Biological treatment methods can be divided into aerobic and anaerobic methods according to the aerobic conditions of the microorganisms involved. Generally speaking, the aerobic method is more suitable for low concentration sewage, such as ethylene plant sewage, while the anaerobic method is more suitable for treating sludge and high concentration sewage. Aerobic biological treatment can be divided into two categories: activated sludge process and biofilm process. Activated sludge process is an artificial strengthening method of water self-purification, and it is a method of removing organic matter from sewage by relying on the main body of activated sludge. Aerobic microorganisms existing in activated sludge must be able to function under conditions of oxygen. In the aeration tank of sewage treatment biochemical system, the aeration efficiency is positively correlated with the growth of aerobic microorganisms. The supply of dissolved oxygen should be considered according to the quantity, physiological characteristics, substrate properties and concentration of aerobic microorganisms. In this way, activated sludge can be in the best state of degradation of organic matter. According to the test results, it is appropriate to maintain the dissolved oxygen in the aeration tank at 3-4 mg/L. If the oxygen supply is insufficient, the performance of activated sludge is poor, resulting in the degradation of wastewater treatment effect. To ensure adequate oxygen supply, we must rely on a device to complete, such as aerator.

Aeration principle

Aeration is a means of making air in strong contact with water. Its purpose is to dissolve oxygen in the air into water, or to release unwanted gases and volatile substances into the air. In other words, it is a means of promoting the exchange of matter between gas and liquid. It also has other important functions, such as mixing and mixing. Oxygen in air is transferred to water through aeration, and oxygen is transferred from gas phase to liquid phase. At present, the theory of mass transfer and diffusion proposed by Lewis and Whitman is widely used.

According to the double-film theory, there are gas and liquid film on the gas-water interface, and air and liquid flow outside the gas film and liquid film, which belong to turbulent state. If the concentration of oxygen in the liquid membrane is lower than the saturated concentration of oxygen in the water, oxygen in the air continues to diffuse inward through the liquid membrane into the water, so the liquid membrane and the gas membrane will become a barrier to oxygen transfer, which is called the double membrane theory. Obviously, the most effective way to overcome the barrier is to change the gas-liquid interface quickly. Aeration stirring is exactly like this, the specific approach is: reduce the size of bubbles, increase the number of bubbles, improve the turbulence of liquid, increase the installation depth of the aerator, prolong the contact time between bubbles and liquid. Aeration equipment is widely used in sewage treatment based on this practice.

Aeration type and function of aerator

There are two types of aeration: one is blowing aeration（fine bubble membrane diffuser）, the other is mechanical aeration. Aeration is aeration by introducing bubble into the water by diffuser or diffuser. Sewage treatment in ethylene plant generally adopts this way. Mechanical aeration means aeration by introducing bubbles into the impeller and other devices.

All aeration equipment should meet the following 3 functions:

(1) To produce and maintain effective gas-water contact, and to maintain a certain dissolved oxygen concentration in water under the condition of continuous consumption of oxygen by biological oxidation;

2. In the aeration zone, there will be enough mixing action and water ring flow.

(3) maintain enough liquid speed to keep the biosolids in water suspended.

More inquiries can be contacted from：

KHN water treatment equipments Co., Ltd.

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Email: sales@khnwatertreatment.com