THE COMPLETE GUIDE OF WATER TREATMENT IN SLIDE SHOW.Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Water Treatment

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Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Water Treatment 

• Slide 1

  Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Water Treatment 

  Slide 2

  Reflections ä What are the two broad tasks of environmental engineers? ä What is the connection between the broad tasks of environmental engineers and building a water treatment plant? ä Why may the water need to be changed/treated? ä What are the two broad tasks of environmental engineers? ä What is the connection between the broad tasks of environmental engineers and building a water treatment plant? ä Why may the water need to be changed/treated?

  Slide 3

  Simple Sorting ä Goal: clean water ä Source: (contaminated) surface water ä Solution: separate contaminants from water ä How? ä Goal: clean water ä Source: (contaminated) surface water ä Solution: separate contaminants from water ä How?

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  Where are we going? particles dissolved chemicals pathogens ä Unit processes* designed to ä remove ___________ ä remove __________ ___________ ä inactivate __________ ä *Unit process: a process that is used in similar ways in many different applications ä sedimentation ä filtration ä... ä Unit processes* designed to ä remove ___________ ä remove __________ ___________ ä inactivate __________ ä *Unit process: a process that is used in similar ways in many different applications ä sedimentation ä filtration ä...

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  Unit Processes Designed to Remove Particulate Matter ä Screening ä Sedimentation ä Coagulation/flocculation ä Filtration ä slow sand filters ä rapid sand filters ä diatomaceous earth filters ä membrane filters ä Screening ä Sedimentation ä Coagulation/flocculation ä Filtration ä slow sand filters ä rapid sand filters ä diatomaceous earth filters ä membrane filters

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  Conventional Surface Water Treatment Screening Coagulation Flocculation Sedimentation Filtration Disinfection Storage Distribution Raw water Alum Polymers Alum Polymers Cl 2 sludge

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  Screening ä Removes large solids ä logs ä branches ä rags ä fish ä Simple process ä may incorporate a mechanized trash removal system ä Protects pumps and pipes in WTP ä Removes large solids ä logs ä branches ä rags ä fish ä Simple process ä may incorporate a mechanized trash removal system ä Protects pumps and pipes in WTP

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  Sedimentation ä the oldest form of water treatment ä uses gravity to separate particles from water ä often follows coagulation and flocculation ä occurs in NYC’s __________ ä the oldest form of water treatment ä uses gravity to separate particles from water ä often follows coagulation and flocculation ä occurs in NYC’s __________ reservoirs

  Slide 9

  Sedimentation: Effect of the particle concentration ä Dilute suspensions ä Particles act independently ä Concentrated suspensions ä Particle-particle interactions are significant ä Particles may collide and stick together (form flocs) ä Particle flocs may settle more quickly ä Particle-particle forces may prevent further consolidation ä Dilute suspensions ä Particles act independently ä Concentrated suspensions ä Particle-particle interactions are significant ä Particles may collide and stick together (form flocs) ä Particle flocs may settle more quickly ä Particle-particle forces may prevent further consolidation

  Slide 10

  How fast do particles fall in dilute suspensions? Gravity Fluid drag ä What are the important parameters? ä Initial conditions ä After falling for some time... ä What are the important forces? ä _________ ä __________ ä What are the important parameters? ä Initial conditions ä After falling for some time... ä What are the important forces? ä _________ ä __________

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  projected Sedimentation: Particle Terminal Fall Velocity Identify forces

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  Particle Terminal Fall Velocity (continued) Force balance (zero acceleration) We haven’t yet assumed a shape Assume a _______ sphere

  Slide 13

  Drag Coefficient on a Sphere laminar turbulent turbulent boundary Stokes Law

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  Drag Coefficient: Equations Laminar flow R < 1 Transitional flow 1 < R < 10 4 Fully turbulent flow R > 10 4 General Equation

  Slide 15

  Example Calculation of Terminal Velocity Determine the terminal settling velocity of a cryptosporidium oocyst having a diameter of 4  m and a density of 1.04 g/cm 3 in water at 15°C [  =1.14x10 -3 kg/(sm)]. Reynolds? Work in your teams. Use mks units (meters, kilograms, seconds). Convert your answer to some reasonable set of units that you understand. Solution

  Slide 16

  Sedimentation Basin Settling zone Sludge zone Inlet zone Outlet zone Sludge out ä long rectangular basins ä 4-6 hour retention time ä 3-4 m deep ä max of 12 m wide ä max of 48 m long ä long rectangular basins ä 4-6 hour retention time ä 3-4 m deep ä max of 12 m wide ä max of 48 m long We can’t do this in our laboratory scale plants!

