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a new decision framework

a new decision framework. Extending Hydraulics Modelling to Water Quality George Kastl 1 , Ian Fisher 2 , Feng Shang 1 and Michael Price 1 1 MWH 2 Watervale Systems, PO Box 318, Potts Point NSW 1335, Australia. Outline. Acceptance of drinking water modelling

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a new decision framework

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  1. a new decision framework Extending Hydraulics Modelling to Water QualityGeorge Kastl1, Ian Fisher2, Feng Shang1 and Michael Price11MWH 2Watervale Systems, PO Box 318, Potts Point NSW 1335, Australia

  2. Outline • Acceptance of drinking water modelling • Drivers for drinking water quality modelling • Task Example • Modelled water quality parameters • Capability needed for drinking water quality modelling • Tools required for modelling • State of various process models • Conclusion

  3. Acceptance of drinking water modelling • Hydraulic model for flow, pressure ... • Used for pipeline design • Pumping station • Provision of supply • Tank levels • Water age • Water quality • Not routinely used • Academic interest (neural network, security) • Chlorine and THM

  4. Drivers in drinking water quality modelling • More stringent health regulations (DBP-THM, microbiological) & customers’ expectations • Pressure on resources and use of lower quality sources • Integration of water utilities and serving of larger geographical areas (longer residence time in the distribution system & multiple water sources) • More complex operation of networks (balancing of water resources)

  5. US Drivers for Water Quality Modelling • Stage 2 DBP Rule ( THM <0.08mg/L, HAA <0.06mg/L, >95% of samples Cl>0.2mg/L) Locational Running Annual Average (LRAA) • ISDE sampling to identify sample sites • Compliance required at all individual sample sites • Total Coliform Rule Compliance • Measurable residuals in all TCR samples • Nitrification in chloraminated systems • Contaminant Warning Systems • Potential overfeed of chemicals • Single source contamination (e.g., well supply) • Deliberate contamination

  6. Task examples • Existing DS, can it meet Cl (>95% >0.2mg/L) THM (max 0.2 mg/L)? • What improvement can be achieved by a re-chlorination station(s) • How to optimise operation of a DS (demand & temperature) • What would be chlorine and THM in new part of DS • A new WTP, what level of treatment guarantees the system compliance?

  7. Disinfection Requirements • Residual disinfectant declines with time • Whether concentration stays within given limits (“envelope”) as time elapses depends on • water type (natural organic matter) • temperature • wall material and attached biofilm/particles Increasing indicator failure Desired level at tap for bacterial control Increasing DBP & taste/odour problems 0.2 0 0.6 [Cl]

  8. Why Water Quality modelling has low up take rate? • Multidisciplinary • Chemical experiments • Chemical kinetics • Numerical analysis deriving parameters • Qualification of wall reaction • Network hydraulic model • Network water quality model • Missing a good example (use of first order decay – not accurate)

  9. Concept of bulk and wall reaction Measurement in system Bulk & wall reaction model Concentration Reacted with bulk Bulk Model Reacted with wall 0 distance (km)

  10. Methods for Water Quality studies • Physical & online sampling and analysis, essential but costly and burdened by errors – only for existing systems. • Batch experiments and relating them via water age to network water quality • Batch experiments described by a simple Epanet water quality module and • Batch experiments described by chemical kinetics based MSX models

  11. Batch experiments and relating them via water age to network water quality

  12. Water Age

  13. Chlorine concentration

  14. Chlorine decay description • Reaction scheme • Cl + Fast → inerts + αTHM • Cl + Slow → inerts + αTHM • Cl → inerts + αTHM • Rate equation:Can be extended for multiple sources by having fast and slow components for each source

  15. H2OMap InfoWater & MSX Multi-Species Extension Reaction rate in bulk Reaction rate on surface Equilibrium reactions Generic formulation of “any” kinetics scheme Windows interface

  16. Essentials for drinking water quality modelling • Hydraulic & water quality software to project water quality processes into a distribution system, • MSX, originally by EPANET, available in H2OMap Water • Quantitative description of processes of interest • Chlorine decay (bulk, walls & mixtures) • Chloramine decay (bulk, walls & mixtures) • Method to derive model parameters

  17. Quantitative description of processes of interest • Accurate description of bulk reaction based on laboratory measurements including effects of: • Dose • Temperature • Re-chlorination • Description of effect of wall (biofilm, sediment) based on field measurements

  18. Status of chlorine and chloramine modelling • Chlorine decay • reaction with DOC • modelled as 2 groups of organic compounds reacting with chlorine • verified model used since 1994. • Chloramine decay • has slow chemical decay (reduction with organics and auto-oxidation ) • potentially fast (within a day) due to microbiologically facilitated decay (harder to model) • can be described and modelled.

  19. Happy Valley Treated water

  20. Desalinated water

  21. 50 % Happy Valley + 50% desalinated

  22. Wall reaction “equivalent diameter” proportional to surface reaction rate

  23. Measurements vs. Model Elanora

  24. Conclusion • Use of water age is not adequate for water quality modelling • Only MSX enables accurate water quality modelling • Chlorine decay and THM concentration can be accurately modelled in distribution systems (including mixtures of water) • Sampling and modelling provides “best available” insight into what is happening in a distribution system • Chloramine decay modelling is developing (more complex due to microbiological decay)

  25. 75 % Happy Valley + 25% desalinated

  26. 25 % Happy Valley + 75% desalinated

  27. Chloramine decay description …. continuation • Chemical decay rate slow & well described • Biologically assisted decay characterised by Fm

  28. Chloramine decay description • Chemical Reaction scheme • NH2 Cl → NH3+inert • NH2 Cl + C → NH3+inert • Microbiological decay • NH3 + O2 + AOB → NO2 + xAOB • 4NH2 Cl + 3H2O + CRB → 3NH3 + 4HCl + HNO3+ xCRB • Mixing - just combining microbial concentration??

  29. Examples of chlorine decay modelling • Maximizing of delivery area in the desirable Cl range (0.2-0.6mg/L) • Optimizing the dose with temperature and flow • Re-chlorination optimization • THM compliance • Forecast of Cl & THM profile for “planned” system and WTP process

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