Water Distribution Systems Water Quality Modelling for Civil Engineers 1 Helena M Jetmarova, GWMWater Helena M Jetmarova, GWMWater George J Kastl, MWH George J Kastl, MWH

NH 3 + O 2 + AOB → NO 2 -+ xAOB NH 2 Cl < 0.5 mg/L AOC, TTHM, HAA ?? NH 3 + O 2 + AOB → NO 2 -+ xAOB NH 2 Cl < 0.5 mg/L AOC, TTHM, HAA Cl + F → inert + αTHM KMnO 4 GAC (O3 & BAC) 4NH 2 Cl + 3H 2 O + CRB → 3NH 3 + 4HCl + HNO 3 + xCRB ??!??!!? NH 3 + O 2 + AOB → NO 2 -+ xAOB NH 2 Cl < 0.5 mg/L AOC, TTHM, HAA Cl + F → inert + αTHM KMnO 4 GAC (O3 & BAC) 4NH 2 Cl + 3H 2 O + CRB → 3NH 3 + 4HCl + HNO 3 + xCRB pH H2OH2O –NH 2 Cl + C → NH 3 +inert ??!!???!!!!? !!!???!!!!

24 March 2010 Talk about 1. Introduction to water quality 1. Introduction to water quality - Type of constituent - Transport mechanisms 2. Water quality modelling 2. Water quality modelling - Water age - Single species versus multi species - Reactions - Water disinfection & chlorine decay 3. Multi species modelling 3. Multi species modelling - Capabilities - Practical example

24 March Introduction to water quality

Treated water Quality: Turbidity Colour DOC Cl decay TTHM formation Cl dose [mg/L] Trunk Main Treatment Plant Customer’s Tap Raw water Quality: Turbidity Colour DOC Cl decay TTHM formation Delivered water Quality: Turbidity Colour DOC Cl decay DBP (TTHM, HAA) Cl concentration 24 March 2010 Water Treatment / Distribution System Distribution System

24 March 2010 Type of constituent Conservative Conservative = Non-reactive = Non-reactive - Are not normally physically or chemically transformed in the water - Concentration does not change while flowing through a pipe - Easy to model Non-conservative Non-conservative = Reactive = Reactive - Are transformed through physical, chemical or biological processes in the water - Concentration change (decay or growth) by reacting with other compounds - Difficult to model

24 March 2010 Type of constituent Conservative Conservative = Non-reactive = Non-reactive Eg. salinity, fluoride C in = C out Q C in C out Non-conservative Non-conservative = Reactive = Reactive Eg. disinfectants (Cl) C in  C out Q bacteria Cl NOM C in C out

Advection Advection - carrying a constituent along with the flow of water 24 March 2010 Transport mechanisms Mechanisms to transport constituent in water: v cleaning “pig” Dispersion Dispersion - axial spreading of a constituent mass due to non- uniform velocities Diffusion Diffusion - Molecular (Brownian motion) (Brownian motion) - Turbulent

24 March 2010 Transport mechanisms Which mechanisms are important for transport of constituent? Advection (m/sec) contributes the most to transport of constituent. Some modelling packages use advection only. Advection (m/sec) contributes the most to transport of constituent. Some modelling packages use advection only. Dispersion is important in laminar flow. Some 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 Water quality modelling

24 March 2010 Water quality modelling Benefits of modelling Benefits of modelling - Limits experimentation on a real system - Predict water quality in planed systems Understanding mechanism Understanding mechanism - single versus multi species - bulk and wall reaction Tool to project “mechanism” into a distribution system Tool to project “mechanism” into a distribution system - built on top of hydraulic model - EPANet-MSX, H2OMap/InfoWater-MSX

24 March 2010 Water age Time since water parcel entered system Time since water parcel entered system Said to indicate water quality Said to indicate water quality - hidden assumption: concentration (quality) is proportional to age concentration (quality) is proportional to age - highly inaccurate for many variables including disinfectants & disinfection by-products (DBP) disinfectants & disinfection by-products (DBP) - neglects effect of temperature

24 March 2010 Single species vs multi species Single species modelling: Single species modelling: - limited to tracking a single component (Cl, water age). - limited to accurately describe the reactions between two or more chemical or biological species. Multi species extension (MSX): Multi species extension (MSX): - generic formulation of “any” kinetics scheme. - eg. free chlorine reacts with natural organic matter (NOM), a heterogeneous mixture of organic compounds. - more than one water source supplies a distribution system.

24 March 2010 Reactions Reaction rate in bulk water- pipes and tanks Reaction rate in bulk water- pipes and tanks - laboratory jar test Reaction rate on pipe surface- pipes Reaction rate on pipe surface- pipes - field measurement

24 March 2010 Water disinfection & Cl decay We disinfect water to kill bacteria We disinfect water to kill bacteria Disinfectants: Disinfectants: - Chlorine - Chloramine - Ozone (decay too fast does not need to be modelled in DS) - UV (no residual, in DS without residual, only re-growth) - Chlorine dioxide (relatively fast decay) Side-effect: Disinfection by-products (DBP) Side-effect: Disinfection by-products (DBP) The most common disinfectant is chlorine (Cl) The most common disinfectant is chlorine (Cl)

24 March 2010 Components 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 decay Distance [km] Bulk prediction Measurement in system Chlorine [mg/L] 0 Combined prediction Reacted with bulk Reacted with wall

24 March 2010 Chlorine decay Common chlorine dose 1 – 5 mg/L Common 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) - time available for reaction - temperature Increasing indicator failure Desired level at tap for bacterial control Increasing DBP & taste/odour problems [Cl]

24 March Multi species modelling

24 March 2010 Capabilities Which water quality parameters can be modelled? Practically any, important enough Practically any, important enough Chlorine, chloramine Chlorine, chloramine By-product formation By-product formation pH changes pH changes Disinfection of microorganisms Disinfection of microorganisms Microbial regrowth Microbial regrowth Dirty water episodes / sediment formation Dirty water episodes / sediment formation Corrosion Corrosion

24 March 2010 Developing Reaction Scheme 1/ “What is happening” 1/ “What is happening” Compound A reacts with Chlorine to form chloride which is inactive and small portion of THM A + Cl = Cl- + aTHM 2/ “How quickly it is happening” 2/ “How quickly it is happening” 3/ Implementation to MSX 3/ Implementation to MSX

24 March 2010 Practical example Chlorine decay in Horsham treated water: Experiments

24 March 2010 Practical example Chlorine decay in Horsham treated water: Experiments vs Model

24 March 2010 Practical example Chlorine decay in Horsham treated water: Model prediction – 3 25C

Thank you! Questions please Thank you! Questions please 24 March 2010