Disolve Oxygen levels

[urbanfarmer]

I felt that the discussion of Oliver's article distracted from his post. To be fair I split off the discussion on dissolved oxygen levels. See Aquaponics 101 Part Three: System Design, Continue (http://www.diyaquaponics.com/forum/showthread.php?758-Aquaponics-101-Part-Three-System-Design-Continue) for the original post...... Badflash
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20% of 240 GPH to jet back is 48 GPH not 40 GPH, but we know what you meant! :ugeek:

Metal isn't intrinsically toxic, but I know you meant that it will reach toxic concentrations with that much metal surface area dissolving into the water. Remember, some people put iron nails and the like into their grow bed to provide the essential trace minerals for the plants, fish, and microorganisms.

The DO is not really helped by air bubbles, per se. You get far more gas exchange at the surface from agitating the water. A simple PVC with many small holes pumping that 20% return water over the surface will give you a ton more DO. Tilapia only need about 4 ppm DO. As far as the growth performance, that depends on so many variables. To say that the growth rate doubled form below 3 ppm DO to 6 ppm DO sounds very misleading. The pH is more important, as considering that low of a DO given the correlation to all the other factors involved, I really question causality you are implying in your statement. Anyway, I digress... Of course, the bubbles will agitate the surface, but I don't recommend spending money on a fancy air pump or air stone when a simple one will yield the same results. Making use of the return water in an efficient way will provide more than enough DO. I understand not wanting a single point of failure. A cheap $20 air pump with a few air stones will be enough to agitate the surface. A water wheel would be the best option, but I'm not sure how much those run these days. Heck, get a 2nd water pump!

So far, this has been my favorite section in the series, lots of practical information here!

[rfeiller]

although it is true that the majority of gas is exchanged at the surface, there is a gas exchange at the bubbles. the finer the bubbles the better. it would be interesting to compare the agitation created by a 20watt air pump verses a 20watt water pump and the resulting DO. since water falling back in from one tank to another would not produce the greatest circulation, the water pump would have to be located at the bottom of the tank pumping straight from the pump outlet and not a hose.

using a power head at the surface, the water stream is weakened by hitting the opposite side of the tank and the circulation of water in the tank is incomplete. the most effective direction is from the floor of the tank at one of the long ends of the container aimed straight up. it will create a complete circulation of the water. you can check this out with dyes added to the water.

[urbanfarmer]

although it is true that the majority of gas is exchanged at the surface, there is a gas exchange at the bubbles. the finer the bubbles the better. it would be interesting to compare the agitation created by a 20watt air pump verses a 20watt water pump and the resulting DO. since water falling back in from one tank to another would not produce the greatest circulation, the water pump would have to be located at the bottom of the tank pumping straight from the pump outlet and not a hose.

using a power head at the surface, the water stream is weakened by hitting the opposite side of the tank and the circulation of water in the tank is incomplete. the most effective direction is from the floor of the tank at one of the long ends of the container aimed straight up. it will create a complete circulation of the water. you can check this out with dyes added to the water.
The DO added by bubbles under the surface, even with the finer bubbles, is crap. I have seen some numbers showing that for the power you get 50x times less gas exchange under the surface. Let me see if I can find that info or paraphrase it (it was in an email from a PhD I was having a conversation with).

[rfeiller]

Read my post again, it is undisputed that the majority of gas exchange is at the surface. When you are maximizing every additional source is valuable. Note the air gap on powerheads to push air into the water jet stream. This was designed for reef tanks for agitation and to add as much oxygen into the crevices of living rock, even tho it was minimal.
I found Badflash's comments on increasing the DO with a column under pressure extremely interesting and I will incorporate the concept in NV as I build there.
Forum's are an exchange of info only to discuss/cuss, accept/reject everything is up for question.

[badflash]

Can you povide a paper or something that supports the idea that bubbles are not as effective as disturbing the surface? I have not found this to be the case myself. I may set up an experiment.

[Oliver]

I need to chime in here, been away since last post, Aquaponics 101 part 4 - system start up.

The older system where the DO measurements were made and reported with increasing DO did NOT have any water being jetted back into the tank. I have built systems like that, however. Regardless of theory and what someone else has written about aerators not providing DO I have the data to prove otherwise, as was given in my original post.

I included water jet back in the "system design" portion of Aquaponics 101; for I have information from others that tell me this is a good way to inject DO into the fish tank water, but again, it was not implemented in the system where I made and reported the DO measurements above.

In the systems I built where the water jet back was part of the system, I measured a DO of over 8.0 ppm. But, there were no fish in that system at the time of measurement; for I was testing a new design and trying to determine how to increase the DO in the water. I still have more testing to do on that system by turning off certain sources of aeration and then testing the DO. Unfortunately, due to some building construction, I had to dismantle the test system before completing all of the DO measurements. I will be resuming those measurements soon and then I will hopefully have a better idea of what elements add DO to the water and how much.

To measure is to know.

