CO2 reactor and air pump question
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Old 11-27-2003, 08:33 PM   #1
Rabbit
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I've just read the excellent article by John LeVasseur (http://www.qsl.net/w2wdx/aquaria/diyco2.html#3) and Ive a question I'm hoping someone might be able to answer.
WHY would a CO2 enriched air feed not work? I understand that there would be a loss of CO2 due to the difficulty of mixing with the water properly, but if the yeast lasts longer when airated, wouldn't the net result be the same? THat is, you get less CO2 into the water, but it works for longer period.
What am I missing?
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Old 11-27-2003, 11:37 PM   #2
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Not sure if I understand your suggestion completely, but if bubbling air into the CO2 creating yeast sugar mix is what you are suggesting, I see the following problems:

- The yeast producing CO2 and alcohol from sugar is an anaerobic reaction. I have never heard that adding air would make that last longer.

- Keep it simple... the beauty of the DIY setup is that it is easy to do. If you want to add additional stuff, chances for failure increase.

- Pure CO2 dissolves completely in water. That is the principle most reactors use. If CO2 is mixed with air, those reactors will not work, and just airlock. The CO2/air mix will just bubble out... what's the point?

Perhaps I misunderstood the whole question... my apologies if that is the case :mrgreen:
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Old 11-27-2003, 11:59 PM   #3
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Wasserpest: you got the gist of what I was asking, but thats the thing you see. In an aerobic reaction, yeast produces Carbon dioxide + Water + Energy, alcohol production only occurs in an aneorobic raction. So technically, if there is enough air in the mixture, there should be no alcohol produced, and the yeast should continue to work for as long as there is enough sugar.
Secondly, CO2 and O2 exist independently of each other. That is to say, if you stick an O2 pipe and a CO2 pipe together into one pipe, then the stuff comming out the other end will still be CO2 and O2. THey don't mix.
So what Im going to do is run an aerator stone from a pump into the CO2 reactor (thereby oxygenating the mixture) and then run a hose into the aquarium.
The only diff between what I want to do, and a regular CO2 yeast generator is that since O2 wont dissolve as easily in water, you'd get a lot more gas escaping out of the system.
At least that's the only thing that I can see wrong with doing this. I was hoping that someone else (with maybe some science background) might be able to tell me if Im missing something. Im sure SOMEONE mustve tried this before and there must be a reason why it won't work.
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Old 11-28-2003, 12:21 AM   #4
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Here is the flaw in your logic. Standard Air pumps are not pumping straight O2, they are pumping in AIR. Air is made up from a lot more gasses then simply O2.... Including CO2. Therefore when the air mixes with the CO2 you are simply going to increase the CO2 concentration of the air itself, and your reactor will not be able to keep up with the level of gas you are pumping through it. It will be trying to diffuse not just the CO2, but the other gasses in the mixture as well.

Here is a breakdown for you;

Nitrogen N
Oxygen O
Argon Ar
Carbon Dioxide CO2
Neon Ne
Methane CH
Helium He
Krypton Kr
Hydrogen H
Xenon Xe
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Old 11-28-2003, 03:07 AM   #5
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should still not be a problem. The yeast mixture reaction will be as stated as long as its getting enough O2. And worse case scenario (from what Im seeing) is that the air filter in the tank is putting out a higher concentration of CO2 than normal (normal ambient air that is). Since oxygenation doesnt come from air pumps but from surface currents, that shouldnt really do anything. Unless Im wrong of course. :P
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Old 11-28-2003, 06:58 AM   #6
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The yeast solution might last longer by doing what you suggest. What you want is a specific concentration of CO2 in the water, you will not get that concentration by doing what you suggested. No point having the yeast solution last longer when you plant is not getting the benefit of the CO2.
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Old 11-28-2003, 08:29 PM   #7
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Let me help settle this, because I used to homebrew.
Yeast require fairly oxygenated water for the first phase of their lifecycle...which is before heavy fermentation occurs.
Some homebrewers run an airstone and inject pressurized O2 into their fermenter for the first few days after starting a batch. Relatively few do this...the rest of them make sure to splash the liquid in the fermenter around right before adding the yeast, or if the yeast has already been rehydrated or a 'starter' solution made, you can just shake up the main fermenter after adding the yeast.

