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??!!???!!!!?

!!!???!!!!

24 March 2010

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

24 March 2010

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

24 March 2010

Water Treatment / Distribution Water Treatment / Distribution SystemSystem

Distribution System

24 March 2010

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

24 March 2010

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

24 March 2010

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

24 March 2010

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.

24 March 2010

2. Water quality modelling2. Water quality modelling

24 March 2010

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

24 March 2010

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

24 March 2010

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..

24 March 2010

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

24 March 2010

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)

24 March 2010

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

24 March 2010

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

24 March 2010

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]

24 March 2010

3. Multi species modelling3. Multi species modelling

24 March 2010

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

24 March 2010

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**

24 March 2010

Practical examplePractical example

Chlorine decay in Horsham treated water:

Experiments

24 March 2010

Practical examplePractical example

Chlorine decay in Horsham treated water:

Experiments vs Model

24 March 2010

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