Process optimization for continuous ethanol fermentation by alginate-immobilized cells of Saccharomyces cerevisiae HAU-1
✍ Scribed by B. S. Yadav; Usha Rani; S. S. Dhamija; Dr. Poonam Nigam; Dalel Singh
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 453 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0233-111X
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✦ Synopsis
Continuous ethanol production by immobilized cells of Saccharomyces cerevisiae HAU-1 has been studied using synthetic and molasses based medium in column reactors. Immobilization of 30% yeast cells biomass (wet) in 1.5% calcium alginate gel resulted in the production of 20.8 g . I-' . h-' alcohol at a dilution rate of 0.36 h-' with approximately 1/3rd volume of the column reactor packed with gel beads. Optimum diameter of the beads was found to be 3.5 mm for efficient fermentation. The size of the column reactor (length to diameter ratio) also affected the productivity and fermentation efficiency due to gas hold-up and mass transfer effects. Molasses could also be fermented by this system but at a lower fermentation efficiency which could be improved, to some extent, by supplementation with nutrients.
Ethanol is one of the major bio-energy sources for organic feed stocks and liquid fuels that can be derived from renewable biomass (DAHIYA et al. 1980, GODIA et al. 1990). In India, production of industrial alcohol from sugarcane molasses using strains of Saccharomyces cerevisiae has been in practice through traditional batch fermentation process. In order to meet the ever increasing demand of ethanol, several approaches for increasing productivity e.g. yeast recycling (SEDHA et al. 1984) application for fed-batch (KOSHIMIZU et al. 1984), strain selection (SHARMA et al. 1980) and continuous fermentation (MURDIYATMO and TEDJOWALIJONO 1987, JAIN and MISHRA 1989) have been adopted.
It has been reported by various workers that immobilization of microbial cells in alginate systems provides an ideal means of biocatalyst recycling ( , SMIDSROD and SKJAEK 1990.
The size of gel beads affects the fermentation because of mass transfer, rate of substrate and product between gel and medium by affecting surface to volume ratio as well as the path length for the diffusion of molecules (CHEETAM et al. 1979). It also affects the mechanical strength, packing behaviour and flow regimes of the medium through the fermentor. Similarly, the dimension and geometry of the reactor and the pattern, density and characteristics of the packing material affected the performance of the system (NUNEZ and LEMA 1987). The problem of CO, adversely affecting the fermentation was also highlighted by QURESHI et al. (1987) and. To overcome this problem, different designs of reactor have been suggested (FANG et al. .
We have conducted studies on the immobilization of S. cerevisiue HAU-1 for continuous production of ethanol using a simple column reactor, whereby high productivity and fermentation efficiency have been obtained. In this communication, we report the effect of some parameters such as bead size, column dimensions and medium composition on ethanol productivity and fermentation efficiency in an immobilized yeast cell reactor.