Aeration is the process of taking oxygen from the surrounding air. High BOD in sewage results in high O2 being given in the aeration tank. Aerators are used to artificially provide O2 since this cannot be done naturally. Anaerobic activity begins when the dissolved oxygen level (D.O.) drops below 2 mg/l.
Aeration Methods in Activated Sludge Process There are three methods for aeration in activated sludge process.
1. Diffused air aeration
2. Mechanical aeration
3. Combine aerator
1. Diffused air aeration
Diffusers are used to spread air into the sewage as part of the diffused air aeration process. There are two types of diffusers: Diffusers with plates and tubes.
Plate Diffuser
They are square or rectangle-shaped plates made of high-silica sand or crystalline alumina. This technique involves blowing compressed air through a diffuser with perforated plates. The air escapes through the diffuser plate’s holes and rises in the form of bubbles. As a result, the sewage takes up oxygen from the air.
Tube Diffuser
It comprises of a perforated tube that may be removed for cleaning that is suspended in the waste water near the bottom. The tube is dented with compressed air. Strong air blasts out of the apertures, stirring up the sewage as it does so.
2. Mechanical Aeration
With the aid of some mechanical equipment, the surface of the sewage is vigorously agitated in this way to promote oxygen absorption from the atmosphere. The mechanical aerator comes in two distinct varieties both a horizontal and vertical surface aerator
They are made up of vane-shaped propellers that are powered by electricity and installed on either floating or stationary supports. When they toss the bulk liquid (sewage) through the air, oxygen is transferred to both the surface of the droplets and the surface of the bulk liquid. The currents created by agitation subsequently mix the two surfaces. Ice development during the winter months has a significant impact on this method’s performance.
3. Combine Aerator
This device combines mechanical and diffused air aeration into a single unit. The Dorroco aerator is a popular example of such a combo. Air diffusers and mechanical aerators are both used to aerate sewage. The bottom of the tank has air diffuser plates, and the submerged paddles rotate in the opposite direction from how the compressed air rises from the air diffusers. A motor rotating paddles on a horizontal shaft at 10- to 12-rpm speed.
