| Summary: | 碩士 === 逢甲大學 === 化學工程學所 === 92 === Abstract
Recently the increasing emission of air pollutants such as: CO2, CO, NOx ,and SOx cause the green house effect in global atmosphere due to the massive usage of fossil fuels. The consumption rate of fossil fuels is also exponentially increased that may induce the shortage of energy source in the recent future. To develop a clean and new energy source will become one of the important subjects in the future. Biohydrogen has a great potential to act as an alternate with a cheap, clean and sustainable energy source. It may be the solution that not only reduces environmental pollutions, but also achieves source usage recycling.
In this study, different conditions were investigated for the processes of biohydrogen production. The thermophilic bacterium was screened from sewage sludge for the dark fermentation of hydrogen production in several temperatures. First, the sludge was used for hydrogen production without acid and heat pretreatment. The result was found that the optimization hydrogen production rate is 0.26 L/h/L at a hydraulic retention time (HRT) of 6 h. with 50℃ temperature in a CSTR system. Second, the process was carried out in a continuous decrease of temperature from 50℃, 45℃, 40℃, and 35℃ with one hour heat pretreatment of the sludge at 70℃ in one bioreactor. The hydrogen production rate was performed in the order of 45℃ > 40℃ > 35℃ > 50℃. The highest hydrogen production rate was 0.77 L/h/L at 45℃ with HRT=4h. .
The hydrogen bacterium became spore-form in its growth when temperature is unsuitable in the above continuous decrease of temperature process. The other process was studied that bioreactors were investigated in separated temperature at 50℃, 45℃, 40℃, and 35℃ for each bioreactor. The highest hydrogen production rate 0.77 L/h/L and hydrogen production yield 3.65 mol H2/mol sucrose were obtained at 40℃ with HRT=4h. . The hydrogen production performance in this process was in the order of 40℃ > 35℃ > 45℃ > 50℃.
The metabolic pathway of microorganisms were greatly influenced by temperature effects. The hydrogen production performance was demonstrated to be related to the liquid metabolites of the pathway. When the liquid metabolite was ethanol oriented fermentation, the poorer hydrogen production performance was obtained. However, the major components of acetic acid and butyric acid were found in the liquid metabolites of the above process at 40℃., the better hydrogen production performance was resulted.
The phenomenon of wash out of the bacterium was occurred in the CSTR system at low HRT process. The activated charcoal (AC) powder was added in the bioreactor to improve the situation. The flocculation of microorganism was induced as a microfilm in the surface of AC. Both hydrogen production rate and hydrogen production yield were enhanced to 1.24 L/h/L and 3.97 mol H2/mol sucrose, respectively, at 40℃ with HRT=4h. and stirring speed=105rpm. The substrate conversion was almost completed in 98.1%.
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