Polyacrylamide is a high molecular polymer. When the sludge is dewatered, polyacrylamide solution is added to combine with the sludge to produce large flocs. After the water is filtered out by the filter cloth of the filter press, the water in the sludge is squeezed out by the filter cloth, and then the dry sludge remaining on the filter cloth is scraped off and flows into the dry sludge pool. Or the water in the flocs is removed by the centrifugal force of the centrifuge, and then the sludge is discharged for treatment. Polyacrylamide plays the role of flocculation and dehydration here, and belongs to a kind of flocculant. Whether it is plate and frame, centrifuge, filter belt, turbine, etc. Most of them improve the dehydration rate through the efficient flocculation dehydration of polyacrylamide.
Due to the disadvantages of long time and large floor space, in many cases, only relying on concentration and dehydration can not meet the engineering requirements. In order to improve the dewatering efficiency, the sludge needs to be conditioned. In actual production, the chemical conditioning method of adding flocculants is the main method. Flocculants mainly remove surface adsorbed water.
Commonly used flocculants are mainly divided into inorganic flocculants and organic flocculants. Iron flocculants and aluminum polymers are commonly used in inorganic flocculants. Commonly used organic polymer flocculants are polyacrylamide and sodium polyacrylate.
As the most commonly used organic polymer flocculant for sludge treatment, polyacrylamide can quickly cause coagulation, and its flocculation performance is beyond the reach of inorganic flocculants. Cationic polyacrylamide is widely used in sludge dewatering treatment, and its mechanism is as follows:
Charge neutralization effect: The stable existence of colloidal particle suspensions in sewage (wastewater) is because the particles are charged, and the repulsion between the charges prevents them from approaching each other. If a polyelectrolyte with an opposite charge to that of the colloidal particles is added to the suspended solid, the potential of the particles will decrease, ie, the surface potential will be low, so that the colloidal particles will become unstable and coagulate and settle.
Adsorption bridging: Polyacrylamide has a large molecular weight and can be adsorbed on the particles in the dispersion system through some active functional groups on the long carbon bonds. Since PAM is a long linear structure, each segment has a corresponding specific functional group, which can adsorb multiple particles on the same polymer, so it acts as a connection between particles, which is called bridging. After the cationic polyacrylamide was added, it was first adsorbed on the surface of the sludge colloidal particles. At first, when the concentration of CPAM is low, the long polymer chains adsorbed on the surface of colloidal particles may be adsorbed on the surface of another particle at the same time, and two or more colloidal particles are connected together by this "bridging" method, resulting in flocculation, which is the "bridging" mechanism of polymer flocculation.