Aeration performance

Nonstatic cultures of animal cells are common with agitation and aeration performed as associated operations. These processes, allied to the fact that animal cells do not possess a cell wall, can result in cell damage if they are intense, provoking effects that alter cell metabolism, cell cycle, DNA synthesis, and protein expression, and induce cell death by apoptosis or necrosis. 

DO profile during control. The sensitivity of the DO concentration to load changes is largest in subreactor 3, so DO(3) has been chosen for control. With a discrete time controller supplied with a feed-forward signal from the influent flow rate the total air supply to the four subreactors was controlled to keep DO(3) as constant as possible, fig 9. Even if the regulator is not optimally tuned, the improvement of the aerator performance as seen by the DO profile is significant. 

Glucose conversion is essentially 100%. There is reason to believe that, with the new aerobe, production time might be reduced and cell density increased to, hopefully, 50 g/liter and, perhaps 100 g/liter. The allowable cell density will depend on viscosity restrictions to aeration performance of the new bacterium. 

Previous to our work, no Kj a data in HRS-agitated systems were available, and scepticism about the use of helical impellers in gas-liquid systems was only supported by the argument of their limited capacity of gas dispersion. We have shown, quantitatively, that provided this drawback is compensated with a suitable device, the aeration performance of the HRS is comparable to that observed in remote impellers. Currently, we are continuing oxygen transfer studies in non-Newtonian fluids in vessels equipped with helical ribbon impellers used together with more efficient gas sparging devices. 

Guibert, D., Ben Aim, R., Rabie, H., and Cote, P. (2000). Aeration performance of immersed hoUow-fiber membranes in a bentonite suspension. Desalination 148, 395-400. 

Until recently most industrial scale, and even bench scale, bioreactors of this type were agitated by a set of Rushton turbines having about one-thind the diameter of the bioreactor (43) (Fig. 3). In this system, the air enters into the lower agitator and is dispersed from the back of the impeller blades by gas-fiUed or ventilated cavities (44). The presence of these cavities causes the power drawn by the agitator, ie, the power requited to drive it through the broth, to fall and this has important consequences for the performance of the bioreactor with respect to aeration (35). k a has been related to the power per unit volume, P/ U, in W/m and to the superficial air velocity, in m/s (20), where is the air flow rate per cross-sectional area of bioreactor. This relationship in water is... 

Microorganisms requite several minerals such as ferrous and potassium ions which play important roles in glutamic acid fermentation. Other important culture conditions include regulating aeration stirring. The biosynthesis of L-glutamic acid is performed under regulated aerobic conditions. 

Process performance is affected by temperature. The reaction rate decreases with temperature over a range of 4—31°C. As the temperature decreases, dispersed effluent suspended sohds increase. In one chemical plant in West Virginia, the average effluent suspended sohds was 42 mg/L during the summer and 105 mg/L during the winter. Temperatures above 37°C may result in a dispersed floe and poor settling sludge. It is therefore necessary to maintain aeration basin temperature below 37°C to achieve optimal effluent quahty. 

A few variations on the standard fermenter have been attempted, but none has become popular. An obsolete design in which the fermenter was rotated to aerate the medium is shown in Fig. 24-5. Performance was unsatisfactory, and the units were turned on end, with spargers and agitation added. One of the largest fermenters used for antibiotics is a horizontal cylinder with several agitators, as in Fig. 24-6. Multiple agitator motors and shafts have also been used with vertical cylindiic vessels. 

Bioprocess Control An industrial fermenter is a fairly sophisticated device with control of temperature, aeration rate, and perhaps pH, concentration of dissolved oxygen, or some nutrient concentration. There has been a strong trend to automated data collection and analysis. Analog control is stiU very common, but when a computer is available for on-line data collec tion, it makes sense to use it for control as well. More elaborate measurements are performed with research bioreactors, but each new electrode or assay adds more work, additional costs, and potential headaches. Most of the functional relationships in biotechnology are nonlinear, but this may not hinder control when bioprocess operate over a narrow range of conditions. Furthermore, process control is far advanced beyond the days when the main tools for designing control systems were intended for linear systems. 

Gladysheva, V. P. and Shatalov, A. Ya., Effect of Hydrogen-ion Concentration on the Performance of Differentially Aerated Couples , Izv. Vysshikh. Uchebn. Zavedenii, Khim. i Khim. Tekhnoi., 9, 48 (1966) C.A., 65, 5002a... 

There are in addition several other factors that accelerate corrosion and must betaken into account these include crevices, galvanic coupling, tensile stress, aeration, presence of impurities, surface finish, etc. If these were also taken into consideration then several million experiments would have to be performed to compile such data. There are many instances where two or more chemicals exert a marked synergistic action such that low dissolution rates obtained in either environment become much greater in the presence of both. Further, the corrosiveness of a chemical will be affected by the presence of certain impurities, which may act as either accelerators or inhibitors. To take all these factors into account would add to an already impossible task and as Evans has remarked, There are not enough trained investigators in the world to obtain the empirical information to cover all combinations of conditions likely to arise . Unfortunately corrosion science has not yet reached the stage where prediction, based on a few well established laws, allows selection of materials to be made without recourse to a vast amount of data. 

The growth of cells on a large scale is called industrial fermentation. Industrial fermentation is normally performed in a bioreactor, which controls aeration, pH and temperature. Microorganisms utilise an organic source and produce primary metabolites such as ethanol,... 

The activated sludge process for domestic wastewater treatment was introduced to the world in 1914.1 Since then, many studies have been conducted to improve the oxygen transfer efficiency. Among the aeration devices introduced have been a porous diffuser, a filter type diffuser, a mechanical aeration device, an orifice type diffuser and a fine-pore air diffuser. The aeration market is in a substantial state of flux in the USA today. Emphasis on high efficiency has led many intensive research programmes to aim at the evaluation of the design, operation and control processes to improve overall system performance. 

Modelling oxygen transport in the aeration system is important as it can be used as a reference for overall process performance improvement as well as process design and simulation. The oxygen transfer process mentioned above is based on the concentration gradient between... 

Non-stirred, aerated vessels are used in the process for traditional products such as wine, beer and cheese production. Most of the newly found bioprocesses require microbial growth in an aerated and agitated system. The percentage distribution of aerated and stirred vessels for bioreactor applications is shown in Table 6.1. The performances of various bioreactor systems are compared in Table 6.2. Since these processes are kinetically controlled, transport phenomena are of minor importance. 

BalHca and Ryu [158] correlated reductions in cell yield in Datura stramonium suspensions with the increased Reynolds stresses associated with higher aeration rates in a 1.2-1 ALR. A more recent study [159] of C. roseus suspensions cultivated in a 1.5-1 bubble column showed that the increased bubble sizes associated with both larger sparger pores and higher aeration rates caused a reduction in system performance. Here, also, it was postulated that the effects were due to increased Reynolds shear stresses in the flow field. However, it was not possible to rule out gas-stripping effects. 

Water-soluble root exudates are most frequently collected by immersion of root systems into aerated trap solutions for a defined time period (Fig. 1 A). The technique is easy to perform and permits kinetic studies by repeated measurements over time using the same plants. While it is possible to get a first impression about qualitative exudation patterns and even quantitative changes in response to different preculture conditions, the technique also includes several restrictions that should be taken into account for the interpretation of experimental data. 

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