Aerobic microbes rely on oxygen to carry out their life functions. Oxygen, being only moderately soluble in water, must be constantly added to aerobic wastewater treatment systems to ensure proper waste treatment. Aeration energy use is one of the largest costs in running a treatment system, so finding the best aeration type is a key part of running and maintaining a system.
How oxygen is transferred into water
Oxygen dissolves into water at the air/water interface. Oxygen from the atmosphere (20% O2) naturally enters water at the surface. In most aerobic treatment systems oxygen transfer is done via air bubbles passing through the water (diffuser or jet type aeration) or through the mechanical action of surface aerators. Key is the surface to volume of the bubble - the smaller the bubble the higher ratio of surface area for diffusion compared to larger or coarse bubbles.
What we want aeration systems to do
How oxygen is transferred into water
Oxygen dissolves into water at the air/water interface. Oxygen from the atmosphere (20% O2) naturally enters water at the surface. In most aerobic treatment systems oxygen transfer is done via air bubbles passing through the water (diffuser or jet type aeration) or through the mechanical action of surface aerators. Key is the surface to volume of the bubble - the smaller the bubble the higher ratio of surface area for diffusion compared to larger or coarse bubbles.
What we want aeration systems to do
- Provide efficient DO transfer
- Keep biological solids suspended
- Provide sufficient mixing to avoid short circuiting or dead zones
- Problem is you cannot have everything!
- Best solution may be combining multiple types into a hybrid system
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