1. PAPER REVIEW NURHAYATI / 林海亞 N36017011
Topic : Bio-Ethanol Advisor : Prof. Jo-Shu Chang
NURHAYATI / 林海亞 N

2. Due to date: 22 October 2012
Title : Ethanol Fermentation in an Immobilized Cell Reactor Using Saccharomyces
cerevisiae
Authors : Ghasem Najafpour, Habibollah Younesi, Ku Syahidah Ku Ismail
Journal : Bioresources Technology
Year : 2004
Impact Factor :

3. Discussion Experimental Reactor System
The purpose of this study was to obtain high ethanol production with high yield of productivity and to lower the high operating costs.
For continuous ethanol fermentation, an immobilized cell reactor (ICR) was employed in this study using Saccharomyces cerevisiae.
The cell was entrapped by calcium alginate with various concentration (1.5%, 2%, 3% and 6%).
Experimental Reactor System
The picture exhibits the schematic diagram of ICR experimental setup. The ICR was a plug flow tubular column. The fresh feed was pumped in an up-flow manner. Also, a flow breaker was installed between the column and feed pump, which prevented the growth of microorganism and contamination of feed line and feed tank. The experimental setup shows that there was no evidence of cell leakage from the beads to the surrounding media, the matrix was permeable to substrate and product.

4. Discussion Evaluation of Immobilized Cells Batch Fermentation
The physical criteria of the prepared beads are summarized in the table above. Beads with low alginate were too soft and easily breakable. Also, the overgrowth and expansion of beads diameter in sugar/medium solution will occur. Otherwise, the high alginate beads were very hard and almost unbreakable by manual pressing. Because of the rigidity of the beads, diffusion was the most probable cause since ethanol production declined.
Batch Fermentation
This figure depicts glucose concentration, cell density and production of ethanol in batch fermentation with initial concentration of 50 g/L glucose versus time. The aim of batch experiment was to compare the amount of glucose concentration and ethanol production in batch fermentation and immobilized cells reactor (ICR). After 27 h, the sugar consumption and ethanol production obtained were 99.6% and 12.5% v/v, respectively. The maximum cell density was 13.7 g/L. The rate of ethanol productivity for 24 h was 1.4 g/L.h.

5. Discussion Effect of Sugar Concentration
The fermentation was performed with various sugar concentration in order to increase ethanol production. The initial sugar concentrations were 25, 35 and 50 g/L. As presented by this figure, the sugar consumption trends of various glucose concentrations were similar, with a sharp reduction of substrate within the first 3 h of retention time.
Then, conversion of glucose versus dilution rate, used in the continuous fermentation process with immobilized S. cerevisiae is depicted by this figure. The maximum sugar conversion at 6 h retention time was obtained from 74.3%, 80.5%, and 88.2% for 25, 35, and 50 g/L of glucose concentrations, respectively. At a higher sugar concentration, it required a longer retention time to achieve higher conversion.

6. Critical Thinking
Based on this study purpose, to obtain high ethanol production, high yield of productivity, and low cost of operation (include low cost of substrate), the continuous ethanol fermentation was carried out by using immobilized cells reactor. It has several advantages likes, the inhibition of substrate and product were not apparent even with high sugar concentration. Also there was no evidence of cell leakage from the beads to the surrounding media, and the removal of microorganism from downstream product can be omitted and finally the lost of intracellular enzyme activity can be kept to a minimum level.