Oxygenation Tech Info

Dissolved oxygen levels in aquaculture water are consumed through the respiration of fish and by the bacteriological degradation of organic matter. As fish densities increase, supplementation of the dissolved oxygen may be required to sustain a healthy environment for the fish. This process, called oxygenation, may be achieved through the use of specialized gas transfer equipment.

When a gas is in contact with water, the gas will continue to transfer in or out of the water at the water surface until equilibrium is reached. This point is the saturation concentration of the gas. The saturation concentration depends primarily on the temperature, pressure and the gas composition.

Surface area is increased through one of two ways. Either the water is broken up into thin films or small streams or droplets, or the gas is broken up into small bubbles. The surface area is proportional to the size of the droplet or bubble; small bubbles have more surface area per unit volume than large bubbles.

Under normal conditions, oxygen is approximately 21% of the total gas in air. Increasing the concentration of oxygen in an atmosphere will proportionately increase the saturation concentration of dissolved oxygen in water. Oxygenation systems typically use an input of pure (or almost pure) oxygen which allows for greatly increased oxygen levels over systems that use an input of air (with only 21% oxygen). Discharge of water with the resulting high concentration of dissolved oxygen into culture tanks, which are open to the air, means that the water could be “supersaturated” with oxygen. If the fish (and associated bacteria) do not consume the excess oxygen, oxygen transfer from the water out to the air will occur in the culture tanks. Normally, however, rapid mixing with under-saturated water prevents the excess oxygen from coming out of solution.