If I saturate the water with the maximum O2 possible as determined by its temperature, is there any benefit to additional bubbles directly under the rootball?
2 Likes
I’m a fan of dissolved oxygen (DO). Not really an answer to your question but more thoughts on possible inquiry.
It’s an interesting question, I don’t think so but I don’t really know. There’s a partial pressure thing with gas bubbles within a fluid which suggests they may not actually contribute to the dissolved oxygen of the surrounding fluid. Those are the claims that I’ve read and my current understanding are that actual gas absorption occurs at the point where the bubble meets the surface of the fluid and ‘pops’. I’m not feeling entirely confident with that though. That does have the effect of increasing the surface area in contact with the atmosphere.
Whether roots can take up oxygen directly from a bubble or directly from the atmosphere without first dissolved in a fluid, say adhered to a root, is an interesting question as well.
I do know that if you can achieve ultrafine bubbles in solution you can achieve a state of supersaturation. In fact, if the bubbles are small enough, the surrounding pressure will collapse the bubble and all of the gas is immediately absorbed into solution. That is, you are able to exceed the normal capacity of the fluid to hold oxygen in solution exceeding what the dissolved oxygen equations produce. There’s a whole field of inquiry on such dynamics. Very specialized. This is a somewhat different scenario as to the more macro, more typical, sized bubbles.
In some past data collection, I have employed a set-up to produce bubbles using a needlewheel pump with the theory that it will produce some quantity of ultra-fine bubble and/or some cavitation such that any gases contained could be absorbed on collapse. The majority of the bubbles, however, are of the macro size. With a bunch of testing there are some indication that supersaturation was achieved … but it was some rather nominal amount that I don’t quite recall without digging back into the results.
There are a number of individuals around that have measured dissolved oxygen using a variety of different techniques. Water fall, stones, injection, nothing at all, etc and, in many cases, the results tend to follow the DO equations with even the most simple techniques showing full saturation. Which, sort of makes sense, as the solution will come to equilibrium with the atmosphere over time per the DO equations. However, in most of the experiments that I’ve seen, the trials have no plants in the system and there is no data on the rate of root O2 consumption. So, add another question, what is the uptake rate for a fully developed root system? I think this is the key area that would contribute a great deal to the overall understanding. That is, figuring out how much oxygen is utilized by the roots and how quickly. For that matter, how much of an effect will a change produce?
Also note, the measurement of DO is somewhat tricky and prone to error.
Currently, my presumption on your original question is that it probably doesn’t make a difference to have bubbles under and coming into contact with the roots. But, it’s only my presumption. I think there is some value into digging into some of the available literature out there. Much of the literature I’ve seen revolves around waste water treatment or oxygenation of large bodies of water (lakes, ponds), et al primarily to feed aerobic bacteria or to reduce certain types of anaerobic processes / growth.
10 Likes
This is an area I was looking for information on supersaturation.
There are a few ideas on YouTube for example , that a shallow well pump converted into a nano bubble machine , which in turn over time creates a fog of nano sized bubbles that seem to suspend in the mixture rather than float and break quick like.
This would make your ph rise , not sure how quick or if such a bubbly mix would be beneficial or not.
4 Likes
airstones are a liability imo
especially if you already have sufficient DO
4 Likes
I get you on wanting more o2 but to what end? I don’t think you would even need full saturation (nevermind supersaturation or bubbles on roots) to give the plant the oxygen it needs. If I had to guess the limiting factor in most grows would be co2 and then maybe light?
If you are really worried keep the water level somewhat down and there will be great absorption in the roots that are above the water level but are still moist and exposed to air.
4 Likes
Actually this is an interesting thought….plants grown in co2 enriched enviro. I wonder if you could get to a high enough level where there is so much growth and so much co2 that it would become a limiting factor…and…if so could you supplement o2 to the roots to get over that.
Poor plants….
3 Likes
Posting some references.
This was from a study done for NASA:
Note, this is for staple and salad crops such as Lettuce.
