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CHEMICAL CLARIFICATION – COAGULATION METHODS

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CHEMICAL CLARIFICATION – COAGULATION METHODS. Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit. CLARIFICATION. Removal of Settleable and Floatable Solids. CHEMICAL CLARIFICATION. Increase Removal Amount (More Solids Out)

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  1. CHEMICAL CLARIFICATION – COAGULATION METHODS Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit

  2. CLARIFICATION Removal of Settleable and Floatable Solids

  3. CHEMICAL CLARIFICATION • Increase Removal Amount (More Solids Out) • Increase Removal Rates (Solids Settle Faster)

  4. CHEMICAL CLARIFICATION • Less Solids • More Sludge (in effluent) (for disposal)

  5. 2(p - po)g 9n (d/2)2 VF = Stoke’s Law VF = Fall Velocity (p - po) = Density difference between particle and water n = viscosity of water g = gravitational acceleration constant d = diameter of the particle

  6. 2(p - po)g 9n (d/2)2 VF = Stoke’s Law VF = Fall Velocity (p - po)= Density difference between particle and water n = viscosity of water g = gravitational acceleration constant d = diameter of the particle

  7. 2(p - po)g 9n (d/2)2 VF = Stoke’s Law VF = Fall Velocity (p - po)= Density difference between particle and water n = viscosity of water g = gravitational acceleration constant d = diameter of the particle

  8. 2(p - po)g 9n (d/2)2 VF = Stoke’s Law VF = Fall Velocity (p - po)= Density difference between particle and water n = viscosity of water g = gravitational acceleration constant d = diameter of the particle

  9. CHEMICAL CLARIFICATION • Increase Particle Size (Average Diameter)

  10. Particle Size versus Settling Time Particle Size mm Order of Size Time to Settle

  11. CHEMICAL CLARIFICATION • Increase Particle Size • Encourage Contact

  12. CHEMICAL CLARIFICATION 1. Coagulation 2. Flocculation 3. Separation

  13. Coagulation • Chemical Addition • Rapid Mixing • “Pin-point” Floc Formation

  14. Flocculation • Slow Mixing • Floc Growth • Increased Diameter

  15. Solids Separation • Clarified Liquid • Concentrated Suspension (sludge) Usually Gravity Settling Other Processes (dissolved air flotation, etc.)

  16. CHEMICAL CLARIFICATION • Increase Particle Size • Encourage Contact

  17. * Fine Suspended Particles Have an Electrostatic Charge (Usually +) Like Charges Repel Natural Stabilizing Force Keeps Solids Apart Purpose of Chemical Clarification * Encourage Contact * Destabilize Charges

  18. Mechanisms • Electrostatic Charge Reduction • Interparticle Bridging • Physical Enmeshment

  19. Electrostatic Charge Reduction • Solid Particles have an Electrostatic Charge usually negative solids repel one another • Add Chemical to Neutralize Charge positive charge (cationic) • Must Not Overdose excess positive charge

  20. Interparticle Bridging • Polyelectrolytes (polymers) long chains electrostatic charges • Adsorb on the Charged Particles bridges particles together

  21. Interparticle Bridging Negative Colloidal Particles Cationic Polymer Unit

  22. Interparticle Bridging • Polyelectrolytes (polymers) long chains electrostatic charges • Adsorb on the Charged Particles bridges particles together • Must Not Overdose

  23. Physical Enmeshment • Ions Combine with Hydroxyl Ions OH- • Gelatinous Precipitate Forms flakes void spaces • Collects Particles as it Forms co-precipitate enlarges the floc

  24. Mechanisms • Electrostatic Charge Reduction • Interparticle Bridging • Physical Enmeshment

  25. CHEMICAL CLARIFICATION 1. Coagulation 2. Flocculation 3. Separation

  26. COAGULATION Rapid Mix Adequate Contact FLOCCULATION Slow Mixing Increase Floc Size

  27. PROCESS CONTROL 1. Provide complete mixing. 2. Control mixing for floc. 3. Control chemical dose.

  28. Chemical Treatment Addition of Positive Ions (Cations) or Polymers

  29. CHEMICAL TREATMENT Positive Ions Added by Adding Metal Salts Such As Aluminum Sulfate (Al+3) Calcium Hydroxide (Ca+2) Ferric (Iron) Chloride (Fe+3)

