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Water Distribution Systems Water Quality Modelling for Civil Engineers 1

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.

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Water Distribution Systems Water Quality Modelling for Civil Engineers 1

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

  2. ??!!???!!!!? !!!???!!!! ?? NH2Cl < 0.5 mg/L NH2Cl < 0.5 mg/L NH2Cl < 0.5 mg/L NH3 + O2 + AOB → NO2-+ xAOB NH3 + O2 + AOB → NO2-+ xAOB NH3 + O2 + AOB → NO2-+ xAOB 4NH2 Cl + 3H2O + CRB → 3NH3 + 4HCl + HNO3+ xCRB 4NH2 Cl + 3H2O + CRB → 3NH3 + 4HCl + HNO3+ xCRB AOC, TTHM, HAA AOC, TTHM, HAA AOC, TTHM, HAA • NH2 Cl + C → NH3+inert GAC (O3 & BAC) GAC (O3 & BAC) Cl + F → inert + αTHM Cl + F → inert + αTHM H2O KMnO4 KMnO4 pH ??!??!!?

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

  4. 1. Introduction to water quality 24 March 2010

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

  6. Conservative = 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 = 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 Type of constituent 24 March 2010

  7. Non-conservative = Reactive Eg. disinfectants (Cl) bacteria Cl Cin Cout NOM Cin Cout Q Q Cin = Cout Cin¹ Cout Conservative = Non-reactive Eg. salinity, fluoride Type of constituent 24 March 2010

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

  9. Which mechanisms are important for transport of constituent? Transport mechanisms 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. Turbulent diffusion – mixing in tanks. 24 March 2010

  10. 2. Water quality modelling 24 March 2010

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

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

  13. Single species modelling: - limitedto tracking a single component (Cl, water age). - limited to accurately describethe reactions between two or more chemical or biologicalspecies. Single species vs multi species 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 watersource supplies a distribution system. 24 March 2010

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

  15. We disinfect water to kill bacteria 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) The most common disinfectant is chlorine (Cl) Water disinfection & Cl decay 24 March 2010

  16. Chorine decay in system Decay due to bulk water reaction Decay due to wall interaction Biofilm / sediment interaction Wall material interaction Components of chlorine decay 24 March 2010

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

  18. Increasing indicator failure Desired level at tap for bacterial control Increasing DBP & taste/odour problems 0 0.2 0.6 [Cl] Common chlorine dose 1 – 5 mg/L Dose required to stay within given limits (“envelope”) depends on: - water type (natural organic matter – NOM) - time available for reaction - temperature Chlorine decay 24 March 2010

  19. 3. Multi species modelling 24 March 2010

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

  21. 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” • 3/ Implementation to MSX Developing Reaction Scheme 24 March 2010

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

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

  24. Chlorine decay in Horsham treated water: Model prediction – 3 mg/L @ 25C Practical example 24 March 2010

  25. Thank you!Questions please  24 March 2010

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