Theory of natural water aeration without complicated terms and mathematics.
Normal atmospheric pressure is about 1013 mbar. Below this pressure will be rounded up to 1 bar. The earth’s atmosphere is made of various gasses, 78% nitrogen (N2), 21% oxygen (O2), and 1% is other gasses and below we will not mention. Since the atmosphere of 21% oxygen, it is called partial pressure of oxygen at sea level 0,21 bar or 210 mbar. The altitude of the gas ratio does not change; only air pressure is changing, so on the altitude of 5500 m air pressure is only 0.5 bars, and partial pressure of oxygen is 0,1 bar. For humans and most animal, life is impossible at this height to survive due to lack of oxygen. Even too much of partial pressure of oxygen for metabolism is dangerous (oxygen toxicity). In the Water partial pressure of oxygen is very variable, in general, we can say that with the depth partial pressure of oxygen rapidly declines. Because this is the biochemical processes and oxidation. All the animals on land and in the sea have its maximum and minimum PPO (partial pressure of oxygen) where they can typically survive.
If we fill the pool with fresh water, in a few days the gas saturation in the pool will be completed. We can say that the saturation of gasses in this pool will be 100%, the partial pressure of dissolved oxygen in the water will be about 0.21 bar. When it blows a strong wind above the pool, the gas saturation, it will be several times faster. In these moments may also occur Hyper-saturation, and then in some areas of oxygen pressure will be more than 0.21 bar. This phenomenon took place when strong winds and currents pushed microbubbles in greater depth, which is going to transfer oxygen under increased pressure. When the wind loosened the inverse saturation occurs (gas transfer from the water back into the core).
If we put an excessive number of fishes in such pool, their number will begin to decrease until there is a balance between intake and oxygen consumption.
Constant winds over the lake slightly tilt the surface, causing vertical and horizontal movement of the entire water in the pool. The transfer of oxygen thereby increases several times.
The thermocline is formed in the spring and early summer when the surface layer of the water is heating up fast. If during this period, is no wind, the thermocline stabilizes at some depth, and it ‘s hard to break it after that. The Thermocline strongly inhibits the transfer of oxygen into the depths, and for that first organism that is not able to swim in higher layers like crustaceans, mollusks, worms are slowly disappearing.
If over the lake with a stable thermocline the wind blows, the water begins to circulate separately in the upper and lower layers (In this case, the level of the lake is slightly tilted). Both layers, in this case, are very poorly miscible. Long-term wind can break the thermocline and then it can establish a normal transfer of oxygen throughout the depth. If we want to raise more fish in the pool than nature allows with oxygen transfer, then we need to approach the artificial aeration. In the world today, we have many manufacturers of aeration systems, and all these systems have its good and bad properties. We will not go to analyze these aeration systems for now because it would be excessively broad.
Theory of artificial water aeration
As was initially mentioned, the partial pressure of oxygen in the atmosphere is 0.21 bar. In oceans, lakes, rivers the partial pressure of oxygen is very variable and is constantly changing. It is crucial that the transfer of oxygen can be established only if the concentration of oxygen in the media is varied. The greater is the difference of partial pressure; the faster is the transfer. To determine the efficiency of aeration systems we use oxygen tester. Through it, we will send the air out of the aeration basin.
On The graph B1, we can see that the percentage or of the partial pressure of oxygen in the air in the first moment is quite low. A few minutes later the partial pressure of oxygen begins to rise; this is because we aerate a new water in the beginning. However, since the air bubbles cause a vertical movement of the water, therefore, the same water begins to return to the aeration place, which happens that the transfer of oxygen into the water almost stops.
Aerating efficiency somewhat is improved if the pool is placed in a vertical tube. The bubbles in such tubes establish the vertical movement of water (buoyancy). In this way, we have established the conditions with aerating the water that has less oxygen. So one water that is clean in the bottom of the pool, as well as its weight of water in motion is significantly higher in Figure B1.
Even better performance is achieved with the extended tube in the horizontal direction at the bottom of the pool. Thereby it creates a movement of water in almost the entire basin. If the water in the bottom of the pool is considerably cooler than at the surface, it will rapidly fall back to the bottom, and come back into the tube. Such a phenomenon can be prevented or stopped by proper selection of compressor power.
If under the aerated basin is blowing the wind, at oxygen tester we will see that the aeration efficiency slightly decreased. This is happening due to the wind blowing over the pool and thus is additionally aerating the water in the pool. In this case, we could reduce the power of the compressor, thereby reducing energy consumption.