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by Amy Stone*
As things continue to heat up in the Aquaculture Industry in the United States, it is becoming more and more important to understand the key pieces to success. One piece to being successful is to avoid waste. As we all know, the lower the production costs, the more possible profit there is to be had and a quicker return on investment.
Ozone is a major capital cost for a production facility so maximizing its efficiency only makes sense so that nothing is wasted. In a prior article, we discussed different types of ozone generators. In this article, we will review typical ozone contact vessels. Important ozone considerations that can never be reiterated enough.
Ozone is a deadly gas. It attacks all organic material, including animals and humans. When using ozone, proper safety and maintenance protocols are critical to avoid injury. It is a very powerful disinfectant and when used properly, can help facilities avoid disease and remove off-flavors. In marine systems, it can help increase the efficiency of protein skimmers.
Regardless of how the ozone gas is generated, it still must be dissolved into the system water in order to work properly. There are several types of contact vessels and methods.
Unpressurized Contact Chambers
Unpressurized contact chambers are any open to atmosphere vessel that is meant to provide contact time for the ozone and water. These can be repurposed Low Head Oxygenators that have been modified to include ozone safe materials. They can be degassing towers that have ozone safe materials, including media in some cases.
When using unpressurized chambers, a vacuum should be applied to remove any residual ozone and send it to an ozone destruct system. Ozone gas destruction can be done through heat or by having the gas pass through a special “destruct” media. This is an important step as uncontrolled ozone gas release is not only dangerous to living animals/humans, it can also damage equipment.
Pressurized Contact Chambers
Pressurized contact chambers are exactly what they sound like. They are often made from structured fiberglass tanks made to withstand high pressures. The concept behind these chambers is that it is sized to match the volume that the engineer has determined to be the contact time.
Meaning, if the engineer has created a system that has a two-minute contact time and the flow is 100gpm, the chamber will be around 200 gallons in volume.
“These tanks can vary in their complexity based on the engineer’s requirements.“
Some of these tanks include intricate internal plumbing to assist with mixing and others are merely an empty vessel. Ultimately, the water just needs to be able to mix with the ozone for the required contact time.
Speece Cones
Speece cones are a more novel way of dissolving ozone into water. They work on the concept of creating a bubble of gas that is sheared as the water travels down the cone. With this cone style vessel, the ozone gas is not wasted to atmosphere. It stays in the cone until it is dissolved into the water. Traditional contact vessels are unable to dissolve 100% of the ozone into solution so a portion of the ozone is wasted through a destruct system.
Other Considerations
As with all designs, there are pros and cons. Some are more capital intensive than others. Some are more labor intensive than others. In general, unpressurized chambers are less capital intensive but they tend to be least efficient in dissolving ozone.
Pressurized chambers are more capital intensive but tend to be more efficient than contact towers in dissolving ozone. The Speece cones are average in pricing and highly efficient but also require steady gas flow and water flow as they do not react well to fluctuations in either input. Site conditions as well as the overall system design will ultimately reveal the most effective style of contact chamber.
Amy Riedel Stone is President and Owner at Aquatic Equipment and Design, Inc. She was formerly a Manager at Pentair Aquatic Eco-Systems, and she studied Agriculture at Purdue University. She can be reached at amy@aquaticed.com
