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Questions and Answers
What is the main goal of the coagulation/flocculation process in water treatment?
What is the main goal of the coagulation/flocculation process in water treatment?
Define coagulant.
Define coagulant.
A chemical that is added to water that causes small particles to come together to form large particles that can settle due to gravity.
Coagulation is a chemical process in which a coagulant is added and suspended in water by rapid mixing to aggregate dispersed nonsettleable solids by ________.
Coagulation is a chemical process in which a coagulant is added and suspended in water by rapid mixing to aggregate dispersed nonsettleable solids by ________.
destabilization
Match the coagulant with its description:
Match the coagulant with its description:
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What laboratory technique is used to determine the proper coagulant and dosage required in water treatment?
What laboratory technique is used to determine the proper coagulant and dosage required in water treatment?
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What is the main goal of the coagulation/flocculation process?
What is the main goal of the coagulation/flocculation process?
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Define coagulant.
Define coagulant.
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What is meant by coagulation in water treatment?
What is meant by coagulation in water treatment?
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Which of the following are typical coagulants used in water treatment?
Which of the following are typical coagulants used in water treatment?
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Coagulation destabilizes colloids through charge neutralization.
Coagulation destabilizes colloids through charge neutralization.
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Study Notes
Coagulation and Flocculation
- The main goal of coagulation/flocculation process is to reduce turbidity in water
- Turbidity is a measure of the amount of suspended solids in water sample that causes cloudiness
- Removing turbidity can remove unwanted taste and odor compounds
- Lower turbidity allows for higher rates of disinfection
What is a Coagulant?
- A chemical that is added to water to cause small particles to come together to form large particles that can settle due to gravity
- Typical coagulants: Alum (Aluminum sulfate) and Ferric sulfate (Fe2(SO4)3)
Coagulation Process
- A chemical process in which a coagulant is added and suspended in water by rapid mixing to aggregate dispersed non-settleable solids by destabilization
- Keywords:
- Coagulant: a floc-forming chemical reagent
- Nonsettleable solids: solids that cannot settle down by virtue of gravity, having negligible settling velocities
Theory of Coagulation
- Solid colloids stay in suspension due to repulsive forces, making the system stable
- Colloids can be destabilized by charge neutralization using positively charged ions (Na+, Mg2+, Al3+, Fe3+, etc.) to neutralize the colloidal negative charges
- With destabilization, colloids aggregate in size and start to settle
Points to Consider
- Low particulate concentration: sludge recycling
- Large coagulant dosage: restabilization of colloids with positive charge
Coagulation of Colloids by Organic Polymers
- Coagulation by bridging: the ionizable groups on the polymer surface react with the groups or the active sites on the surfaces of the colloids
- Several colloids may bind to a single polymer
Coagulants
- Aluminum sulfate (Al2(SO4)3.14 H2O)
- 1 mole of alum consumes 6 moles of bicarbonate (HCO3-)
- If alkalinity is not enough, pH will reduce greatly, which can be overcome by adding Ca(OH)2 or NaHCO3 (soda ash)
- Ferrous sulfate (FeSO4.7H2O)
- Forms dense, quick-settling floc
- pH must be raised to 9.5
- Ferric sulfate (Fe2(SO4)3)
- pH should be in the range from 4 to 12
- Ferric chloride (FeCl3)
- pH should be in the range from 4 to 12
Coagulation and Flocculation Process
- Coagulation: rapid mixing to aggregate dispersed non-settleable solids
- Flocculation: gentle mixing to form large flocs
- Agitation devices:
- Mechanical agitators
- Pneumatic agitators
- Baffle basins
Jar Test
- A laboratory technique used to determine:
- The proper coagulant and coagulant aid
- The chemical dosage required
- Variables:
- Speed of rotation
- Time of settling
- Dosage
- Size of flocs
- Turbidity removal
- Color removal
- pH
Velocity Gradient
- Measures the degree of mixing
- Velocity gradient (G): relative velocity of the two fluid particles divided by distance
- Higher G value, intenser mixing
Mixing by Impellers and Pneumatic Mixing
- Equations for power input and velocity gradient for mechanical and pneumatic agitation
Coagulation and Flocculation
- The main goal of coagulation/flocculation process is to reduce turbidity in water
- Turbidity is a measure of the amount of suspended solids in water sample that causes cloudiness
- Removing turbidity can remove unwanted taste and odor compounds
- Lower turbidity allows for higher rates of disinfection
What is a Coagulant?
- A chemical that is added to water to cause small particles to come together to form large particles that can settle due to gravity
- Typical coagulants: Alum (Aluminum sulfate) and Ferric sulfate (Fe2(SO4)3)
Coagulation Process
- A chemical process in which a coagulant is added and suspended in water by rapid mixing to aggregate dispersed non-settleable solids by destabilization
- Keywords:
- Coagulant: a floc-forming chemical reagent
- Nonsettleable solids: solids that cannot settle down by virtue of gravity, having negligible settling velocities
Theory of Coagulation
- Solid colloids stay in suspension due to repulsive forces, making the system stable
- Colloids can be destabilized by charge neutralization using positively charged ions (Na+, Mg2+, Al3+, Fe3+, etc.) to neutralize the colloidal negative charges
- With destabilization, colloids aggregate in size and start to settle
Points to Consider
- Low particulate concentration: sludge recycling
- Large coagulant dosage: restabilization of colloids with positive charge
Coagulation of Colloids by Organic Polymers
- Coagulation by bridging: the ionizable groups on the polymer surface react with the groups or the active sites on the surfaces of the colloids
- Several colloids may bind to a single polymer
Coagulants
- Aluminum sulfate (Al2(SO4)3.14 H2O)
- 1 mole of alum consumes 6 moles of bicarbonate (HCO3-)
- If alkalinity is not enough, pH will reduce greatly, which can be overcome by adding Ca(OH)2 or NaHCO3 (soda ash)
- Ferrous sulfate (FeSO4.7H2O)
- Forms dense, quick-settling floc
- pH must be raised to 9.5
- Ferric sulfate (Fe2(SO4)3)
- pH should be in the range from 4 to 12
- Ferric chloride (FeCl3)
- pH should be in the range from 4 to 12
Coagulation and Flocculation Process
- Coagulation: rapid mixing to aggregate dispersed non-settleable solids
- Flocculation: gentle mixing to form large flocs
- Agitation devices:
- Mechanical agitators
- Pneumatic agitators
- Baffle basins
Jar Test
- A laboratory technique used to determine:
- The proper coagulant and coagulant aid
- The chemical dosage required
- Variables:
- Speed of rotation
- Time of settling
- Dosage
- Size of flocs
- Turbidity removal
- Color removal
- pH
Velocity Gradient
- Measures the degree of mixing
- Velocity gradient (G): relative velocity of the two fluid particles divided by distance
- Higher G value, intenser mixing
Mixing by Impellers and Pneumatic Mixing
- Equations for power input and velocity gradient for mechanical and pneumatic agitation
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Description
This quiz covers the importance of coagulation and flocculation in water treatment, including reducing turbidity and removing unwanted taste and odor compounds.
