cee 370 environmental engineering principles

CEE 370 Environmental Engineering Principles Lecture #27 Water - PowerPoint PPT Presentation

Print version Updated: 13 November 2019 CEE 370 Environmental Engineering Principles Lecture #27 Water Treatment I: Introduction, Process Flow, Coagulation Reading: Mihelcic & Zimmerman, Chapter 8 Reading: Davis & Cornwall, Chapt


  1. Print version Updated: 13 November 2019 CEE 370 Environmental Engineering Principles Lecture #27 Water Treatment I: Introduction, Process Flow, Coagulation Reading: Mihelcic & Zimmerman, Chapter 8 Reading: Davis & Cornwall, Chapt 4-1 to 4-3 Reading: Davis & Masten, Chapter 10-1 to 10-3 David Reckhow CEE 370 L#27 1

  2. Definitions  Pathogens  An agent that causes infection in a living host  Most are microorganisms, but most microorganisms are not pathogens  Infection  A pathological condition due to the growth of microorganisms in a host  Toxin  A poisonous substance from certain organisms  Virulence  The capacity of a microorganism to cause disease 2 CEE 370 L#27 David Reckhow

  3. Types of pathogens  Viral  Hepatitis, polio, yellow fever  Rickettsial (between bacteria and viruses) Many  Typhus can  Bacterial be water  Antrax, Botulism, Cholera, Plague, Salmonellosis, borne Shigellosis, Typhoid  Protozoan  Amebiasis, Malaria, Giardiasis, Cryptosporidiosis  Helmenthic  Hookworm, Tapeworm, Schistosomiasis 3 CEE 370 L#27 David Reckhow

  4. Chlorination  1-2 punch of filtration & chlorination Greenberg, 1980, Water Chlorination, Env. Impact & Health Eff., Vol 3, pg.3, Ann Arbor Sci. US Death Rates for Typhoid Fever Melosi, 2000, The Sanitary City, John Hopkins Press 4 CEE 370 L#27 David Reckhow

  5. Engineering & Disease  Filtration & chlorination From: The Sanitary City 5 CEE 370 L#27 David Reckhow

  6. Water Supply and Distribution Distribution Storage Water Treatment Plant Water Source Pumping Distribution System 6 CEE 370 L#27 David Reckhow

  7. 7 CEE 370 L#27 David Reckhow

  8. Purposes for Water Treatment  Disinfection  Removal of Turbidity  Removal of Color, and Tastes & Odors  Removal of Iron & Manganese  Hardness removal  Protection from Toxic Organics and Inorganics 8 CEE 370 L#27 David Reckhow

  9. Raw Water Quality  Hillsborough River: Tampa FL  An extreme case 9 CEE 370 L#27 David Reckhow

  10. How to Treat Drinking Water  Historical  Use fine granular media to “sieve” out particles  Slow Sand Filtration  Too labor intensive, land intensive and slow  Modern  Use coarser media with coagulant  Rapid Media Filtration  Better to precede it with settling 10 CEE 370 L#27 David Reckhow

  11. Drinking Water Treatment Processes  Gas Transfer (stripping)  Oxidation  Coagulation & Flocculation  Sedimentation or Flotation  Softening  Adsorption  Disinfection 11 CEE 370 L#27 David Reckhow

  12. Conventional Water Treatment  Coagulation, settling, filtration & disinfection Alum Chlorine Dist. Sys. Clear well raw rapid flocculation Settling Filtration water mix Corrosion Control Fluoride Coagulant Disinfectant Dist. Sys. Clear well raw rapid flocculatio Settling Filtration water mix n 12 CEE 370 L#27 David Reckhow

  13. Some WTP video tours  Beaufort Jasper WTP, SC (5:25)  Conventional treatment  https://www.youtube.com/watch?v=0bXIqS5NcRY  Winnipeg, Manitoba (7:28)  DAF, ozone & UV  https://www.youtube.com/watch?v=20VvpASC2sU  Severn Trent, England (3:20)  Screening, sludge blanket clarifiers, GAC, Ozone  https://www.youtube.com/watch?v=9z14l51ISwg 13 CEE 370 L#27 David Reckhow

  14. An advanced water treatment process Direct Filtration Pre- Lime & coagulant Soda Ash oxidant Settling Water Supply Rapid Flocculation Mix Flotation Chlorine Intermediate Filtration GAC Ozonation Clear Well Ads. To the distribution system 14 CEE 370 L#27 David Reckhow

  15. Coagulation: Purpose  Initiate the chemical reactions that render conventional treatment effective  When combined with subsequent physical removal, it achieves:  Removal of turbidity  historically the reason for coagulation  Requires that particles be “destabilized”  Removal of natural organic matter  more recently of importance  Some removal of pathogens  Giardia, Cryptosporidium 15 CEE 370 L#27 David Reckhow

  16. Overview of conventional treatment Direct Filtration coagulant Settling Rapid Water Filtration Flocculation Mix Supply Flotation Coagulation Dissolved Organics Settleable Unstable Stable Particles Particles Particles 16 CEE 370 L#27 David Reckhow

  17. Conventional Treatment  rapid mix, flocculation, sedimentation in one long tank with baffles H&H, Fig 7-4, pg. 212 17 CEE 370 L#27 David Reckhow

