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Home - News - What are the classifications of dissolved air flotation?

What are the classifications of dissolved air flotation?

July 29, 2025

When it comes to dissolved air flotation, some friends may sound a bit unfamiliar, but in fact, this thing is widely used in fields such as sewage treatment and industrial purification. Simply put, it dissolves a large amount of gas in water and suddenly releases it, producing a pile of small bubbles that stick to impurities and float to the surface with them, thus separating dirt from water. However, there is not only one type of dissolved air flotation. According to different working principles and structures, it can be divided into several types. Today, let's break it down and talk about it to ensure that it is down-to-earth and easy for you to understand.

Fully dissolved air flotation

Let's talk about fully dissolved air flotation first. The name sounds quite "realistic", meaning that all the water to be treated must first go through the "dissolved air" step. How to operate it specifically? It is to extract a portion of the water to be treated, pressurize it, and then introduce gas, such as air, into it to fully dissolve the gas in the water, forming dissolved gas water. Then mix this portion of dissolved air water with the remaining water to be treated, and send it to the air flotation tank. As soon as the air enters the floating pool, the pressure suddenly drops, and the gas dissolved in the water will "bang" out, turning into countless small bubbles. These bubbles are like small balloons that will "grab" suspended solids and oil droplets in the water, float together to the surface, form floating debris, and finally scrape them off.

What are the advantages of this type? Because all water has been dissolved or mixed with dissolved water, a large number of bubbles are generated and evenly distributed, and the treatment effect is generally good. Whether it is treating oily wastewater or wastewater with suspended solids, it can cope with it. However, it also has a small drawback, which is that a portion of the water needs to be pressurized and dissolved, which requires specialized pressure pumps and dissolved gas tanks. The energy consumption may be slightly higher, and the equipment is relatively complex, taking up a larger area.

Partial dissolved air flotation

As the name suggests, the difference between it and fully dissolved air flotation is that not all water dissolves the air. Generally speaking, only a small portion (about 10% to 30%) of the water to be treated is extracted to make dissolved air water, and the remaining majority of the water is directly introduced into the floating pool. Then spray the prepared dissolved water into the floating pool and mix it with the water in the pool to release bubbles.

The benefits of this method are obvious, as only a portion of the water is treated, so the required pressure equipment power does not need to be too high, energy consumption can be reduced significantly, and the equipment is relatively simple, making operation more convenient. However, because the amount of dissolved air water is small, the bubbles generated may be a little less than that of fully dissolved air, so the effect of treating water with particularly high pollutant concentration may not be as awesome as that of fully dissolved air. But for general sewage treatment, such as the pretreatment of some industrial wastewater or municipal sewage, partial dissolved air flotation is still quite commonly used, with high cost-effectiveness.

 

Reflux pressurized dissolved air flotation

This name is a bit longer, let's talk slowly. Its idea is to extract the treated clean water (also known as reflux liquid) from the air flotation tank, pressurize it and dissolve it into air to make dissolved water. Then, the dissolved water is sent back to the air flotation tank and mixed with the raw water to be treated, releasing bubbles.

Why do we have to do this? Because the treated water has fewer impurities, it is easier for the gas to dissolve when used for gas dissolution, and will not be disturbed by pollutants in the water. Therefore, the gas dissolution effect is better, and more and finer bubbles can be generated. Moreover, the reflux is clear water, so there is no need to worry about the pollutants in the raw water affecting the gas dissolution process. In this way, even if the water quality of the raw water fluctuates greatly, such as having more pollutants at one time and less pollutants at another, it can still operate stably.

However, it also has its own characteristics, which are that the treated water needs to be pumped back and pressurized, which is equivalent to an additional reflux step. Therefore, in addition to the pressurization pump and dissolved gas tank, there must also be a reflux pump in the equipment. But fortunately, the reflux is clear water with fewer impurities, which causes less wear on the pump and pipeline, and can extend the lifespan of the equipment. This type has obvious advantages when dealing with wastewater that contains a lot of organic matter and is prone to clogging equipment, such as food processing wastewater and printing and dyeing wastewater. Using it for treatment yields stable and good results.

Electrolytic dissolved air flotation

This type is a bit 'high-tech', as it does not require specialized gas injection into the water, but relies on electricity to 'produce' gas. What's going on specifically? It is to insert two electrodes into the water to be treated and apply direct current. At this point, the electrode will undergo a chemical reaction, such as the anode producing oxygen and the cathode producing hydrogen. When these gases are first generated, they are very small bubbles that can float directly in water, playing a role in air flotation.

Where is the cow in this way? Firstly, it does not require an additional air compressor to supply gas, saving a lot of equipment. Moreover, the bubbles generated are really small, even finer than those produced by the previous methods, so the contact area with pollutants is larger, and the ability to capture pollutants is stronger. It is particularly effective in treating particularly fine suspended solids. In addition, during electrolysis, in addition to generating bubbles, the electrode reaction can also oxidize some organic matter in the water, playing a certain role in oxidative decomposition, which is equivalent to air flotation and "disinfection" at the same time, killing two birds with one stone.

 

Electrolytic dissolved air flotation

This type is a bit 'high-tech', as it does not require specialized gas injection into the water, but relies on electricity to 'produce' gas. What's going on specifically? It is to insert two electrodes into the water to be treated and apply direct current. At this point, the electrode will undergo a chemical reaction, such as the anode producing oxygen and the cathode producing hydrogen. When these gases are first generated, they are very small bubbles that can float directly in water, playing a role in air flotation.

Where is the cow in this way? Firstly, it does not require an additional air compressor to supply gas, saving a lot of equipment. Moreover, the bubbles generated are really small, even finer than those produced by the previous methods, so the contact area with pollutants is larger, and the ability to capture pollutants is stronger. It is particularly effective in treating particularly fine suspended solids. In addition, during electrolysis, in addition to generating bubbles, the electrode reaction can also oxidize some organic matter in the water, playing a certain role in oxidative decomposition, which is equivalent to air flotation and "disinfection" at the same time, killing two birds with one stone.

However, it also has a disadvantage, which is that it consumes a lot of electricity because the electrodes need to be constantly powered on to react. When the processing capacity is large, electricity bills may be a significant expense. Moreover, the electrodes will wear out over time and require regular replacement, resulting in slightly higher maintenance costs. So electrolytic dissolved air flotation is generally used in some small-scale treatment scenarios, or to treat difficult fine pollutants, such as laboratory wastewater, purification of some valuable materials, and so on.

To summarize

At first glance, these types of dissolved air flotation are actually designed around the core of "how to better dissolve gas in water and release bubbles to carry impurities". Fully dissolved gas has good effect but high energy consumption, partially dissolved gas is economical and practical, stable resistance to reflux pressure, and precise and efficient electrolysis but high cost. In practical use, it is necessary to consider what type of water is being treated, how many pollutants are present in the water, the amount of treatment, and the budget in order to select the most suitable type.

In fact, regardless of the type, the goal is to clean the water, turn sewage into clean water, and recycle useful things. Nowadays, environmental protection is receiving increasing attention, and the technology of dissolved air flotation is constantly improving. In the future, it will definitely be more efficient and energy-saving, and play a significant role in more fields. I estimate that when we hear this word again in the future, we won't feel unfamiliar.