The coagulation treatment of water and wastewater includes three stages: mixing of water and agents, reaction and separation of flocculant and water. Clarification pool is to complete the above three processes and one of the special equipment, the quality of polyaluminum chloride directly affects the treatment effect of the water quality of the clarification pool. Therefore, it is critical to choose a suitable water purification agent (polyaluminum chloride).
The medium that plays the role of interception and separation of impurity particles in the clarifying tank is the suspended sludge. In the clarifying tank, the settling sludge is lifted up and made to be in a uniformly distributed suspension state, forming a high concentration of stable active sludge layer in the tank, and the concentration of suspended solids in the layer is about 3-10g /L. Raw water flows upward in the clarifying pool and the sludge layer is in a dynamic equilibrium state in the upward flow due to the action of gravity. When the raw water passes through the activated sludge layer, using the contact flocculation principle, the suspended matter in the raw water will be retained by the activated sludge slag layer, so that the water can be clarified. Clear water is collected above the clarifying pool. The rising velocity of the suspended sludge layer is related to the volume and concentration of the sludge, so the correct selection of the rising velocity and keeping a good suspended sludge layer are the basic conditions for the clarifying tank to obtain a better treatment effect.
At present, the commonly used clarifying tanks in wastewater treatment are: mechanical accelerating clarifying tank, hydraulic cycle clarifying tank, suspension clarifying tank, pulse clarifying tank.
There are many reasons for the alum floating in the clarifying tank, which will directly affect the water quality, so attention should be paid to it. Polyaluminum chloride manufacturers summarized the polyaluminum chloride in the clarifying pool appeared a large number of alum floating on the following points:
1. The speed of the clarifying tank mixer is too fast, which breaks the alum, and it is more difficult to agglomerate the broken alum flowers, so that the strength of the sludge decreases and the alum flowers float up. In this case, the line of the outer edge of the impeller of the mixer should be well controlled and shall not exceed the design provisions. And appropriately increase the dosage of coagulant to form the suspended sludge layer again.
2, clarification pool backflow 綘 jams, active mud cannot backflow, alum flowers floating along the pool wall. At this time, it is necessary to open the reflux seam to flush the pipeline, dredge the blockage, properly carry out the central sewage, and increase the adding flow of the mixer to 4~5 times the effluent water quantity, so as to avoid the phenomenon of floating up.
3. There is no regular mud discharge in time, or the height of the sludge layer fluctuates greatly, and the sludge layer is too high, causing the alum flower to float up. At this time, it is necessary to timely discharge mud, adjust or control the height of the sludge layer.
4, the amount of coagulant is small, it is difficult to form alum flower, poor coagulation effect, suspended solids can not be separated and precipitation; Or the amount of coagulant is too large, producing counterion phenomenon, difficult to coagulate, will also produce alum flower floating phenomenon.
5. The sudden change of water temperature will disturb the water flow and cause the sludge layer to float up. At this time, the stirring speed can be appropriately reduced, the dosage of coagulant can be appropriately increased, and the water output can be adjusted to make the water flow stable. If possible, the active mud or clay mud can be appropriately pumped back.
6. If it is a clarifying pool with lime slurry, the CaCO3 colloid will be generated due to the excessive amount, so that the alum flower has a large volume and a small density and is easy to float. However, if the addition amount is too small, the CaCO3 precipitation generated will be small, the volume of alum will be small, and the strength of the sludge layer at the upper part of the reaction zone will decrease and float up. At this time, the speed of the mixer should be adjusted appropriately, the basicity should be controlled stably, and the coagulation dose should be increased appropriately.
