Disolve Oxygen levels

[rfeiller]

i've enjoyed this thread and the opposing positions on the best way to increase the DO of your water. it made me go back and go through a number of studies on the best way to oxygenate water and gas transfer. (i won't go into supersaturation of the water with air to the point of killing the fish.)

there are many variables that have an impact on the ability and limitations of gas absorption and exchange. temp, ph, TDS, turbidity, size, depth, and shape of container.

for an aquarium, tank or vat, i will without question stick with small bubbles in a controlled column. large wastewater treatment companies use this type of air diffusing system as the preferred method of gas exchange. the small bubbles do transfer gas very effectively. ask companies such as GE that provide equipment, and engineering for these facilities.

the old formula, when we did not have air diffusers that could produce such small bubbles, the ration was 90% at the surface 10% through the large bubbles. the smaller bubbles rise to the surface much slower than the large bubbles because of the higher impact of gravity on the ascention of the larger bubbles.

i believe the most effective method of transfer, incorporates the affect of water over rocks or waterfalls; is a column of large biomedia suspended over the water as water decends down the column, air is is forced up through the column. this would be very difficult to do in aquaponics. i have done this over large vats containing fish. the drawback is that hanging above the water the water does not have the upheavel of a submersed air diffuser.

i'm not sure if this is worth 2 cents

[JeffW]

No expert here are you all talking about exchange of gas or how much O2 you can create? What is the point (just curious) is raising fish in a tank that complex? Like I said I am ignorant you are all the ones that do this to high degrees but the O2 thing..well I work with that allot making ACT and the amount of oxygen agitation that is created when I use a high power regenerative blower seems to do best when it is introduced lower in the tank and air bubbles rise up and out. Make sense? Just asking is all

[JCO]

It has been my understanding for more years than I care to mention but in any body of water, aquarium or pond, it is the surface area that matters when it comes to DO in the water.

If you have two 100 gal tanks filled with water only (no fish), (over simplification here) one that is extremely tall with a surface area of 2' X 2' and one that has a surface area of 4' X 4', the 4 footer will have more DO of the the two as it has more surface area coming into contact with atmospheric pressure.

Now to the purpose of the airstone in this equation. It has always been my understanding that there was actually only a minute amount of DO is produced from the bubbles rising through the water.

The real purpose of an airstone was basically to agitate the surface area of the water (create surface movement) thereby increasing the amount of water that actually made contact with atmospheric pressure thereby increasing the DO in the water.

[badflash]

I personally believe this is a myth. I've yet to see a conclusive experiment that shows an airstone does not directly add oxygen to the water. I have seen conclusive studies that show that if you use a deep water air stone like are used for some tilapia recirculating raceways, you can get oxygen saturation. By deep water I mean 50 feet or more. The system is designed to provide the motive force to move the water through the biofilter and raceway. It has the added benefit of providing water that is oxygen saturated.

I also know that in my aquariums, simply agitating the surface with water flow from a filter is not nearly as effective as using an airstone for DO.

[badflash]

Have a look at this paper:
http://aquanic.org/systems/recycle/docu ... tingVT.pdf

Check out the U-Tube diffuser. They have a U tube that goes down 40'. They inject air at the top and have water flow high enough to carry the air with the water. The water goes down with the bubbles and back up and exists with the water oxygen saturated. The system I saw was similar, but injected the air at the bottom of the U-Tube and was used as an air-lift water circulator. It requires a little more air pressure.

[JCO]

I knew I should have kept my mouth shut and stayed out of the controversy.

I didn't say airstones do not put oxygen into the water, only that you can have all the airstones you want, but it won't help unless you have surface area for the airstones to move.

Airstones actually increase surface area by moving the water upward (upheaval from the bottom) and replacing what is on the surface. The movement of the water is what puts the DO in the water.

I think if someone will check, DO in the water in a pond without agitation, say one in Denver, Co. and one in Swanee, Fl., you will find that free standing, non-agitated water in Denver will have less DO than the same sized pond in Fl..Less atmospheric pressure in Denver and less Oxygen in the air (what air there is there)....! Atmospheric pressure and surface area plus agitation of the surface is what increases DO in the water. That's my opinion and I'm sticking to it.

Love Ya Jack

[rfeiller]

God I love this!! This is what forums are about, exchanges of opposing conclusions created through ones school of hard Knox or a good research paper. The success of a method is impacted by the varied applications right?

[JCO]

rfeiller...whatever you do, just try to remain calm. I understand your symptoms and have informed the EMTs about your delirium when I called 911. Don't distress, help is on the way.

[rfeiller]

I think it's them at the door now!!

[badflash]

Here is how I believe things work. Surface area is surface area. It doesn't matter if it is a bubble or the surface of the pond. The higher the pressure, the faster the diffusion takes place. If you have enough transit time and enough pressure you can super saturate the water with oxygen. A good airstone with lots of little bubbles has much more surface area than the surface of a tank. It is also in contact with lower O2 water so transfers it faster. It has the added effect of turning over the surface water. Once the top layer of water has absorbed as much O2 as it can, it blocks entry of more.

One of our new members, Spooky_Fish hatches cichlid eggs in a tank that has a piece of insulation floating on the surface with holes cut in it for small strainers. He puts the eggs in the strainer. Under each strainer he has a bubbler that releases large bubbles to keep the eggs moving. He has a drip supply of water that constanly overflows to a drain. This system is more than adequate to keep the DO levels high for egg hatching. There is nearly 0 surface turbulence, just inough to swirl the eggs in the strainers. The bubble escape around the edges of the strainer, they are too large to go through the screens.

Spooky_Fish, can you post a picture?