General information about water aeration
There are many types of aeration systems offered throughout the world, particularly for wastewater treatment. Air is added to water to enrich it with oxygen. This enables the existence and development of both marine life and micro-organisms in the water (ponds, pools, lagoons, and lakes).
One of the most critical applications of dissolved oxygen is in wastewater treatment systems, the so-called aeration basins. In these pools, the wastewater has large amounts of organic matter. When such water is aerated, it starts to ramp up the population of specific microorganisms that decompose organic matter in the wastewater. This phenomenon is what makes dissolved oxygen so critical in municipal sewage treatment plants.
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Aeration Underwater Effect
There are three primary groups of aerator as described below:
The most common way to inject dissolved oxygen into water is by using an air compressor. Reciprocating or rotary screw compressors draw air from the atmosphere and push this air through a pipe into the water. This is the most energy-efficient approach, but it is also financially and technically complex.
Jet aerator –
In a Jet Aerator, a pump pushes water through pipes that exit under high pressure through a nozzle in special air chambers. This technique is known as JET aeration. Again, this is a financially and technically tricky design, as well as being very energy-inefficient.
Turbine aerator –
The most straightforward and least expensive technique for the aeration of water is the turbine aerator. This class of aerator is known as self-aspirating aerator on the SAA (Standards Association of Australia). The standard feature of these aerators is that they do not need any external systems. The entire aeration process takes place within the aeration chamber or in the immediate vicinity.
The advantages of turbine aerator are as follows:
1.) They are relatively inexpensive,
2.) They combine the physics principles of centrifugal force and precession as it applies to rotating fluids,
3.) They are easy to install,
4.) They require minimal maintenance, and
5.) They are very energy-efficient with most of the mechanical energy of the electric motor being converted into water turbulence.
6.) They are self-suction so no need extra pressure to work
Many global manufacturers of water aeration equipment refer to the energy efficiency of their product with the formula: Kg O² / kWh. This simplified formula explains how many kilograms of dissolved oxygen can be placed into the water per kilowatt-hour. A detailed look at this equation shows that it does not take into account two essential elements that are:
1.) The depth of the water at which the transfer of oxygen takes place, and
2.) The saturation of water with oxygen during the aeration process.
Turbine Aeration Performance
Given the following parameters, what is the length of time it will take one Turbine Aerator to aerate a water basin?
1.) The length of time for complete oxygenation is dependent upon some contaminants in the water. If the contaminant level is high, the microbes will grow dramatically in numbers. As they grow, they will consume almost all the dissolved oxygen as quickly as the Turbine can inject it into the water. At first, a dissolved oxygen meter would show little or no increase in the dissolved oxygen content. As the contaminants are processed and eliminated by the microbes, the microbe population will begin to decline for lack of a food source. When this happens, the microbes will consume less dissolved oxygen, and the dissolved oxygen level will start to rise.
2.) The length of time for complete oxygenation will also depend upon the throughput if any, of the contaminated water. If there is a large flow-through of contaminated water, the dissolved oxygen will be consumed almost as rapidly as it is injected. It likely would never reach saturation. If the water is static, meaning no throughput of contaminated water, then the level of dissolved oxygen will eventually begin to rise. Septic conditions (i.e., Toxic conditions caused by bacteria) are considered to occur at a dissolved oxygen level of 2.0 parts per million (ppm) or less. If the dissolved oxygen is greater than 2.0 ppm, then the aeration process is working positively.
3.) The amount of time for complete oxygenation throughout the basin will depend somewhat on the shape of the basin. Around or circular basin eventually will be covered with dissolved oxygen. On the other hand, in a very long and narrow basin, which has the same volume of water, the dissolved oxygen might never reach its extremities.
Two Basic Turbine Setup
4.) The amount of time that a single aerator can be allowed to work will decide how much volume of water can be treated. Given enough time in a static pit, a single Turbine can aerate a rather large basin.
Based on the above empirical performance and other such tests, a single Medium Aerating Turbine can be expected to process up to 20,000 m³ of contaminated water in a static basin. In two days, any odor likely will be much diminished. In 7 days, large patches of clear water will be observed around the Turbine. In 30 days, the dissolved oxygen level will begin to rise significantly. Notwithstanding this performance, a static 20,000 m³ basin should realistically have at least two Medium Turbine aerator for optimal performance. If there is a flow-through of contaminated water, then more Turbines would be needed.
Sample of the Technical Summary of Turbine Aerator Performance