  Slide 17

  Sedimentation Basin: Critical Path Horizontal velocity Vertical velocity L L H H Sludge zone Inlet zone Outlet zone Sludge out A = WH Q = flow rate What is V c for this sedimentation tank?

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  Sedimentation Basin: Importance of Tank Surface Area L L H H W W Suppose water were flowing up through a sedimentation tank. What would be the velocity of a particle that is just barely removed? Want a _____ V c, ______ A s, _______ H, _______ . smalllarge Time in tank smalllarge

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  Lamella ä Sedimentation tanks are commonly divided into layers of shallow tanks (lamella) ä The flow rate can be increased while still obtaining excellent particle removal ä Sedimentation tanks are commonly divided into layers of shallow tanks (lamella) ä The flow rate can be increased while still obtaining excellent particle removal Lamella decrease distance particle has to fall in order to be removed

  Slide 20

  Settling zone Sludge zone Inlet zone Outlet zone Design Criteria for Sedimentation Tanks Minimal turbulence (inlet baffles) Uniform velocity (small dimensions normal to velocity) No scour of settled particles Slow moving particle collection system Q/A s must be small (to capture small particles) This will be one of the ways you can improve the performance of your water treatment plant. ä _______________________________

  Slide 21

  Sedimentation of Small Particles? ä How could we increase the sedimentation rate of small particles? Increase d (stick particles together) Increase g (centrifuge) Decrease viscosity (increase temperature) Increase density difference (dissolved air flotation)

  Slide 22

  Particle/particle interactions ä Electrostatic repulsion ä In most surface waters, colloidal surfaces are negatively charged ä like charges repel __________________ ä van der Waals force ä an attractive force ä decays more rapidly with distance than the electrostatic force ä is a stronger force at very close distances ä Electrostatic repulsion ä In most surface waters, colloidal surfaces are negatively charged ä like charges repel __________________ ä van der Waals force ä an attractive force ä decays more rapidly with distance than the electrostatic force ä is a stronger force at very close distances stable suspension

  Slide 23

  Energy Barrier ä Increase kinetic energy of particles ä increase temperature ä stir ä Decrease magnitude of energy barrier ä change the charge of the particles ä introduce positively charged particles ä Increase kinetic energy of particles ä increase temperature ä stir ä Decrease magnitude of energy barrier ä change the charge of the particles ä introduce positively charged particles + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Layer of counter ions van der Waals Electrostatic

  Slide 24

  Coagulation ä Coagulation is a physical-chemical process whereby particles are destabilized ä Several mechanisms ä adsorption of cations onto negatively charged particles ä decrease the thickness of the layer of counter ions ä sweep coagulation ä interparticle bridging ä Coagulation is a physical-chemical process whereby particles are destabilized ä Several mechanisms ä adsorption of cations onto negatively charged particles ä decrease the thickness of the layer of counter ions ä sweep coagulation ä interparticle bridging

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  Coagulation Chemistry ä The standard coagulant for water supply is Alum [Al 2 (SO 4 ) 3 *14.3H 2 O] ä Typically 5 mg/L to 50 mg/L alum is used ä The chemistry is complex with many possible species formed such as AlOH +2, Al(OH) 2 +, and Al 7 (OH) 17 +4 ä The primary reaction produces Al(OH) 3 Al 2 (SO 4 ) 3 + 6H 2 O  2Al(OH) 3 + 6H + + 3SO 4 -2 ä The standard coagulant for water supply is Alum [Al 2 (SO 4 ) 3 *14.3H 2 O] ä Typically 5 mg/L to 50 mg/L alum is used ä The chemistry is complex with many possible species formed such as AlOH +2, Al(OH) 2 +, and Al 7 (OH) 17 +4 ä The primary reaction produces Al(OH) 3 Al 2 (SO 4 ) 3 + 6H 2 O  2Al(OH) 3 + 6H + + 3SO 4 -2 pH = -log[H + ]

  Slide 26

  Coagulation Chemistry ä Aluminum hydroxide [Al(OH) 3 ] forms amorphous, gelatinous flocs that are heavier than water ä The flocs look like snow in water ä These flocs entrap particles as the flocs settle (sweep coagulation) ä Aluminum hydroxide [Al(OH) 3 ] forms amorphous, gelatinous flocs that are heavier than water ä The flocs look like snow in water ä These flocs entrap particles as the flocs settle (sweep coagulation)

