CEE 370 Lecture #27 11/13/2019 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 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 Lecture #27 Dave Reckhow 1
CEE 370 Lecture #27 11/13/2019 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 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 Lecture #27 Dave Reckhow 2
CEE 370 Lecture #27 11/13/2019 Engineering & Disease Filtration & chlorination From: The Sanitary City 5 CEE 370 L#27 David Reckhow Water Supply and Distribution Distribution Storage Water Treatment Plant Water Source Pumping Distribution System 6 CEE 370 L#27 David Reckhow Lecture #27 Dave Reckhow 3
CEE 370 Lecture #27 11/13/2019 7 CEE 370 L#27 David Reckhow 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 Lecture #27 Dave Reckhow 4
CEE 370 Lecture #27 11/13/2019 Raw Water Quality Hillsborough River: Tampa FL An extreme case 9 CEE 370 L#27 David Reckhow 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 Lecture #27 Dave Reckhow 5
CEE 370 Lecture #27 11/13/2019 Drinking Water Treatment Processes Gas Transfer (stripping) Oxidation Coagulation & Flocculation Sedimentation or Flotation Softening Adsorption Disinfection 11 CEE 370 L#27 David Reckhow 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 Lecture #27 Dave Reckhow 6
CEE 370 Lecture #27 11/13/2019 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 An advanced water treatment process Direct Filtration Pre- Pre- Lime & Lime & coagulant coagulant Soda Ash Soda Ash oxidant oxidant Settling Settling Water Water Supply Supply Rapid Rapid Flocculation Flocculation Mix Mix Flotation Flotation Chlorine Chlorine Intermediate Intermediate Filtration Filtration GAC GAC Ozonation Ozonation Clear Well Ads. Ads. To the distribution system 14 CEE 370 L#27 David Reckhow Lecture #27 Dave Reckhow 7
CEE 370 Lecture #27 11/13/2019 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 Overview of conventional treatment Direct Filtration coagulant coagulant Settling Settling Water Water Rapid Rapid Filtration Filtration Flocculation Flocculation Supply Supply Mix Mix Flotation Flotation Coagulation Dissolved Organics Unstable Settleable Stable Particles Particles Particles 16 CEE 370 L#27 David Reckhow Lecture #27 Dave Reckhow 8
CEE 370 Lecture #27 11/13/2019 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 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 Lecture #27 Dave Reckhow 9
CEE 370 Lecture #27 11/13/2019 Rapid mix Tank Impeller Iron deposits Reading, MA David Reckhow 19 CEE 370 L#27 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 2 P VG V 20 CEE 370 L#27 David Reckhow Lecture #27 Dave Reckhow 10
CEE 370 Lecture #27 11/13/2019 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 In-line static mixers Many manufacturers 22 CEE 370 L#27 David Reckhow Lecture #27 Dave Reckhow 11
CEE 370 Lecture #27 11/13/2019 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 RESTABILIZATION ZONE CHARGE NEUTRALIZATION OPTIMUM SWEEP Common in TO ZERO ZETA POTENTIAL WITH practice SWEEP COAGULATION 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 2 + POTENTIAL WITH Al(OH) 4 C Al(OH) (s) 3 -5 3 2 B Al (OH) 4 + 1 8 20 A Chemistry of -6 0.3 Al + 3 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 Lecture #27 Dave Reckhow 12
CEE 370 Lecture #27 11/13/2019 Charge neutralization 25 CEE 370 L#27 David Reckhow 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 Lecture #27 Dave Reckhow 13
CEE 370 Lecture #27 11/13/2019 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 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 Lecture #27 Dave Reckhow 14
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