Caring for the environment is now reaching the global level. This is especially true for wastewater treatment, which is subsequently discharged into ponds and soil. To ensure high quality wastewater treatment and completely neutralize the negative impact of pathogenic microorganisms on the environment, many methods are used depending on the type of water pollution. The most effective method is the flotation method or simply the flotation of effluents in an electric flotation machine.
This method is optional after mechanical wastewater treatment, since not all impurities are of sufficient weight to succumb to the force of gravity. As a result, after the mechanical treatment of wastewater and their settling in gray water, particles of debris remain, the mass of which is many times lighter than the molecules of the liquid. It is for the purpose of removing such impurities that flotation is used as a method of post-treatment of wastewater.
About what is flotation and what are its types, we understand in our material.
Flotation is a peculiar way of cleaning polluted water, translated from English as "floating". That is, the removal of debris impurities from the liquid medium occurs due to their ascent to the surface as a result of the addition of special dispersed air to the drains. Under its influence, all molecules and particles of debris are either wetted by water (which is hydrophilia) or not subject to wetting (hydrophorbia).
The principle of operation and the scheme of the wastewater flotation method is as follows:
- In a special machine (electric flotation machine), wastewater passes through the working chamber;
- At this moment, depending on the type of pollution, the effluents are enriched with dispersed air;
- Pollutant particles come into contact with oxygen bubbles;
- As a result of contact, a reaction occurs in the form of the formation of a foam layer on the surface of the water. It is these floating particles of impurities that are called the fleet. That is floating debris.
- The foam layer, as it forms, is removed from the surface of the medium being cleaned by special rakes.
Important: the flotation method is used mainly for the treatment of wastewater with impurities of soluble fats, petroleum products, surfactants, any fibrous impurities, etc.
Flotation Method Efficiency: Important Parameters
During the purification of gray water with the use of reagents (flotation) may have different efficiency. And it depends on the following parameters:
- The more impurities in the water are prone to hydrophobicity, the higher will be the efficiency of the flotation method of water purification. But, unfortunately, not all impurities have an increased or even optimal tendency to wetting. To change this property, special reagents are added to the water in the electric flotation machine, which change the level of hydrophobicity of the garbage upwards. Reagents are called floating.
- All air bubbles must have increased resistance to destruction, which is also achieved by adding reagents to the water.
- The size of the air bubbles is also important for the efficiency of the flotation wastewater treatment process. So, too large bubbles quickly float to the surface of the water without making contact with debris impurities. And small bubbles, on the contrary, just burst. The oxygen bubble must be large enough to make contact with the debris and lift it to the surface of the wastewater.
- The total number of air bubbles and the uniformity of their distribution in the drains are also important when cleaning the liquid by this method.
Pros and cons of using flotation
The flotation method as a method of wastewater treatment has both its advantages and disadvantages. The first ones include:
- The low cost of the liquid treatment method itself in order to purify it;
- High efficiency of the process in case of separation of certain impurities from water;
- High wastewater treatment rate as a result of using one of the flotation methods;
- The ability to purify water even from the molecules of petroleum products.
The disadvantages of the flotation method include:
- Selective action of air on debris particles due to their low hydrophobicity;
- The need for additional use of reagents to increase the level of hydrophobicity of garbage particles in wastewater;
- The need to fine-tune the electric flotation machine in order to obtain air bubbles of a certain diameter.
Types and methods of flotation
Effluent treatment by flotation can be carried out in various ways. That is, it is the formation of air bubbles that occurs using various methods. Let's consider all possible.
Isolation of air bubbles from a special solution
Moreover, here the air can be released both by the pressure method and by vacuum. In the first case, air is launched into the water under high pressure, as a result of which the necessary bubbles form on all layers of the water. In the case of vacuum flotation, the waste water passes through an aeration chamber, where it is strongly saturated with air. After that, the effluents enter the deaerator, where excess air (not dissolved) is removed from the water. Then the gray liquid is poured into the flotation chamber, where the pressure drops to a critical point, from which the formation of air bubbles occurs.
Important: such methods do an excellent job of purifying water from fine and fine impurities.
Mechanical way to saturate water with air
This method of enriching wastewater with air consists of three main methods:
- Mixing wastewater in a special centrifuge using a turbine. In this case, the installation is called an impeller and makes it possible to achieve the formation of bubbles of small diameter. Basically, the impeller is used to purify water from oil products or fats. The impeller is good in that it allows you to vary the size of the air bubbles as a result of the flotation scheme. That is, the higher the speed of rotation of the turbine, the smaller the bubbles in the water.
- Mixing of water by means of a special impeller with blades. This method is non-pressure and is good for removing coarse and fibrous impurities from water, such as hair, threads, wool, etc. Bubbles with a non-pressure flotation method are quite large.
- Enrichment of wastewater with air using special pipes, which are located at the bottom of the receiving tank for dirty water. This method is called pneumatic. It is used when there is a need to treat effluents that are aggressive to be treated in an impeller or free wheel.
Important: with any of the methods, the scheme consists in conducting water through the swirling stage, as a result of which the necessary air bubbles are formed.
Saturation of water with air using a porous material
This method consists in conducting an air flow through special porous structures. An example is special thin plates with thin slots around the entire perimeter. Moreover, the thinner the gap in the plate, the smaller the air bubbles will be.
Electrolysis
This method of forming air bubbles is considered one of the most effective. The scheme of the method consists in placing special electrodes into the water, through which current is conducted into the drains. At the location of the electrodes (at the point of their contact with water), the necessary bubbles are formed.
Important: the use of special aluminum or iron electrodes is now common. In addition to the function of conducting current into the water, they are also coagulants, which makes it possible to form flakes from suspended debris particles in the water. As a result, cleaning becomes more efficient.
Reagents in flotation
To improve the quality of dirty liquid cleaning by flotation, special reagents are used. They are designed to increase the level of hydrophobicity of impurity particles in water. There are two types of reagents for flotation:
- Reagents to enhance the hydrophoricity of impurities. They are also called collectors. These are various petroleum products, ammonium salts, oils or mercaptan.
- Substances for stabilizing foam on the surface of the water, i.e. foam concentrates. Such reagents prevent premature destruction of air bubbles. Most often, cresol, pine oil, phenols, etc. are used for foaming.
Important: for the flotation method of wastewater treatment, electric flotation devices are installed exclusively after sedimentation tanks and filtration chambers, since flotation is not an independent method of treating dirty water, but is only an additional method of neutralizing dirty liquid.
Loading...