Fermentors types

Figure 4.5 Fermentor types used in the production of SCP from sugar sources, (a) Stirred baffled system, (b) and (c) air lift systems...

Figure 4.7 fermentor types used In the production of SCP from n-parafflns... 

The raw materials for solid-state fermentation should be sterilized at 121 °C. The sterilization is carried out in situ or in vitro dependent on the fermentor type and scale. In order to enhance the heat transfer in the solid material, the medium pile should not be too tight and direct steam is generally employed. The heating time is in the range 30 - 60 min. For in vitro sterilization, a fixed bed, fluidized bed, rotating drum or belt sterilizer, etc. can be used. 

Fed-batch fermentation process is a production technique between batch and continuous fermentation. A proper medium feed rate is required to add sequentially into the fermentor during the process and the product is harvested at the end of fermentation just like a batch type. 

Protoplast fusion induced by polyethyleneglycol and Ca was carried out between two auxotrophic mutants of Aspergillus sp. CH-Y-1043. The hybrids obtained showed significant differences in endopectinase activity and morphology compared to the prototrophic strain. Strains grown on lemon peel showed production improvement with respect to the parental strain. Since H15 hybrid showed up to 90% higher endopectinase production than the wild type CH-Y-1043, kinetics of enzyme production in Fernbach flasks and Fermentor (14L) by H15 were determined. 

A similar level of automation is found in the biochemical industry. Although the volumes of production of biochemicals are smaller by several orders of magnitude than those of bulk chemicals, companies that operate fermentors and other types of biochemical reactors must still work within... 

Reactions of cell growth or those using immobilized enzymes are instances of gas-liquid-solid reactions. In principle, accordingly, any of the types of reactors described in Section 8.3 could be employed as fermentors. Mostly, however, mechanically agitated tanks are the type adopted. Aeration supplies additional agitation as well as metabolic need, and moreover sweeps away C02 and noxious byproducts. 

Let us consider, as an example, a case of aerobic fermentation. The maximum amount of oxygen that can be absorbed into the unit volume of a fermentation medium at given temperature and pressure (i.e., the equilibrium relationship) is independent of the type and size of vessels used. On the other hand, the rates of oxygen absorption into the medium vary with the type and size of the fermentor and also with its operating conditions, such as the agitator speeds and rates of oxygen supply. 

Stirred-tank reactors can be used for continuous fermentation, because cells can grow in this type of fermentors without their being added to the feed medium. In contrast, if a plug flow reactor is used for continuous fermentation, then it is necessary to add the cells continuously in the feed medium, but this makes the operation more difficult. 

Two major types of fermentors are widely used in industry. The stirred tank, with or without aeration (e.g., air sparging) is most widely used for aerobic and anaerobic fermentations, respectively. The bubble column (tower fermentor) and its modifications, such as airlifts, are used only for aerobic fermentations, especially of a large scale. The important operating variables of the sparged (aerated)... 

Industrial fermentors, as well as pipings, pipe fittings, and valves, and all parts that come into contact with the culture media and sterilized air are usually constructed from stainless steel. All ofthe inside surfaces should be smooth and easily polished in order to help maintain aseptic conditions. All fermentors (other than the glass type) must incorporate glass windows for visual observation. Naturally, all fermentors should have a variety of fluid inlets and outlets, as well as ports for sampling and instrument insertion. Live steam is often used to sterilize the inside surfaces of the fermentor, pipings, fittings, and valves. 

Estimate the stirrer power requirement P for a tank fermentor, 1.8 m in diameter, containing a viscous non-Newtonian broth, of which the consistency index A = 124, flow behavior index n = 0.537, density p = 1050 kg m", stirred by a pitched-blade, turbine-type impeller of diameter d = 0.6 m, with a rotational speed AT of 1 s . ... 

