 400 mM sodium formate was found to be an optimal initial concentration for maximizing cell growth-associated H-2 production. Under optimal conditions, the repeated batch culture with cell recycling showed high cell density of OD600 of 1.7 in 3 and 30 L bioreactor, and the volumetric H-2 production rate was enhanced up to 235.7 mmol L-1 h(-1), which is one of the highest values reported to date.