  Slide 27

  Coagulant introduction with rapid mixing ä The coagulant must be mixed with the water ä Retention times in the mixing zone are typically between 1 and 10 seconds ä Types of rapid mix units ä pumps ä hydraulic jumps ä flow-through basins with many baffles ä In-line blenders ä The coagulant must be mixed with the water ä Retention times in the mixing zone are typically between 1 and 10 seconds ä Types of rapid mix units ä pumps ä hydraulic jumps ä flow-through basins with many baffles ä In-line blenders

  Slide 28

  Flocculation ä Coagulation has destabilized the particles by reducing the energy barrier ä Now we want to get the particles to collide ä We need relative motion between particles ä Brownian motion is too slow ä _________ _____________ rates ä __________ shears the water ä Coagulation has destabilized the particles by reducing the energy barrier ä Now we want to get the particles to collide ä We need relative motion between particles ä Brownian motion is too slow ä _________ _____________ rates ä __________ shears the water Differential sedimentation Turbulence

  Slide 29

  Flocculation ä Turbulence provided by gentle stirring ä Turbulence also keeps large flocs from settling so they can grow even larger! ä High sedimentation rate of large flocs results in many collisions! ä Retention time of 10 - 30 minutes ä Turbulence provided by gentle stirring ä Turbulence also keeps large flocs from settling so they can grow even larger! ä High sedimentation rate of large flocs results in many collisions! ä Retention time of 10 - 30 minutes

  Slide 30

  Coagulation/Flocculation ä Inject Coagulant in rapid mixer ä Water flows from rapid mix unit into flocculation tank ä gentle stirring ä flocs form ä Water flows from flocculation tank into sedimentation tank ä make sure flocs don’t break! ä flocs settle and are removed ä Inject Coagulant in rapid mixer ä Water flows from rapid mix unit into flocculation tank ä gentle stirring ä flocs form ä Water flows from flocculation tank into sedimentation tank ä make sure flocs don’t break! ä flocs settle and are removed

  Slide 31

  Jar Test ä Mimics the rapid mix, coagulation, flocculation, sedimentation treatment steps in a beaker ä Allows operator to test the effect of different coagulant dosages or of different coagulants ä Mimics the rapid mix, coagulation, flocculation, sedimentation treatment steps in a beaker ä Allows operator to test the effect of different coagulant dosages or of different coagulants

  Slide 32

  Unit Processes in Conventional Surface Water Treatment ä We’ve covered ä Sedimentation ä Coagulation/flocculation ä Coming up! ä Filtration ä Disinfection ä Removal of Dissolved Substances ä We’ve covered ä Sedimentation ä Coagulation/flocculation ä Coming up! ä Filtration ä Disinfection ä Removal of Dissolved Substances

  Slide 33

  Conventional Surface Water Treatment Screening Coagulation Flocculation Sedimentation Filtration Disinfection Storage Distribution Raw water Alum Polymers Alum Polymers Cl 2 sludge

  Slide 34

  Filtration ä Slow sand filters ä Diatomaceous earth filters ä Membrane filters ä Rapid sand filters (Conventional Treatment) ä Slow sand filters ä Diatomaceous earth filters ä Membrane filters ä Rapid sand filters (Conventional Treatment)

  Slide 35

  Slow Sand Filtration ä First filters to be used on a widespread basis ä Fine sand with an effective size of 0.2 mm ä Low flow rates (10 - 40 cm/hr) ä Schmutzdecke (_____ ____) forms on top of the filter ä causes high head loss ä must be removed periodically ä Used without coagulation/flocculation! ä First filters to be used on a widespread basis ä Fine sand with an effective size of 0.2 mm ä Low flow rates (10 - 40 cm/hr) ä Schmutzdecke (_____ ____) forms on top of the filter ä causes high head loss ä must be removed periodically ä Used without coagulation/flocculation! filter cake

  Slide 36

  Diatomaceous Earth Filters ä Diatomaceous earth (DE) is made of the silica skeletons of diatoms ä DE is added to water and then fed to a special microscreen ä The DE already on the microscreen strains particles and DE from the water ä The continuous DE feed prevents the gradually thickening DE cake from developing excessive head loss ä Was seriously considered for Croton Filtration Plant ä Diatomaceous earth (DE) is made of the silica skeletons of diatoms ä DE is added to water and then fed to a special microscreen ä The DE already on the microscreen strains particles and DE from the water ä The continuous DE feed prevents the gradually thickening DE cake from developing excessive head loss ä Was seriously considered for Croton Filtration Plant

