Abstract
The successful industrial production of ethanol and fine chemicals requires the development of new biocatalytic reactors and support materials to achieve economically viable processes. In this work, a Stirred-Catalytic-Basket-BioReactor using various immobilizing foams as support material and compared to free cells were used, focusing mainly on; (i) effect of mass-transfer on cells physiology and (ii) ethanol productivity. The performance of the reactor was further evaluated by ethanol volumetric productivity, yield and time for process completion and it was found that the variation of ethanol production and diffusion of the substrate in fermentation process are co-related with the stirrer speed and initial glucose concentration. It was also observed that the time difference for glucose consumption between free and immobilized cells (alginate and sponges) tends to increase by increasing the glucose concentration in the medium. We found that at higher stirrer speed (500 rpm) when using higher glucose concentration (200 g/l), ethanol volumetric productivity increased significantly in the sponge (85 g/l) as compared to alginate beads (79 g/l) and free cells (60 g/l). From the data obtained, it can be concluded that sponges are the best support material for attaining higher ethanol productivity. A stirred catalytic basket bioreactor with yeast cells immobilized in polyethylene sponge gives higher ethanol production at a higher glucose consumption rate, and this productivity is due to higher mixing efficiency and reduced external as well as internal mass transfer limitations. The potentials of the reactor rank it as a remarkable ethanol/fine-chemical production approach that needs further investigations.
Highlights
Air-pollution currently witnessed globally, caused mainly by the extensive usage of fossil fuel has brought about devastating effects both environmentally and health, thereby encouraging extensive scientific research in finding alternative and cheaper bio-fuel like ethanol via microbial fermentation in the bioreactor
For free cells or those immobilized in alginate beads as while as in chemically modified sponges, it can be seen that glucose consumption pattern was more or less the same though the time for consumption of glucose decreases with increase in
We can conclude that the fluid velocity improves the mass transfer of yeast cells immobilized in different matrixes and the magnitude of mass transfer resistance has an inverse relation with stirrer speed
Summary
Air-pollution currently witnessed globally, caused mainly by the extensive usage of fossil fuel has brought about devastating effects both environmentally and health, thereby encouraging extensive scientific research in finding alternative and cheaper bio-fuel like ethanol via microbial fermentation in the bioreactor. The traditional setups used in the ethanol production like membrane bioreactor, airlift bioreactor, fixed bed bioreactors and stirred tank reactors have some drawbacks of less. There are three microbial fermentation processes currently used for ethanol production namely: batch, fed-batch and continuous. In traditional ethanol fermentation technology, freely suspended yeast cells have been used in the batch. Several drawbacks like more fermentation time and low volumetric productivity were found in this technology, and this is due to continuous changes in the external physical factors and biological activity of yeast. Additional most important factor and aim of this study were the need to prepare support material for cell immobilization and further use in newly developed stirred catalytic basket bioreactor (SCBBR) (Fig. 1). Cell immobilization is defined as the localization of intact cells into a defined region of space with the preservation of catalytic activity
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