Aeration

Aeration plays a key role in aerobic fermentations, and often the rate of oxygen transfer from the gas phase sparged into the liquid phase ends up controlling the overall rate of the 

Detailed information on predictive kiU correlations for various bioreactor configurations and in media with different rheologies can be found in the literature [13, 27, 28]. 

A condition typical of heterogeneous flow in a column of diameter (f) is given by the following equation  

Airlift bioreactors are used as an alternative to bubble columns the configuration of the former permits more defined liquid flows, since upward- and downward-moving streams are physically separated. Airlift bioreactors typically allow better mixing than bubble columns, particularly if they are of the external-loop configuration, but at low liquid velocity. 

Heat transfer is a relevant feature of bioreactor operation, although biological reactions do not display high exo- or endothermicity typical of many chemical reactions, nor do they occur at such high temperatures. Nevertheless, the temperatures at which enzyme- or cell-catalyzed reactions (including fermentations) occur have to be controlled under strict limits. Hence, bioreactors incorporate heat transfer surfaces either as external jackets or coils, as internal coils, or as external heat exchangers. These surfaces are used to adjust the temperature of the stream 

The dissolution of a sparingly soluble gas in a liquid is discussed in Volumes 1 and 2, and the reader is referred to the relevant sections (Volume 1, Chapter 10 and Volume 2, Chapter 12) for detailed discussion of the mechanisms involved. In the 

Oxygen consumption rate of yeast at various oxygen concentrations 

The interfacial area per unit volume a is, again, a difficult quantity to measure in a fermenter since it depends on the number and size of the air bubbles entrained in the fermentation broth. These, in turn, are dependent on such factors as the aeration rate, the rheology of the broth at that instant and the presence or otherwise of surfactants. As a result, the quantity KLa tends to be treated as a single entity in experimental measurements of oxygen transfer rates in fermenters. 

The static method of estimating KLa for a fermenter is not always satisfactory. The use of pure water instead of the fermentation medium can lead to inaccuracies, and the deoxygenation of a complex broth with sodium sulphite can result in undefined changes to the broth and be expensive to carry out on a large scale. An 

If during the beginning of the experiment the fermentation is at a quasi-steady state, that is the growth rate is such that the biomass concentration X may be considered to be constant during the experiment, then a material balance for the oxygen gives  

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Bioremediation enhances natural transformation by optimizing the conditions necessary for the process. The process is carried out by organisms capable of degrading the compounds. Both anaerobic and aerobic conditions may be involved in enhancing transformation. Commonly, four possible approaches for bioremediation of hazardous contaminants are employed  

---

Table 11.2 provides a summary of the main features of aerobic and anaerobic wastewater treatment. Aerobic treatment processes are generally restricted to BOD < 1000 mg/liter unless pure oxygen is used for aeration. 

Two molecules of vitamin A are formed from one molecule of -carotene. Vitamin A crystallizes in pale yellow needles m.p. 64 C. It is optically inactive. It is unstable in solution when heated in air, but comparatively stable without aeration. Vitamin A is manufactured by extraction from fish-liver oils and by synthesis from / -ionone. The role of vitamin A in vision seems to be different from its systemic function. See also relincne and rhodopsin. 

In aerated or oxygen saturated solutions, the fullerene triplet lifetime suffers a marked reduction [147, 148]. 

When heated, sodium hydrogencarbonate readily decomposes evolving carbon dioxide, a reaction which leads to its use as baking powder when the carhon dioxide evolved aerates the dough. In the soda-ammonia process the carbon dioxide evolved is used to supplement the main carbon dioxide supply obtained by heating calcium carbonate ... 

Carbon dioxide is used in the manufacture of sodium carbonate by the ammonia-soda process, urea, salicyclic acid (for aspirin), fire extinguishers and aerated water. Lesser amounts are used to transfer heat generated by an atomic reactor to water and so produce steam and electric power, whilst solid carbon dioxide is used as a refrigerant, a mixture of solid carbon dioxide and alcohol providing a good low-temperature bath (195 K) in which reactions can be carried out in the laboratory. 

Before use, the marble chips are washed repeatedly with hot water, and then de-aerated by first etching them with concentrated hydrochloric acid and then boiling them with air-free water under reduced pressure. The chips are then rapidly transferred to the generator small chips should be used and the bulb... 

The relatively concentrated hydrochloric acid is employed so that with ordinary use of the apparatus, spent liquor does not accumulate very rapidly the concentrated acid also ensures a brisk and delicately controlled flow of gas. When the generator is replenished with acid, marble or both, the de-aeration procedure detailed above is repeated until a sufficiently air-free gas supply is obtained. 

It is reported that mild carbon steels may be effectively protected by as little as 55 ppm of KTc04 in aerated distilled water at temperatures up to 250oC. This corrosion protection is limited to closed systems, since technetium is radioative and must be confined. 9sTc has a specific activity of 6.2 X lOs Bq/g. Activity of this level must not be allowed to spread. 99Tc is a contamination hazard and should be handled in a glove box. 

For the aqueous solution Place 16mL of cool distilled water into your bubbler setup. The "expected, not theoretical, yield of Methylamine from this amount of reactants is 7 grams. I have used a plastic aquarium aerator tube as the bubbler with excellent results. Sure beats using an inverted funnel. 

COLORANTSFORFOOD,DRUGS,COSTffiTICSANDTffiDICALDEVICES] (Vol6) -aeration in [AERATION - BIOTECITNOLOGY] (Vol 1)... 

---