Oxygen Transfer

Circulation VS Diffused Air

A common misconception in the aeration business is that injected air bubbles (diffused air) under water will create a significant oxygen transfer.

According to Professor A.B. Sparling head of the Department of Civil Engineering of the University of Manitoba and an expert on stabilization pond technology, studies conducted in the 1960's proved otherwise.

With diffused air bubble aerators, several facts should be known:
1) an air bubble contains less than 20% oxygen;
2) most diffused air bubble systems only attain a 6% oxygen transfer;
3) most diffused air systems now mostly talk about their circulation capabilites.

What are the main sources of oxygen transfer?
1) Absorption from the atmosphere, where the surface of the water contact the air.
2) Wind and wave action, which drives the air in to the water, thus exposing more surface area.
3) Photosynthesis. The beneficial forms of green algae present in the upper 6-18" of water produce oxygen as a waste by-product as an interaction with the sun.

How can circulation increase or aid in oxygen transfer and production?
1) Oxygen depletion normally occurs at the bottom of the water. By deep circulating and bringing the oxygen depleted water from the bottom to the surface, the normal oxygen transfer can take place. If the circulation pattern is deep enough, the oxygen-rich water is drawn back down to the bottom where it is most needed.
2) EPA manuals for waste pond operation show that through pond circulation the oxygen producing zone can be drawn down from a typical 6-18 inches to about 4 feet, thereby increasing direct oxygen production by over 2.5 times.
3) Typical surface scum and algae matting stops wave action and blocks photosynthesis. Circulation reduces surface encrustation and matting, thereby increasing oxygen transfer.


BACK