Fermentation vessels cleaning

Pipework systems, valves and vent filters should be properly designed to facilitate cleaning and sterilization. The use of clean in place and sterilize in place systems should be encouraged. Valves on fermentation vessels should be completely steam sterilizable. Air vent filters should be hydrophobic and validated for their scheduled lifespan. 

Typical units for productivity are kg m h Factors that influence productivity include the production time of the fermentation, tire time required to clean and set up the reactor, the sterilisation time and the length of the lag phase of growth. Figure 2.2 shows how total productivity and maximal productivity can be calculated for a batch fermentation. The decision as to when Ae fermentation is terminated (maximum or total productivity) depends on the operating costs, which include the capacity of the fermentation vessel, energy costs and labour costs. 

An unusual extraction procedure is shown in Scheme 6 for the purification of soraphen Aj from a myxobacterium. An adsorbent resin was added to a large-scale fermentation vessel prior to inoculation so that the metabolite was continuously adsorbed as it was produced. Not only did this simplify the isolation, but it also resulted in increased production of the compound by the organism, possibly because adsorbent effectively removed metabolite from the system, thus reducing any feedback inhibition. The eluate from the resin was sufficiently clean that it required only solvent extraction prior to a crystallization step that yielded reasonably pure soraphen A[ (8). 

Fermentation vessels are usually 2-6 m (6 5-18 6 ft) deep, although deeper ones are used successfully. The material of construction should present an internal surface which is smooth, easy to clean, and hard to scratch or pit. It must not corrode, be subject to electrolysis, release toxic material, or deform. It should be chemically inert to wort, beer and to cleansing and sterilizing solutions. Expensive or deformable materials which are otherwise suitable for vessel construction are often used as liners for less expensive or more durable materials (Tables 19.1 and 19.2). 

Fig, 21.6 Rotary cleaning jet equipment for top-entry fermenting vessels and road tankers. 

Lime-Sulfuric. Recovery of citric acid by calcium salt precipitation is shown in Figure 3. Although the chemistry is straightforward, the engineering principles, separation techniques, and unit operations employed result in a complex commercial process. The fermentation broth, which has been separated from the insoluble biomass, is treated with a calcium hydroxide (lime) slurry to precipitate calcium citrate. After sufficient reaction time, the calcium citrate slurry is filtered and the filter cake washed free of soluble impurities. The clean calcium citrate cake is reslurried and acidified with sulfuric acid, converting the calcium citrate to soluble citric acid and insoluble calcium sulfate. Both the calcium citrate and calcium sulfate reactions are generally performed in agitated reaction vessels made of 316 stainless steel and filtered on commercially available filtration equipment. 

A vertical cylindrical, and mechanical agitated pressure vessel, equipped with baffles to prevent vortex formation is the most widely used fermenter configuration. The baffles are typically one-tenth of the fermenter diameter in widtli, and are welded to supports tliat extend from the sidewall. A small space between the sidewall and the baffle enables cleaning. Internal heat transfer tube bundles can also be used as baffles. The vessels must withstand a 45 psig internal pressure and full vacuum of -14.7 psig, and comply with the ASME code. 

As you might have already gathered, the majority of industrial fermentations are batch processes. In closed batch systems, the growth medium is inoculated with cells and growth and product formation is allowed to proceed until the required amount of conversion has taken place. After harvesting the culture the vessel is cleaned, sterilised and filled with fresh medium prior to inoculation. For some processes, addition of all the feedstock prior to inoculation, as is done in closed batch fermentations, is undesirable and it is preferable to incrementally add the carbon source as the fermentation proceeds. Such a process is known as fed-batch culture and the approach is often used to extend the lifetime of batch cultures and thus product yields fed-batch cultures are considered further in Section 2.7.4. 

Figure 4.11. a so liter bench fermenter that can be scaled for production of recombinant proteins. The bench-top scale configuration contains all the control valves and ports necessary to monitor and control cell cultivation while maintaining sterility of the culture. The stainless steal reaction vessel allows easy cleaning and permits heat and pressure sterilization in place by connecting the vessel to a steam supply. (New Brunswick Bioflo-4500, adapted from the manufacturer s literature with permission)... 

If you are not satisfied with an alcohol strength of 35-40% another procedure can be followed. Distil a good 8 litres measure of mash as usual but wait until you have 4 litres of spirit instead of three. Repeat this with the rest of the mash. After this you are left with 12 litres of weak spirit. Clean out the apparatus and distil the 12 litres you have just distilled. Now you have a higher strength and a more pure spirit. It is possible to get out 7-8 litres of 50% spirit. You will now have a remaining 10% of spirit in the 10-litre vessel, which you can add to the next batch of mash (after it has finished fermenting). 

Fermenter contaminated[ [inoculum tank contaminated] /inoculum line con-taminated/procedure wrong/tank dirty/air leak/leak from the coil or jacket/faulty sensors/antifoam is not sterile/dirty gaskets, bottom valve, sample line and valve, vent line valve, vacuum breaker/nutrient feed tank or line not sterile/all lines wee not up to sterilization temperature/steam condensate left in lines/the humidity of the fermenter air upstream of the sterile filter is > 90%/pH and DO probes were not deaned between runs/probe holders were not brushed and deaned with a hypochlorite or formaldehyde solution/for a previously contaminated vessel the valves and gaskets were not replaced, instrument sensors were not removed and cleaned high boiling germicide, such as sodium carbonate or sodium phosphate was not used. 

Enclosed vessels are more easily cleaned by in-place methods and indeed some open vessels are covered temporarily by a light metal or plastic canopy, in order to clean them in-place. Again fermentations in enclosed vessels are less likely to become infected by air-borne or water spray-borne microorganisms. The advantages of open vessels are that they are somewhat less expensive, are easier to clean manually, and permit easier dipping of the vessel to judge the volume of wort present. The latter procedure is required by Excise authorities in Britain unless the volume of wort is measured in a collecting vessel used specially for this purpose. 

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