of course in a natural lake oxygen exchange occurs at the surface, which is why there
are the OLD recommendations for X amount of surface per inch of fish.
then came aeration and it wasnt necessary to calculate surface area any more.
Yes, of course oxygen change occurs across a bubble and much much more efficiently
since exchange occurs as a function of the entire surface of the bubble (the smaller
the bubble the higher the surface to volume ratio). at the same time when the
bubbles break the surface and are blown into the air now there is exchange going on
the inside and the outside of that air bubble. even more efficient. it is a myth
that it doesnt happen.
the water at the bottom of the pond in summer is going to be cooler than the water at
the top if there is no circulation and cooler water holds more oxygen than warm
water. the water at the top is heating up and losing oxygen. there is no reason the
water on the bottom is depleted of oxygen unless there is a thick layer of rotting
organics on the bottom.
correct, airstones are easy to maintain AND most efficient at aerating water. more
so than "fountains" altho fountains are lovely to look at.
In sewage plants the last thing anybody wants is to aerate the water in such a way
that blows bubbles up into the air. this would put potentially pathogenic bacteria,
viruses and parasites right up into the air where it would get blown all over the
city. but sewage is broken down by both aerobic and anaerobic bacteria so pumping
it up without actual aeration may be the reason.
INgrid

Sean Dinh wrote:
I have to disagree here. Fine air bubbles can't really blows any gases out of the water.
Gas exchange need to happen at water/air interface. What fine air bubbles really doing
for gas exchange is to move water from the bottom to the surface. In this pump mode, fine
air bubbles has little efficiency without the aid of ducting.

Any pump that move water from bottom to the water/air interface could be considered
'vastly increasing' oxygenation, in a sense that oxygenation rate is higher for
relatively oxygen poor water from the bottom as compared to water from the top. I won't
go as far as claiming airstone 'vastly increases' oxygenation. I reserve that for cooling
tower/TT.

The main reason that airstones are so popular in aerating large ponds, lakes, and sewage
treatment plants is that it's very low maintenance water pump. The only thing to maintain
is to clean the air filter. It's considered the most reliable way to aerate water. There
is nothing more besides that feature.

As for flooming, it does work. If it's good enough for sewage treatment plants, it's good
enough for our ponds.



wrote:

the fine air bubbles put into the water by good
airstones lifts the entire water column from below, it blows toxic gases out while it
vastly increases oxygenation of the water.



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