Coagulation and Flocculation
What is in the water being treated?
•Chemicals in solution
•Colloidal solids (solids that don’t dissolve in water)
•Bacteria, Pathogens
•Fine clay and silt
See a list of contamination categories here:
•Chemicals in solution
•Colloidal solids (solids that don’t dissolve in water)
•Bacteria, Pathogens
•Fine clay and silt
See a list of contamination categories here:
The Goal of Coagulation/Flocculation:
The purpose of the coagulation/flocculation step in the treatment process is to reduce turbidity in the water. Turbidity is a measure of the suspended particles in a water sample, with high turbidity corresponding with cloudiness. High levels of turbidity result in poor aesthetic quality of the water and unwanted taste and odor.
The purpose of the coagulation/flocculation step in the treatment process is to reduce turbidity in the water. Turbidity is a measure of the suspended particles in a water sample, with high turbidity corresponding with cloudiness. High levels of turbidity result in poor aesthetic quality of the water and unwanted taste and odor.
The Process
Particles suspended in water most frequently possess a negative charge and as a result, they repel one another and remain dissolved.
Because these individual particles are too difficult to remove, the goal is to make them larger so they may be removed from the water. In order to increase their size, coagulant chemicals are added to the water. These chemicals generally have a positive charge, which neutralize the negative charge of the particles. Particles with no charge are weakly attracted to one another via Van de Waal forces, which force the particles to aggregate into larger clusters, known as floc. Common coagulants are metallic salts and polymers, the with aluminum sulfate (alum) and ferric sulfate being the most widely used. During flocculation, these small floc particles are aggregated into even larger particles through a gentle stirring of the water. When these products are denser than water, they sink and may be collected; if they are less dense than water, they float to the surface and are skimmed off of the top (Pizzi, 2010).
Particles suspended in water most frequently possess a negative charge and as a result, they repel one another and remain dissolved.
Because these individual particles are too difficult to remove, the goal is to make them larger so they may be removed from the water. In order to increase their size, coagulant chemicals are added to the water. These chemicals generally have a positive charge, which neutralize the negative charge of the particles. Particles with no charge are weakly attracted to one another via Van de Waal forces, which force the particles to aggregate into larger clusters, known as floc. Common coagulants are metallic salts and polymers, the with aluminum sulfate (alum) and ferric sulfate being the most widely used. During flocculation, these small floc particles are aggregated into even larger particles through a gentle stirring of the water. When these products are denser than water, they sink and may be collected; if they are less dense than water, they float to the surface and are skimmed off of the top (Pizzi, 2010).
Fluid Dynamics
Laminar flow is a term used to describe water that is not turbulent, but rather uniform, smooth, and constant in parallel layers. Water traveling with laminar flow will easily flow past a suspended object. Conversely, turbulent flow interacts with the object and creates vortexes and eddies behind the suspended object, creating a flow that is no longer laminar (Pizzi, 2010). Reynold’s number is a mathematical representation of turbulence. A high Reynold’s number corresponds with turbulence, and a low Reynold’s number corresponds with laminar flow. Turbulence is controlled in a water purification system by managing energy input.
Laminar flow is a term used to describe water that is not turbulent, but rather uniform, smooth, and constant in parallel layers. Water traveling with laminar flow will easily flow past a suspended object. Conversely, turbulent flow interacts with the object and creates vortexes and eddies behind the suspended object, creating a flow that is no longer laminar (Pizzi, 2010). Reynold’s number is a mathematical representation of turbulence. A high Reynold’s number corresponds with turbulence, and a low Reynold’s number corresponds with laminar flow. Turbulence is controlled in a water purification system by managing energy input.