The Current Status and Development of Air Floatation Technology

The Current Status and Development of Air Floatation Technology

Abstract: Air flotation technology is an increasingly widely used sewage treatment process in recent years. On the basis of traditional air flotation process, some new processes have been developed, such as cavitation air flotation (CAF) process, shallow air flotation process, etc. A review and analysis of the development and application of various types of air flotation processes were conducted, and their evolution was discussed.

Keywords: air flotation; sewage disposal

Preface: Air flotation is a long-standing solid-liquid separation technology, and air flotation water purification technology is widely used both domestically and internationally. The principle is to introduce a large number of tiny bubbles into wastewater, which interact with particles through surface tension, including complex processes such as adsorption, flocculation, and hydrodynamics. Make it adhere to suspended particles, forming a state where the overall specific gravity is less than 1, and float to the water surface according to the principle of buoyancy, achieving solid-liquid separation and purifying sewage.

In the field of water treatment, as early as 1920, C.L.PECK considered using air flotation to treat wastewater. In 1930, a Swedish paper mill tried a water treatment method that dissolved air in white water under pressure, but the above experimental results were publicly published and received sufficient attention [1].

Before the 1960s, the development of air flotation technology was slow, and there were few reports on its research and application. The main reason for this was that the technology for producing microbubbles was not up to standard, especially when using dispersed air flotation. The bubbles produced were not fine enough, and the adhesion ability of particles was long. Large bubbles also generated severe turbulence and crushed flocs. At first, dissolved air flotation mainly used cloth air flotation to treat wastewater containing water and substances with lower specific gravity than water, such as oil, fat, and fiber.

In the late 1960s, China had pressure dissolved gas devices applied to the purification of salt solutions and the treatment of petroleum wastewater.

In the 1970s, air flotation technology developed rapidly, and the use of partial reflux dissolved air flotation significantly improved the status of air flotation.

At present, pressure dissolved air flotation is the most widely used method.

According to the different methods of bubble generation, it can be divided into the following categories.

Induced Air Flotation (IAF)

The working principle is that the generation of microbubbles in the air entraining aerator is achieved by using a motor to drive a diffuser disk with micro pores around it to rotate at high speed, forming a negative pressure zone in the water. The air on the liquid surface is sucked into the water to fill the vacuum. When air enters the water, it is cut into bubbles with a diameter of 10-100 microns by the turntable.

The sewage to be treated first enters a small inflatable section equipped with an air guiding aerator through the inlet. During the process of sewage rising in the inflatable section, it mixes with microbubbles generated by the aerator to form an air-water mixture. Due to the density imbalance between the air-water mixture and the liquid, a vertical upward buoyancy is generated. During the upward movement, microbubbles attach to the solid suspension, floating it to the water surface and maintaining it on the water surface with the support of the bubbles. They are intermittently pushed from the inlet to the outlet of the air flotation tank by a chain scraper and discharged through a screw conveyor. The purified sewage is discharged through overflow channels or sent to the next level of treatment facilities.

Aeration air flotation

The blower sends air directly to the air flotation tank water filling device, forming small bubbles that enter the wastewater. Inflators generally use diffusion plates, perforated plates, or micro air tubes, with an aeration pressure of 1kg/cm2, an air volume of 2-3m3/m2 · water, and an aeration time of 15-25min.

Electrolytic Flotation

Under the action of direct current, insoluble anodes and cathodes are used to directly electrolyze wastewater to generate hydrogen and oxygen microbubbles at the positive and negative poles, bringing particulate pollutants in the wastewater to the surface for solid-liquid separation.

The bubbles generated by electrolytic air flotation are much smaller than those generated by gas dissolution and diffusion methods. Electrolytic air flotation is not only used for solid-liquid separation, but also for reducing organic matter, oxidation, and sterilization. It has strong adaptability to changes in wastewater, generates small amounts of sludge, occupies a small area, and does not produce noise.

Dissolved Air Floatation

Dissolved air flotation is currently the most commonly used air flotation method both domestically and internationally.

According to the different pressures at which bubbles precipitate, dissolved air flotation can be divided into true air flotation and pressure air flotation. The former air dissolves into water under pressure and precipitates under normal pressure; The latter air dissolves into water under normal pressure or pressure and precipitates under negative pressure.

At present, pressure gas flotation is the most widely used method, which is divided into fully dissolved gas, partially dissolved gas, and partially refluxed dissolved gas.

It has the following advantages:

Under pressurized conditions, the solubility of air is high, and there are more bubbles used for gas flotation.

In recent years, a new generation of dissolved air flotation machines has emerged in China, which use gas-liquid mixing pumps instead of dissolved air tanks and air pumps, resulting in higher processing efficiency and lower operating costs. The QTRF series air flotation machine from Qingdao Qingtian Environment Company is the second-generation new dissolved air flotation machine.

Cavitation Air Flotation

The working principle is that untreated sewage first enters a small inflatable section equipped with a patented vortex aerator. During the rising process of sewage, flocs and suspended solids are fully mixed and contacted with microbubbles through the inflation section. Due to the density difference between the gas-solid mixture and the liquid, a vertical upward buoyancy is generated, which brings the solid suspended solids to the water surface. During the process of floating, scattered bubbles adhere to suspended solids. After reaching the water surface, solid suspended solids are supported and maintained on the water surface by these bubbles, and are scraped into the sludge tank by a continuously moving chain scraper for removal.

In March 1997, the American company Maiwang introduced the first CAF cavitation air flotation system, which was successfully put into operation at the wastewater treatment plant of Kunming Second Paper Mill in China, ending the history of using pressure dissolved air flotation (DAF) in wastewater treatment in China. Qingdao Qingtian Environmental Engineering Co., Ltd., as the first company in China to introduce Maiwang technology, has been promoted nationwide through absorption and improvement. More than 600 sets have been installed in various parts of the country, and good results have been achieved. Compared with traditional DAF pressure air flotation, CAF cavitation air flotation system has the following significant advantages:

1. The system distributes air into water in a simple and special way in the form of tiny bubbles, unlike dissolved air flotation which requires an air compressor, pressure dissolved air tank, dissolved air release device, and high-pressure pump;

2. The unique design of the automatic reflux pipe makes it difficult for sludge to settle at the bottom of the air flotation tank;

3. There are very few sports and maintenance parts, and the operation is very simple;

4. Avoiding frequent blockage of the release device in dissolved air flotation;

5. The equipment has good overall integrity, easy installation, and saves 40% -60% of floor space;

6. Low operating costs. According to the investigation and testing conducted by the world-renowned ERM environmental consulting company, compared with container air flotation, it saves 40% -90% of operating costs.

Conclusion

Air flotation technology is an efficient treatment process that has the advantages of simple process flow, stable treatment effect, small footprint, strong impact load resistance, etc. It is currently a new sewage treatment technology under deep research.

With the continuous development of China's economic construction and the deepening of research, the application of air flotation and the air flotation process developed on its basis in production will become more widespread in the near future.

Welcome to Qingdao Qingtian Environmental Engineering Co., Ltd. Our company specializes in producing environmental protection equipment such as vortex concave and dissolved air flotation machines for sewage treatment, stacked screw sludge dewatering machines, aerators, slag scrapers, scraper suction machines, and filters. We are willing to work together to create a beautiful home with clear water and blue sky. For more information, please consult 0532-83131258 or 137918405000, or log in http://www.qdhuanbao.cn/ Refer to.