Process, absorption aerobic

The function of aeration in a wastewater treatment system is to maintain an aerobic condition. Water, upon exposure to air, tends to estabUsh an equihbrium concentration of dissolved oxygen (DO). Oxygen absorption is controlled by gas solubiUty and diffusion at the gas—hquid interface. Mechanical or artificial aeration may be utilised to speed up this process. Agitating the water, creating drops or a thin layer, or bubbling air through water speeds up absorption because each increases the surface area at the interface. 

Gas/liquid contacting is frequently encountered in chemical reaction and bioprocess engineering. For reactions in gas/liquid systems (oxidation, hydrogenation, chlorination, and so on) and aerobic fermentation processes (including biological waste water treatment), the gaseous reaction partner must first be dissolved in the liquid. In order to increase its absorption rate, the gas must be dispersed into fine bubbles in the liquid. A fast rotating stirrer (e.g. a turbine stirrer), to which the gas is supplied from below, is normally used for this purpose (see the sketch in Fig. 34). 

A second very important eukaryotic organelle is the mitochondrion, which, like the nucleus, has a double membrane (Figure 1.13). The outer membrane has a fairly smooth surface, but the inner membrane exhibits many folds called cristae. The space within the inner membrane is called the matrix. Oxidation processes that occur in mitochondria yield energy for the cell. Most of the enzymes responsible for these important reactions are associated with the inner mitochondrial membrane. Other enzymes needed for oxidation reactions, as well as DNA that differs from that found in the nucleus, are found in the internal mitochondrial matrix. Mitochondria also contain ribosomes similar to those found in bacteria. Mitochondria are approximately the size of many bacteria, typically about 1 pm in diameter and 2 to 8 pm in length. In theory, they may have arisen from the absorption of aerobic bacteria by larger host cells. 

Mechanically agitated gas-liquid contactors are widely used in industrial processes for absorption, stripping, oxidation, hydrogenation, chlorination, carbony-lation, fermentation, and so on. They are also used for carrying out biochemical processes such as aerobic fermentation, manufacture of protein, and wastewater treatment. The fractional hold-up of gas (([)) in these contactors is a basic measure of their efficiency. The hold-up in conjunction with Sauter mean bubble diameter (d32) determines the interfacial area (i.e., a = 6ct)/d32) and hence the mass transfer rate. Knowledge of cj) also gives the residence time of each phase. 

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