water distribution systems water quality modelling for civil engineers 1
DESCRIPTION
Water Distribution Systems Water Quality Modelling for Civil Engineers 1. Helena M Jetmarova, GWMWater George J Kastl, MWH. ??!!???!!!!? !!!???!!!!. ??. NH 2 Cl < 0.5 mg/L. NH 2 Cl < 0.5 mg/L. NH 2 Cl < 0.5 mg/L. NH 3 + O 2 + AOB → NO 2 -+ xAOB. NH 3 + O 2 + AOB → NO 2 -+ xAOB. - PowerPoint PPT PresentationTRANSCRIPT
Water Distribution SystemsWater Distribution Systems
Water Quality Modelling Water Quality Modelling for Civil Engineers 1for Civil Engineers 1
Helena M Jetmarova, GWMWaterHelena M Jetmarova, GWMWater
George J Kastl, MWHGeorge J Kastl, MWH
NH 3 + O 2
+ AOB → NO 2
-+ xAOB
NH2Cl < 0.5 mg/L
AOC, TTHM, HAA
??
NH 3 + O 2
+ AOB → NO 2
-+ xAOB
NH2Cl < 0.5 mg/L
AOC, TTHM, HAA
Cl + F → inert + αTHM
KMnO
4
GAC (O3 & BAC)
4NH2 Cl + 3H
2O + CRB → 3NH3 + 4HCl + HNO
3+ xCRB
??!??!!?
NH 3 + O 2
+ AOB → NO 2
-+ xAOB
NH2Cl < 0.5 mg/L
AOC, TTHM, HAA
Cl + F → inert + αTHM
KMnO
4
GAC (O3 & BAC)
4NH2 Cl + 3H
2O + CRB → 3NH3 + 4HCl + HNO
3+ xCRB
pH
H2O
Cle cd
15.0
3.0
–NH2 Cl + C → NH3+inert??!!???!!!!?
!!!???!!!!
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Talk aboutTalk about 1. Introduction to water quality1. Introduction to water quality
- Type of constituent- Type of constituent
- Transport mechanisms- Transport mechanisms
2. Water quality modelling2. Water quality modelling
- Water age- Water age
- Single species versus multi species- Single species versus multi species
- Reactions- Reactions
- Water disinfection & chlorine decay- Water disinfection & chlorine decay
3. Multi species modelling3. Multi species modelling
- Capabilities- Capabilities
- Practical example- Practical example
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1. Introduction to water quality1. Introduction to water quality
Treated water Quality:TurbidityColourDOCCl decayTTHM formationCl dose [mg/L] Trunk Main
Treatment Plant
Customer’s Tap
Raw water Quality:TurbidityColourDOCCl decayTTHM formation
Delivered water Quality:TurbidityColourDOCCl decayDBP (TTHM, HAA)Cl concentration
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Water Treatment / Distribution Water Treatment / Distribution SystemSystem
Distribution System
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Type of constituentType of constituent
ConservativeConservative
= Non-reactive= Non-reactive
- - Are notAre not normally normally physically or chemically physically or chemically transformed in the watertransformed in the water
- Concentration does not - Concentration does not change while flowing change while flowing through a pipethrough a pipe
- Easy to model- Easy to model
Non-conservativeNon-conservative
= Reactive= Reactive
- - AreAre transformed through transformed through physical, chemical or biological physical, chemical or biological processes in the waterprocesses in the water
- Concentration change (decay - Concentration change (decay or growth) by reacting with or growth) by reacting with other compoundsother compounds
- Difficult to model - Difficult to model
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Type of constituentType of constituent
ConservativeConservative
= Non-reactive= Non-reactive
Eg. salinity, fluorideEg. salinity, fluoride
Cin = Cout
QCin Cout
Non-conservativeNon-conservative
= Reactive= Reactive
Eg. disinfectants (Cl)Eg. disinfectants (Cl)
Cin Cout
Q
bacteria
ClNOM
Cin Cout
AdvectionAdvection
- carrying a - carrying a constituent constituent along with the along with the flow of waterflow of water
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Transport mechanismsTransport mechanisms
Mechanisms to transport constituent in water:Mechanisms to transport constituent in water:
v
cleaning “pig”cleaning “pig”
DispersionDispersion
- axial spreading - axial spreading of a constituent of a constituent mass due to non-mass due to non-uniform velocities uniform velocities
DiffusionDiffusion
- Molecular- Molecular
(Brownian motion)(Brownian motion)
- Turbulent- Turbulent
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Transport mechanismsTransport mechanisms
Which mechanisms are importantWhich mechanisms are important
for transport of constituent?for transport of constituent?
Advection (m/sec) contributes the most to transport of Advection (m/sec) contributes the most to transport of constituent. Some modelling packages use advection only.constituent. Some modelling packages use advection only.
Dispersion is important in laminar flow. Some Dispersion is important in laminar flow. Some modelling packages use both advection and dispersion.modelling packages use both advection and dispersion.
Molecular diffusion (feet/day) is neglected.Molecular diffusion (feet/day) is neglected.
Turbulent diffusion – mixing in tanks.Turbulent diffusion – mixing in tanks.
