Water Treatment: Coagulation and Flocculation
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Questions and Answers

What is the primary goal of the coagulation/flocculation process in water treatment?

  • To increase the rate of disinfection
  • To add chemicals to the water
  • To remove taste and odor compounds
  • To reduce turbidity in water (correct)

    • What is turbidity a measure of in water?

  • The pH level of water
  • The amount of bacteria in water
  • The amount of dissolved solids
  • The amount of suspended solids (correct)

    • What is the role of a coagulant in the coagulation/flocculation process?

  • To add flavor to water
  • To cause small particles to come together to form large particles (correct)
  • To increase the pH level of water
  • To remove suspended solids from water

    • What is an example of a typical coagulant used in the coagulation/flocculation process?

    <p>Aluminum sulfate</p> Signup and view all the answers

    What is the term for solids that cannot settle down by virtue of gravity?

    <p>Nonsettleable solids</p> Signup and view all the answers

    What is the purpose of rapid mixing in the coagulation process?

    <p>To aggregate dispersed nonsettleable solids</p> Signup and view all the answers

    What is the term for the process of neutralizing the colloidal negative charges to destabilize them?

    <p>Charge reduction</p> Signup and view all the answers

    What is the result of destabilizing colloids in the coagulation process?

    <p>The colloids settle down due to gravity</p> Signup and view all the answers

    What occurs when colloids undergo destabilization?

    <p>Colloids aggregate in size and start to settle</p> Signup and view all the answers

    What is the result of low particulate concentration in coagulation?

    <p>Sludge recycling</p> Signup and view all the answers

    What is the mechanism of coagulation by organic polymers?

    <p>Bridging between colloids and polymers</p> Signup and view all the answers

    What is the reaction between aluminum sulfate and bicarbonate?

    <p>Al2(SO4)3 + 6HCO3- → 2Al(OH)3 + 6CO2 + 14H2O + 3SO4-2</p> Signup and view all the answers

    What is the purpose of adding Ca(OH)2 or NaHCO3 in coagulation using aluminum sulfate?

    <p>To overcome alkalinity issues</p> Signup and view all the answers

    What is the characteristic of the floc formed by ferrous sulfate?

    <p>Dense and quick settling</p> Signup and view all the answers

    What is the purpose of rapid mixing in coagulation?

    <p>To form microflocs</p> Signup and view all the answers

    What is the function of agitation devices in coagulation?

    <p>To mix coagulants and colloids</p> Signup and view all the answers

    What is the primary purpose of a jar test in a laboratory?

    <p>To determine the proper coagulant and coagulant aid, as well as the chemical dosage required</p> Signup and view all the answers

    What is the unit of velocity gradient (G)?

    <p>s-1</p> Signup and view all the answers

    What is the condition for laminar flow?

    <p>NRe &lt; 20</p> Signup and view all the answers

    What is the formula for power input (P) in pneumatic mixing?

    <p>P = C1Ga log (h+C2)/C2</p> Signup and view all the answers

    What is the purpose of measuring velocity gradient in mixing?

    <p>To determine the degree of mixing</p> Signup and view all the answers

    What is the relationship between the velocity gradient (G) and the power input (P) in mixing?

    <p>G is directly proportional to P</p> Signup and view all the answers

    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

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    Description

    This quiz covers the basics of coagulation and flocculation in water treatment, including the goals of the process and how it affects turbidity, taste, and odor.

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