  18. Coagulant Addition: Rapid Mix  Purpose  to provide rapid and complete mixing of chemicals at the head of a plant  Two types: tank mixer or in-line  Tank Mixer  Tank  3 to 10 ft diameter  flow through, top to bottom  10 to 60 second detention time  vertical shaft turbine impeller  G=600-1000 s -1 18 CEE 370 L#27 David Reckhow

  19. Rapid mix Tank  Impeller  Iron deposits Reading, MA David Reckhow 19 CEE 370 L#27

  20. Rapid Mix Design  Detention Time  10-60 seconds is most common  Mixing Energy dv  differences in fluid velocity: velocity gradient G ≡  change in velocity as you move up or down vertically dy in a reactor  since velocity is [L/T] and vertical distance is [L], the G value is in units of reciprocal time [T -1 ]  Camp: related it to power input (P), tank volume (V) and viscosity (µ) 1   P 2 =   G = µ   2 P VG µ V   20 CEE 370 L#27 David Reckhow

  21. Typical values for mixing Type Gradient (G) in Detention Gt values sec -1 Time 5x10 4 – 5x10 5 Mechanical Mixing 600-1,000 10-120s 1x10 3 – 1x10 5 In-line mixing 3,000-5,000 1 s 1x10 4 – 1x10 5 Horizontal-shaft paddle 20-50 10-30 min flocculator 1x10 4 – 1x10 5 Vertical-shaft turbine 10-50 10-30 min flocculator From: M&Z table 8.12 21 CEE 370 L#27 David Reckhow

  22. In-line static mixers  Many manufacturers 22 CEE 370 L#27 David Reckhow

  23. Coagulant chemistry Ferric Sulfate (also ferric chloride) → ⇓ Fe ( SO ) + 6 OH - 2Fe(OH ) 2- + 3 SO 2 4 4 3 3 Alum (the most common coagulant) − + • → ⇓ + + + 2 Al SO ( ) 18 H O 2 Al OH ( ) 3 SO 6 H 12 H O 2 4 3 2 3 4 2 GFW= 666 AW= 27 Alum is Mechanisms Neutralized by ~8.4% Al by wt. natural alkalinity • Charge Neutralization (bicarbonate) • Sweep Floc (enmeshment) • Adsorption / complexation for Dissolved substances 23 CEE 370 L#27 David Reckhow

  24. RESTABILIZATION ZONE CHARGE NEUTRALIZATION OPTIMUM SWEEP Common in TO ZERO ZETA POTENTIAL WITH SWEEP COAGULATION practice n+ Al (OH) /Al(OH) (s) X Y 3 ALUM AS Al (SO ) x 14.3 H O-mg/l 100 2 LOG (Al) (mol/L) -4 30 CHARGE NEUTRALIZATION CORONA TO ZERO ZETA 10 3 POTENTIAL WITH Al(OH) 2 + 4 C Al(OH) (s) 3 -5 3 2 B Al (OH) 4 + 1 8 20 A Chemistry of -6 0.3 + 3 Al Al(OH) 4 - Aluminum Al TOTAL + Al(OH) (s) 3 ZETA POTENTIAL IEP IEP (IOSOELECTRIC PAINT) UNCOATED COLLOID 0 COLLOID COATED D E n + WITH ( Al(OH) (s) ) 3 - 2 4 6 8 10 12 24 CEE 370 L#27 David Reckhow pH OF MIXED SOLUTION

  25. Charge neutralization 25 CEE 370 L#27 David Reckhow

  26. Colloid Stability  DLVO theory Repulsive Electrostatic Repulsive Force Net Force Energy Distance between Primary centers Van der Waals Minimum Attractive Force Attractive 26 CEE 370 L#27 David Reckhow

  27. Colloid Stability  Impact of Repulsive Charge neutralization Electrostatic Repulsive Force Net Force Energy Distance between centers Van der Waals Attractive Force Attractive 27 CEE 370 L#27 David Reckhow

  28. Destabilization with Polymers  Natural polymers  Alginates  Synthetic polymers  Cationic, anionic, non-ionic  No need to reach “primary minimum” distance  Also used to strengthen floc 28 CEE 370 L#27 David Reckhow

  29. Coagulation: Empirical Tests  Jar Testing  Laboratory experiments with varying coagulant doses at varying pHs 29 CEE 370 L#27 David Reckhow

  30. Flocculation: Purpose  Provides slow mixing to allow “destabilized” particles and precipitates to grow in size  Larger size helps with subsequent physical removal  Gravity settling  Flotation  Filtration 30 CEE 370 L#27 David Reckhow

  31. Flocculation: Purpose  Promote agglomeration of particles into larger floc  Units often designed on the basis of mixing intensity as described by the velocity gradient, G  some mixing is needed to keep particles in contact with other particles  too much mixing can cause floc break-up 31 CEE 370 L#27 David Reckhow

  32. Flocculators Drive shaft Usually 4 arms with 3-4 slats per arm 32 CEE 370 L#27 David Reckhow

  33. Flocculation  Horizontal Shaft MWDSC Weymouth Plant 12 Dec 05 33 CEE 370 L#27 David Reckhow

  34. Flocculation  4 Wooden paddles Chicago 34 CEE 370 L#27 David Reckhow

  35. Flocculation  2 parallel shafts New Orleans 35 CEE 370 L#27 David Reckhow

  36. Vertical Shaft Flocculator  Motor and gear box Andover, MA 36 CEE 370 L#27 David Reckhow

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