Modern Industrial Microbiology and Biotechnology

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Fermentors and Fermentor Operation 197Fluidized Bed Fermentor (FB)Fig. 9.6Different Fermentor Configurations (Left) and Graphs Depicting Substrate Usage in the VariousConfigurations (Left) (see also Fig. 9.7)
198 Modern Industrial Microbiology and BiotechnologyThese advantages when adapted to the microbiological industries, potentially includethe following:(i) More intensive use of the equipment, especially the fermentor, and therefore greaterreturn on the initial capital outlay made in installing them. A great deal of timeinvolved in the cycle of batch production is not employed in direct production ofthe final goods. Part of such ‘dead’ time is used in emptying the batch fermentorduring harvest, for cleaning, sterilizing, cooling and recharging with freshmedium in between each batch. Furthermore, much of the period of a batchfermentation is required for a lag period when the organisms are merely growingand not yet producing (where the product is a metabolite), or the maximumpopulation has not been attained (where the product is the cell itself). In acontinuous fermentation, as soon as the steady state has been attained andprovided no contaminations occur, and other production activities permit theplant to run for a reasonably long time, the ‘dead’ time required for all the above iseliminated.(ii) Allied to the above are savings in labor which do not have to repeatedly performthe various operations linked with the ‘unproductive’ portions of batchfermentation.(iii) Continuous processes are more easily automated. This helps eliminate humanerror and thus ensures greater uniformity in the quality of the products.Automation also further saves labor costs additional to those mentioned in (ii).Despite the possible advantages of continuous fermentation, the fermentationindustry has not in general adopted it. The areas where it has been employed include beerbrewing, food and feed yeast production, vinegar manufacture, and sewage treatment.The reasons for the slow adoption of continuous fermentation since interest developedin it several decades ago, are to be found in technical and economic factors. One of theearly deterrents was the fact that many early continuous fermentations became easilycontaminated. It is easy to see that while slow growing contaminants might not havedeveloped to the point where they can be noticed in the 4, 5, or 10 days of a batchfermentation they can pose a serious threat to production, in a continuous culture whichgoes on for up to three, six, or nine months. If the contaminant is fast growing then thedanger while serious in a batch fermentation is infinitely more so in a continuousfermentation. Another problem was that mutants better adapted to the environment of thecontinuous fermentor are easily selected. Where they perform better than the parent typethe difference was hardly noticed, except perhaps that a particular continuousfermentation was inbued with an apparently inexplicable efficiency. On the other hand,where the mutants were less productive, the reputation of continuous fermentation wasnot helped.9.4.1.1 Theory of continuous fermentationIn a batch culture four or five phases of growth are well recognized: the lag phase, thephase of exponential or logarithmic growth, the stationary phase, the death or declinephase. Some others add the survival phase. In the lag phase individual cells increasesomewhat in size but there is no substantial increase in the size of the population. In the
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Modern IndustrialMicrobiology and B
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DedicationThis book is dedicated to
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PrefaceThe field of industrial micr
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ContentsixContentsPrefaceviiSECTION
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Contentsxi5.6 Carbon Pathways for t
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Contentsxiii10.3 Purification 21710
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Contentsxv16.5 Yeast Products 314Su
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Contentsxvii21.2 Methods for the Ma
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Contentsxix26.3.2 Fermentation cond
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Modern Industrial Microbiology and Biotechnology

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