Comparative analysis of ethanolic fermentation in two continuous flocculation bioreactors and effect of flocculation additive
✍ Scribed by M. L. Sousa; J. A. Teixeira; M. Mota
- Publisher
- Springer
- Year
- 1994
- Tongue
- English
- Weight
- 709 KB
- Volume
- 11
- Category
- Article
- ISSN
- 1615-7605
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✦ Synopsis
Two types of bioreactor using a flocculating strain of Saccharomyces cerevisiae and continuous ethanolic fermentation as model were compared in terms of start-up evolution, overall performance and power costs. Also, the effect of adding to the medium a polymer -Magna Floc LT25 -that increases floc porosity was studied.
The main difference between the reactors lies on the system that is used to recycle the flocculated cells one presents an external loop with mechanically forced recycling and the other has an airlift configuration with an internal loop.
During start-up of both bioreactors, no significant differences between the fermentation kinetics were established, either with or without Magna Floc. In the airlift bioreactor no positive effect of the dilution rate on substrate uptake was observed. Concerning ethanol productivity, both systems behave in a similar way. The best ethanol productivity, 12. 9 kg/kg/h, was obtained for the airlift system. This value is 7 times higher than in conventional systems and justifies the interest devoted to flocculation bioreactors. The results also indicate that the activity of the cells that are kept inside the airlift bioreactor is higher and compensates its lower cell retention capacity at higher dilution rates. The addition of Magna Floc to the medium causes a reduction on the ethanol yield on glucose for the external loop system, but allows for an increase in the maximal dilution rate for total glucose consumption. Such a behavior is not observed for the airlift system.
The analysis of the power cost associated with the operation of the two bioreactors indicates that the differences between them are only relevant at laboratory and pilot scales. However, from an industrial scale point of view the airlift bioreactor is advantageous because no mechanical parts are involved in recycling.