Analysis of methods and principles for measuring dissolved oxygen
The molecular oxygen contained in the air dissolved in water becomes dissolved oxygen. For industrial wastewater treatment, the indicator of dissolved oxygen is an important data. In different treatment processes, the value of dissolved oxygen needs to be controlled within a certain range. Too low or too high is not conducive to the treatment effect.
For the measurement of dissolved oxygen in water, methods such as iodimetry and membrane electrode method can generally be used.
The principle of using iodimetry to determine dissolved oxygen is to add an appropriate amount of manganese sulfate solution and alkaline potassium iodide solution to the water sample. The dissolved oxygen in the water can rapidly oxidize divalent manganese to tetravalent manganese, while generating precipitates of hydroxides. After adding acid, the precipitate dissolves, and iodine ions are oxidized by tetravalent manganese, releasing free iodine equivalent to dissolved oxygen. Using starch as an indicator, the free iodine released from the reaction is titrated and calibrated with sodium thiosulfate standard solution. After calculation, the content of dissolved oxygen is obtained.
The principle of membrane electrode method is that the electrode used is composed of a box body, which contains two metal electrodes containing electrolytes, and is sealed with a selective thin film. Water and soluble substances will not be able to penetrate this film, but oxygen and some other gases can enter through this film. Put this electrode into wastewater to measure dissolved oxygen. However, substances such as sulfur dioxide, hydrogen sulfide, hydrogen, and carbon dioxide can also penetrate the thin film, affecting the measured dissolved oxygen data.
With the progress and development of technology, the emergence of various dissolved oxygen measuring instruments has provided a faster and more convenient selection method for the determination of dissolved oxygen.
