Aquaculture Engineering

Aerators - Principle of aeration

Unit 12 - Management of ponds

Aerators

Principle of aeration
Atmosphere contains 21% oxygen. The rate of oxygen transfer into the pond water is an important parameter that governs the intensity of aeration. According to Dalton’s law, total atmospheric pressure (also known as barometric pressure) is the sum of partial pressures of the gases in the atmosphere.

BP = P(O₂) + P(N₂) + P (A_r)+P (CO₂)

The partial pressure of each gas in a mixture of gases is directly proportional to the mole fraction of the gas. For example, partial pressure of oxygen in dry air is,



When air is in contact with water oxygen enters the water until the pressure of oxygen in the water equals the pressure of oxygen in the air. This stage is called as equilibrium stage. The concentration of oxygen is normally given as the concentration (expressed in mg/lt) at equilibrium for water in contact with dry air at standard pressure (760 mm Hg) and specific temperature and salinities. Oxygen concentration is generally expressed as “C_s”.

If water contains the amount of dissolved oxygen that it should hold theoretically at a given temperature, pressure and salinity then it is said to be saturated with oxygen. But due to numerous factors, it may be saturated or super saturated with oxygen.Percentage of saturation is calculated as follows,