What does dissolved oxygen mean?
The molecular oxygen in air dissolved in water is called dissolved oxygen. The content of dissolved oxygen in water is closely related to the partial pressure of oxygen in air and the temperature of water. Under natural conditions, the oxygen content in the air does not change much, so the water temperature is the main factor, the lower the water temperature, the higher the dissolved oxygen content in the water. The molecular form of oxygen dissolved in water is called dissolved oxygen, and is often referred to as DO, expressed in milligrams of oxygen per liter of water. The amount of dissolved oxygen in water is an index to measure the self-purification capacity of water body.
Dissolved oxygen usually comes from two sources: one source is the infiltration of atmospheric oxygen into the water when the dissolved oxygen in the water is not saturated; Another source is oxygen released by plants in the water through photosynthesis. So the dissolved oxygen in the water is constantly replenished by the dissolution of oxygen in the air and by photosynthesis in green aquatic plants. But when the water body is polluted by organic matter, oxygen consumption is serious, the dissolved oxygen can not be replenished in time, the anaerobic bacteria in the water body will soon multiply, and the water body will become black and smelly due to the corruption of organic matter.
Dissolved oxygen literally means the amount of free oxygen in a body of water and is expressed as DO in mg/L. Theoretically, when the value of dissolved oxygen monitored at each point of the aeration tank is slightly greater than 0, oxygenation can be considered to meet the requirements of microorganisms in activated sludge for dissolved oxygen. As for the whole aeration tank, the distribution of dissolved oxygen is different from the demand of dissolved oxygen in each aeration tank area, so in order to conservatively stabilize the demand of dissolved oxygen in the process of decomposition of organic matter or its own metabolism of activated sludge, the dissolved oxygen in the effluent of aeration tank should be controlled within the range of 1~3mg/L theoretically.
Monitoring of dissolved oxygen
Because dissolved oxygen is easily affected by oxygen in the air, temperature, humidity and other factors, so it is often used online testing instrument or portable dissolved oxygen detector for on-site monitoring.
