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The difference between coagulation flotation and dissolved air flotation

By: Kate Chen
Email: [email protected]
Date: Jun 27th, 2024

Coagulation flotation

Coagulation flotation is a commonly used water treatment pretreatment process, which occupies a relatively large area.

Coagulation equipment mainly includes:

Coagulant metering and dosing device: used to accurately add coagulants to water.

Mixer: used to fully mix coagulants with water.

Flocculation reactor: provides sufficient space and time for flocculation reaction.

Remove suspended particles in water through the following steps:

Adding coagulants: Adding coagulants can make small suspended particles in water aggregate to form larger flocs.

Flocculation: After a period of mixing, these flocs will collide and adhere together to form larger flocs.

Floatation: Dissolve air into the water and release tiny bubbles, which will attach to the flocs and rise to the water surface due to the overall buoyancy.

Scraping: Scrape off the flocs floating on the water surface to complete the pollutant removal process.

Treatment effect: The clarity of water quality will be improved after coagulation, but the removal of color pollutants is limited. Since coagulants mainly aggregate fine particles through charge neutralization or flocculation bridging, they are less effective for non-suspended soluble substances.

Scope of application: Coagulation flotation is suitable for removing pollutants with small particle size and density close to water, such as colloidal pollutants, algae, etc.

Operating cost: Coagulation flotation requires the use of coagulants, which will increase operating costs. In addition, the dosage of coagulants needs to be adjusted according to the water quality. If the dosage is too much or too little, it may affect the treatment effect.

Dissolved air flotation (DAF)

The main difference between dissolved air flotation and coagulation flotation is that no coagulant is required. The footprint is relatively small.

Dissolved air flotation: Dissolved air flotation equipment mainly includes:
Dissolved air system: Including pressure pump, dissolved air tank, releaser, etc., used to dissolve air into water.
Flotation tank: Used for flotation separation of pollutants.
Slag scraper: Used to scrape pollutants floating on the water surface.
DAF uses the following steps to remove pollutants:

Dissolved air: A part of the water body is pressurized to dissolve air, so that air dissolves in the water.
Degassing: The pressurized dissolved air-water mixture is decompressed and released, and the air dissolved in the water becomes tiny bubbles.
Floatation: The bubbles will attach to the pollutant particles, and the total buoyancy of the particles will increase, rising to the water surface.
Scraping: The pollutants floating on the water surface are scraped off to complete the pollutant removal process.

Treatment effect: In addition to removing suspended particles, dissolved air flotation can also remove grease and other loose materials. This is because bubbles can effectively attach to the surface of grease and loose materials, causing them to rise to the water surface.

Scope of application: Dissolved air flotation is suitable for removing loose pollutants that are easy to adhere to bubbles, such as grease, floating solids, etc.

Operation cost: The operation cost of dissolved air flotation mainly includes power consumption and maintenance costs. Power consumption mainly depends on the energy consumption level of the dissolved air system, and maintenance costs depend on the quality and use of the equipment.

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