Dissolved Air Flotation (DAF) System | Micro-Bubble Wastewater Treatment

In both industrial production and daily life, wastewater treatment plays a pivotal role in safeguarding the ecological environment. Much wastewater contains significant amounts of fine suspended solids, oils, or colloidal substances—impurities with densities close to or slightly greater than that of water. Traditional sedimentation methods are not only inefficient for handling such impurities but often fail to meet discharge standards.

As a highly efficient physical treatment device, the dissolved air flotation (DAF) machine has emerged as a core solution to these challenges. Leveraging the unique principle of micro-bubble lifting, it is widely used across various sectors, balancing treatment efficiency with the dual benefits of environmental protection and energy conservation.

Why DAF Replaces Traditional Sedimentation

To understand the function of a dissolved air flotation machine, one must first grasp the specific pain points it addresses. In traditional wastewater treatment, sedimentation relies on gravity to settle impurities; however, gravity has a negligible effect on tiny suspended particles, emulsified oils, and colloids. Consequently, large quantities of chemical agents are often required, which not only drives up treatment costs but also risks causing secondary pollution.

For instance, wastewater from industries such as food processing, aquaculture, and textile printing and dyeing contains abundant fine oils and fibers; sedimentation alone often leaves the water visibly turbid and unable to meet discharge regulations. The advent of the dissolved air flotation machine overcomes this limitation. Instead of relying on gravity, it generates tiny air bubbles that cause impurities to float to the surface, thereby achieving efficient separation.

Working Principle: Four Key Stages

The core principle of the dissolved air flotation machine is straightforward, comprising four steps: pressurized air dissolution, pressure-release bubble formation, micro-bubble adhesion, and separation via flotation. The entire process is scientifically sound and highly efficient, involving no complex chemical reactions.

Stage 1: Pressurized Air Dissolution

The equipment uses a high-pressure pump to feed a portion of treated effluent or raw water into a dissolution tank while simultaneously injecting compressed air. Under high pressure (0.3–0.5 MPa), the air is forced to dissolve into the water, creating saturated dissolved-air water—a process analogous to how carbonated beverages dissolve large amounts of carbon dioxide under high pressure, though here the gas is simply air.

Stage 2: Pressure-Release Bubble Formation

The saturated dissolved-air water passes through a specialized release valve into the flotation tank, causing the pressure to drop instantly from high pressure to atmospheric pressure. According to Henry's Law, the solubility of gas in water decreases as pressure drops; air previously dissolved in the water instantly comes out of solution, forming a multitude of tiny bubbles ranging from 20 to 100 micrometers in diameter. These bubbles are distributed evenly throughout the water—far smaller than the bubbles we typically see—yet they possess exceptional adsorption capabilities.

Stage 3: Micro-Bubble Adhesion

Upon entering the DAF tank, the wastewater mixes with a flocculant, causing tiny impurities to aggregate into larger flocs. The released micro-bubbles rapidly adhere to the surfaces of these flocs and hydrophobic impurities; thanks to their large surface area and high surface energy, the bubbles latch firmly onto the impurities, creating gas-particle aggregates. With an overall density lower than that of water, these aggregates slowly rise due to buoyancy, eventually gathering at the surface to form a layer of scum.

Stage 4: Separation and Discharge

A surface skimmer operates according to a preset program, scraping the scum into a collection trough for discharge, while the clarified water is collected via pipes at the bottom of the tank. This water can either be discharged in compliance with standards or partially recycled to generate the dissolved-air water needed for the process, thereby enabling water resource reuse. The entire treatment process is integrated into a single unit, offering simple operation and a high degree of automation without the need for complex manual intervention.

Key Advantages Over Traditional Equipment

High Separation Efficiency

DAF systems achieve removal rates of over 85%–95% for suspended solids and oils, effectively handling fine impurities that are difficult to remove via sedimentation.

Compact Footprint

For the same volume of wastewater, the unit occupies only one-third to one-half the space of a sedimentation tank, making it ideal for enterprises and municipal plants with limited space.

Wide Adaptability and Pretreatment Value

DAF is capable of treating high-oil wastewater from food processing and slaughterhouses, as well as wastewater containing colloidal substances from industries like printing, dyeing, and electroplating. It also serves as a pretreatment step for water reuse systems, protecting downstream membrane modules from clogging.

Conclusion: Precision and Efficiency in Wastewater Treatment

In essence, the widespread adoption of dissolved air flotation machines reflects a shift in wastewater treatment from crude processing to precision and high efficiency. It operates on simple principles yet solves challenging problems in wastewater treatment in the most straightforward way, helping enterprises meet environmental compliance standards while simultaneously boosting economic returns through resource recovery.

Learn more about DAF systems: Brator Dissolved Air Flotation Units.