Flotation is an effective wastewater treatment process designed to treat for total suspended solids (TSS), BOD/COD (Biological/Chemical Oxygen Demand), and Fats, Oils, & Grease (FOG).
Dissolved air flotation (DAF) is the process of attaching small bubbles to suspended solids, making them less dense than water and floating to the surface, where they are removed off by a scraper. The microbubbles are created by dissolving air in water under pressure. When this air-saturated water is mixed with the raw water, very fine bubbles are formed which give it a milky appearance .The microbubbles usually have a diameter of between 30 and 50 μm: this small size is essential to the efficiency of the flotation unit as it facilitates their adhesion to the suspended solids. The rising suspended solids is called a "float". The water flow also has an effect on the resulting bubbles, which tend to dissipate easily if the flow is large.
To further improve the performance of DAF unit, chemical substances can be added to increase separation. The two common chemicals used in the DAF process are coagulants and flocculants. Coagulant additives, such as ferric chloride or aluminum sulfate, carry positive charges and neutralize negatively charged particles in wastewater, producing micro flocculation. Related to coagulation, flocculation refers to the addition of polymers to promote the binding of micro flocs together.
The dissolved air flotation system is highly effective in industrial wastewater pretreatment and has been used in various applications of water, wastewater, and seawater desalination. Chemical pretreatment of wastewater before entering the dissolved air flotation device can improve removal efficiency, with TSS and FOG typically exceeding 95%.
Most common DAF treatment applications include:
Process water production
Pretreatment for TSS and FOG removal from Industrial wastewater
Fats, oils and grease resource recovery
Wastewater biological treatment as activated or anaerobic sludge flotation
Wastewater tertiary treatment to remove phosphorus and nutrients
Pretreatment for Desalination systems
Drinking water intake solids removal
The generation of microbubbles is crucial for dissolved air flotation, and pressurisation constitutes the most widespread technique used to produce microbubbles. This usually involves an issue:
DAF, its core is equipped with a boost air system that generates microbubbles by injecting compressed air.
FAD, I.e. free air flow rate, uses negative pressure to suck in gas and generates bubbles without the need for theair compressor.
FAD can improve the efficiency of gas-liquid production, save operating and maintenance costs. But, when it comes to generating microbubbles, it is still recommended to choose DAF.
Advantages of DAF in generating microbubbles:
1. High efficiency
DAF can efficiently compress air, and under pressurized conditions, it can suddenly reduce pressure and release a large number of bubbles.
2. Adjustability
DAF has pressure regulation function, which can adjust the pressure of compressed gas according to actual needs to meet different process requirements.
3. Stability
The bubbles generated by DAF are not only numerous, but also fine and uniform in size, with stable density, and can effectively adhere to suspended solids.
Dissolved air flotation is an efficient water treatment equipment that can effectively remove suspended solids from wastewater and is the first choice for wastewater treatment. DAF flotation is the process of dissolving air in water under pressurized conditions, and then releasing a large number of microbubbles instantly through depressurization, which is the key to determining the effectiveness of dissolved air flotation in removing suspensions.