  Slide 37

  Membrane Filters ä Much like the membrane filters used to enumerate coliforms ä much greater surface area ä Produce very high quality water (excellent particle removal) ä Clog rapidly if the influent water is not of sufficiently high quality ä More expensive than sand and DE filters ä Much like the membrane filters used to enumerate coliforms ä much greater surface area ä Produce very high quality water (excellent particle removal) ä Clog rapidly if the influent water is not of sufficiently high quality ä More expensive than sand and DE filters

  Slide 38

  Rapid Sand Filter (Conventional US Treatment) Sand Gravel Influent Drain Effluent Wash water Anthracite Size (mm) 0.70 0.45 - 0.55 5 - 60 Size (mm) 0.70 0.45 - 0.55 5 - 60 Specific Gravity 1.6 2.65 Specific Gravity 1.6 2.65 Depth (cm) 30 45 Depth (cm) 30 45

  Slide 39

  Particle Removal Mechanisms in Filters Transport Attachment Molecular diffusion Inertia Gravity Interception Straining Surface forces

  Slide 40

  Filter Design ä Filter media ä silica sand and anthracite coal ä non-uniform media will stratify with _______ particles at the top ä Flow rates ä 2.5 - 10 m/hr ä Backwash rates ä set to obtain a bed porosity of 0.65 to 0.70 ä typically 50 m/hr ä Filter media ä silica sand and anthracite coal ä non-uniform media will stratify with _______ particles at the top ä Flow rates ä 2.5 - 10 m/hr ä Backwash rates ä set to obtain a bed porosity of 0.65 to 0.70 ä typically 50 m/hr smaller

  Slide 41

  Sand Gravel Influent Drain Effluent Wash water Anthracite Backwash ä Wash water is treated water! ä WHY? ä Wash water is treated water! ä WHY? Only clean water should ever be on bottom of filter!

  Slide 42

  Disinfection ä Disinfection: operations aimed at killing or ____________ pathogenic microorganisms ä Ideal disinfectant ä _______________ ä Disinfection: operations aimed at killing or ____________ pathogenic microorganisms ä Ideal disinfectant ä _______________ inactivating Toxic to pathogens Not toxic to humans Fast rate of kill Residual protection Economical

  Slide 43

  Disinfection Options ä Chlorine ä chlorine gas ä sodium hypochlorite (bleach) ä Ozone ä Irradiation with Ultraviolet light ä Sonification ä Electric Current ä Gamma-ray irradiation ä Chlorine ä chlorine gas ä sodium hypochlorite (bleach) ä Ozone ä Irradiation with Ultraviolet light ä Sonification ä Electric Current ä Gamma-ray irradiation Poisonous gas – risk of a leak

  Slide 44

  Chlorine ä First large-scale chlorination was in 1908 at the Boonton Reservoir of the Jersey City Water Works in the United States ä Widely used in the US ä Typical dosage (1-5 mg/L) ä variable, based on the chlorine demand ä goal of 0.2 mg/L residual ä Trihalomethanes (EPA primary standard is 0.08 mg/L) ä First large-scale chlorination was in 1908 at the Boonton Reservoir of the Jersey City Water Works in the United States ä Widely used in the US ä Typical dosage (1-5 mg/L) ä variable, based on the chlorine demand ä goal of 0.2 mg/L residual ä Trihalomethanes (EPA primary standard is 0.08 mg/L) Pathogen/carcinogen tradeoff Chlorine oxidizes organic matter

  Slide 45

  Chlorine Reactions Cl 2 + H 2 O  H + + HOCl + Cl - HOCl  H + + OCl - ä The sum of HOCl and OCl - is called the ____ ______ _______ ä HOCl is the more effective disinfectant ä Therefore chlorine disinfection is more effective at ________ pH ä HOCl and OCl - are in equilibrium at pH 7.5 Cl 2 + H 2 O  H + + HOCl + Cl - HOCl  H + + OCl - ä The sum of HOCl and OCl - is called the ____ ______ _______ ä HOCl is the more effective disinfectant ä Therefore chlorine disinfection is more effective at ________ pH ä HOCl and OCl - are in equilibrium at pH 7.5 free chlorine residual low +1-2+10Charges Hypochlorous acid Hypochlorite ion

