Kinetics of CO conversion into H2 by Carboxydothermus hydrogenoformans

Abstract

The objective of this study was to improve the biological water-gas shift reaction for producing hydrogen (H 2 ) by conversion of carbon monoxide (CO) using an anaerobic thermophilic pure strain, Carboxydothermus hydrogenoformans. Specific hydrogen production rates and yields were investigated at initial biomass d e n s i t i e sv a r y i n gf r o m5t o2 0m gv o l a t i l es u s p e n d e d solid (VSS) L −1 . Results showed that the gas-liquid mass transfer limits the CO conversion rate at high biomass concentrations. At 100-rpm agitation and at CO partial pressure of 1 atm, the optimal substrate/biomass ratio must exceed 5 mol CO g −1 biomass VSS in order to avoid gasliquid substrate transfer limitation. An average H 2 yield of 94±3% and a specific hydrogen production rate of ca. 3m o lg −1 VSS day −1 were obtained at initial biomass d e n s i t i e sb e t w e e n5a n d8m gV S S −1 . In addition, CO bioconversion kinetics was assessed at CO partial pressure from 0.16 to 2 atm, corresponding to a dissolved CO concentration at 70°C from 0.09 to 1.1 mM. Specific bioactivity was maximal at 3.5 mol CO g −1 VSS day −1 for a dissolved CO concentration of 0.55 mM in the culture. This optimal concentration is higher than with most other hydrogenogenic carboxydotrophic species.

Modeling of syngas biomethanation and catabolic route control in mesophilic and thermophilic mixed microbial consortia

“…Kinetic characterization studies on carboxydotrophic hydrogenogens are very limited. To the best knowledge of the authors, there is only one study reporting kinetic parameters for carboxydotrophic hydrogenogenic growth, corresponding to the species Carboxydothermus hydrogenoformans [19]. The estimated value of µmax,carb_hyd found here was consistent with the range of µmax values 3.07-12.93 d -1 obtained in their study, from where the ks value was originally extracted [19].…”

“…Vega et al [18] modelled the growth of the acetogen Ruminococcus productus on CO using the Andrew model to study the effect of the gas loading rate and the volumetric mass transfer on the conversion rate of CO in stirred tank and bubble column reactors. Similarly, the hydrogenogen Carboxydothermus hydrogenoformans was characterized kinetically to study the effects of the partial pressure of 4 CO (PCO) and the ratio substrate/microbial biomass on the activity of the culture [19]. The growth kinetics of other microbial trophic groups such as hydrogenotrophic and aceticlastic methanogens have also been studied [20,21].…”

Syngas biomethanation: state‐of‐the‐art review and perspectives

“…The productivity of H 2 was then optimized by using this model to determine the optimum dilution rate for the particular process configuration of this reactor. Another hydrogenogen, C. hydrogenoformans , was characterized kinetically using the Han and Levenspiel model in order to study the effects of the P CO and the influence of the ratio of substrate/biomass on the activity of the culture . The growth kinetics of other relevant microbial groups in syngas biomethanation processes such as methanogenic archaea have also been evaluated using a number of kinetic models based on Monod kinetics, the Andrew equation and a modified Gompertz model, among others .…”

“…Another hydrogenogen, C. hydrogenoformans, was characterized kinetically using the Han and Levenspiel model in order to study the eff ects of the P CO and the infl uence of the ratio of substrate/biomass on the activity of the culture. 115 Th e growth kinetics of other relevant microbial groups in syngas biomethanation processes such as methanogenic archaea have also been evaluated using a number of kinetic models based on Monod kinetics, the Andrew equation and a modifi ed Gompertz model, among others. [116][117][118][119] However, the infl uence of the partial pressure of CO on the kinetics of this microbial group has not been determined yet, as most of these studies have been carried out in the frame of anaerobic digestion processes.…”

CO-Dependent H 2 Production by Genetically Engineered Thermococcus onnurineus NA1

“…So far, however, this application has not been reported using carboxydotrophic hydrogenogenic microbes. Over the years, numerous studies have been performed to improve the H 2 productivity from CO with regard to selecting strains resistant to CO toxicity and stimulating CO gas-liquid mass transfer rates (16,20,21). In the present study, a different approach to increase the H 2 productivity was examined.…”