Oxygenation in Aquaculture

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OXYGENATION IN AQUACULTURE  2002 Point Four Systems Inc. A Simple Equation Managing and controlling dissolved gases (O2, N2, NH3, CO2) is a key factor when controlling water quality for successful fish culture. In general (for re-circulating and flow thru systems), the higher the fish density and the lower the water flow rate, the more critical this issue becomes. In intensive fish culture, dissolved oxygen is usually the first limiting factor. It's about Balance When water is in contact with air, each of the gases contained in air (N2, O2, etc) will move into or out of solution to achieve equilibrium between the liquid and gas pressure phase. At the point of equilibrium, the water is said to be "air-saturated". If the concentration of any of the dissolved gases is altered (i.e. consumption of O2, production of CO2), the said gas will diffuse into or out of the water until equilibrium returns. The rate at which a particular gas dissolves in water depends on the following factors: surface area, pressure, salinity and concentration. When the consumption rate of oxygen becomes greater than the resupply rate through aerators or the available oxygen in water supply, supplementation with pure oxygen becomes necessary. Supplementing Nature Three common methods of increasing the concentration of dissolved oxygen in water are: Aerators, Oxygen Diffusers and Pressurized Packed Columns. Aerators - add oxygen to water by increasing the air-water surface area by spraying water droplets into air or bubbling air into water. Although aerators can be very efficient, the amount of oxygen that can be dissolved in water is limited by the concentration of oxygen in the air (21%). Oxygen Diffusers - diffuse very fines bubbles of pure oxygen into the water. The oxygen transfer rate is increased through the extremely high surface area of the bubbles and the use of pure oxygen. Pure oxygen
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