At present, sewage and industrial wastewater are mostly treated by aerobic microorganisms, and aerobic microorganisms must be decomposed into carbon dioxide, water, and nitrate under aerobic conditions. In the treatment of industrial wastewater by the activated sludge method, the content of dissolved oxygen (free oxygen dissolved in the treated water) is usually measured to adjust the respiration and metabolism of microorganisms, thereby speeding up the purification process. However, the dissolved oxygen content of general industrial wastewater is low, and various aeration devices are often used to aerate to meet the microbial oxygen supply. Dissolved oxygen affects the metabolism and reproduction of microorganisms. Therefore, controlling the content of dissolved oxygen can accelerate the oxidation and decomposition process of organic matter. The activated sludge method to treat industrial wastewater in the aeration zone generally controls dissolved oxygen at (2~4) mg/L, dissolved oxygen Too high or too low will affect the metabolism of microorganisms and reduce the effect of water treatment.

Excessively high dissolved oxygen (greater than 4mg/L) will accelerate the consumption of organic matter in sewage, cause the aging of activated sludge due to lack of nutrients in microorganisms, reduce the flocculation performance and adsorption capacity of activated sludge, and the dissolved oxygen content will be too low (less than 1.5mg/L) will inhibit the life activities of microorganisms, leading to the decay, disintegration and deterioration of microorganisms, which will affect the respiration of microorganisms and the purification ability of activated sludge, and the sludge will float up and decompose and expand.