Characteristics of microbial water gas shift reaction by carboxydotrophic archaeon Thermococcus onnurineus NA1 with various carbon monoxide concentrations

Abstract

Thermococcus onnurineus NA1 is a hyperthermophilic archaeon which is able to produce hydrogen utilizing single carbon substrates such as carbon monoxide (CO) and formate in a growth-associated manner. It was reported that the H2 productivity of T.onnurineus NA1 on CO is outstanding compared to other carboxydotrophic strains, and thus demonstrating its possibility for replacing conventional water gas shift processes based on metal catalysts. However, for the process development using T. onnurineus NA1, it is necessary to optimize fermentation parameters including dissolved CO concentration in the reactor. In this study, we carried out a series of batch fermentations of T. onnurineus NA1 to investigate the effect of dissolved CO concentration on the initial and the maximum H2 production rate. To determine CO consumption and H2 production rate accurately, two-stage fermentor system equipped with on-line gas chromatograph was employed. The CO metabolism of T. onnurineus NA1 shows substrate-inhibition kinetics and there is the optimum CO concentration. Also, severe mass transfer limitation was occurred within several hours after inoculum and the H2 productivity remained constant. The maximum H2 productivity could be linearly correlated with the partial pressure of CO in the feed gas. Using the fermentation data, a kinetic model of the CO fermenation of T. onnurineus NA1 combined with mass transfer characteristics was deriy of T.onnurineus NA1 on CO is outstanding compared to other carboxydotrophic strains, and thus demonstrating its possibility for replacing conventional water gas shift processes based on metal catalysts. However, for the process development using T. onnurineus NA1, it is necessary to optimize fermentation parameters including dissolved CO concentration in the reactor. In this study, we carried out a series of batch fermentations of T. onnurineus NA1 to investigate the effect of dissolved CO concentration on the initial and the maximum H2 production rate. To determine CO consumption and H2 production rate accurately, two-stage fermentor system equipped with on-line gas chromatograph was employed. The CO metabolism of T. onnurineus NA1 shows substrate-inhibition kinetics and there is the optimum CO concentration. Also, severe mass transfer limitation was occurred within several hours after inoculum and the H2 productivity remained constant. The maximum H2 productivity could be linearly correlated with the partial pressure of CO in the feed gas. Using the fermentation data, a kinetic model of the CO fermenation of T. onnurineus NA1 combined with mass transfer characteristics was deri