How Many Types of Aeration System in STP Plant?

The functioning of Sewage treatment plants is very important in the sense that they are used to remove pollutants from wastewater and discharge it back. But the most significant step in the treatment process is aeration, which involves spraying or injecting air in the wastewater. The oxygen provided assists bacteria in digesting the waste materials making the water cleaner. There are various aeration systems that apply in sewage treatment plants All these systems are meant to aerate in particular ways. In this blog let us discuss about various types of aeration systems, which are installed in STPs and their operation.

Various types of aeration systems used in sewage treatment plants

These are the following types of aeration systems commonly used in STPs and all of them serve to have their benefits.

a) Diffused Aeration System

The diffused aeration system involves the infusing of air into the water through the use of diffusers which is in the form of fine bubbles. These diffusers are placed at the bottom of the tank and blows air in the form of bubbles. The small bubbles move slowly upward and thus disperse oxygen within the water body.

Advantages of Diffused Aeration:

· It ensures distribution of oxygen in water is evenly distributed since water is comparatively more dense than the air.

· Smaller bubbles in the foam provide better distribution and enhance the efficiency of oxygen transfer.

· It must be noted that this system is somewhat energy efficient with respect to some other types.

Limitations:

· It may cost more since the process involved requires complex equipment such as air blowers and diffusers among others.

· Clogs the diffusers often and hence needs frequent cleaning.

b) Surface Aeration System

Surface aeration systems act in such a way that forces the surface water in contact with fresh air. To mix the surface of the water, such as with a motorized rotor, or paddle wheel type. This stirring action help to bring more water nearer to the surface and lets in oxygen.

Advantages of Surface Aeration:

· Easy to operate and its installation is also easy.

· Compared to diffused aeration methods, it is cost effective to implement as well.

· Quite capable of holding relatively significant quantities of water.

Limitations:

· It offers less efficient form of oxygen exchange relative to diffused systems.

· It could be less efficient in deeper tanks because oxygen is required in the lower part of the tank.

· The system can use more energy, leading to higher operational costs.

c) Mechanical Aeration System

In a mechanical aeration system, machines are used to physically mix water with air. These machines, called aerators, can either float on the water’s surface or be submerged. They move water around, creating turbulence that helps oxygen dissolve into the water. Mechanical aerators come in different designs, such as floating aerators, brush aerators, or turbine aerators.

Advantages of Mechanical Aeration:

· It’s effective in shallow tanks.

· Mechanical aerators are powerful and can treat high loads of wastewater.

· Simple operation and easy to maintain.

Limitations:

· High energy consumption compared to other systems.

· The equipment can wear out over time, requiring more maintenance.

· May not be suitable for deep water bodies.

d) Jet Aeration System

Jet aeration systems use a combination of air and water jets to mix oxygen into the wastewater. High-pressure water is mixed with air and released into the sewage tank through nozzles. The jets create a forceful mix of water and air, which helps distribute oxygen effectively.

Advantages of Jet Aeration:

· High oxygen transfer efficiency.

· Works well in deep tanks.

· Can be used for a variety of wastewater types and is flexible in design.

Limitations:

· It’s an energy-intensive process.

· It may also be more expensive to implement and maintain because of the use of pumps and jets.

e) Cascade Aeration System

The cascade aeration system is very basic in that water is caused to flow over falls in the form of cascades. When the water cascades from one tier to the next it also draws in air with it and thus enriches it with oxygen. This type of aeration is mostly restricted in the regions where water is in a flowing manner such as in rivers or streams.

Advantages of Cascade Aeration:

· It is easy and a natural way of increasing oxygen content in the water at a negligible cost.

· No machinery is required hence no or little costs will be incurred on this aspect.

· Commonly applied in the water treatment of small to medium sized sewage systems or streams.

Limitations:

· Lesser efficiency in terms of oxygen transfer than the mechanical aerators or diffused aerators.

· Limited use in highly polluted or industrial water situations.

· It yields best in areas that there is ample space to build step-down structures such as cascades.

Selecting the Appropriate Aeration equipment

The decision of which aeration system to have in a sewage treatment plant owes its decision to some factors. Some of these factors include:

a) Size of the treatment plant: Large plants require more effective ways of aeration and the common methods are diffused aeration and mechanical aeration.

b) Depth of the tanks: Diffused and jet aeration systems are suitable to use in deep tanks more than the surface aeration in the shallow tanks.

c) Energy costs: While methods like jet and mechanical aeration require more energy, diffused aeration is a more energy conserving method.

d) Cost of installation and maintenance: Cascade and surface aeration system are cheaper but not so efficient in their oxygen releasing as the other ones.

Thus, taking into account discussed factors, plant operators can select the most suitable aeration system.

Conclusion

Aeration is an important stage of sewage treatment since it aids in the breakdown of the wastes and clarifies the water. There are different types of aeration systems depending upon the requirement of the treatment process. For the diffusion of air, a diffused aeration system is very useful but needs constant maintenance while surface and cascade aeration are not that efficient though easy to maintain. Jet and mechanical aeration are the strong systems that can be applied to deep and high volume sewage treatment plants.

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