Here is the paper: Monje_FactorsControllingO2DeliveryHydroponics_2001-01-2425.pdf (275.8 KB)
Here is a snippet from a paper studying O2 uptake rates:
And, the associated paper: veen1988.pdf (557.4 KB)
Plant injury due to oxygen deficiency: Plant injury due to oxygen deficiency.pdf (1.2 MB)
Oxygen Deficiency on Mineral Nutrition of Excised Tomato Roots: morard2004.pdf (533.9 KB)
A paper that discussing gas transfer (surface vs bubble) with the following comments:
Conflicting claims have been made regarding the contribution of surface transfer and bubble transfer to overall aeration in diffused aeration systems. In activated sludge applications, it is commonly believed that bubble transfer is the primary location of oxygen transfer. For diffused aeration systems in lakes and reservoirs, the most influential location of oxygen transfer, across the free surface or the bubble interface, is still being debated. Values of kL for bubble–water and air–water transfer have been determined by a number of researchers under various test conditions (Table 1). The most relevant papers relating to the determination of separate transfer locations are more thoroughly discussed below.
Impact of bubble and free surface oxygen transfer.pdf (226.2 KB)
Some info on nano bubbles: Nanobubbles (ultrafine bubbles).pdf (541.2 KB)
Nanobubbles and surfactants: ZetaPotentialOfNanobubbles.pdf (279.8 KB) FWIW, I’ve verified that surfactants do indeed stabilize bubbles in solution, not just nanobubbles.
I have quite a bit of reference materials on various aspects for this topic, let me know if there is interest and I can upload additional stuff.
5 Likes
Now you may need to consider Co2 saturation.
I am not sure on this, but I feel Co2 and O2 will compete for saturation levels.
Keep you air pump remote so as not to intake Co2.
Also there are venturi and other systems, some even inject pure O2 directly into the water.
Kinda like a water treatment plant does.
That is where my research took me anyhow. 
Good luck
Shag
4 Likes
That’s super interesting. So it looks like from that chart if you have reasonable temp water (I looked at a o2 water temp sat. chart) you will be well above the needed amount for growth…and assuming the pumps supply more than what is used at any given moment (and I imagine they replace the o2 much quicker than a plant could use it up) you wouldn’t even be anywhere close to having o2 as a limiting factor.
3 Likes
Actually above 70f I bet things would get dicey…but pumps wouldn’t be able to help you much at that point.
3 Likes
Keeping the water line lower would create more o2 and if one had a falls as I do this would help create more o2 to mix on the surface.
But say look at the explosive growth people have in spraying in an arrow system.
I’m sure just changing my single falls into two then downsizing the stream size with create more force to disrupt water even more.
Have seen the tote in turn pressurize ( not exactly sure could just be an ole air pump ) to create as much air available to mix on the top surface.
2 Likes
Yes, according to that study. Bearing in mind, NASA does some weird things and the crops are for leafy vegetables, so applicability remains a question. For uptakes rates, tomato in that case, I’m not sure of the conversion to PPM as it’s labeled mg/g per hour. I think the conversion is 1mg/g = 1000 PPM. Some fiddling with units to get the rate being pulled from solution which, for DO, is also in PPM.
Some of the other papers do point out nutrient translocation is effected by DO PPMs.
Sorry, MrWizard. Making a straight forward question into something complicated.
4 Likes
I think that was in reference to CO2 supplementation in the room where O2 becomes the limiting factor (like light or water) within the solution. I’m not seeing that as probable based on some of those papers but needs some quiet time to think about it and convert units around.
4 Likes
So i have a question, can you get away with a single or multiple falls (assuming more volume and water disruption upon surface contact means more DO) without any airstones? I know that of course there is going to be a point of if you do a huge waterfall ofcourse there will be enough DO to reach saturation or sufficient levels but can i stick a submersible pump and drop the water 12 inches at a whatever L/hour and have equal oxygen or should it be 24 inches fall or whatever height or whats the difference of two instead of one falls at 12 inches vs one at 24 inches?.. i want a DO tester but they be pricey 
1 Like
From another thread here.
2 Likes
Do NOT be sorry. I am grateful for the engagement from all who have posted. And especially for the reference material. All of the facets that have been brought up are of interest to me.
I bought a titration kit and plan to do some testing of my own, just to prove it out in my own environment. Not sure if the titration kit will have enough resolution, but I intend to measure the delta between the supply and the return, that may give me an idea of consumption.
I agree, wholeheartedly, that air pumps and airstones are liabilities. However I will error on the side of caution until I can prove it out. I need to wait for the temp to drop another 10 degrees outside before I will be able to maintain my sump at 67f stably (no chiller). But… I may well find that I have enough DO, even at a slightly higher temp, to support my 4 plants.
2 Likes
So basically it is possible. Thankyou. Probably now to get those drops and see what levels i will produce