Awesome story what a better way to start an addiction than doing thorough research. Look forward to picking your brain some more.
p.s. do you know anyone on here that is an expert in raft systems?
Gina and Tonya of Green Acres do raft Aquaponics
Chris Smith does Raft aquaponics
and Ryan (hum last name not coming to mind right now) knows Raft aquaponics.
There are many others but those three have quite a bit of experience (commercial grade) and Chris and Ryan are fairly active and if you go to the Green Acres group you can probably get Gina or Tonya's attention.
When using a diffuser to saturate the water with oxygen, you want small bubbles injected as deep as possible that rise as slowly as possible allowing for a longer period of oxygen diffusion to take place.
This is a commonly held mis-conception.... yes finer bubbles are preferable.... but NOT because they allow a greater time for the air/oxygen to diffuse as they rise...
The oxygen diffusion/exchange... takes place at the surface of the water... as the bubble breaks... not during the "bubbles" rise through the water column....
Think about it... for the oxygen in a bubble to diffuse into the water column as it rises... the oxygen in the bubble would have to diffuse through the surface tension layer of the "bubble"... effectively causing the bubble to lose pressure... and break...
It doesn't happen, certainly not in the time it takes for a bubble to rise in most systems...
The benefit of lots of smaller bubbles... is the surface area of the water exposed to air/oxygen diffusion... at the water surface... when it breaks....
That's why paddle wheel aerators are so efficient... they toss huge amounts of water... thus surface area,,, into the air, exposing it to diffusion...
Air diffusers are used in deep ponds/dams... but their benefit is not primarily any direct diffusion of air/oxygen into the water column... but the fact that they lift deep water to the surface.... thus exposing it to possible surface diffusion.. and mixing and more uniformly oxygenating the pond/dam...
A natural pond/dam... receives it's oxygenation at the water surface... primarily by surface area disturbance by wind...
A still, undisturbed body of water... will de-oxygenate.. and become stagnant for this reason... as any biological oxygen demand exceeds the oxygen diffusion at the undisturbed surface...
Again, we are going to agree to disagree. In large bodies of water you are trying to mix as well as aerate to bring surface water to the bottom and de-stratify the body of water. Surface aerators (like paddle wheels) are more efficient in shallow bodies of water but as depth increases diffusers take over.
To say air doesn't diffuse through the bubble wall into the body of water is again, absurd. With a raft ontop of the water you aren't going to have any device throwing water into the air like a paddle wheel and you don't have a massive surface of water exposed to the air. Your comparisons just don't make sense.
Oxygen is absorbed in water by direct diffusion and by surface-water agitation. Solubility of oxygen in water is so small and by diffusion process alone in still water, it was caculated that it would take 6 years for oxygen to diffuse from surface to a depth of 6 meters in quiet water.
Absorption of water is very minor, that almost all the oxygen enrichment of natural waters takes place by agitation of water.
The same is true of AP systems aerated by air stones....fountain heads, waterfalls etc
There are other reasons Rakocy uses airstones every 4 feet. I am not sure where I read it but there is some kind of bug/crustacean that can invade your system. I'll see if I can find the article or maybe Rupert knows.
Rupert's correct. Dr Wilson Lennard has made the same observations.
The idea that the oxygenation rate is greatest as the bubbles surface makes sense, especially in only 30 cm of water.
Do yall know what a good flow rate through a trough system is? I have heard 2 gpm but that sounds really low.
2 gpm I believe is the bare minimum through the troughs and I've heard 5 gpm is a better minimum.