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?

[Tony Gilliam]

The de-gassing tank can be looked at as a place to aerate the water. I plan on a heavy load in the fish tanks, and can imagine that DO will be a limiting factor in the heat of summer. I can finish this de-gassing unit and install it for very little cash right now, as i have most of what is needed to complete it on hand. It may get used very little, but if i plan for it now, then when it is needed it will be a matter of turning a valve to put it in use.

The bio tanks mentioned before is a 10 gallon aquarium with the water inlet going through a 1/2" ring in the bottom of the tank. Next to the water ring is an air line, The tanks is filled with pea gravel and over flows to my 275 gallon IBC tote. I have 5 totes and 5 10 gallon bio tanks. These are inside my fish room, so i can easily heat them in the winter.

[Jon Parr]

Got it, Tony, thanks. So...more food for thought...fish demand the most oxygen in AP, especially in high density, so the extra air may be better served (or additional to...) just prior to fish, perhaps the sump. I like your bio tank idea. That is similar to "downdraft" aerators used in aquaculture, which I just recently discovered. They work by spraying water over a rock bed in a container with a screened bottom, and O2 is pumped into the container. The surface area and tumbling of water over rocks increases DO in a huge way, as compared to bubbling the O2 up thru rocks submerged in water. Efficiency is a big deal for aquaculture folks in this regard because they are buying bottled O2.

I look forward to some pics

[Tony Gilliam]

Jon, After all the discussion on this de-gassing unit. Ive been thinking that it may be better if i placed it after the raft just before the sump. That way the growbeds get all the good stuff that would be removed in the froth / foam. The CO2 will be released inside the greenhouse.

[Tony Gilliam]

Here is a pic of one of the bio-tanks. It doesn't have the airline or pea gravel in it yet, and the overflow piping still needs finished, but you should get the idea. The 1/2" PVC waterline has about 40 holes drilled in the bottom. The holes are 1/16th

[Jon Parr]

Thanks Tony. Maybe you could aerate the sump itself, and omit the separate degas tank. May be better than aerating and then letting the water settle in the sump.

A word of caution on the 1/16" holes...bioslime plugs everything up. I don't like anything smaller than 1/2", and that pipe array you have at the bottom of a pea gravel looks like it would be difficult to clean and maintain.

[Tony Gilliam]

Jon, I was planning to slightly aerate the sump. My sump is a 3 foot wide plastic coulvert pipe, that is buried 10 foot deep in the ground. It is not 100% sealed at the bottom, so it will leak AP water out and leak ground water in. When i installed the sump i had not yet heard of Aquaponics and planned on using ground water in my greenhouse. With the bottom totally open the ground water will fill the pipe overnight. Now that im using it as a sump tank, My plan is to pump out the ground water, lower a bottom of a 55 gallon drum in and sprayfoam between the drum bottom and coulvert pipe wall to seal it. I believe this will slow the tranfer of water but i dought it will 100% seal it. Im not looking forward to climbing down that ladder.

I think this is my only option because i installed the coulvert pipe and then built the greenhouse on top of it.

The yellow thing in the pic is a sealed lid on top of the sump.

[TCLynx]

Interesting.  The spray foam may surprise you at how well it can seal things.

Only worry is if the level in the sump drops much and you have a high ground water event it could try to float the sump up.

[Tony Gilliam]

Yea that could be a problem. At work we floated the floor on a 22 millon gallon concrete waste water tank buried 35 ft deep because the ground water pressure was to high when the tank was empty. $8 millon dollar oops. On my little tank, if it floats up i will make repairs and start the system up again. But a few stainless screw to start with couldn't hurt.

[Vlad Jovanovic]

Could you weigh down part of the bottom of the 55 gallon drum with a few inches of concrete and seal the concrete with bees wax, or acid wash it (so it doesn't mess with your pH) before sealing the 55 gal drum to the coulvert pipe (sump)? Or would that not help at all with possible floating..?

[Tony Gilliam]

That may help, I am going to put a ball float valve (toilet) to keep the sump topped off. I live in the country so i have a well with great water (no chlorine). I think that if i keep the sump full then the danger of floating the bottom will be alot less.

Another way to deal with it would be to leave the bottom partially open, this would relieve any pressure build that could lift the bottom. A couple unwanted things will happen, #1 my AP water will leak out when the ground water level is low, The ball valve will take care of that. #2 Radon gas will come out of the sump, That is controlled by the yellow lid. It is an old EPA container that is designed to put a leaking 55 gallon drum in. I cut off the top 10" and bolted it to the coulvert pipe. It has a rubber gasket to seal the lid, and now i can run a vent line outside the greenhouse.

[TCLynx]

Is there radon Gas leaking into that pipe?  If so I'm not sure you want to have that leaking through your AP water.  I don't really know anything about it but that doesn't sound good so I would want to do more research into it for my own system.

Keep in mind that the whole point of a sump is to handle water level fluctuations so if you are putting a valve in it to keep it topped up, then when things drain into it, it would overflow which would also loose you your good AP water.  So make sure that the top up level is below the "normal" low water level of the flood and drain.  I admit to having sump tanks sunk part way in the ground but I like to keep them filled up to as close to ground level as I can so that ground water levels can't float them.  I have a benefit of having much of my system out in the open so when we get heavy rains, my sump tanks get filled up too so I'm not likely to experience a rain event floating my sump since my sumps are getting filled by such rain events along with the ground.  However, if your systems and sump tank are protected from rain, then it becomes more likely that a rain event could catch your sump tank empty enough to float.

[Tony Gilliam]

The fill valve will be placed as to leave room for the level to fluctuate in the sump, but the raft will take most of the system fluctuation. Have a set overflow out of the raft and let it take the hit when the syphons dump. The raft will float up and down as this happens. (it works really well in my head) Now i have to build it.

Radon gas is a problem here in north central Ohio. It is a naturally occuring gas that is released from the soil and is linked to cancer. It is usually not a problem unless concentrated such as in a basement or greenhouse. So if you plan for it and properly vent it out of the confined space, its really a non-issue.

I just had a thought about the froth / foam from the de-gasser. Concentrate it back to a liquid and inject it back in the grow beds or use it as fertilizer in my traditional (dirt) garden. Any thoughts?