Oxygen dissolved, in seawater

Ocean Power Supplies. Batteries based on the use of oxygen dissolved in seawater have an advantage over others as all reactants, except for the anode material, are supplied by the seawater. In these batteries a cathode, which is open to the ocean, is spaced around an anode so that the reaction products can fall out into the ocean. Relatively large surface areas are required as there is not much oxygen in seawater. In addition, because of the conductivity of the ocean, there can be no series arrangement of cells. Higher voltages are obtained by the use of a DC-to-DC converter. 

TABLE 1.5 Oxygen Dissolved in Seawater in Equilibrium with a Normal ... 

This equation describes the ratios with which inorganic nutrients dissolved in seawater are converted by photosynthesis into the biomass of "average marine plankton" and oxygen gas 02. The opposite of this reaction is respiration, or the remineralization process by which organic matter is enzymatically oxidized back to inorganic nutrients and water. The atomic ratios (stoichiometry) of this reaction were established by... 

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...

Solutions Seawater is a solution that contains nearly every element found on Earth. Most elements are present in tiny quantities. Sodium and chloride ions are the most common ions in seawater. Several gases, including oxygen, nitrogen, and carbon dioxide, also are dissolved in seawater. 

The main gases dissolved in seawater are nitrogen, oxygen, and carbon dioxide. In well-aerated waters, the concentrations of O2 and CO2 are about 5 x 10 " and 10 mol/L, respectively. 

The solute oxygen content is of primary importance as a component influencing the corrosion behaviour of most metals in seawater. The solute oxygen content can either increase or inhibit corrosion. In nearly neutral aqueous salt solutions, i.e. in seawater as well, the reduction of solute oxidants is the principal cathodic reaction step. The cathodic reaction step in corrosion of metals in seawater is the reduction of the oxygen dissolved in the water as per this formula... 

The content of solute oxygen depends mainly on temperature and salt content. The gases dissolved in seawater do not reach saturation levels by a long shot, not even in areas close to the surface. Table 4 lists the balanced saturation values for oxygen, nitrogen and carbon dioxide at a gas pressure of 101 kPa and at different temperatures and salt contents [9]. 

Zinc, aluminum, or magnesium alloys are being used in reserve batteries using air as the cathode. With aluminum or magnesium, these batteries may be activated with saline electrolytes, and in some underwater application they may use oxygen dissolved in the seawater. Reserve or mechanically rechargeable air batteries, for higher-power applications such as for standby power or electric-vehicle propulsion, use zinc or aluminum alloys with alkaline electrolytes (also see Chapter 38). 

Anodic-stripping voltaimnetry (ASV) is used for the analysis of cations in solution, particularly to detemiine trace heavy metals. It involves pre-concentrating the metals at the electrode surface by reducmg the dissolved metal species in the sample to the zero oxidation state, where they tend to fomi amalgams with Hg. Subsequently, the potential is swept anodically resulting in the dissolution of tire metal species back into solution at their respective fomial potential values. The detemiination step often utilizes a square-wave scan (SWASV), since it increases the rapidity of tlie analysis, avoiding interference from oxygen in solution, and improves the sensitivity. This teclmique has been shown to enable the simultaneous detemiination of four to six trace metals at concentrations down to fractional parts per billion and has found widespread use in seawater analysis. 

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). 

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