Increasing DO

[Oliver]

Re-posted from private messages

thechaossmurf

ok I got an idea that literally might blow up in my face --so I thought id ask u if u know if anyines tried it yet ----
im going to be building a homemade oxygen & hydrogen separator to fuel another experiment that im needing the hydrogen ----so I was wondering if I could pupe the unwanted oxy inot my air pump to add extra oxygen to my aquaponics system --granted it wont be insanely huge amounts ---but do you think itd make the air pump go boom ??? ---feel free to repost this onto the site if you want ---I didn't know where to put it at so I sent it too you

Oliver: "First, please do not use private message for your questions. They need to be shared with everyone on the forum.

"I see no reason why it would not work. What kind of separator are you using? I've been thinking of doing this myself."

thechaossmurf "Oliver im going to be using a home-built oxygen separator design --basically a you-tube design I found somewhere ---my main question was if there is any chance of an explosion from an air pump if it had a tad extra oxygen in its intake though && honestly I got no idea where to post it at here"

[Oliver]

It should work, but as you say, depending on the amount of O2 will determine how much increased DO you get.

Oliver

[David - WI]

Have you seen this: https://youtu.be/IOuGQ6TEDFk

[Oliver]

Thanks,

Interesting, pricey and power consuming.

Oliver

[Jason]

I have to agree with Oliver. I checked out their website and was shocked at the price of the units. Very pricey, but hopefully will come down with time. It would be interesting to see if the initial price and cost to operate could be offset by increased growth.

Jason

[Oliver]

Also,

What happens to the hydrogen that is generated in the electrolysis process? Is it also absorbed in the water as well as the O2, and how does that affect the pH?

Oliver

[David - WI]

Just gasses off according to the faqs. I imagine that electrode could be at/near the surface in most cases?
I'm not promoting it, I just thought it would be a useful site for the OP/e-mail person.

[Oliver]

I think a better way would be to do the electrolysis externally, as thechaossmurf is suggesting. That way you could place the aerators in deeper water, allowing for better absorption of the O2 as the water pressure is a factor in amount of absorption. Also, probably at a lower equipment cost.

I was a little surprised at the small amount of increase in DO they were getting, as I thought it would be higher. Although, I am not familiar with the use of pure O2 in that application, so I don't have a reference for my metric.

What I see are fine bubbles of H2 and O2 (assumed) to be rising up and out of the shallow water and escaping into the atmosphere. Not sure why the H2 would not be absorbed along with the O2. The deeper the water the more pressure at the bottom, which translates into more exchange of gas into the water and a longer time to the surface allowing for more contact of the bubbles' surface with the water, and again, more gas exchange.

By the way, a misnomer I detected early on in my Aquaponics learning curve. When the term "surface" is used regarding aeration it does not mean the surface of the water in the fish tank, it means the interface of the surface of the air bubbles with the water they are rising through. So, placing the aerators on the surface of the water in the fish tank is the worst and least effective place you can put them. Even though it may break the surface tension of the surface of the water by placing them at the top of the water, it does little good for adding DO to the water in the tank. For that, you need depth.

You don't need a 6 foot deep fish tank but you do need a tall tower, which can be just a relative large diameter (say 4 to 6 inches) of pipe standing on end with an aerator in the bottom and an air pump capable of pushing air that deep. Just flow the water through the pipe by pumping it into the bottom and letting it overflow out the top and back to the fish tank or directly into the grow beds or wherever. With that configuration, the water coming out the top of the pipe will be super saturated with atmospheric gases, including O2, or just pure O2 as suggested above.

More to chew on,

Oliver

[David - WI]

Normally in electrolosys one electrode produces hydrogen and the other oxygen, so I suggested putting the hydrogen producing electrode closer to the surface o it would gas off more readily.

[Oliver]

David,

Yes, you could do that. However, you would then have electrical current traveling between the electrodes. If you were to shield the configuration so no fish could swim in between, or place it in another water container, it could the be answer to put more O2 in the water than H2.

The greater the distance between the electrodes, the greater the voltage for the same current. Although, there is something called ohms per square, and in this case ohms per cube. It suggests that regardless of distance on the surface of a conductor, such as a sheet of copper (ohms per square), that the resistance doesn't change with distance. Maybe with three dimensions, as in a tank of conductive water, the resistance would actually decrease with distance, requiring less voltage the further apart the electrodes. Just a thought.

Good idea, though,

Oliver