A fermentation broth contained in a batch-operated stirred-tank fermentor, 2.4m in inside diameter D, is equipped with a paddle-type stirrer of diameter (L) of 0.8 m that rotates at a speed Af = 4s -. The broth temperature is maintained at 30 °C with cooling water at 15°C, which flows through a stainless steel helical coil that has a 50 mm outside diameter and is 5 mm thick. The maximum rate of heat evolution by biochemical reactions, plus dissipation of mechanical energy input by the stirrer, is 51000 kcal h , although the rate varies with time. The physical properties of the broth at 30 °C were density p = 1000 kg m " , viscosity p = 0.013 Pa s, specific heat Cp = 0.90 kcal kg °C , and thermal conductivity K = 0.49 kcal h m °C = 0.000136 kcals m °C . ... 

Fermentation broths are suspensions of microbial cells in a culture media. Although we need not consider the enhancement factor E for respiration reactions (as noted above), the physical presence per se of microbial cells in the broth will affect the k a values in bubbling-type fermentors. The rates of oxygen absorption into aqueous suspensions of sterilized yeast cells were measured in (i) an unaerated stirred tank with a known free gas-liquid interfacial area (ii) a bubble column and (iii) an aerated stirred tank [6]. Data acquired with scheme (i) showed that the A l values were only minimally affected by the presence of cells, whereas for schemes (ii) and (iii), the gas holdup and k a values were decreased somewhat with increasing cell concentrations, because of smaller a due to increased bubble sizes. 

Aerated stirred tanks, bubble columns, and airlifts are usually used for aerobic fermentations. One criterion of scaling-up aerated stirred tank fermentor is k a, approximate values of which can be estimated by Equation 7.36a or b. For the turbulent range, a general correlation for k a in aerated stirred fermentors is of the following type [3] ... 

As this trend levels off with larger columns, it is recommended that values estimated for a 60 cm column are used. If heat transfer is a problem, then heat transfer coils within the column, or even an external heat exchanger, may become necessary when operating a large, industrial bubble column-type fermentor. Scale-up of an internal loop airlift-type fermentor can be achieved in the same way as for bubble column-type fermentors for external loop airhfts see Section 7.7. 

Temperature Ihe temperature in a bioreactor is an important parameter in any bioprocess, because all microorganisms and enzymes have an optimal temperature at which they function most efficiently. For example, optimal temperature for cell growth is 37 °C for Escherichia coli and 30 °C for Saccharomyces sp, respectively. Although there are many types of devices for temperature measurements, metal-resistance thermometers or thermistor thermometers are used most often for bioprocess instrumentation. The data of temperature is sufficiently reliable and mainly used for the temperature control of bioreactors and for the estimation of the heat generation in a large-scale aerobic fermentor such as in yeast production or in industrial beer fermentation. 

The second type of semibatch reactor is when some material is removed from the reactor during the batch. The material is typically one of the products of the reaction. A common example is in fermentors producing ethanol in which the byproduct carbon dioxide is vented off during the batch cycle. 

One of the most important biochemical reactors is the fermentor. We provided a simple example of a batch fermentor in Chapter 4. But there are many other types including continuous, batch, and fed-batch. There are some other useful references in the literature.16-17... 

Fermentation generates heat, and red wines must have some type of temperature control during their fermentation. They must not be allowed to get too hot or to become too cold. Ough and Amerine (18) recommended temperatures of 18°-29° C and found that cap temperatures can exceed liquid temperatures by over 6° C. In large stainless steel fermentors, the author has noted cap-liquid temperature differences of 11°. 

The final system, shown in Figure 30.4D, is the continuous system with a partial (PRF) or complete (RF) cell recycle. It is similar to the continuous system, but cells are returned to the fermentor by means of a biomass separation device. Cross-filtration units, centrifuges, and settling tanks have all been used for biomass separation.22 In the partial cell recycle fermentor, a steady state is achieved as in the continuous system. This process is typically used to increase the productivity of the system and is used commonly in wastewater treatment and ethanol production type applications. 

Yokoi, H Koga, J., Yamamura, K., Seike, Y., and Tanaka, H. (1993). High density cultivation of plant cells in a new aeration-agitation type fermentor, Maxblend Fermentor. J. Ferment. Bioeng. 75,48-52. 

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