Cavitation air flotation, or CAF for short, is mainly used in sewage treatment. It can easily remove the difficult suspended solids, grease, and colloids in industrial and domestic sewage. Whether it is a food factory, a printing and dyeing factory, or a municipal sewage treatment plant, you can often see it in operation.
The core of the vortex flotation principle is "flotation". Simply put, it turns air into small bubbles, which stick to the pollutants in the sewage and float to the surface with them, scraping away the scum on the water surface, and the sewage becomes clean!
1. The birth of bubbles
In the vortex flotation system, the most critical component is the vortex aerator. This aerator is like a "bubble maker". There are many specially designed tooth structures on the edge of its impeller. When the impeller rotates at high speed, the surrounding water will rotate with it, and a low-pressure area will be formed in the center of the impeller. The air is sucked in along the air inlet pipe and fully mixed with the water under the stirring of the impeller. Under the action of high-speed shearing and stirring of the impeller, the air is cut into countless tiny bubbles, and the diameter of these bubbles is usually around 20-40 microns.
2. Contact between bubbles and pollutants
After the bubbles are generated, they begin to play a role in the sewage. Pollutants such as suspended matter, grease, and colloids in sewage have a certain degree of hydrophobicity on their surfaces, which means that they are more likely to stick to bubbles. When tiny bubbles rise in sewage, they encounter these pollutants and are firmly adsorbed like magnets.
For example, when bubbles touch grease droplets in sewage, they will wrap up the grease. And those tiny suspended particles will also be tightly grasped by bubbles.
3. Formation and removal of scum
The pollutants adsorbed by bubbles rise with the bubbles, and when they reach the water surface, they will form a thick layer of scum on the water surface. At this time, the scraper moves slowly along the water surface, scrapes the scum into the scum tank, and then discharges it from the system uniformly. The treated clean water flows out from the outlet at the bottom of the system and enters the next treatment link.
Although the principle of vortex flotation is simple and the operation is not complicated, there are still many things to pay attention to during the actual operation.
1. Inspection before starting the equipment
Before starting the vortex flotation equipment, first check whether the connection parts of each component are loose. For example, if the screws of the connecting shaft of the impeller and the motor of the aerator are not tightened, the equipment may vibrate violently during operation, and even cause the impeller to fall off.
Also check whether there are any leaks in the water tank and pipes. If there are leaks, it will not only waste water resources, but also affect the flotation effect. You can apply some soapy water on the surface of the water tank and pipes to see if there are any bubbles. If there are bubbles, it means there is a leak and it needs to be repaired quickly.
In addition, don't forget to check the running track of the scraper to see if there are any debris blocking the track to ensure that the scraper can run smoothly.
2. Parameter control during operation
Flow and concentration of sewage: The flow of sewage entering the vortex flotation system cannot fluctuate. If the flow rate is too large, the sewage will stay in the equipment for a short time, and the bubbles will not have time to fully contact with the pollutants, and the treatment effect will definitely be poor; if the flow rate is too small, it will cause waste of equipment. Generally speaking, the sewage flow rate should be controlled within an appropriate range according to the design and treatment capacity of the equipment.
The concentration of sewage is also critical. If the concentration of pollutants in the sewage is too high and exceeds the treatment capacity of the equipment, the scum layer will be too thick, and the scraper may not be able to scrape it, which will also affect the rising speed of the bubbles. Therefore, before entering the water, it is best to monitor the concentration of the sewage first, and dilute it when necessary.
The speed of the aerator: The speed of the aerator directly affects the amount and size of bubbles. If the speed is too fast, although the number of bubbles will increase, the bubbles may be too small, which is not conducive to adsorption with pollutants; if the speed is too slow, the bubbles will be too large and rise quickly, which will also affect the adsorption effect. In general, the speed of the aerator should be adjusted to an optimal value according to the nature and treatment requirements of the sewage. The most suitable speed can be determined by trial operation and observing the flotation effect.
Pressure of dissolved air water: Although vortex flotation does not require special preparation of dissolved air water like other flotation equipment, the relevant water pressure will also affect the flotation effect during the operation of the system. Ensure that the dissolved air water has sufficient pressure so that the bubbles can be released smoothly and evenly distributed in the sewage. If the water pressure is unstable or too low, the generation and distribution of bubbles will be affected, thereby reducing the treatment efficiency.
3. Daily maintenance of equipment
The aerator impeller of the vortex flotation equipment will be worn by impurities in the sewage during long-term operation. Therefore, the impeller should be removed and checked every once in a while. If the impeller is found to be severely worn, it should be replaced in time, otherwise it will affect the generation of bubbles.
The chain and scraper of the scraper also need to be checked frequently. If the chain is loose, it must be adjusted quickly; if the scraper is deformed or damaged, it will affect the scraping effect and should be replaced in time. In addition, it is necessary to regularly clean up the debris and sludge inside the equipment to prevent these things from accumulating too much and affecting the normal operation of the equipment.
4. Handling of abnormal situations
During the operation of the equipment, it is inevitable to encounter some abnormal situations. For example, if you find that the scum layer on the water surface is uneven, thick in some places and thin in others, this may be caused by uneven distribution of bubbles or unstable sewage flow. At this time, you should check the operation of the aerator and the sewage inlet flow and make corresponding adjustments.
If the equipment makes abnormal noise during operation, it may be that a part is loose or seriously worn. Stop the machine immediately to check, find the source of the noise, and deal with it in time. Don't think that a little noise is okay and continue to let the equipment run, which is likely to cause more serious equipment damage.