Seawater dissolved oxygen

Dissolved matter lowers oxygen solubihty. At 20°C and 101.3 kPa (1 atm), the equihbrium concentration of dissolved oxygen in seawater is 7.42 mg/L. It is 9.09 mg/L in chloride-free water and 9.17 mg/L in clean water. This lessening of oxygen solubihty is of importance to wastewater treatment. The solubihty of atmospheric oxygen in a domestic sewage is much less than in distilled water (12). 

Karabashev [469] devised a method to estimate the influence of dissolved oxygen on remote sensing measurements of chlorophyll a in seawater. The relationship between fluorescence and absorption was studied in this investigation. 

The predicted pH is 8.34, a value lying within but toward the alkaline end of the range 7.8 to 8.5 observed in seawater (Fig. 6.1). The dissolved oxygen content predicted by the calculation is 215 qrnol kg-1, or 6.6 mg kg-1. This value compares well with values measured near the ocean surface (Fig. 6.2). 

Let us illustrate this phenomenon with a practical example, the variation of oxygen and of nitrogen equilibrium solubilities with depth in the ocean [1]. For seawater, the density p depends on temperature and salinity, and it could vary from 1.025 to 1.035 g cm. For dissolved oxygen, V2 = 0.97 cm g in seawater at a water temperarnre near 25°C. If d is expressed in meters, then at the lower limit of the water density. Equation (21.17) becomes... 

These membranes have exceptional properties, including seawater salt rejections of up to 99.6 % and fluxes of 23 gal/ft2 day at 800 psi. Unfortunately, they are even more sensitive to oxidants such as chlorine or dissolved oxygen than the polyamide/polyurea interfacial composites. The membranes lose their excellent properties after a few hundred hours of operation unless the feed water is completely free of dissolved chlorine and oxygen. A great deal of work was devoted to stabilizing this membrane, with little success. 

Seawater contains about 3.5% salts, in which the content of sodium chloride is about 80%. The concentration of dissolved salts as well as temperature and pressure influence the physical properties of seawater. The total salt concentration is usually called salinity . Salinity is generally measured by the electrical conductivity or determination of chloride content. At present, salinity(S) is defined as S = 1.80655 Cl (Cl is the concentration of chloride in seawater) [5]. Dissolved oxygen and silica are usually measured as additional parameters to characterize seawater. The concentrations of nitrogen and phosphorus are the indices of nutrients and measure the fertility and production of the oceans. 

Figure 2 Depth profiles of oxygen concentration dissolved in seawater for several latitudes in the Pacific (a) and Atlantic (h). Broad trends of saturation or supersaturation at the surface, high dissolved oxygen demand at mid-depths, and replenishment of O2 through lateral advection of recharged deep water are revealed, although regional infiuences of productivity and intermediate and deep-water heterotropy are also seen (source Ingmanson...

Solution Cathodic protection is widely used to protect immersed metallic structures from corrosion. When this technique is applied, in the range of—0.8 to —1.2 V (SCE), dissolved oxygen from seawater reduces onto metallic surface according to... 

The reaction of 1,1-dimethylhydrazine with dissolved oxygen in water may proceed by a process catalyzed by copper ions or by an uncatalyzed reaction (Baneijee et al. 1984). The products include dimethylnitrosamine, formaldehyde, dimethylamine, and other related chemicals. Dimethylnitrosamine did not form in dilute solutions, which might be encountered in ambient waters, but was reported in concentrated solutions, which could be present in the vicinity of spills (EPA 1984a). The reported half-life of 1,1-dimethylhydrazine in ponds and seawaters ranged from 10 to 14 days, presumably because of reaction with oxygen and other free radicals (EPA 1984a). 

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