  Slide 46

  EPA Pathogen Inactivation Requirements ä SDWA requires 99.9% inactivation for Giardia and 99.99% inactivation of viruses ä Giardia is more difficult to kill with chlorine than viruses and thus Giardia inactivation determines the CT ä SDWA requires 99.9% inactivation for Giardia and 99.99% inactivation of viruses ä Giardia is more difficult to kill with chlorine than viruses and thus Giardia inactivation determines the CT Concentration x Time Enumerating Giardia is difficult, time-consuming and costly. How would you ensure that water treatment plants meet this criteria? Safe Drinking Water Act

  Slide 47

  EPA Credits for Giardia Inactivation Treatment typeCredit Conventional Filtration99.7% Direct Filtration*99% Disinfectionf(time, conc., pH, Temp.) Treatment typeCredit Conventional Filtration99.7% Direct Filtration*99% Disinfectionf(time, conc., pH, Temp.) * No sedimentation tanks

  Slide 48

  Disinfection CT Credits Contact time (min) chlorinepH 6.5pH 7.5 (mg/L) 2°C10°C2°C10°C 0.5300178430254 115994228134 Contact time (min) chlorinepH 6.5pH 7.5 (mg/L) 2°C10°C2°C10°C 0.5300178430254 115994228134 To get credit for 99.9% inactivation of Giardia : Inactivation is a function of _______, ____________ ______, and ___________. concentrationtime pH temperature

  Slide 49

  NYC CT? Kensico Hillview Delaware Pipeline 21.75 km long 5.94 m diameter peak hourly flow = 33 m 3 /s Delaware Pipeline 21.75 km long 5.94 m diameter peak hourly flow = 33 m 3 /s 3.4 x 10 6 m 3 volume =603,000 m 3 5 hour residence time!

  Slide 50

  NYC CT Problem ä Hillview Reservoir is an open reservoir ä Should the chlorine contact time prior to arrival at Hillview count? ä Hillview Reservoir is an open reservoir ä Should the chlorine contact time prior to arrival at Hillview count? Giardia contamination from Upstate Reservoirs will be decreased, but recontamination at Hillview is possible

  Slide 51

  Ozone ä Widely used in Europe ä O 3 is chemically unstable ä Must be produced on site ä More expensive than chlorine (2 - 3 times) ä Typical dosages range from 1 to 5 mg/L ä Often followed by chlorination so that the chlorine can provide a protective _______ ä Widely used in Europe ä O 3 is chemically unstable ä Must be produced on site ä More expensive than chlorine (2 - 3 times) ä Typical dosages range from 1 to 5 mg/L ä Often followed by chlorination so that the chlorine can provide a protective _______ residual

  Slide 52

  Removal of Dissolved Substances (1) ä Aeration (before filtration) ä oxidizes iron or manganese in groundwater ä oxidized forms are less soluble and thus precipitate out of solution ä removes hydrogen sulfide (H 2 S) ä Softening (before filtration) ä used to remove Ca +2 and Mg +2 ä usually not necessary with surface waters ä Aeration (before filtration) ä oxidizes iron or manganese in groundwater ä oxidized forms are less soluble and thus precipitate out of solution ä removes hydrogen sulfide (H 2 S) ä Softening (before filtration) ä used to remove Ca +2 and Mg +2 ä usually not necessary with surface waters

  Slide 53

  Removal of Dissolved Substances (2) ä Activated Carbon (between filtration and disinfection) ä extremely adsorbent ä used to remove organic contaminants ä spent activated carbon can be regenerated with superheated steam ä Reverse Osmosis ä semi-permeable membrane allows water molecules to pass, but not the larger ions and molecules ä primarily used for desalination ä also removes organic materials, bacteria, viruses, and protozoa ä Activated Carbon (between filtration and disinfection) ä extremely adsorbent ä used to remove organic contaminants ä spent activated carbon can be regenerated with superheated steam ä Reverse Osmosis ä semi-permeable membrane allows water molecules to pass, but not the larger ions and molecules ä primarily used for desalination ä also removes organic materials, bacteria, viruses, and protozoa

  Slide 54

  Conventional Surface Water Treatment Screening Coagulation Flocculation Sedimentation Filtration Disinfection Storage Distribution Raw water Alum Polymers Alum Polymers Cl 2 sludge

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  Summary Clearwell Backwash Lagoon Flocculation Sedimentation Filtration Rapid Mix

  Slide 56

  Cryptosporidium Oocyst

  Slide 57

  Reynolds Number Check R<<1 -6="" 10="" and="" in="" law="" r="1.1" range="" stokes="" td="" therefore="" x="">

  Slide 58

  Diatomaceous Earth DE Clay

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