Studies were carried out to develop the process for ethanol production using immobilized living whole cell of Saccharomyces cerevisiae SC 4126.
Immobilized yeast cell was prepared by entrapping the low concentration of cell within calcium alginate gels. This immobilized yeast pellet was activated by incubation in complete medium to obtain maximum fermentative activity. The gel incubated for 40 hours was shown that the maximum specific metabolic activity, 0.320 g glucose/ml gel/hr.
To achieve more efficient ethanol production, the performance of packed column reactor and continuous stirred reactor by $CO_2$ gas recycle were compared. As a result, packed column reactor system showed more efficient performance than continuous reactor by $CO_2$ gas recycle. This result was due to mainly decrease the specific metabolic activity of gels by vigorous mixing in continuous stirred reactor system.
Moreover, to design the most efficient packed column reactor for ethanol production, the effect of reactor geometry (H/D ratio) on production of ethanol was investigated. The rate of ethanol production was independent of the column dimension over a range of H/D ratios from 1.6 to 11.9.
During the operation of packed bed reactor, the effect of residence time, substrate concentration on ethanol productivity were investigated. The highest ethanol concentration, 98 g/l could be obtained at a residence time of 3.82 hours in a medium containing 250 g/l glucose. And it was found that 100% of theoretical conversion which could be obtained was a problem of residence time.
In ethanol fermentation substrate as well as product inhibits the rate of ethanol production. The effect of substrate and product was investigated using an immobilized cell differential reactor system. The results represented the typical substrate inhibition mode and the related apparent kinetic constant (Vm, Ks, Kis) were 0.345 g glucose/ml gel/hr, 41.7 g/l, 132.6 g/l respectively. And it was also shown that the inhibition of ethanol is a linear pattern, which ethanol concentration for complete inhibition was 139.3 g/l.
From the profile of system productivity, the maximum productivity obtained was 49.6 g/liter/hr at 100 g/l glucose solution. If we consider the system economics to meet 90% conversion or more, high ethanol concentration and long operational stability, fermentation should be operated at a residence time of 1.86 hr and 150 g/l glucose medium. Under this condition, effluent ethanol concentration, ethanol productivity and operational stability were 70 g/l, 38 g/l/hr and 20 days or more respectively.
Calcium alginate겔에 고정화된 효모, S. cerevisiae (SC 4126) 을 이용하여 효과적인 에탄올 생산공정을 개발하기 위한 방편으로 다음과 같은 실험을 수행하였다.
먼저, 보다 효과적인 에탄올 생산능을 보이는 반응기를 선정하기 위해 충진식 연속반응기와 에탄올 발효시 발생되는 탄산가스를 순환시켜 기질과 효과적으로 반응하게끔 하는 가스 순환식 연속반응기 와의 성능을 비교 검토한 결과 충진식 연속반응기의 성능이 월등히 우수함을 알았고, 또한 보다 효율적인 충진식 연속 반응기의 설계를 위하여 같은 부피의 반응기 이지만 그의 기하학적 비, 즉 높이와 지름의 비가 다른 여러 종류의 반응기를 사용하여 알콜 생산능을 비교 하였다. 그 결과 반응기의 기하학적 비는 에탄올 생성속도 에는 상관없음이 밝혀졌다. 즉, 기질 용액의 유효속도는 에탄올 생성속도와는 무관함을 알수있었다.
여러 종류의 포도당 농도를 주입시키면서 충진식 반응기를 작동시킨 결과 최고 에탄올 농도는 포도당 농도 250 g/ℓ 일때 98 g/ℓ였고 얻어진 최고 생산성은 포도당 농도 100 g/ℓ 에서 49.6 g/ /hr였다. 그리고, 기질과 생성율은 에탄올 생성에 저해작용을 함을 알수 있었는데, 이를 명확하게 밝히기 위해 미분 고정화 균체 반응기 (differential immobilized packed column reactor)를 사용하여 실험하였다. 기질인 포도당은 전형적인 기질 저해 모형을 나타내는데 관련 된 걷보기 상수들은 $K_s = 41.7 g/ℓ$, $V_m = 0.345g glucose/ml gel/hr$, $K_{is} = 132.6 g/ℓ$ 였다. 한편 생성물인 에탄올은 직선 모형으로 저해작용을 하였다.
