Submerged aerators

Aeration may be accomphshed in a variety of ways using different types of equipment including surface aeration, submerged aeration, and falling water unit (1-6). The equipment types are listed below ... 

Submerged Aerators (commonly used in the wastewater and water industries)... 

Horizontally Mixing Aspirator Aerators. An aerator using a horizontally mixing aspirator has a marine propeller, submerged under water, attached to a soHd or a hoUow shaft. The other end of the shaft is out of the water and attached to an electric motor. When the propeller is rotated at high velocity, at either 1800 or 3600 rpm, a pressure drop develops around the propeller. Air is then aspirated under the water and mixed with the water, and moved out. This type of aerator, shown ia Figure 3g, is very efficient ia mixing wastewater. 

Submerged-Culture Generators. Adaptation of the surface-film growth procedure for producing antibiotics to an aerated submerged-culture process has been successful in making vinegar. A mechanical system keeps the bacteria in suspension in the Hquid in the tank, in intimate contact with fine bubbles of air. The excess heat must be removed and the foam, which accumulates at the top of the tank, must be destroyed. 

Submerged culture oxidizers can also be operated on a continuous basis. Continuous monitoring of ethanol and acetic acid concentrations, temperature, and aeration rates permit control of feed and withdrawal streams. Optimum production, however, is achieved by semicontinuous operation because the composition of vinegar desired in the withdrawal stream is so low in ethanol that vigorous bacterial growth is impeded. Bacterial... 

Evaporation. The process of evaporation or distillation in the past was carried out in submerged-tube evaporators. These have been superseded by flash-type evaporators, which are more economical to run and reduce scale problems. The prcKess is suitable for brackish water, where the cost of chemical methods is excessive. The resulting distilled water is not palatable and re quires aeration to make it potable. 

After seeding the nutrient medium with the preformed inoculum previously described, the mixture was subjected to agitation and aeration under aseptic conditions for 72 hours at 27°C to 28°C for the first 24 hours, then at 25°C to 26°C for the next 48 hours during this period, the pH was in the range of 6.4 to 6.8. Aeration was accomplished by cultivation under submerged conditions at an air flow rate of one volume of air per volume of medium per minute. After termination of the process, the mycelium was removed by filtration and the filtered broth found to contain 450 7of oleandomycin per ml of solution. 

B. A second and also successful method accounts to a certain extent for the aeration effect, based on test data from many references. This method is not quite as conservative when estimating total tower pressure. This follows the effective head concept of Hughmark et al. [31]. Effective head, hg, is the sum of the hydrostatic head plus the head to form the bubbles and to force them through the aerated mixture. Figure 8-130 is the correlation for hg plotted against submergence, hji [31]. See Dynamic Liquid Seal. ... 

The entrainment of air in lubricating oil can be brought about by operating conditions (for example, churning) and by bad design such as a return pipe that is not submerged. The air bubbles naturally rise to the surface, and if they do not burst quickly, a blanket of foam will form on the oil surface. Further air escape in thus prevented and the oil becomes aerated. Oil in this condition can have an adverse affect on the system that, in extreme cases, could lead to machine failure. The function of an anti-foam additive is to assist in the burst of air bubbles when they reach the surface of the oil. 

The liquid feed line is known as the submergence limb and the line carrying the aerated mixture as the rising main. The ratio of the submergence (hs) to the total height of rising main above the air injection point (hr + hs) is known as the submergence ratio. + hr/hs)]-K... 

The perceived sensitivity of plant cells to the hydrodynamic stress associated with aeration and agitation conditions is typically attributed to the physical characteristics of the suspended cells, namely their size, the presence of a cell wall, the existence of a large vacuole, and their tendency to aggregate. Table 1 illustrates some of the differences between plant cells and other biological systems. Chalmers [19] attributed shear sensitivity in mammalian cultures at least in part to the fact that these cells occur naturally as part of a tissue, surrounded by other cells. The same is true for plant cells. The more robust microbial systems, on the other hand, exist in nature as single organisms or mycelial structures, very close to the forms they assume in submerged culture. 

Other systems, in which the sprouts are grown in a tank and submerged in water at intervals of several hours, are used often for commercial production of sprouts for food. Light and aeration conditions are not fully uniform in such systems, because inside the sprout mass less light is available. The use of light-inducible promoters clearly demands another kind of sprouting system. 

In our case, sprouting in an effectively aerated water medium was selected as the sprouting method of choice. In our system the sprouts are moving and circulating vigorously with the water flow. Effective aeration is necessary seeds submerged in water without aeration do not sprout and eventually die. Normal tap water or reverse osmosis purified water (RO-water) can be used. 

The cell culture was carried out under the following conditions temperature 30 °C pH 7.0 controlled by the addition of 2 m KOH. The fermenter was aerated at 1 vvm via a submerged sparger and the agitation rate was controlled between 600 and 1000 rpm in order to maintain the dissolved oxygen concentration above 20 % air saturation. Foaming was controlled by addition of antifoam (Mazu DF 204, BASF). 

Although O2 leakage compromises the root s internal aeration, some leakage is desirable for a number of purposes. These include oxidation of toxic products of anaerobic metabolism in submerged soil such as ferrous iron (van Raalte, 1944 Bouldin, 1966 van Mensvoort et al., 1985) nitrification of ammonium to nitrate, there being benefits in mixed nitrate-ammonium nutrition (Kronzucker et al., 1999, 2000) and mobilization of sparingly soluble nutrients such as P (Saleque and Kirk, 1995) and Zn (Kirk and Bajita, 1995) as a result of acidification due to iron oxidation and cation-anion intake imbalance. 

Armstrong W, Beckett PM. 1987. Internal aeration and the development of stelar anoxia in submerged roots. A multishelled mathematical model combining axial diffusion of oxygen in the cortex with radial losses to the stele, the wall layers and the rhizosphere. New Phytologist 105 221-245. 

Kirk GJD. 2003. Rice root properties for internal aeration and efficient nutrient acquisition in submerged soil. New Phytologist 159 185-194. 

Du C, Wu Z, Xiao E et al (2008) Bacterial diversity in activated sludge from a consecutively aerated submerged membrane bioreactor treating domestic waste water. J Environ Sci (China) 20(10) 1210-1217... 

T0715 Smith Technology Corporation, Low-Temperature Thermal Aeration (LTTA) T0755 Supercritical Carbon Dioxide Extraction—General T0817 T-Thermal Company, Submerged Quench Incineration... 

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