Dissolved Oxygen (DO)

Definition - What does Dissolved Oxygen (DO) mean?

Dissolved oxygen (DO) is the volume of oxygen in water. Oxygen penetrates water through aquatic biota photosynthesis and oxygen transfer across water-air interference.

An analysis of dissolved oxygen levels can prevent the harmful effects of corrosion such as the destruction of hydrogen film, which forms on almost all metals, as well as rust deposition.

Corrosionpedia explains Dissolved Oxygen (DO)

Dissolved oxygen is the measure of the gaseous oxygen (O2) within an aqueous solution. The amount of oxygen in water depends on factors such as:

  • Temperature
  • Pressure
  • Salinity

Gas solubility elevates along with reduced temperature. This means that colder water can accommodate more oxygen. Moreover, gas solubility elevates along with low salinity, meaning that freshwater can contain more oxygen than saltwater. Both the saturation degree and partial pressure can undergo transformation with altitude. Lastly, gas solubility reduces when pressure decreases. Therefore, oxygen in water decreases along with an increase in altitude due to relative pressure drop.

In boiler systems, dissolved oxygen is dealt with by removing almost all of it through mechanical means and then scavenging what remains through chemical techniques. The mechanical removal is performed with vacuum degasifiers that can make oxygen levels drop below 0.5 to 1.0 mg/L, and via deaerating heaters that can make the concentration of oxygen fall to around 0.005 to 0.010 mg/L. Even the minutest amount of oxygen in a boiler system can be corrosive.

Elimination of oxygen can be accomplished through water treatments by using reducing agents that act as oxygen scavengers. Some of the best examples include sulfite and hydrazine that are broadly utilized for the purpose of removing oxygen in water. However, sulfite should not be used in systems that operate at more than 1000 psi, as breakdown may take place and this leads to the formation of corrosive sulfur dioxide and hydrogen sulfide.

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