  30. Metal Salts Used Most Common Alum (Aluminum Sulfate) Ferric Chloride Lime ( Calcium Hydroxide) Others Sodium Aluminate Ferric Sulfate Ferrous Sulfate Ferrous Chloride

  31. Aluminum Sulfate (Dry)Al2(SO4)3 . 14 H2O “Alum” or “Filter Alum” Available in Various Grades Lump (rarely used) Ground (granulated) Rice Powdered Feeds Easily doesn’t “bulk”

  32. Aluminum Sulfate (Dry)Al2(SO4)3 . 14 H2O Must be kept dry cake to solid lump corrosive equipment must be cleaned Irritant skin mucus membranes eyes Dosage Approximately 75 - 250 mg/L

  33. Aluminum Sulfate (Liquid)Al2(SO4)3 Approximately 11 pounds / gallon Approximately 5.4 pounds of “dry”/gal Ease of Handling vs. Transportation Costs Corrosive equipment must be protected Supports Bacterial Growth / Deposits Reduces Alkalinity

  34. Ferric Chloride (FeCl3) Anhydrous Absorbs Moisture from the Air Corrosive with Water Releases Heat as it is Dissolved Crystal Absorbs Moisture Releases Less Heat Liquid Lined Containers Shipped at 30 - 40 % Approximately 12 pounds per gallon

  35. Ferric Chloride (FeCl3) Corrosive equipment must be protected Stains Safety Concerns Dosage Approximately 45 - 90 mg/L

  36. LIME Hydrated Lime Ca(OH)2 Coagulant pH Adjustment Absorbs Moisture Quicklime (anhydrous) CaO Absorbs Moisture Must be “Slaked” Heat Generated Costs vs. Handling

  37. LIME Erode or Wear Equipment Scale Build-up

  38. LIME Erode or Wear Equipment Scale Build-up Irritant skin eyes mucus membranes lungs Dosage Approximately 200 - 400 mg/L

  39. Polymeric Flocculants “Polyelectrolytes” “Polymers” Organic Compounds - Repeating Units Long Chain - High Molecular Weight

  40. Polymers Classified By: Charge Charge Density Size (Length)

  41. Polymers Charge: “Cationic” - positive charge “Anionic” - negative charge “Nonionic” - no free charge

  42. Polymers Charge Density: Relative Number of Locations Along the Chain That Carry a Charge Percent of Maximum Possible Low Charge (<25%) Medium Charge (25 -50%) High Charge (>50%)

  43. Polymers Size (Length): Designated by Molecular Weight “Low” - <10,000 gm/mole “Medium” - 10,000 to 100,000 gm/mole “High” - 100,000 to 1,000,000 gm/mole “Very High” - 1,000,000 to 10,000,000 gm/mole “Ultrahigh” - >10,000,000 gm/mole

  44. POLYMER MAP Nonionic Polymers Anionic Polymers Cationic Polymers MW > 107 gm/mole Ultrahigh MW Sludge Dewatering MW = 107 gm/mole Very High MW Flocculating after Coagulation MW = 106 gm/mole High MW MW = 105 gm/mole Medium MW MW = 104 gm/mole Low MW Coagulation -50 % 0 % +100 % -100 % +50 %

  45. Polymers Available as: Liquid Dry Gel Emulsion Must be Diluted usually <1% Can Be Very Viscous may build up in pipes and pumps clean regularly salt water - dilute bleach

  46. Polymers Dry Polymers: absorb moisture - ineffective may form “fish-eyes” aged for maximum efficiency 2 hours minimum 7 days maximum

  47. Polymers Considered Non-Hazardous Extremely Slippery Clean Up Immediately Salt Chlorine Drying Agents Absorbent Materials

  48. Polymers Dosage Rate usually less than 1 mg/L (0.25 to 1.5 mg/L) Overdose Worse Than No Polymer

  49. CHEMICAL CLARIFICATION 1. Coagulation 2. Flocculation 3. Separation

  50. PROCESS CONTROL 1. Provide complete mixing. 2. Control mixing for flocculation. 3. Control chemical dose.