A conventional randomly packed bed reactor of immobilized whole cell has much disadvantages, such as plugging and channeling, to reduce the productivity of a biological reactor.
In this research, a new fixed biofilm reactor has been employed to improve the productivity of the reactor. Saccharomyces cerevisiae was chosen as a microorganism and fixed on the ceramic rods with diameter of 3.7 mm and length of 45 cm. The ceramic rods were coated with gelatin crosslinked by glutaraldehyde and then packed vertically into the column of the reactor with inside diameter of 3 cm and length of 50 cm. The temperature of this fixed-biofilm reactor and feed pH were fixed at 25℃ and 4.0 respectively.
As a basic study, batch and continuous experiments were carried out. In batch experiment, the limiting glucose concentration was 25 g/l and the cell yield from glucose, the product yield from glucose, the product yield from cell were 0.106, 0.38, 3.58 respectively. If the initial substrate concentration presented higher than 33 g/l, the specific growth rate was inhibited.
In the continuous experiment using continuous stirred tank reactor (CSTR), the washout rate was 0.25 $hr^{-1}$, and the maximum productivity was obtained 1.82 g/l/hr at the dilution rate of 0.185 $hr^{-1}$ and the values of maximum specific rate of product formation and maximum growth rate were determined as 0.917 $hr^{-1}$ and 0.278 $hr^{-1}$, respectively.
In the fixed-biofilm reactor, for a given initial concentration of glucose, the production of ethanol changed rapidly with dilution rate in low flow rate region, but slowly in high flow rate region. When the initial concentration was 30 g/l, the maximum productivity was 12.5 g/l/hr which is much higher than 7.4 g/l/hr of others. This higher productivity may be due to reduction of the carbon dioxide hold up. Especially when the initial substrate concentration was 150 g/l, the maximum productivity was obtained 27.5 g/l/hr at the dilution rate of 1.6 $hr^{-1}$.
The value of apparent saturation constant (2.36 g/l) was significantly higher in the fixed-biofilm reactor than the value of 1.73 g/l in the CSTR. This may be explained by the diffusional barrier of glucose due to the production of carbon dioxides is greater in the fixed-biofilm reactor than in the CSTR.
To investigate the tolerance of ethanol, a different initial concentration of ethanol was added to the CSTR and the fixed-biofilm reactor. The result indicated that the fixed-biofilm reactor had a better tolerance for the high ethanol concentration in the fixed-biofilm reactor than in the CSTR.
지금까지 사용되어온 고정화 미생물반응기는 생산성을 감소시키는 plugging이나 channeling과 같은 현상을 유발하기 때문에 본 연구는 이를 개선하기위해 가늘고 긴 ceramic rod를 반응기내에 수직으로 충진한 고정 미생물막 반응기에 대한 연구를 하였다. ceramic rod는 gelatin으로 coating하고 glutaraldehyde에 의해 cell과 crosslinking 되어 있으며, S. cerevisiae를 균주로 사용하였다.
기초 연구로써 회분식 발효 결과, 포도당에 대한 cell yield와 product yield가 각각 0.106, 0.38 이었으며, 초기 포도당 농도가 약33 g/ℓ 이상이면 비생장 속도가 억제되었다.
연속식 발효 결과, Washout 속도는 0.25 $hr^{-1}$이며, 최대 비생장속도와 최대 비생산속도는 각각 0.278 $hr^{-1}$와 0.917 $hr^{-1}$ 이었다.
고정 미생물막 반응기에서 실험한 결과, 초기 포도당 농도가 30g/ℓ일때 최대생산성이 12.5 g/ℓ/hr이었다. 이 값은 다른 실험 결과 보다 약1.5배 높다. 그 이유는 반응기 내의 이산화탄소 holdup이 감소되었기 때문이다. 또한 CSTR에서보다 고정 미생물막 반응기에서 apparent saturation constant가 크게 나왔다. 이것은 이산화탄소의 생성으로 말미암아 포도당의 확산이 장애를 받게 되기 때문이다. 그리고 에탄올에 대한 tolerance가 CSTR에서 보다 훨씬 좋은 것으로 나타났다.
