[Hongjie Water Service] Several influencing factors for poor air flotation effect!

Air flotation method is a water purification process that introduces air or other gases into wastewater to generate bubbles, causing some small suspended solids or solid particles in the water to adhere to the bubbles and float to the surface of the water to be scraped off, thus completing the separation of solid and liquid.

1. The Effect of Coagulation Pretreatment on Air Floatation Water Purification Efficiency

A good coagulation effect is extremely important for the air flotation process, and the effect of coagulation pretreatment can be controlled by floc particle size, stirring strength, reaction time, etc.

1. Requirements for floc particle size in air flotation

The air flotation process is similar to the sedimentation process, and also requires floc particles of hundreds of micrometers or even larger sizes. When the size of microbubbles and floc particles is similar, their adhesion efficiency is the highest. The diameter of the microbubbles used in the air flotation process is generally between 10 and 100um, so the particle size of the flocs we use can meet the requirements from tens of micrometers to 100um.

2. Requirements for reaction stirring strength of air flotation

Throughout the entire air flotation process, large-sized floc particles are mostly not used, so we can increase the intensity of reaction stirring (increasing G value), which has been verified by many experts' experiments. Through research, we found that the optimal G value applied in the air flotation process depends on the type of coagulant: FeCl3 is 70s-1, aluminum salt is 70-80s-1, and the G value of PAC is greater than 30s-1. If the G value is within the range of 10-50s-1, the particle removal effect through the air flotation process is also very good. High energy input can effectively reduce the number of small particles (<50um), so it can better ensure the water purification effect of air flotation.

3. Requirements for reaction time of air flotation

In Europe, early water treatment processes such as sedimentation and air flotation used the same time for flocculation, usually lasting 45 minutes. Some experts also pointed out that the process of air flotation only takes 15-20 minutes, so many water plants use two-stage flocculation and the flocculation time is generally 20 minutes.

2. The Influence of Chemical Dosing on the Air Floatation Effect

In general, hydrophobic or hydrophilic substances require the addition of chemical agents to alter the surface properties of particles, enabling better adsorption of particles and bubbles.

(1) Coagulant

Coagulants are divided into two types of polymer coagulants: inorganic and organic. They can cause small particles in sewage to flocculate into large flocs, increasing the floating speed of particles. It is also possible to change the hydrophilicity of suspended particles in sewage.

(2) Flotation agent

Petroleum, rosin oil, stearates, surfactants, etc. are all flotation agents, which have many types and are generally composed of polar non polar molecules. After the surface of hydrophilic suspended particles adsorbs the polar group of the flotation agent, the non-polar group will face the water, and the hydrophilic substance will be converted into hydrophobic substance, which will then adhere to the fine bubbles.

(3) Coagulant aid

The main function of coagulant aids is to improve the water tightness of the surface of suspended particles, thereby improving the floatability of particles, such as polypropylene phthalamide.

(4) Inhibitors

The main function of inhibitors is to suppress the upward mobility of some substances without affecting the impurities that need to be removed, such as sodium sulfide and lime.

(5) Regulator

The main function of regulators is to regulate the pH value of wastewater, thereby regulating the dispersion of bubbles in water and their adhesion to suspended particles, such as various acids and alkalis.

3. The influence of microbubble characteristics on the water purification effect of air flotation

The most crucial aspect of air flotation technology is the formation of a large number of microbubbles, and the characteristics of microbubbles have a significant impact on the effectiveness of air flotation for water purification.

1. Size of microbubbles

Numerous experiments have shown that smaller microbubbles are not necessarily better, mainly due to the following reasons:

(1) If the microbubbles are very small, the floc particles will require a lot of bubbles during the process of floating, and it is still difficult to make the floc particles adhere to a particularly large number of microbubbles.

(2) Microbubbles are generated by consuming energy, and smaller bubbles require more energy.

(3) If the microbubble is very small, it is easy to follow the water flow into the next filter, which can cause air blockage.

(4) The load on the surface of the separation zone can also affect the size of microbubbles. When the surface load of the air flotation tank increases, the residence time of the foam floc combination in the water decreases, and only by increasing its floating rate can it float to the water surface. Obviously, adhering a certain number of small bubbles has a higher apparent relative density and a smaller buoyancy rate than adhering the same number of larger bubbles, which is not conducive to increasing the surface load of the atmospheric floating pool.

2. Surface characteristics of microbubbles

Usually, microbubbles in water preferentially adsorb certain negative ions and carry negative charges, resulting in a higher negative surface potential. The measurement results indicate that the surface potential of microbubbles in the air flotation process is generally around -100m V, while the surface potential of floc particles is usually negative. Therefore, when they approach each other, there will be electrostatic repulsion, which will have a negative impact on their collision and adhesion process. The strength, surface hydrophobicity, and electrical properties of microbubbles vary depending on the quality of raw water and the type and quantity of ions adsorbed. Adding electrolytes to water can alter the above characteristics of microbubbles and affect the flotation efficiency.

The above is the "Several Factors Influencing Poor Air Floatation Effect!" introduced by Hongjie Water, hoping to be helpful to you. Before purchasing equipment, we need to have a certain understanding of its composition, then understand its characteristics and defects, and make a comprehensive selection.