Oxygen or Aeration
Tech Talk 80
Aerators that spray water through the air or put bubbles in the water can typically compete with the economics of pure oxygen up to about 70 percent of saturation. Pure oxygen becomes more economical when raising oxygen to levels above 70 percent.
Pure oxygen can be a very cost-effective tool for raising fish. It can unclutter the culture tank, reduce suspended solids, improve feed-conversion ratios and reduce stress. When used in large intensive culture systems, liquid oxygen can be purchased at a low price. It's especially cost-effective when used to raise the ambient dissolved oxygen a few parts per million to or above the saturation level.
But a high-tech approach is not necessary if a low-tech one will do. Simple old-fashioned aeration (done correctly) will provide one pound of dissolved oxygen (at 75 percent of saturation) for about one kilowatt of energy. That's about 10 cents per pound. Can you buy pure oxygen that cheap? If you can buy it that cheap, will 100 percent of it be absorbed, or will you lose some through escaping bubbles, leaks, etc.? Is a water pump or other energy source required? A 1-horsepower water pump by itself can burn another 10 cents per hour. However, if your operation is large enough or intensive enough to warrant aerating with pure oxygen, it can be a great tool when used wisely. Here are a few tips:
- Be sure to total all pure oxygen costs when figuring cost effectiveness, including storage vessel rent, water pumping cost and oxygen loss. If you're thinking about making your own oxygen, include the actual cost of compressed air, back-up compressor and increased generator size, plus repairs.
- Use a saturation technique that is at least 80 percent efficient.
- Inject supersaturated water over a wide area to prevent large oxygen gradients in the fish tank.
- In a recirculating system you will need to "aerate" (de-gas), in addition to oxygenation, to remove carbon dioxide.
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