OXYGENATION IN AQUACULTURE
A SIMPLE EQUATION
Managing and controlling dissolved gases (O2, N2, NH3, and CO2) is a key factor when controlling water quality for successful fish culture. In general, (for recirculating 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.
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 fine 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 systems achieve much higher dissolved oxygen levels than aerators. See page 63 in the Master Catalog for more information or learn about Point Four Micro Bubble Oxygen Diffusers on the product page.
Pressurized Packed Columns (PPC)—Sealed - mixing water with pure oxygen under high or low pressure conditions can achieve very high oxygen transfer rate. Pressurized Packed Columns can achieve 100% oxygen utilization (or absorption efficiency) and there are no oxygen losses. Initial equipment costs are relatively high and can be offset by lower operating costs. See page 76 in the Master Catalog for more information or learn about Pressurized Packed Column systems on the product page.
PENTAIR AES EXPERTISE
Suitable methods of oxygen supplementation are application dependent and site specific.
Contact a Pentair AES representative for assistance with your oxygenation needs today.
Phone Orders and Tech Advice: 407.886.3939 • Online Orders: PentairAES.com • Email: PAES.General@Pentair.com • 2395 Apopka Blvd., Apopka, FL 32703