The coagulation air flotation equipment introduces air into water in the form of tiny bubbles, causing the tiny bubbles to adhere to suspended particles in the water, forming a three-phase mixed system of water, gas, and particles. After the particles adhere to the bubbles, their density is lower than that of water and they float to the surface, forming a floating slag layer that is separated from the water. Coagulation air flotation equipment is a type of water treatment equipment that introduces or generates a large number of fine bubbles in water, causing air to adhere to suspended particles in the form of highly dispersed small bubbles, resulting in a state of lower density than water. It uses the principle of buoyancy to make it float on the water surface, thereby achieving solid-liquid separation.

Explanation of the working principle of coagulation air flotation equipment:

1. The relationship between the buoyancy of air carrying flocs and the surface load of air flotation: When flocs adhering to bubbles float in water, they will be macroscopically affected by external forces such as gravity G, buoyancy F, etc. The velocity of gas carrying flocs when floating can be derived from Newton's second law, which depends on the density difference between water and gas carrying flocs, the diameter (or characteristic diameter) of gas carrying flocs, as well as the temperature and flow state of water. If the proportion of bubbles in the air carrying flocs is larger, the density of the air carrying flocs will be smaller; And its characteristic diameter increases accordingly, and this change in both can greatly increase the buoyancy speed.

However, in actual water flow; The size of the air carrying flocs varies, and the resistance caused by it also constantly changes. At the same time, the external force in the air flotation also changes, resulting in the formation of bubbles and the floating speed also constantly changing. The specific buoyancy speed can be determined experimentally. The surface load of air flotation can be determined based on the measured buoyancy velocity value. The determination of the buoyancy speed must be based on the requirements of the outflow.

2. The adhesion of flocs to bubbles in water: As mentioned earlier, the main separation objects of pollutants in water by air flotation treatment are generally divided into two types: flocs and particle monomers in coagulation reactions. During the air flotation process, there are three ways in which bubbles can bind to concrete flocs and individual particles, namely, bubble support, bubble entrainment, and gas particle adsorption. Obviously, the strength of the binding and adhesion between them, that is, the firmness of the combination of gas and particles (including floc waste), is not only related to the shape of the particles and flocs, but more importantly, influenced by the interfacial properties of water, gas, and particles. The content of active agents in water, the hardness of water, and the concentration of suspended solids are all closely related to the adhesion and buoyancy strength of bubbles. The quality of air flotation operation is fundamentally related to this. In practical applications, water quality needs to be adjusted.

Coagulants are generally used in conjunction with precipitation and air flotation processes. One method is to use gravity to cause coagulation reactions of pollutants in water and precipitate them together with sludge at the bottom of the tank. The other method is to use the viscosity generated by coagulants and bubbles to make suspended solids in water adhere to bubbles, forming flocs with a surface density lower than that of water and floating to the surface. The treatment effect is achieved by using ferrous sulfate air flotation and scraping sludge.

The two processing methods have different requirements for the coagulant used. Air flotation often occurs together with aeration and stirring, and has relatively high requirements for flocs. If the formed alum particles have a small volume and are easily crushed, it will result in high suspended solids content in the effluent and other pollutants that cannot meet the standards. Therefore, the effect of iron salts such as polyferric sulfate and pentaferric sulfate on air flotation treatment is better than that of aluminum salts.

When using a combination of iron salts and air flotation technology for wastewater treatment, a solution of polymerized iron sulfate (or ferrous sulfate) can be first introduced and stirred to allow it to fully react. Then, a small amount of polyacrylamide aqueous solution can be added as a coagulant aid to accelerate the reaction rate, improve viscosity, and enhance the effectiveness of the action.

The air flotation method is commonly used to treat suspended solids with a density close to water, such as emulsified wastewater, oily wastewater, fiber wastewater, and algae wastewater. The specific type of coagulant to be used can be selected based on experimental trials and on-site pilot tests.