Water dissolved oxygen concentration

Figure 18.12 Bar graph of N-recycling efficiency as a function of bottom water dissolved oxygen concentration. Bars were based on Chesapeake Bay data reported in Kemp et al. (1990) and Cornwell (unpublished data). Solid dots were based on data from Rysgaard-Petersen et al. (1994) collected from Vilhelmsborg So, Denmark. Terms in the recycling efficiency calculation (y-axis) are Ffjj — flux of N2 from sediments = flux of ammonium from sediments FjsjOj flux of nitrate from sediments.

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). 

Biochemical Oxygen Demand. The biochemical oxygen demand (BOD) test is an empirical determination of the oxygen requirement of a sample. It is most often appHed to wastewaters, industrial effluents, and poHuted waters. The decrease in the dissolved oxygen concentration resulting primarily from biological action is measured after storage for 5 d at 20°C. 

Oxygen corrosion of steel doubles for every 35-55°F (20-30°C) rise in temperature, beginning near room temperature. Corrosion is nearly proportional to temperature up to about 180°F (80°C) in systems open to the air. Although reaction rates increase with temperature, dissolved oxygen is driven from solution as temperatures increase. As temperatures approach boiling, corrosion rates fall to very low values, since dissolved-oxygen concentration also decreases as water temperature rises (Fig. 5.4). 

Many factors influence acid corrosion. Metallurgy, temperature, water turbulence, surface geometry, dissolved oxygen concentration, metal-ion concentration, surface fouling, corrosion-product formation, chemical treatment, and, of course, the kind of acid (oxidizing or nonoxidizing, strong or weak) may markedly alter corrosion. 

The explicit aims of boiler and feed-water treatment are to minimise corrosion, deposit formation, and carryover of boiler water solutes in steam. Corrosion control is sought primarily by adjustment of the pH and dissolved oxygen concentrations. Thus, the cathodic half-cell reactions of the two common corrosion processes are hindered. The pH is brought to a compromise value, usually just above 9 (at 25°C), so that the tendency for metal dissolution is at a practical minimum for both steel and copper alloys. Similarly, by the removal of dissolved oxygen, by a combination of mechanical and chemical means, the scope for the reduction of oxygen to hydroxyl is severely constrained. 

A thin film dissolved oxygen sensor was fabricated by entrapping erythrosin B in a sol-gel matrix95. The silica sol-gel doped with the dye was deposited onto the cleaned glass slides by the spin-coating method. The sensor was linear in the most useful range of dissolved oxygen concentrations, up to 9.1 mg l 1 concentration obtained in air saturated water at 20 °C. 

McCloskey, J.T. and J.T. Oris. 1991. Effect of water temperature and dissolved oxygen concentration on the photo-induced toxicity of anthracene to juvenile bluegill sunfish (Lepomis macrochirus). Aquat. Toxicol. 21 145-156. 

Matos, J.S. and E. R. de Sousa (1996), Prediction of dissolved oxygen concentration along sanitary sewers, Water Sci. Tech., 34(5-6), 525-532. 

The balance between relative rates of aerobic respiration and water movement were considered in Section 4.3.4. We saw that a subsurfece concentration minimum, the oxygen minimum zone (OMZ), is a common characteristic of vertical profiles of dissolved oxygen and is produced by in situ respiration. Waters with O2 concentrations less than 2.0 ppm are termed hypoxic The term anoxic is applied to conditions when O2 is absent. (Some oceanographers use the term suboxic to refer to conditions where O2 concentrations fall below 0.2 ppm but are still detectable.) As illustrated by Figure 4.21b, this water column is hypoxic in the OMZ. The dissolved oxygen concentrations are presented as % saturations in Figure 4.21c. With the exception of the mixed layer, the water column is undersaturated with respect to dissolved oxygen with the most intense undersaturations present in mid-depths. Surface supersaturations are the result of O2 input from photosynthesis and bubble injection. 

Given a concentration, Co, in the overlying water, and a first-order sink of oxygen in the sediments, develop an equation to describe the dissolved oxygen concentration profile in the sediments (see Figure E2.1.1). 

---