Introduction
Wastewater often contains a large amount of suspended solids, oils, and other pollutants. As a water treatment process, Dissolved Air Flotation (DAF) can remove these pollutants and produce high - quality treated wastewater. Therefore, it is commonly used in municipal sewage and industrial wastewater projects, as well as in the pretreatment steps before other wastewater treatments. So, how exactly does DAF work, and why do we choose it?
What is a Dissolved Air Flotation System?
The DAF system can separate suspended solids, oils, as well as Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and metal particles from liquids. First, the system introduces tiny bubbles into the sewage. Then, under atmospheric pressure, these bubbles attach to the suspended particles or oil droplets, reducing their overall density. Finally, these bubbles rise to the surface of the liquid, forming a scum layer, which is removed by a skimming device.
The Main Components
(1) Air Dissolution System: It consists of an air compressor, a pressure dissolved air tank, and a release device. This system is responsible for compressing air and injecting it into the pressure dissolved air tank, making the air dissolve in water to form saturated dissolved air water.
(2) Flocculation Reaction Tank: Before the sewage enters the DAF system, flocculants and coagulants need to be added in the flocculation reaction tank. This is to make the tiny suspended particles in the sewage aggregate to form larger flocs.
(3) Flotation Tank: At this time, the saturated dissolved air water enters the flotation tank, and the pressure drops sharply. The air dissolved in the water is released in the form of tiny bubbles, with a diameter between 10 and 100 microns. They collide with and attach to the floc particles, making the floc particles float to the water surface.
(4) Skimming System: When the scum accumulates on the surface of the flotation tank, we usually remove it through the skimming system. The skimming system consists of a skimming machine and a scum collection tank. The skimming machine scrapes the scum into the scum collection tank, and then it is transported to the subsequent treatment unit through pipelines.
Where is the DAF System Used for?
Fish Farms
In fish farms, the water body is prone to accumulate excessive organic matter, such as fish excreta and residual feed. These substances will consume the dissolved oxygen in the water, leading to water quality deterioration. At the same time, some plankton may breed and multiply excessively in the water body, affecting the living environment of fish. DAF can effectively remove about 80% - 90% of the suspended solids in the water body and reduce the Chemical Oxygen Demand (COD) of the water body.
Industrial Wastewater
Industrial wastewater comes from various factories, including oil refineries, petrochemical and chemical plants, and mines. Among them, mining wastewater contains many suspended solids, such as ore particles and tailings powder, as well as some heavy metal ions, such as lead, mercury, and cadmium. DAF can quickly separate the suspended solids in the wastewater, making the wastewater clearer. Sometimes, we also add specific agents to enrich and separate the heavy metal ions in the wastewater, in order to reduce heavy metal pollution.
Food Processing
Food wastewater contains a large amount of proteins, starches, and oils. When they are discharged randomly, it is easy to cause eutrophication of water bodies, and algae will multiply excessively. DAF uses bubbles to float and separate the oils in the wastewater. For organic matters such as proteins and starches, it adds flocculants to make them form larger flocs, and then uses the buoyancy of bubbles to separate them from the water.
Clarification
DAF can remove tiny particles, colloidal substances, and some microorganisms in water. In the manufacturing process of electronic chips, ultrapure water is required. As a pretreatment step, DAF can effectively remove the suspended particles and colloids in the raw water. It reduces the turbidity of water to an almost undetectable level.
Dissolved Air Flotation Advantages and Disadvantages
Advantages
High Removal Efficiency: DAF is good at removing algae, oils, and metal particles in wastewater. Compared with the sedimentation method, it is more suitable for removing low-concentration light particles.
Space Efficiency: The system is relatively compact and suitable for applications with limited space.
Multiple Applications: DAF is used in various wastewater treatment processes, including primary clarification in biological factories.
Enhanced Pollutant Removal: For specific pollutants, DAF is sometimes more effective than sedimentation and membrane filtration.
Disadvantages:
Energy-Intensive: DAF requires air compression operations, which will generate higher operating costs.
Not Suitable for High-Density Solids: For treating raw water with a very high concentration of suspended solids, DAF may not be the best choice.
Affected by Temperature and Weather: Floating solids will settle when the water temperature is low or it is raining.
Larger Scale Requirements: In large-scale wastewater treatment, DAF requires more equipment investment, installation, debugging, and maintenance.
Form Download
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Contact AquaSust
Since 2013, AquaSust has been a leader in the water treatment industry, manufacturing DAF systems according to the highest standards. Whether you need to consult about the DAF process or require a customized sewage treatment solution, you can contact AquaSust at any time.