[urbanfarmer]

Read my post again, it is undisputed that the majority of gas exchange is at the surface. When you are maximizing every additional source is valuable. Note the air gap on powerheads to push air into the water jet stream. This was designed for reef tanks for agitation and to add as much oxygen into the crevices of living rock, even tho it was minimal.
I found Badflash's comments on increasing the DO with a column under pressure extremely interesting and I will incorporate the concept in NV as I build there.
Forum's are an exchange of info only to discuss/cuss, accept/reject everything is up for question.
Oh, I wasn't disputing you. I just wanted to make that point! :mrgreen:


Can you povide a paper or something that supports the idea that bubbles are not as effective as disturbing the surface? I have not found this to be the case myself. I may set up an experiment.
I am not permitted to copy/paste the conversation, but I am allowed to paraphrase. Dr. Wilson Lennard stated that according to research he has access to there is a 50:1 ratio of gas exchange on the surface versus below the surface. I have asked him if I could have access to the research or if it is public. Hopefully, it is something we can all share because I would love to review it as well, but the way he explained it makes sense. The reason bubbles are not HORRIBLE is because although the do not provide much gas exchange in the form of bubbles, it agitates the surface thereby increase the area on the surface as well as adding motion and water movement. I will wait for his response before saying anything else because to be honest this is new to me too. I had no idea the ratio was as high as 50:1 and that is pretty amazing.


Regardless of theory and what someone else has written about aerators not providing DO I have the data to prove otherwise, as was given in my original post.
Can you provide this? I would love to see any of the research you have based many of your claims on! :D

[urbanfarmer]

This is on YouTube, which is how I heard about the good doc: http://www.youtube.com/watch?v=iitanQgsk2I

Now keep in mind when he did this lecture he was NOT expecting it to be recorded or distributed. Murray Hallam asked him if he could use it, and now it's all over the place, lol

[badflash]

Here is what I would propose. Set up two aquariums. One with a good air stone only, and one with an HOB filter that provides the same mount of surface turbulence. Let it run for 48 hours and measure the DO in both tanks.

Of course the gas exchange occurs at the surface. It has to escape to get away from the water, but I'll get a 6 pack that the DO is better with the air stone than with simple air turbulence. I have tanks with HOB filters, but when I add an air stone the bio load can be pushed more than tripple of the HOB alone.

[jackalope]

I have read that the best way to get higher levels of oxygen in the water is by using a fountain or dropping the water back into the FT from the GBs leaving an air gap of 6 or more inches. If you look at most city reservoirs, this kind of backs up this claim, because they have a fountain in the middle of most reservoirs (and fish ponds in the state fish hatcheries) to add oxygen to the water, rather than air stones. What I read is that the water will not absorb the oxygen molecules from the air being pumped through the stones and up through a water column, as well as it will if the water is picking up oxygen from the air, and forcing it down onto the surface of the water from a fountain or stream (turbulence). These are not my words, ideas or experimentation, I know from nothin' about DO .... some geeky scientist wrote this stuff ... and I'm just quoting it from my bad memory. The water in a creek or river picks up oxygen from turbulence - bubbling brooks and raging rivers with the water running over the rocks and such are a real good example. I can't find it right at hand here, but I have a book on the cichlids (and Tilapia) of Lake Tanganyika and Lake Malawi and it states that in the lower regions of these lakes the fish are more oxygen deprived because there are no currents flowing nor winds blowing the deeper you go - another case for turbulence ;).

Just my 2 centavos .........

[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. :mrgreen:

[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 (http://aquanic.org/systems/recycle/documents/recirculatingVT.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 :mrgreen:

[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. :o :lol: :lol: :lol: :lol: :mrgreen:

[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?

[urbanfarmer]

Hey guys, I can't believe I did not see this discussion earlier... I blame JCO for getting rid of the portal... GRRRRR

Badflash you are right, but my understanding is that the gas exchange in short water columns like we have in most of our systems is minimal compared to what occurs at the surface of the water.

ANYWAY, I have asked Dr. Wilson Lennard to provide me some of the research he has been privy to over the years to share with you guys, but according to him the gas exchange at the surface compared to the gas exchange from bubbles beneath is 50:1. This is pretty significant... I will post when I get a reply. There has to be some good research floating around the web here somewhere as well...

[badflash]

Show me the DATA! :D

[badflash]

OK, I just did a short calculation. I assumed the bubble size of .015" diameter and the air flow was 1/10 cubic foot per minute.

This would give a total surface area for the bubble of 40 square feet per minute. The surface area of a tank, say a 20 gallon long aquarium is 2.5 square feet. This means that to be equal to the bubbles mathematically you would need to turn over the surface 16 times a minute.

Now if we are talking a pond and a few air stones, I can see the surface being a big deal, but if you are talking a 100 gallon pool and some good air stones, that is a totally different story.

Time to buy a DO meter.

[rfeiller]

http://i1130.photobucket.com/albums/m539/rfeiller/IMG_20101211_145627.jpg][/img]12" tube 3 feet long with air difusser in the bottom.

[rfeiller]

http://i1130.photobucket.com/albums/m539/rfeiller/IMG_20101211_145725.jpg

showing bottom of tube construction

[rfeiller]

http://i1130.photobucket.com/albums/m539/rfeiller/IMG_20101218_164314.jpg

air and water column produced by this aerator. this aerator is used in the 1000 gal vat. not shown is the grid and the screen that houses the ceramic biomedia in the lower portion of the tube. since the vat is 4' x 4' x 14' if would be better too have two of these in operation, but it does do a fair job of circulating and aerating the water.

[rfeiller]

in the many different configurations i have used in hatcheries, i have found no other method that produces upheavel, circulation, useability, and aeration in a useuable physical size and shape as microbubble aeration produces. (on central aquatic systems i prefer the cascading water column through biomedia with reverse flow aeration.) this certainly is not the application to end all applications, always looking for a better system design that would provide even better results. :)