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Cortez UV Disinfection

Cortez UV Disinfection. Steven M. Ravel, P.E. Travis E. Meyer, P.E. Richard P. Arber Associates. Introduction. Background Selection of UV Lamp Type Specifying UV Dose Verification of UV Dose. Background. New WWTP for Cortez Sanitation District Treatment Train Headworks

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Cortez UV Disinfection

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  1. Cortez UV Disinfection Steven M. Ravel, P.E. Travis E. Meyer, P.E. Richard P. Arber Associates

  2. Introduction • Background • Selection of UV Lamp Type • Specifying UV Dose • Verification of UV Dose

  3. Background • New WWTP for Cortez Sanitation District • Treatment Train • Headworks • Extended Aeration • Secondary Clarification • UV Disinfection

  4. Background • Design Flows • Average: 1.8 mgd • Peak Month: 2.1 mgd • Peak Hour: 7 mgd

  5. UV Lamp Types Considered • Medium Pressure • Low Pressure / Low Intensity • Low Pressure / High Intensity

  6. Medium Pressure • Advantages • Lowest Number of Lamps Required • UV Intensity Adjustable • Sleeve Wipers Available • Low Space Requirement • Open Channel and Closed Pipe Systems Available

  7. Medium Pressure • Disadvantages • Low Efficiency (Approximately 10 - 20% • Higher Capital Cost (for these flow rates) • Require warm-up period on start-up

  8. Low Pressure / Low Intensity • Advantages • Low Capital Cost • High Efficiency (Approximately 40%) • Simple Design / Simple Operation

  9. Low Pressure / Low Intensity • Disadvantages • Highest Number of Lamps Required • UV Intensity Not Adjustable • Sleeve Wipers Not Available • High Maintenance (Lamp Replacement and Cleaning) • High Space Requirement

  10. Low Pressure / High Intensity(Selected) • Advantages • Low Capital Cost • High Efficiency (Approximately 40%) • Less Lamps Required than Low/Low (Approximately 1/4) • UV Intensity Adjustable • Sleeve Wipers Available

  11. Low Pressure / High Intensity(Selected) • Disadvantages • Relatively Short Track Record Compared to Low/Low and Medium • More Lamps Required than Medium

  12. Specifying UV Dose • EPA UVDIS Computer Model • BioAssay • Performance Based

  13. UVDIS Computer Model • Advantages • Computer program easy and fast to run • Theoretical model developed by EPA

  14. UVDIS Computer Model • Disadvantages • Program designed for Low/Low systems • May not be as applicable for Low/High or Medium Systems • Model results must be adjusted using high safety factors to ensure system will perform as required

  15. BioAssay • Advantages • System sized based on dose response curve for actual equipment to be installed • Dose response curve developed for site specific wastewater effluent quality

  16. BioAssay • Disadvantages • No Standard Protocol for BioAssay • Detailed protocol must be developed to compare results for different systems • Expensive and Time-Consuming • If MS-2 Phage used for bioassay, correlation must be developed to translate results for fecal coliform

  17. Performance Based • Advantages • Specify what you want the system to do, let manufacturers design their system to do it • Most direct method to specify

  18. Performance Based • Disadvantages • Relying on manufacturers to design adequate system • Must determine a method to check performance in the field

  19. Cortez Sanitation District • Pre-selection of UV System based on: • Primary UV Dose Criteria: Performance for Fecal Coliform • In: 500,000/100 mL • Out: 200/100 mL • Secondary UV Dose Criteria: • Min UV Dose of 30,000 µw/cm2 based on UVDIS

  20. Cortez Sanitation District • Other Design Criteria • Minimum Flow: 1 mgd • Average Flow: 1.8 mgd • Peak Hydraulic Flow: 7 mgd • Peak Process Flow: 5 mgd • UV Transmittance: 65% • TSS: 30 mg/l • Number of Channels: 2 • Number of Banks/Channel: 2

  21. Comparison of UV Systems Mfr AMfr B # of Lamps 48 64 Capital Cost $100,000* $110,000 Annual O&M Costs Electricity $1,400 $3,000 Lamps $1,900 $3,200 Total $3,300 $6,200 NPV (20 yrs, 6%) $140,000 $180,000 * Includes Separate Sunshade Structure for Ballast and Controls

  22. Verifying UV Dose • During Performance Test, Need to Account for Differences (Design vs. Actual) in: • Flow • UV Transmittance • Lamp Age (70% output) • Fecal Coliforms

  23. Flow Adjustment • Adjust UV system output in proportion to difference in flow • Example: Design flow = 5 MGD, Actual flow = 1 mgd:Adjust UV system output to 20% of maximum

  24. Transmissivity Adjustment • Adjust UV system output based on correlation between design UVT and actual UVT

  25. Fecal Coliform Adjustment • Two Options • Spike UV influent to bring fecal coliform up to design number • Lower effluent fecal coliform requirement to achieve same log reduction as design

  26. Cortez Sanitation District • Turn down UV system output to min during performance test. • Schedule test for highest flow, lowest UVT, highest Fecal • Record Flow Rate • Test Fecal Coliforms (In vs.Out) • Test UVT • Make determination of performance based on available data

  27. Conclusions • Low Pressure / High Intensity best solution for Cortez • Performance based spec on fecal coliform with min UV dose based on EPA UVDIS • Verification of UV Dose using best available data at time of performance test

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