Oxygen, in water

The strongly electronegative (p. 49) chlorine atom becomes a chloride ion, the proton accepting the electron pair donated by the nitrogen atom. A similar reaction occurs when ammonia is passed into water, but to a much lesser extent as oxygen in water is a poorer donor of the electron pair ... 

The main reason for the importance of aeration Hes in the limited solubiUty of oxygen in water, a value which decreases in the presence of electrolytes and other solutes and as temperature increases. A typical value for the solubiUty of oxygen (the equiUbrium saturation concentration) in water in the presence of air at atmospheric pressure at 25°C is about 0.008 kg 02/m (= Sparts per million = 0.25 mmol/L). Thus, for a yeast or bacterial bioreaction demanding oxygen at the rates given in Table 1, all oxygen is utilized in about 10 to 40 s (3,7). 

Water Treatment. Sodium sulfite is an agent in the reduction of chlorine or oxygen in water. Dissolved oxygen in boiler water tends to enhance pitting and other types of corrosion. In boilers operated at below 4.82 MPa (700 psi), a residual concentration of 30 ppm of sodium sulfite is generally effective. Catalytic amounts of cobalt are often added to accelerate the reaction of oxygen with sulfite (321,322) (see Water, industrial water treatment). 

Oxygen corrosion only occurs on metal surfaces exposed to oxygenated waters. Many commonly used industrial alloys react with dissolved oxygen in water, forming a variety of oxides and hydroxides. However, alloys most seriously affected are cast irons, galvanized steel, and non-stainless steels. Attack occurs in locations where tuberculation also occurs (see Chap. 3). Often, oxygen corrosion is a precursor to tubercle development. 

The solubility of oxygen in water with a salt content up to 1 mol L is only dependent on the temperature. The oxygen concentrations in equilibrium with air amount to (in mg L- ) 0°C, 14 10°C, 11 20°C, 9 and 30°C, 7. The depth of water has no effect in the case of ships. In Hamburg harbor in summer, 7.3 mg L are measured in depths up to 7 m. The value can be much lower in polluted harbors and even fall to zero [8]. In the open sea, constant values are found at depths of up to 20 m. With increasing depth, the Oj content in oceans with low flow rates decreases [12] but hardly changes at all with depth in the North Sea [13]. 

Hydrogen does not appear free in the atmosphere exeept at levels below 1 ppm, sinee rapid diffusivity enables moleeules to eseape the earth s gravitational field and it is eontinuously lost from the atmosphere. It is present in the earth s erust at about 0.87% in eombination with oxygen in water and with earbon and other elements in organie substanees. It is prepared eommereially on a small seale by aetion of sulphurie aeid on zine ... 

BOD Biochemical Oxygen Demand - the rate at which microorganisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic conditions. In decomposition, organic matter serves as food for the bacteria and energy results from this oxidation. 

Figure 9-86. Effect of liquor rate on KLg and Hql for chlorine and oxygen in water. Reproduced by permission of the American Institute of Chemical Engineers, Vivian, J. E. and Whitney, R. R, Chemical Engineering Progress, V. 43 (1947) p. 691 all rights reserved.

It has been shown that pure distilled water is least corrosive when fully aerated and that some inhibitors function better in the presence of oxygen In these cases oxygen acts as a passivator of the anodic areas of the corrosion cells. These facts do not, however, modify the foregoing statements on the significance of oxygen in waters as used in practice. 

The solubility of oxygen in water is influenced by several factors but, generally, most waters contain, at equilibrium, about 8mg/kg at 25°C, although supersaturation may increase this considerably. Some indication of the amount of dissolved oxygen relevant in different situations is shown, on the one hand, by the value of 0-1 mg/kg found in central heating systems and, on the other hand, by the value of 0 005 mg/kg specified by most users of large boilers as the upper limit at the economiser inlet (see Section 5.5). 

The oxygen in water is primarily (99.8%) l60, but water enriched with the heavy isotope, 80 is also available. When an aldehyde or ketone is dissolved in 180-enriched water, the isotopic label becomes incorporated into the carbonyl group. Explain. 

Coppock and Meiklejohn (C9) determined liquid mass-transfer coefficients for the absorption of oxygen in water. The value of k, was observed to vary markedly with variations of bubble velocity, from 0.028 to 0.055 cm/sec for a velocity range from 22 to 28 cm/sec. These results appear to be in general agreement with the results obtained by Datta et al. (D2) and by Guyer and Pfister (G9) for the absorption of carbon dioxide by water. 

The same rate must be found when the rate is expressed as kiAiCfj, where a is the solubility of oxygen in water at 20°C and 1.018 atm. Henry s law... 

FIG. 24 Steady-state diffusion-limited current for the reduction of oxygen in water at an UME approaching a water-DCE (O) and a water-NB (A) interface. The solid lines are the characteristics predicted theoretically for no interfacial kinetic barrier to transfer and for y = 1.2, Aj = 5.5 (top solid curve) or y = 0.58, = 3.8 (bottom solid curve). The lower and upper dashed lines denote the... 

Example Calculate the solubility of oxygen in water at ambient conditions. Assume air-water contact at 20°C (68°F) and sea level (1 atmosphere). 

When the contaminated zone is located below the water table, the availability of oxygen becomes a critical problem due to the low solubility of oxygen in water. In adding the required oxygen, two kinds of systems are usually applied ... 

Subczynski, W. K. and J. S. Hyde. 1984. Diffusion of oxygen in water and hydrocarbons using an electron spin resonance spin-label technique. Biophys. J. 45 743-748. 

The DO mass balance in wastewater of sewer systems is fundamental for the microbial processes. The low solubility of oxygen in water, relatively high resistance to mass transfer across the air-water interface and potentially high removal rate of DO are maj or reasons for the fact that DO is often a limiting factor... 

The first basic aspect is the solubility of oxygen in water and wastewater in equilibrium with an overlaying atmosphere [cf. Henry s law, Equation (4.8), and Example 4.1],... 

Injection of pure oxygen the injection of pure oxygen overcomes some of the problems compared with air. The solubility of pure oxygen in water is compared with oxygen in air increased with a factor of about 5, i.e., it is about 45-50 g02 nr3. Furthermore, the amount of inert gas to be managed is reduced to about nil. The disadvantage is that pure oxygen must be available at the injection point, transported and kept in containers or produced at the site. 

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