In the sewage treatment process system, flotation plays an important role as a common solid-liquid separation technology. In fact, the operating principle of the flotation machine is based on the flotation method. Therefore, flotation equipment is widely used in sewage treatment to remove suspended matter in water, and the effect is significant and can meet specific treatment requirements.
So, why can the flotation equipment using the flotation method efficiently remove suspended matter in the water?
The core principle of the flotation method, also known as the flotation method, is to generate a large number of fine bubbles in the water through specific means, thereby forming a three-phase mixture of water, air and the removed substance. Under the synergistic effect of multiple forces such as interfacial tension, bubble rising buoyancy and hydrostatic pressure difference, the fine bubbles will adhere to the impurity particles to be removed. Since the density of the adhesive is less than that of water, it will float to the surface of the water, thereby achieving the separation and removal of impurities in the water. The flotation process covers the steps of bubble generation, bubble attachment to solid or liquid particles, and floating separation. Therefore, two necessary conditions must be met to achieve flotation separation: first, a sufficient number of tiny bubbles must be provided in the water, and the smaller the bubble diameter, the better. The ideal bubble size is usually 15-30μm; second, the impurity particles must be suspended and hydrophobic.
Compared with gravity sedimentation, flotation has the following significant features:
Extensive pollutant removal capacity: flotation not only has a good removal effect on pollutants in wastewater that are difficult to treat by sedimentation, but also has a good removal effect on pollutants in wastewater that can be treated by sedimentation.
Efficient space utilization: The surface load of the flotation tank may exceed 12m³/(m²·h), the water flow stays in the tank for only 10-20min, and the tank depth is only about 2m. This makes the floor area of the flotation tank only 1/2-1/8 of the sedimentation method, and the tank volume is only 1/4-1/8 of the sedimentation method, which greatly improves the space utilization rate.
Lower scum water content: The scum produced by flotation has a lower water content, generally below 96%. Compared with the same dry weight sludge produced by sedimentation, its volume is 2-10 times less. This not only simplifies the sludge disposal process, but also saves sludge disposal costs. Moreover, sludge removal on the surface of flotation is more convenient than sludge discharge from the bottom of the sedimentation tank.
Multifunctional water quality improvement: In addition to effectively removing suspended matter, flotation equipment also has pre-aeration and decolorization functions. The effluent and scum contain a certain amount of oxygen, which is conducive to subsequent treatment, and the sludge is not easy to rot and deteriorate.
Less reagent usage: The flotation method uses less reagents than the sedimentation method. When a flocculant is used as a destabilizing agent, the method of adding the reagent is basically the same as the coagulation treatment process. The difference is that the flotation method does not need to form a large-sized alum flower, so the required reaction time is shorter. However, the flotation method also has the problem of high power consumption, which is generally 0.02 - 0.04kw·h/m³.