Chương này áp dụng các kỹ thuật của quá trình đơn vị đông máu để điều trị nước và nước thải cho việc loại bỏ các chất keo gây ra độ đục và màu sắc. Nó cũng thảo luận về các chủ đề điều kiện tiên quyết | 12 Coagulation Colloids are agglomerates of atoms or molecules whose sizes are so small that gravity has no effect on settling them but instead they stay in suspension. Because they stay in suspension they are said to be stable. The reason for this stability is the mutual repulsion between colloid particles. They may however be destabilized by application of chemicals. Coagulation is the unit process of applying these chemicals for the purpose of destabilizing the mutual repulsion of the particles thus causing the particles to bind together. This process is normally applied in conjunction with the unit operation of flocculation. The colloid particles are the cause of the turbidity and color that make waters objectionable thus should at least be partially removed. This chapter applies the techniques of the unit process of coagulation to the treatment of water and wastewater for the removal of colloids that cause turbidity and color. It also discusses prerequisite topics necessary for the understanding of coagulation such as the behavior of colloids zeta potential and colloid stability. It then treats the coagulation process in general and the unit process of the use of alum and the iron salts in particular. It also discusses chemical requirements and sludge production. COLLOID BEHAVIOR Much of the suspended matter in natural waters is composed of silica or similar materials with specific gravity of . In sizes of to 2 mm they settle rapidly however in the range of the order of 10-5 mm it takes them a year in the overall to settle a distance of only 1 mm. And yet it is the particle of this size range that causes the turbidity and color of water making the water objectionable. The removal of particles by settling is practical only if they settle rapidly in the order of several hundreds of millimeters per hour. This is where coagulation can perform its function by destabilizing the mutual repulsions of colloidal particles causing them to bind together and .
