Hydrogen (H2) is attracting much attention as a future energy carrier and environmentally friendly fuel. Most H2 production is currently manufactured by steam reforming process of natural gas or petroleum based on fossil fuels. However, this process is causing some problems such as environmental pol...
Hydrogen (H2) is attracting much attention as a future energy carrier and environmentally friendly fuel. Most H2 production is currently manufactured by steam reforming process of natural gas or petroleum based on fossil fuels. However, this process is causing some problems such as environmental pollution and exhaustion of limited fuel reserves. Therefore, the demand for H2 production from renewable, sustainable and environmentally friendly sources has been increasing and biological H2 production could be a solution to meet the needs. The purpose of this study was to demonstrate H2 production potentials of Thermococcus onnurineus NA1 using C1 compounds such as carbon monoxide (CO), formate, and to optimize culture conditions for enhancing its H2 productivity. In Chapter 1, literatures for overall H2 production by microbes were summarized. In Chapter 2, a hyperthermophilic archaeon T. onnurineus NA1 was investigated based on the analysis of its genome have shown the metabolic potential to grow with CO and/or formate as the substrate. The experimental results revealed that T. onnurineus NA1 can grow and produce H2 using CO, formate or starch as substrate. The H2 production by T. onnurineus NA1 at each substrate was closely associated with its cell growth. The H2 yield (mol H2 per mol substrate) on CO, formate and starch was calculated to be 0.98, 1 and 3.13, respectively. In Chapter 3, the culture conditions were investigated for enhancing H2 production from formate in batch experiments. As a result, the salinity and sodium formate concentration were crucial factors for cell growth and H2 production by T. onnurineus NA1. Salinity condition between 3.7 and 4.6%, 400 mM sodium formate was found to be an optimal initial concentration for cell growth and H2 production. H2 production rate of T. onnurineus NA1 in optimal conditions on sodium formate showed linearly increased with increasing cell density and average specific H2 production rate was detected to 404 ± 6 mmol g-1 L-1. This suggests that high cell density culture of T. onnurineus NA1 is important to enhance H2 production from sodium formate. Therefore, to sustain high cell density cultivation, the repeated batch culture with cell recycling was conducted in 3 L and 30 L bioreactor under the optimum condition. The cell density and volumetric H2 production rate were enhanced up to 1.7 (OD600) and 235.7 mmol L-1 h-1, respectively. Cell immobilization of T. onnurineus NA1 was also investigated for improving cultivation process. As a result, T. onnurineus NA1 was immobilized to amine-coated silica particle, showing maximum cell adsorption capacity of 71.7 mg-dried cell weight per g-particle. From repeated batch experiments, immobilization of T. onnurineus NA1 was demonstrated to be feasible for H2 production. Lastly, in Chapter 4, it was focused on the improvement of H2 production by T. onnurineus NA1 from CO. In batch experiments, key parameters on cell growth and H2 production of T. onnurineus NA1 showed the linear correlation with increased mass transfer coefficient (KLa). In addition, T. onnurineus NA1 showed that the ability of H2 production using waste gas generated from the steel industry indicating the waste gas to be a potential substrate. However, the production was inhibited by high CO supply condition (0.48 vvm, 900 rpm) with KLaair of 148 h-1. Based on the results of batch culture, the continuous culture operated for H2 production from CO. As a result, it revealed that the CO mass transfer rate and liquid-feeding rate were key parameters for operating continuous cultivation system using T. onnurineus NA1. The maximum H2 production rate of 121.6 mmol L-1 h-1 was obtained at a continuous culture system using CO. The study showed key parameters and optimal culture conditions for H2 production by T. onnurineus NA1 using sodium formate or CO. Moreover, it found that T. onnurineus NA1 has higher H2 productivity in compared with other H2-producing microbes (Table 5.1).
Hydrogen (H2) is attracting much attention as a future energy carrier and environmentally friendly fuel. Most H2 production is currently manufactured by steam reforming process of natural gas or petroleum based on fossil fuels. However, this process is causing some problems such as environmental pollution and exhaustion of limited fuel reserves. Therefore, the demand for H2 production from renewable, sustainable and environmentally friendly sources has been increasing and biological H2 production could be a solution to meet the needs. The purpose of this study was to demonstrate H2 production potentials of Thermococcus onnurineus NA1 using C1 compounds such as carbon monoxide (CO), formate, and to optimize culture conditions for enhancing its H2 productivity. In Chapter 1, literatures for overall H2 production by microbes were summarized. In Chapter 2, a hyperthermophilic archaeon T. onnurineus NA1 was investigated based on the analysis of its genome have shown the metabolic potential to grow with CO and/or formate as the substrate. The experimental results revealed that T. onnurineus NA1 can grow and produce H2 using CO, formate or starch as substrate. The H2 production by T. onnurineus NA1 at each substrate was closely associated with its cell growth. The H2 yield (mol H2 per mol substrate) on CO, formate and starch was calculated to be 0.98, 1 and 3.13, respectively. In Chapter 3, the culture conditions were investigated for enhancing H2 production from formate in batch experiments. As a result, the salinity and sodium formate concentration were crucial factors for cell growth and H2 production by T. onnurineus NA1. Salinity condition between 3.7 and 4.6%, 400 mM sodium formate was found to be an optimal initial concentration for cell growth and H2 production. H2 production rate of T. onnurineus NA1 in optimal conditions on sodium formate showed linearly increased with increasing cell density and average specific H2 production rate was detected to 404 ± 6 mmol g-1 L-1. This suggests that high cell density culture of T. onnurineus NA1 is important to enhance H2 production from sodium formate. Therefore, to sustain high cell density cultivation, the repeated batch culture with cell recycling was conducted in 3 L and 30 L bioreactor under the optimum condition. The cell density and volumetric H2 production rate were enhanced up to 1.7 (OD600) and 235.7 mmol L-1 h-1, respectively. Cell immobilization of T. onnurineus NA1 was also investigated for improving cultivation process. As a result, T. onnurineus NA1 was immobilized to amine-coated silica particle, showing maximum cell adsorption capacity of 71.7 mg-dried cell weight per g-particle. From repeated batch experiments, immobilization of T. onnurineus NA1 was demonstrated to be feasible for H2 production. Lastly, in Chapter 4, it was focused on the improvement of H2 production by T. onnurineus NA1 from CO. In batch experiments, key parameters on cell growth and H2 production of T. onnurineus NA1 showed the linear correlation with increased mass transfer coefficient (KLa). In addition, T. onnurineus NA1 showed that the ability of H2 production using waste gas generated from the steel industry indicating the waste gas to be a potential substrate. However, the production was inhibited by high CO supply condition (0.48 vvm, 900 rpm) with KLaair of 148 h-1. Based on the results of batch culture, the continuous culture operated for H2 production from CO. As a result, it revealed that the CO mass transfer rate and liquid-feeding rate were key parameters for operating continuous cultivation system using T. onnurineus NA1. The maximum H2 production rate of 121.6 mmol L-1 h-1 was obtained at a continuous culture system using CO. The study showed key parameters and optimal culture conditions for H2 production by T. onnurineus NA1 using sodium formate or CO. Moreover, it found that T. onnurineus NA1 has higher H2 productivity in compared with other H2-producing microbes (Table 5.1).
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#Biohydrogen production hyperthermophilic archaeon C1 compounds
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