Aeration Sewage Treatment - 2 Contrasting Methods in Wastewater Treatment
The primary method employed for aeration sewage treatment of sewage water containing mixed liquor is - diffused air system.
Diffused Air System In this system, sewage is aerated by blowing compressed air, which is applied through porous diffusers.
The diffusers are either porous tubes or porous plates of quartz or aluminum oxide, from which the air is released in the form of fine bubbles.
Tube diffusers are suspended along one side of the tank, whereas the plate diffusers are placed at the bottom of the tank for aeration.
Sewage treatment systems more commonly use this in practice.
They are either flat shaped tiles 30 cm x 30 cm x 25 cm thick or dome shaped tiles 10 cm to 17.
5 cm dia.
The latter are the more popular these days.
In these systems, for about 1/10th of the tank, the diffuser area occupies surface area.
Two arrangements of diffuser tiles are generally adopted: (i) Ride And Furrow Method: In this, the floor of the wastewater aeration tank is formed in a series of ridges and furrows, usually placed longitudinally, with the diffusers laid on the furrows, and connected to the air main through smaller air pipes.
The air is released in the form of fine bubbles, which rise and give impact to the sewage, flowing in a perpendicular direction.
In so doing, the air traces out a path in the aerated sewage.
(ii) Spiral Flow Method: In this, the diffusers are placed only at one side of the tank floor.
The tank corners are chamfered, so that air bubbles rising at one side are deflected.
Longitudinal displacement of the sewage, produces a helical track.
This disperses a certain amount of air across the tank and downwards.
This also provides a longer path of travel for both air bubbles and sewage and permits a greater absorption of the atmospheric oxygen at the sewage surface during aeration.
Sewage treatment systems of this type require lesser number of diffusers and less amount of compressed air.
Hence, this method is more economical.
It has, however, one defect, and that is the formation of stagnant pockets, which interfere with the aeration method.
Diffused Air System In this system, sewage is aerated by blowing compressed air, which is applied through porous diffusers.
The diffusers are either porous tubes or porous plates of quartz or aluminum oxide, from which the air is released in the form of fine bubbles.
Tube diffusers are suspended along one side of the tank, whereas the plate diffusers are placed at the bottom of the tank for aeration.
Sewage treatment systems more commonly use this in practice.
They are either flat shaped tiles 30 cm x 30 cm x 25 cm thick or dome shaped tiles 10 cm to 17.
5 cm dia.
The latter are the more popular these days.
In these systems, for about 1/10th of the tank, the diffuser area occupies surface area.
Two arrangements of diffuser tiles are generally adopted: (i) Ride And Furrow Method: In this, the floor of the wastewater aeration tank is formed in a series of ridges and furrows, usually placed longitudinally, with the diffusers laid on the furrows, and connected to the air main through smaller air pipes.
The air is released in the form of fine bubbles, which rise and give impact to the sewage, flowing in a perpendicular direction.
In so doing, the air traces out a path in the aerated sewage.
(ii) Spiral Flow Method: In this, the diffusers are placed only at one side of the tank floor.
The tank corners are chamfered, so that air bubbles rising at one side are deflected.
Longitudinal displacement of the sewage, produces a helical track.
This disperses a certain amount of air across the tank and downwards.
This also provides a longer path of travel for both air bubbles and sewage and permits a greater absorption of the atmospheric oxygen at the sewage surface during aeration.
Sewage treatment systems of this type require lesser number of diffusers and less amount of compressed air.
Hence, this method is more economical.
It has, however, one defect, and that is the formation of stagnant pockets, which interfere with the aeration method.
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