application of polyacrylamide in water treatment(一)


The main role of PAM in water treatment:
    Reduce the amount of flocculant. Under the condition of achieving the same water quality, polyacrylamide is used as a coagulant in combination with other flocculants (mainly inorganic flocculants), which can greatly reduce the amount of flocculant used. ② Improve water quality. In the treatment of drinking water and industrial wastewater, the use of polyacrylamide in combination with inorganic flocculants can significantly improve water quality. ③Improve floc strength and settlement rate. The floc formed by polyacrylamide has high strength and good settling performance, thereby increasing the speed of solid-liquid separation and conducive to the dewatering of sludge. ④ Anti-corrosion and anti-scale of the circulating cooling system. The use of polyacrylamide can greatly reduce the amount of inorganic flocculant, thereby avoiding the deposition of inorganic substances on the surface of the equipment and slowing down the corrosion and scaling of the equipment.
The main factors affecting coagulation:
    Here, the term "coagulation" represents the entire coagulation and flocculation process. "Coagulation" refers to the destabilization stage of colloids, and "flocculation" refers to the stage where colloids form large particles after destabilization.
    The coagulation phenomenon of water treatment is more complicated. Different types of flocculants and different water quality conditions have different coagulation mechanisms. The current consensus view is that flocculants have three effects on colloidal particles in water: electrical neutralization, adsorption bridging, and net trapping and sweeping. These three effects sometimes occur simultaneously, and sometimes only one or two mechanisms work.
The factors that affect the function of flocculant are also complicated, mainly including three aspects: flocculant, separation and process methods, and coagulation process factors. The main influencing factors are introduced as follows:
①Water temperature. Because the hydrolysis of the flocculant is an exothermic reaction, when the temperature is high, the hydrolysis reaction rate of the flocculant is fast, and the flocs formed are fine. The low temperature water has high viscosity, which weakens the Brownian motion intensity of the impurity particles in the water and reduces the chance of collision, which is not conducive to the destabilization and aggregation of the colloid.
② PH value of water. The inorganic flocculant is greatly affected by pH. For example, when using aluminum sulfate to remove turbidity in water, the optimal PH range is between 6.5-7.5, and when used for color removal, the optimal PH value is between 4.5-5. Organic polymer flocculants are less affected by PH value.
③ Stirring rate and time. Generally speaking, the stirring rate is 40-80r / min and the stirring time is preferably 2-4min.
④The composition and concentration of suspended matter in water. For example, the presence of positive ions of more than two valences in the water is conducive to compressing the electric double layer of colloidal particles; if the water contains mainly clay impurities, the amount of coagulant to be added is small; when the wastewater contains a large amount of organic matter To protect the colloid, you need to add more coagulant (the dosage is 20-100mg / L, or even hundreds of milligrams per liter) to have a good coagulation effect. The more uniform and smaller the impurity particle gradation in water, the less conducive to sedimentation. If the concentration of impurities in the water is too low, it will be unfavorable for the collision between particles and affect the aggregation. In this case, it is necessary to add polymer coagulant, or add mineral particles to increase the coagulation center, etc., in order to improve the coagulation effect.
The factors that affect coagulation are more complicated. At present, it mainly depends on the coagulation test to select the appropriate coagulant variety and the best input.


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