Abstract
In a previous research, it has been found that it could be possible to increase the partial pressure of hydrogen and hydrogen yield by scavenging the $CO_2$ from the heads pace of reactor. In this research, the positive and negative effects of the $CO_2$ scavenging especially on the fate of by-products were investigated by a batch experiment. Production and conversion of by-products had critical relationships with hydrogen evolution and consumption. The maximum hydrogen fraction in the headspace was increased from 66.4 to 91.2% by removing the $CO_2$ in the headspace and the degradation rate of glucose was also enhanced. The removal of $CO_2$ effectively hindered the homoacetogenesis but caused several negative phenomena. The degradation of ethanol, one of the main products, was inhibited by the high partial pressure of hydrogen and/or the absence of $CO_2$. Also it was observed that other by-products such as propionate, propanol, acetone, etc. could not be degraded further after produced from glucose. On the other hand, solventogenesis was not observed in spite of the high hydrogen partial pressure apart from previous researches and it might hinder the excess production of acetate, which could cause overall inhibition. From this research, it could be implicated that the $CO_2$ scavenging method could be recommended if the fermentation was purposed to produce hydrogen and ethanol.
Headspace의 이산화탄소 제거는 수소의 수율을 올릴 수 있는 효과적인 방법이지만, 증가된 수소의 분압(최대 91.2%)과 이산화탄소의 부재에 의해 글루코즈의 발효 경향에 상당한 영향을 미치는 것으로 나타났다. 이산화탄소의 제거는 homoacetogenesis에 의한 수소의 소모를 효과적으로 억제하였지만, 주요발효 부산물인 ethanol 및 기타 발효 부산물의 분해 또한 억제하는 결과를 나타내었다. 또한 소량으로 발생한 부산물들의 분석결과에서 이산화탄소가 제거된 반응에서 반응 후반부에 butyrate의 증가하는 현상이 관찰되었다. 하지만, 기존의 연구결과들처럼 증가된 수소의 분압에 의한 과다한 solvent의 생성은 관찰되지 않았으며, acetate의 과도한 발생을 방지할 수 있어 acetate에 의한 저해현상을 다소 억제할 수 있을 것으로 사료된다. 이산화탄소가 제거될 경우 최종 산물이 수소와 ethanol이므로 목적 반응이 hydrogen-ethanol fermentation이라면 이상적인 방향을 제시할 수 있을 것이다.
