Coagulation &
Flocculation

The strained and sometimes pretreated water exits the screen house and flows by gravity through a thirty-inch underground ductile iron pipe to the Josiah Chase Water Filtration Plant (JCWFP). In order to remove impurities in pond water it must be destabilized by adding a varied but adequate amount of chemical coagulant. Coagulants destabilize the water so that impurities and particle solids present might be removed by filtration. This process is called “coagulation”. Aluminum Sulfate coagulant, commonly known as Alum, is utilized to destabilize and start removal of particles and impurities. Many times, a low dose of a second coagulant chemical polymer is needed to jump start the destabilization process. This secondary coagulant is particularly needed in cold water where chemical reactions are naturally slowed. These coagulants are added under optimum treatment conditions, such as in a specific pH range, to ensure best treatment. To get to and maintain the optimum pH range, sodium hydroxide chemical is added. The destabilized water particles being formed must be brought to a large enough size so that they can be removed by the next processes. This is done by agitating the water with passage through a cork-screw like pipe called a static mixer. When the particles bump into each other during mixing they grow larger in size so that they might be efficiently removed. This growth in size is known as “flocculation” and the particles solids formed known as “floc." With formation and increase in size of these particles, most barely visible to the human eye, the water becomes cloudy or turbid.

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