Backyard Aquaponics
A place to discuss aquaponics

Hey everyone!

I'm new to the forums. I'm currently an aquaponics intern down in the Caribbean and am in charge of finalizing some new system design aspects. The question I am on right now is, do we need a degassing column? I am not all too familiar with degassing columns. How necessary are these devices? Are they at all? The new design will have 8 rearing tanks at 795 gallons each, 2 fingering/fry tanks (not sure of the gallon-capacity, their dimensions are 8' x 2' x 2'), one 750g cull tank, and one 750g tank for females. We'll have 2 clarifying tanks and 2 polygeyser biofilters before the flow runs to 10 beds that measure 24' x 4'. We mostly use air stones and some small, open water falls for aeration right now and don't currently have a DO problem. But, we also only have 2 rearing tanks right now. With the expansion and added volume, would air stones suffice on their own?

I've only had experience with a much smaller system. It was more an educational model than a truly, productive design. Any help and information would be greatly appreciated.

Cheers!
Ashley

out of my league nt sorry

but if your conversion ratios were fine then it may not be required.

I think degassing columns are needed for specific purposes like degassing certain chemicals, CO2, or perhaps if you are using Ozone or pure O2. I've seen some pretty big Aquaponic systems that use nothing more than air stones and slow moving water for aeration.

I've heard a rule of thumb that if you are depending on air pump/blower and air stones for 100% of your aeration, then you need about 1 cubic foot per minute of air per every 400 gallons of tank at your setup's PSI (large air stones often require about 1 psi and every 28" of water depth requires another 1 psi to push the air down there. So in general you need at least 2-3 psi for most blower arrangements.) Anyway, that is all just regurgitated from what I was told at Aquatic eco systems.

What kind of fish are you growing, Tilapia?

You mention bio-filters and long beds. Will the beds have media and be flood and drain? Or are they a DWC set up? Most of use have found that flood and drain media filled grow beds provide ample bio-filter while also allowing for plant growing space and plenty of degassing and aeration.

Truth is, most of us here are only doing backyard aquaponics so your question is really beyond some of us. Good Luck in your search for answers

Degassing is usually accomplished by exposing as much of the surface area of the water to air as possible... "open water falls for aeration"... is one way of acheiving "degassing"...

Good sized airstones with high flow will also "boil" the water... exposing large areas to the natural air...

They also produce a myriad of small bubbles that saturate the water with oxygen... and should themselves help offgas CO2....

The only other times I've heard of "degassing columns" being used are for removal of Nitrogen and/or hydrogen sulphide... either due to anaerobic conditions, which would probably be more than obvious... or from bad source water....

If I remember rightly the polygeyser biofilters incorporate an airlift in their design... may be sufficient in themselves.

Not sure just how much need you might have.... what are your stocking densities and how much feed are you using/projecting per day?

Just an aside... anything over 40kg/m3 stocking density will require direct O2 injection... you just can't saturate sufficiently using normal air to maintain densities above that...

Perhaps you should incorporate some aquaponic growbeds into the system... they'll solve your problem...

Meant to say "flood and drain" growbeds.... I'm assuming, as TCL said, that you have adopted a DWC style of operation... ala UVI...

If so flow rate is the key, with aeration as the flow enters the beds... not sure whether your clarifiers and polygeyser biofilters will remove all the solids or whether you'll need an additional solids removal capability....

UVI removes all solids prior to the DWC beds...

To answer some of your questions ...

Yes, we are growing Tilapia and will continue to do so. We do currently have a DWC set-up. However, the new style of the hydroponic grow bed set-up is not definite. Would we greatly benefit from switching to ebb and flow? All research I had done prior to arriving down here had a flood and drain system showing a lot of benefits...

I'll check on the current and projected stocking densities as well as the amount of feed inputed into the system each day.

These are rather interesting and should be an easy build http://saltaquarium.about.com/cs/skimme ... i.htm?rd=1
Certainly would degass and might even work as a skimmer in fresh water.