This doesn't make it ferment longer...it does tend to make fermentation begin more quickly and more reliably, because you're providing the yeast with everything it needs: food, air, and the right temp.

Adding baking soda will slow down the fermentation process, as it's an alkali, and yeast like a slightly acidic solution. Also, cooler temps, like 65 degrees F will slow fermentation, and also CO2 levels to a degree.
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Old 11-28-2003, 08:41 PM   #8
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confusekid: Concerning what you said, its true that what you are looking for is a CO2 concntration in the water, but if the amount of CO2 being pumped in is greater than what you would've had otherwise, then its a net benefit. And since the water column can only hold so much CO2 (or any other gas at one time) there's no point in going overboard anyway.
What Im trying to say is that SOME CO2 is better than none and in this case, since the tank being used is relatively small, then it might actually still be more than the water can hold.
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Old 11-29-2003, 07:06 AM   #9
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Quote:
Originally Posted by Rabbit
confusekid: Concerning what you said, its true that what you are looking for is a CO2 concntration in the water, but if the amount of CO2 being pumped in is greater than what you would've had otherwise, then its a net benefit. And since the water column can only hold so much CO2 (or any other gas at one time) there's no point in going overboard anyway.
What Im trying to say is that SOME CO2 is better than none and in this case, since the tank being used is relatively small, then it might actually still be more than the water can hold.
Two things:

First, CO2 is far more soluable in water than other the atmospheric gasses your air pump will introduce. Long before you get to the point where you have "more CO2 than the water can hold", all the fish will be dead due to high CO2 levels or exremely low pH or both. Consider a soft drink. Water can "hold" a LOT of CO2. But you'll never get close to having to worry about that... See below:

Second, the thing that makes the CO2 go into the water is a process called diffusion. At the risk of being a little overly detailed... The rate of CO2 diffusion in water (or any other solvent/solute combination (not counting solubility))) is determined by 1) the concentrations of CO2 both in the "bubbles" in the reaction chamber and in the aquarium water and 2) the surface areas that are in contact with one another. The total amount of CO2 diffused also depends on the length of time the bubbles are in contact with the water. So, to maximize this diffusion, we want 1) pure CO2 bubbles; 2) little tiny bubbles in contact with lots of water and 3) keep these tiny bubbles in contact with lots of water for a long time. That's for a best case.

If you put an air pump in the yeast container and run the output into the tank, you're going to be pumping mostly "air" (a mix of mostly nitrogen and oxygen (and CO2 and other gasses in small amounts)) into your tank. Unless your yeast container is absolutely huge, the amount of CO2 the yeast will add to the "air" flowing out to the tank will be minimal.

You can find out just how minimal by hooking some tubing to a sealed yeast container, sticking bare end of the hose under water, and counting the number of bubbles it makes in a minute. For the sake of argument, let's say you count 10 (which is too high, but it makes the math easy).

Now hook your air pump up to the hose and do the same thing - count the number of bubbles the air pump makes. Probably around 10 a second or 600 in a minute.

So if you did your setup as you propose, you would generate a volume of mixed gas (mostly air) equal to the volume of 610 bubbles every minute. Doing the math, you will have increased the CO2 concentration in the "air" leaving the yeast chamber by 1.6%. Since the tank is open to the air, the concentration of CO2 in the water will be about the same as the concentration of CO2 in the air. So your trying to diffuse CO2 into the tank when the concentration of CO2 in the air your pumping in is only 1.6% higher than the concentration in the tank already.

With such a tiny difference in CO2 concentration (between the bubbles and the tank water) the rate at which the CO2 would diffuse into the water will be incredibly low. You would need to hold this air in contact with the water for hours and hours to transfer a noticeable amount of CO2. Given the rate that the air pump will run at, there's no way to hold that much gas in contact with the water long enough to do any good. The CO2 will come out of solution at the surface of your tank MUCH MUCH faster than you could hope to compensate for with this setup.

With conventional CO2 systems, you have bubbles of 100% CO2 (big difference in concentration equals fast diffusion) and these bubbles are held in contact with lots of water for a long time (hopefully until the bubbles completely disappear) so all the CO2 goes into the water. Put the same 10 bubbles a minute of pure CO2 into the reactor and hold them there until they completely dissolve and you ARE increasing the amount of CO2 in the water by an easily measurable amount.

Clear as mud, right?

Take care...

Tim
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