Time to work on a de-gassing unit

[Tony Gilliam]

Ok, My fish tanks are near finished, i have most of the pieces and parts to complete the solids settler (swirl filter). Now im thinking, its time to work on a de-gassing unit. I have an idea as to how it should work and the type of material it should be built with, but would like to see what other have used.

Part of the waste water treatment plant (At work) uses an AFU (Air flotation unit) to separate the material that is lighter that water. Im thinking this would be similar in design. The AFU has a way of skimming froth off the top of the water, my question is, Will a de-gassing unit in an AP system produce alot of froth and is it necessary to have a froth skimmer?

[Phil Slaton]

I want to know if anyone knows of a simple de-gasser unit that works and does not take a rocket scientist to understand it, or assemble it, or install it.

[Bob Terrell]

A bucket with an air stone filled with water.  lol

Phil Slaton said:

I want to know if anyone knows of a simple de-gasser unit that works and does not take a rocket scientist to understand it, or assemble it, or install it.

[Robert Rowe]

And why is a degassing unit necessary?

[Tony Gilliam]

De-gassing is just like heavy aeration,Except that it is done in a separate tank. The effluent flows over a series of bubble makers. Any dissolves gasses are displaced by oxygen. Anything lighter than water will froth up into a layer of foam. By doing this in a separate tank, you can easily remove the foam from the surface for a much cleaner effluent.

Ive got a drawing of a simple de-gasser. I drew this up yesterday before work, so it may get tweeked before i actually build it. Here is the drawing.

[Vlad Jovanovic]

Tony...Just curious...are you going at this as a necessity for your system, or just a fun project? Are you expecting anything other than plant essential elements and bacteria to comprise that foam you want to remove?

[Tony Gilliam]

Vlad, Im not sure if it will be needed full time, but it should remove stuff like cottonwood seeds that plug up everything. The froth / foam can be left in the system if its not a problem. The main thing is de-gassing the water.

Here is another drawing with some explanations

[Tony Gilliam]

I can see this unit being helpful in the heat of summer as well, when it is hard to get enough D.O. and when the fish tanks are stocked heavy. The froth channel can be rotated to stop removing the froth.

As seen in the top view, A small water line can be installed in the end of the froth channel to flush the channel.

I have most of the parts already to build this unit, So it shouldn't cost to much to complete.

[TCLynx]

Tony, you say you have done the settling tank and now you are talking about degassing.  Seems that perhaps you have missed the intermediate step of some sort of net tank or other bio-filter that will also collect more of the fine suspended solids and provide space for mineralization.  I know in the UVI model they use a settling tank or swirl filter to catch the solids that settle quickly and then they send the water into the net tanks which are where the finer solids settle and start mineralization and it is after that when the degassing is really needed since it is in there that if left too long things could start to go anaerobic and you need to degas to remove the gasses that could be dangerous to fish and plants.

Now I know some people will also recommend that you let the degassing happen in the greenhouse or plant space since if there is much CO2 to degas you might as well let it happen where it will be of the most use to the plants rather than just a negative thing being blown out of the water.

[Tony Gilliam]

TCLinx, I don't know what the UVI model is. I have a background in waste water treatment and am building my system on what i know and the few question that have been answered on this site. I have never heard of a net tank. Sounds like a waste of time, If you take out what is heavier than water then take out that which is lighter then what is a net tank going to do.

I'm not trying to be a smart A$$, Im trying to learn.

[TCLynx]

The net tank is really where you do catch the lighter stuff.  The bird netting is just a way to do it that they have found reasonable in large scale operations since you can crank it out onto a hose real as you clean it off, then clean the tank and put it back in. It not only provides a place to collect the fine suspended solids but also provides surface area for bio-filtration.

The reason you put the degassing tank after the net tank is that some anaerobic activity will manage to take place in a very heavily stocked system in the net tank unless you are cleaning it very often.

Now most of this info in based on the UVI system which was run very heavily stocked and depended greatly on solids removal and they used rafts because they had difficulty with media beds in such heavily stocked systems without the net tanks.  They found that only about half the solids got collected in the settling tank and the other half tended to be too find and would settle out far later in the raft tanks and could form an anaerobic mat that would then float up and coat the plant roots and do damage to the plant production.

They also found that they could adjust the makup of nutrient production by how long they waited between cleanings of the net tanks.  If they left it a bit longer the net tank would get more anaerobic and allow for some denitrification which could work to the benefit of flowering and fruiting plant production or if they were wanting higher nitrate levels they would clean the net tank often to get the higher nitrogen content to the green leafy plants that didn't need as much of the other nutrients.

[Tony Gilliam]

Ok, Now i get it. Fish tanks - Solids settler - Net tank - De-gasser - Growbeds - Sump and back to the fish tanks.

In my system, I am going from the fish tanks - solids settler - de-gasser - 2 flood and drain growbeds - raft bed - sump - bio-tanks to the fish tanks. I was thinking of putting a screen between the solids settler and de-gasser. I guess this would do the filtering of the net tank. I have screens that where used for screen printing, the fabric is very tightly woven and is stretched over an aluminum frame that is 24"X30". These will have to be pulled out and rinsed often, but should not go anaerobic.

[Jon Parr]

Hi Tony. There are many ways to skin this cat, and I respect your background in waste water treatment. I think what Robert, Vlad, TC, and myself are wondering is why exactly you want a degassing tank? The answer to me, at least, is not obvious. Degassing tanks are usually used, as TC mentioned, in aquaculture not Aquaponics. High density aquaponics such as the UVI model also benefit from their use, because the growbeds are not sufficient to process all the fish waste without the eventual accumulation of both solids and nitrates. Solids are easy enough to settle and/or filter, and nitrates are converted to atmospheric nitrogen by anaerobic bacteria. Nitrogen is what is degassed in a degassing tank (and perhaps a little hydrogen sulfide and CO2). As you described your system with a swirl filter (usually about 20 minutes retention time), and perhaps an aerobic silk screen array, then there is no chance for any anaerobic activity to do any denitrifying, and hence nothing to degas. The CO2 present in aerobic conditions is not harmful to plants, and the subsequent flood and drain beds and aerated raft bed should supply plenty of aeration and "degassing" before return to FT. Unless I'm missing something (which is quite possible, even probable), then there may not even be a reason for a degas tank. Indeed, seldom are they used for backyard Aquaponics, because we want to use our nitrates for plant growth, not dump them to the air.
Also, what exactly are bio tanks?