Abstract
In this work, effect of the culture medium composition on the fermentation process of Clostridium ljungdahlii, which is acetogenic bacteria to product ethanol from synthesis gas, was examined to improve the microbial growth and ethanol production. Components of the culture medium such as yeast extract, fructose, $NH_4Cl$, and $K_2HPO_4$ were selected as influence factors for the cell growth and ethanol production. As the concentration of yeast extract increased, both of the cell growth and ethanol production increased. And the ethanol productivity was the highest at an yeast extract of 0.05 g/L, which is lower than that of base medium. As the concentration of fructose increased, the cell growth increased, but the ethanol production decreased when the concentration of fructose was higher than that of base medium (5 g/L). In an experiment with the yeast extract of 5 g/L, produced ethanol concentration was the highest (0.297 g/L) when fructose concentration was 5 g/L, however, the specific ethanol productivity was higher (0.281 g/g DCW) when the fructose was not added due to very low cell mass. The cell growth and ethanol production were not significantly influenced by $NH_4Cl$ concentration, however the growth inhibition was observed at a 30 g/L of $NH_4Cl$. When the concentration of $K_2HPO_4$ increased, both of the cell growth and ethanol production increased. In experiments with $NH_4Cl$ and $K_2HPO_4$, specific ethanol productivities were higher when the low concentration of yeast extract was used.
무기탄소원으로부터 에탄올을 생산하는 acetogenic 박테리아인 Clostridium ljungdahlii 발효공정에서 배양 배지 조성에 따른 영향을 분석하여 균주 성장과 에탄올 생산 향상을 시도하였다. 균주 성장 및 에탄올 생산에 영향을 줄 수 있는 배지 구성성분으로 yeast extract, fructose, $NH_4Cl$, $K_2HPO_4$를 선정하였다. Yeast extract 농도가 증가할수록 균주 성장과 에탄올 생산이 증가하였으며 에탄올 비생산성은 yeast extract 기본 배지 농도보다 낮은 0.05 g/L에서 가장 높았다. Fructose 농도가 증가할수록 균주 성장은 증가하였지만 5 g/L을 초과하는 fructose 투입은 에탄올 생산을 감소시켰다. Yeast extract 5 g/L인 조건에서 fructose 5 g/L와 넣었을 때 에탄올 생산농도가 0.297 g/L로 가장 높았으나, fructose를 넣지 않았을 때 매우 낮은 균주 농도로 인해 에탄올 비생산성은 0.281 g/g DCW로 높았다. $NH_4Cl$은 균주 성장이나 에탄올 생산은 큰 차이를 보이지 않았으며 30 g/L 이상 과다 투입하면 성장저해가 나타났다. $K_2HPO_4$에 대해서는 농도가 증가할수록 균주 성장과 에탄올 생산이 모두 증가하였다. $NH_4Cl$과 $K_2HPO_4$를 사용한 경우 에탄올 비생산성은 yeast extract를 적게 사용한 경우 크게 나타났다.
