Oxygen in natural waters

Another important example of redox titrimetry that finds applications in both public health and environmental analyses is the determination of dissolved oxygen. In natural waters the level of dissolved O2 is important for two reasons it is the most readily available oxidant for the biological oxidation of inorganic and organic pollutants and it is necessary for the support of aquatic life. In wastewater treatment plants, the control of dissolved O2 is essential for the aerobic oxidation of waste materials. If the level of dissolved O2 falls below a critical value, aerobic bacteria are replaced by anaerobic bacteria, and the oxidation of organic waste produces undesirable gases such as CH4 and H2S. 

Raoult s law, but now applied to dilute solutions. It is also apparent that Eq. (22) can be applied to the case where gases are only slightly soluble in a solvent. A classic case is to determine the saturation concentration of oxygen in natural waters and in waste treatment plant effluents. 

Phase equilibria are necessary components for any process that requires separation of materials to take place. Phase equilibria have always been necessary in the design of chemical and petroleum processing plants. They are also important in environmental situations like dissolved oxygen in natural waters and the design of air pollution control equipment. The subject is quite complicated and can only be briefly reviewed in this... 

The difficulties with the COD method as a measure of oxygen demand is that acidified dichromate is such a strong oxidizer that it oxidizes substances that are very slow to consume oxygen in natural waters and that therefore pose no real threat to their oxygen content. In other words, dichromate oxidizes substances that would not be oxidized by O2 in the determination of the BOD. Because of this excess oxidation, namely of stable organic matter such as cellulose to CO2, and ofCU to CI2, the COD value for a water sample as a rule is slightly higher than its BOD. 

From these data, one can conclude that under environmental conditions, phenols are not oxidized rapidly by singlet oxygen in natural waters, but on the other hand, one would not anticipate that phenols would be persistent contaminants like PCBs. It is also of interest to note that the rate constants for both the neutral and anionic (Fig. 6.16) forms correlate well with substituent a constants. 

This procedure is called Winkler method and it is often used to determine dissolved oxygen in natural waters (33). 

In addition, oxygen will usually be present as a depolarizing agent. For the cell to function there must be a difference in potential between the anode and cathode. This difference in potential is mainly due to contact between dissimilar metallic conductors or differences in concentration of the solution, generally related to dissolved oxygen in natural waters. Almost any lack of homogeneity on the metal surface or in its environment may initiate attack by causing a differential in potentials that results in more or less localization of corrosion. 

---