A Pond aeration system is essential for the lives of plants and fish, avoiding both the decay of animals, bacteria and organic material, and the accumulation of mosquitos which may spread various diseases. Read More
The transfer of O2 from the air – of which oxygen makes up only 21% – to the water must be carried out either by natural means such as by water waves, currents, or the entry of new water, etc., or through mechanical elements which bring the oxygen needed by plants and fish, until the volume of O2 in the water reaches between 7 and 14 mg/liter of water, as for higher indices the excess O2 will tend to return to the atmosphere.
The majority of the mechanical means used to transfer oxygen to the water are used in the superficial layers where the temperature is higher, and through lower layers this temperature decreases, and with it so does the concentration of oxygen in the water. The maximum concentration of oxygen which water of 15ºC will allow is 17 mg/l (milligrams per liter).
On the surface of the pond stagnant water, a film is formed by dust, pollen, etc., which prevents the direct passage of oxygen into the water. This film is made denser by the CO2 which emanates from the bottom due to the decay of plants, rotting animals and gases which accumulate, preventing the direct passage of oxygen into the water. Therefore it is necessary to move the water to increase the dissolution of O2, or directly input the oxygen from the air into the lower layers of the water, thus achieving the pond aeration.
How to obtain a high pond aeration coefficient in the water.
To achieve a good transfer of air to the water, it is necessary for the air bubbles introduced into the water to be in contact with it for the longest time possible – as the longer this contact lasts the greater the dissolution of O2 in the water will be – and additionally that the bubbles are of the smallest size possible, as the dissolution of the O2 in the water occurs on the surface in contact between both elements.
Procedure for pond aeration system.
In practice, and even when there are a multitude of methods, the most commonly used are mechanical paddle wheel aerators, floating fountains, and submerged aerators which use the Venturi effect.
- Mechanical Aerators: consist of a motor which makes paddles turn, which move the surface of the water, producing splashes which meet the atmosphere and are covered by a fine layer of air, then fall again into the pond bringing this air with them and transferring it to the rest of the pond. This system is often used in purification plants to recycle water, but only aerates the superficial layers.
- Floating fountains: this type of fountain, as well as achieving a pleasing aesthetic effect, allows the pond and lake aeration. The method is simple, as it is aided by the jets which break up into small spheres of water, making contact with the atmosphere and returning with a film of air, falling back into the pond to transfer the air which surrounds them to the rest of the water.
Additionally, the splashes which the falling water creates generate a wave motion on the surface, aiding the breakage of the superficial film formed by dust, pollen and CO2, thus increasing the pond aeration.
- Submerged aerators (1- Floating fountain + Horizontal aerators; 2- Horizontal aerators): these bring the greatest quantity of O2 to the water per KW used, optimizing the pond aeration. This type of aerator is based on the Venturi effect, creating a depression capable of sucking air into the Venturi chamber or Hydro-air-ejector through another tube which connects with the atmosphere. Once both water and air are mixed, they are pushed to the interior of the pond, and it is advisable to direct this combination downwards, forming a 45º angle with the surface of the water to obtain a greater transfer of air to the water.
In the specific case of the submersible aerators made by Safe-Rain, they must be provided with a 45º elbow with a female ø 1-1/2” thread in case of adding a section of tube which will bring this mixture of water and air to a determined depth, although this depth must not be greater than 1.5 meters.
In our floating aerators, two pumps of the same power are installed, each one with a Hydro-air-ejector. In the interior of each of these and due to the strong velocity they achieve, the air mixes with the water in a multitude of small bubbles which due to their small volume rise slowly towards the surface, thus allowing more time for the maximum transfer of air to the water. This type of aerator requires low pressure to function, which implies low consumption motors, as the best performance is achieved with pressures between 0.2 and 0.5 Kg/cm2.
In trials carried out by Safe-Rain, the best results were obtained with pumps of 130W - 220W and 420W which, through the Hydro-air-ejector, provided the pond with the flows indicated in the following table:
|Pump Voltage||Power in W||Flow of water in liters/ hour by Aerator||Flow of O2 in liters/ hour by Aerator|
|230 V-50Hz||130 W||10.800||2.268|
|230 V-50Hz||220 W||12.000||2.520|
|230 V-50Hz||420 W||14.760||3.099|
|120 V-60Hz||420 W||14.760||3.099|
Of these amounts of air brought to the water by the Hydro-air-ejectors, only 21% is oxygen and the rest nitrogen and other noble gases which are in the atmosphere. Therefore, in calculating the amount of O2 necessary for the total volume of water to be treated, the information on the air provided by the Aerator must be taken into account (1 Submerged Aerator = 2 Hydro-air-ejectors), as well as the number of hours per day that it will function. It must also be taken into account that most of the water transferred to the pond rises through the water to the surface where it evaporates. Therefore it is necessary for the function time of the aerators to be at least 4 times that of the results obtained with the previous data.
Calculation of the volume of water to oxygenate
When determining the number of hours that our floating or submerged aerator must function to oxygenate a pond, we must know the volume of water to be oxygenated. Therefore it is necessary to calculate the surface and depth information of the pond or lake.
If the pond is large, with a uniform shape and a horizontal bottom, it will take the measurements indicated in the image. If it has a constant slope from one side to the other, it will involve greater measurement. Enter the water if you cannot make the measurements from outside, and measure the depth at nine or more points in the pond to obtain the average depth.
If the pond is large, with an irregular shape and an irregular depth, draw a 5m x 5m grid over its surface. Enter the water if necessary and measure the depth at each intersection of the grid. Make an average of all the measurements.
Once the area of the pond is calculated in square meters (m2) and the average depth of the water is calculated in meters according to the above, the volume of water in cubic meters (m3) can be calculated, multiplying the number of square meters of the surface by the average depth in meters.
|Surface area in m2||Average water depth in meters||Volume of water in m3|
|235 m2||1,00 m||235 m3|
|450 m2||1,20 m||540 m3|
|2.500 m2||1,50 m||3.750 m3|
In cases where the installation of several submerged aerators is necessary because the volume of the pond requires it, it is advisable to place them with sufficient distance to cover the whole surface of the pond, although the depth of each area must be taken into account so that the distribution of aerators is carried out not only by the area covered but also by the volume of water corresponding to that area.
We hope that this post helps you to achieve a suitable artificial pond aeration.