Degas Towers

A degas tower strips dissolved carbon dioxide from recirculating water by breaking the flow into droplets over packing in a counter-current air stream; it is the piece of equipment most often missing when a recirculating aquaculture system underperforms.

Degassing is frequently overlooked in recirculating systems that otherwise appear to have adequate circulation and oxygenation.

What it does

CO₂ removal. Fish produce carbon dioxide continuously. In a recirculating system, CO₂ can accumulate, affect pH, and impair growth or feed conversion before it becomes acutely dangerous. Aeration and oxygenation do not necessarily provide adequate CO₂ removal, so a system can maintain dissolved oxygen while still being limited by carbon dioxide.

Nitrogen removal. Where supersaturation is a risk, certain groundwater sources, or systems with air entrainment on the suction side, degassing prevents gas bubble disease.

Incidental oxygenation. A degassing tower adds some dissolved oxygen as a by-product. It is not a substitute for dedicated oxygenation on a heavily stocked system.

Where it’s used

Recirculating aquaculture at higher stocking densities. Hatcheries. Marine and freshwater holding systems with high biomass. Systems using groundwater or well water where dissolved-gas conditions or supersaturation may require treatment.

Why specification matters

It is sized on CO₂ production, not on flow alone. Carbon dioxide output follows feed input. A tower sized against circulation rate without reference to feed load will be undersized on exactly the systems that need it, the heavily stocked ones.

Air-to-water ratio is the performance variable. Stripping efficiency depends on how much air passes each unit of water. That sets the blower duty, and blower duty is where the operating cost lives. Under-specify the air side and the tower is decorative.

Packing height and media selection determine contact. Taller towers with appropriate media strip more per pass. Ceiling height in the building frequently constrains this, which is a constructability question to answer before the equipment is bought rather than after.

The tower has to sit at the right elevation. Water falls through it and has to be collected and re-pumped. That places it high in the hydraulic profile and adds a pumping step. Systems designed without accounting for this end up with a tower that cannot be installed where the drawings show it.

Ventilation is a real requirement. The stripped gas has to leave the building. Venting CO₂-laden air into an enclosed equipment room creates both a staff hazard and a system that re-absorbs what it just removed.

Media fouls. Biofilm accumulates on packing and reduces transfer. Access for cleaning or media replacement has to exist.

How SIVAT helps

We size degassing against feed loading and target CO₂ concentration rather than flow alone, confirm the air side is specified to match, and check that the tower fits the building’s hydraulic profile and ceiling height.

Where a recirculating system arrives with aeration specified and no degassing, that is one of the first things we flag.

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Common questions

Why is degassing necessary in a recirculating system?

Fish and biological filtration both produce carbon dioxide. In a system with little water exchange it accumulates, depresses pH and suppresses feeding and growth long before it becomes visibly obvious. A degas tower strips it out by exposing a large surface area of water to counter-current air.

How is a degas tower sized?

On the gas load the system produces rather than on flow rate alone. Feed load, biofilter output and the target carbon dioxide concentration set the packing depth and air-to-water ratio.

Can a degas tower be added later?

It can, but retrofitting is costly. The tower needs head, floor space and a return path, and a system built without those provisions rarely has anywhere convenient to put one.