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2. Water quality modelling2. Water quality modelling
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Water quality modellingWater quality modelling
Benefits of modellingBenefits of modelling
- Limits experimentation on a real system- Limits experimentation on a real system
- Predict water quality in planed systems- Predict water quality in planed systems
Understanding mechanismUnderstanding mechanism
- single versus multi species- single versus multi species
- bulk and wall reaction- bulk and wall reaction
Tool to project “mechanism” into a distribution systemTool to project “mechanism” into a distribution system
- built on top of hydraulic model- built on top of hydraulic model
- EPANet-MSX, H2OMap/InfoWater-MSX- EPANet-MSX, H2OMap/InfoWater-MSX
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Water ageWater age
Time since water parcel entered systemTime since water parcel entered system
Said to indicate water qualitySaid to indicate water quality
- hidden assumption:- hidden assumption:
concentration (quality) is proportional to ageconcentration (quality) is proportional to age
- highly inaccurate for many variables including - highly inaccurate for many variables including
disinfectants & disinfection by-products (DBP)disinfectants & disinfection by-products (DBP)
- neglects effect of temperature- neglects effect of temperature
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Single species vs multi speciesSingle species vs multi species
Single species modelling:Single species modelling:
- - limitedlimited to tracking to tracking a a single componentsingle component (Cl, (Cl, water age water age).).
- limited- limited to accurately describe to accurately describe the reactions between two the reactions between two or more chemical or biologicalor more chemical or biological speciesspecies..
Multi species extension (MSX):Multi species extension (MSX):
- generic formulation of “any” kinetics scheme.- generic formulation of “any” kinetics scheme.
- eg. free chlorine reacts with natural organic matter - eg. free chlorine reacts with natural organic matter (NOM), a heterogeneous mixture of organic compounds.(NOM), a heterogeneous mixture of organic compounds.
- - more than one watermore than one water source supplies a distribution source supplies a distribution systsysteemm..
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ReactionsReactions
Reaction rate in bulk waterReaction rate in bulk water - pipes and tanks- pipes and tanks
- laboratory jar test- laboratory jar test
Reaction rate on pipe surfaceReaction rate on pipe surface - pipes- pipes
- field - field measurementmeasurement
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Water disinfection & Cl decayWater disinfection & Cl decay We disinfect water to kill bacteriaWe disinfect water to kill bacteria
Disinfectants:Disinfectants:
- Chlorine- Chlorine
- Chloramine- Chloramine
- Ozone (decay too fast does not need to be modelled in DS)- Ozone (decay too fast does not need to be modelled in DS)
- UV (no residual, in DS without residual, only re-growth)- UV (no residual, in DS without residual, only re-growth)
- Chlorine dioxide (relatively fast decay)- Chlorine dioxide (relatively fast decay)
Side-effect:Side-effect: Disinfection by-products (DBP) Disinfection by-products (DBP)
The most common disinfectant is chlorine (Cl)The most common disinfectant is chlorine (Cl)
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Components of chlorine decayComponents of chlorine decay
Chorine decay in system
Decay due to bulk water reaction
Decay due to wall interaction
Biofilm / sediment interaction
Wall material interaction
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Components of chlorine decayComponents of chlorine decay
Distance [km]
Bulk prediction
Measurement in system
Chlorine [mg/L]
0
Combined prediction
Reacted with bulk
Reacted with wall
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Chlorine decayChlorine decay
Common chlorine dose 1 – 5 mg/LCommon chlorine dose 1 – 5 mg/L
Dose required to stay within given limits (“envelope”)Dose required to stay within given limits (“envelope”)
depends on:depends on:
- water type (natural organic matter – NOM)- water type (natural organic matter – NOM)
- time available for reaction- time available for reaction
- temperature- temperature
0 0.2 0.6Increasing indicator
failure
Desired level at tap for bacterial
control
Increasing DBP & taste/odour
problems[Cl]
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3. Multi species modelling3. Multi species modelling
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CapabilitiesCapabilities
Which water quality parameters can be modelled?Which water quality parameters can be modelled?
Practically any, important enoughPractically any, important enough
Chlorine, chloramineChlorine, chloramine
By-product formationBy-product formation
pH changespH changes
Disinfection of microorganismsDisinfection of microorganisms
Microbial regrowthMicrobial regrowth
Dirty water episodes / sediment formationDirty water episodes / sediment formation
CorrosionCorrosion
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Developing Reaction SchemeDeveloping Reaction Scheme
1/1/ “What is happening”“What is happening”
Compound A reacts with Chlorine to form chloride which Compound A reacts with Chlorine to form chloride which is inactive and small portion of THMis inactive and small portion of THM
A + Cl = Cl- + aTHMA + Cl = Cl- + aTHM
2/ “How quickly it is happening”2/ “How quickly it is happening”
3/ Implementation to MSX3/ Implementation to MSX
ClACl cckdt
dc**
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Practical examplePractical example
Chlorine decay in Horsham treated water:
Experiments
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Practical examplePractical example
Chlorine decay in Horsham treated water:
Experiments vs Model
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Practical examplePractical example
Chlorine decay in Horsham treated water:
Model prediction – 3 mg/L @ 25C
Thank you!Thank you!
Questions please Questions please
24 March 2010