Let's understand the aeration of sewage plant with activated sludge process. Since most of the activated sludge process uses aerobic microorganisms to degrade organic pollutants, the biggest feature of aerobic microorganisms is the great demand for oxygen. They need oxygen to participate in their biological reaction and oxygen to obtain electrons from redox reaction. Therefore, in order to ensure the good growth of these microorganisms, we need to create an oxygen rich environment for them. According to the installation mode of aeration machinery, bottom aeration and surface aeration are commonly used for aeration in sewage plants. Bottom aeration generally refers to installing the aeration device at the bottom of the aeration tank, sending high-pressure gas to the bottom of the aeration tank through blowers, and then escaping into the mixed liquid of the aeration tank;
Surface aeration refers to that the aeration device brings air into the mixed liquid of the aeration tank by stirring the water flow on the water surface of the aeration tank.
In some special occasions, the way of falling water aeration is also used. Through the falling of water flow, the air is dissolved into the water to achieve the purpose of aeration.
No matter which aeration method is adopted, the purpose is to dissolve more oxygen in the water. In the oxygen vertical curve in BOD, we can know that an indicator of water pollution is that the dissolved oxygen of the polluted water body is almost zero. Then, because the sewage treatment plant is treating the polluted domestic sewage, the dissolved oxygen in it is very small. When the sewage with low dissolved oxygen enters the aeration tank of biological reaction and dissolves with the microorganisms in the return sludge, the aerobic microorganisms in the activated sludge need a lot of oxygen to maintain their normal survival and reproduction, and complete their degradation of organic pollutants in the influent. Therefore, they need an oxygen rich environment imposed on the influent by the outside. The design of the aeration tank in the sewage plant is to artificially force oxygen into the sewage to meet the oxygen demand of aerobic microorganisms.