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Age of Potable Water

Age of Potable Water. Impacts on DBP’s and Disinfection Residuals. Two Basic Strategies. Keep Your Water Young Strategy Manage residence time in the system Preserve Your Water Quality Strategy Manage water properties to extend the storage life. Water Ageing Factors. System Demands

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Age of Potable Water

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  1. Age of Potable Water Impacts on DBP’s and Disinfection Residuals

  2. Two Basic Strategies • Keep Your Water Young Strategy • Manage residence time in the system • Preserve Your Water Quality Strategy • Manage water properties to extend the storage life

  3. Water Ageing Factors • System Demands • Water conservation programs • Water rates • Seasonal fluctuations • System Storage • Reservoir capacity • Pipeline capacity • Local demands

  4. Manage System Demands • Water Conservation Programs • Often required by situations beyond your control. These could be: • Supply shortage • Funding requirements • Political • Evaluate the down side • Strike a balance

  5. Manage System Demands • Water rates • Higher rates = Lower usage • Evaluate the down side of rate increase • Seasonal rate structure • Strike a balance

  6. Manage System Demands

  7. Manage Reservoir Storage • Set Seasonal Operating Levels • Maintain minimum levels in winter • Fire capacity • Average use • Manage Fill and Drain Cycles • Fluctuate Levels • Manage fill rates

  8. Manage Reservoir Storage • Higher fill rates promote mixing • Mixing reduces dead storage • Down side is higher demand charge for power utility • Pump during low consumption times of the day • Consider you reservoir design

  9. Manage Reservoir Storage Mixing systems Tideflex Solar Bee

  10. Manage Pipeline Storage • Fire flow normally determines the pipe size • Reduce dead ends • Monitor and actively manage the system • Mainline flows • Disinfectant levels • Flush as necessary • Use EPS model • Identify and manage problem areas

  11. Manage Pipeline Storage • Identify and Manage Problem Areas • Dead ends • Stagnate loops • Pressure zone breaks • Long transmission lines • Pipe condition • Age • Material • Lining

  12. Extend Useful Pipe Life Goals • Protect customers from acute illness • Maintain disinfection residual levels • Prevent microbiological contamination • Protect customers from chronic illness • Inhibit disinfection by product formation • Nitrification • Maintain aesthetic quality • Taste & Odor • Color

  13. Manage pH Lower pH Higher pH Bulk Water Disinfection Biofilm Disinfection Corrosion BioFilm Stability Disinfectant Decay Rate Persistent Combine Chlorine residuals DBP formation Nitrification

  14. Manage pH

  15. Chlorine Break point and pH

  16. Manage DBP’s • Remove precursor materials • TOC removal • Color • UV 254 abs • Source water • Minimum Chlorine Levels • Microbes • Distribution system

  17. Manage DBP’s • TOC Removal • Enhanced Coagulation • Absorption • PAC • GAC • Reduce Chlorine Demand

  18. Manage Disinfectant Demand

  19. Manage DBP’s • Reduce Disinfectant • Aeration • Inhibit Formation • Ozone • Oxygen

  20. Starting Conditions Raw Water TTHMFP 350 – 500 ppb Distribution THM 80-100 ppb Chlorine level 0.7- ND pH not managed Coagulation not enhanced Pressure zone flow not managed Current Conditions Raw Water TTHMFP unknown new source Distribution THM 10-40 ppb Chlorine Level 1.0 -0.3 pH managed at 7.6 Enhanced coagulation Active pressure zone flow management Laramie’s Experience

  21. Remove precursor material Inhibit formation Monitor removal by Color removal Chlorine demand TOC removal Chlorine decay rate Monitor inhibition by UV 254 abs Laramie’s Treatment Strategies

  22. Chlorine Decay Rate • Place sample in a series of non reacting glass bottles • Analyze residual over time • Plot Ln(Ct/Co) Should be a straight line. Slope of the line is the decay rate.

  23. Minimize residence time Remove precursors Reservoir operating levels Eliminate dead ends Redesign Low Level reservoir inlet Colorremoval Chlorine demand TOC removal Chlorine decay rate Pressure zone circulation Take advantage of large irrigation flows Flush where necessary Identify and correct problem areas Laramie’s Distribution Strategies

  24. Stabilize Bio-Film Extend usable water age Manage pH Maintain alkalinity Manage corrosion Maintain consistent chlorine residuals Maintain consistent TOC removal Lower chlorine decay rate Promote circulation and mixing Identify problem areas Laramie’s Distribution Strategies

  25. Distribution System Modeling • Long term process requires many iterations • Requires regular maintenance • Calibrate using systematic field measurements • SCADA • Grab

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