Calibration and Characterization of UV Sensors for Water Disinfection

1. Calibration and Characterization of UV Sensors for Water Disinfection 2006 Council of Optical Radiation Measurements Conference Gaithersburg, Maryland 9-11 May 2006 National Institute of Standards and Technology Authors: Thomas Larason and Yoshi Ohno Optical Technology Division Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-8441, USA

2. Outline • Background • Using UV light to disinfect drinking water • NIST Measurements • Relative spectral responsivity, 200 nm to 400 nm • Linearity of response • Temperature dependence • Angular responsivity • Proposed Alternate Calibration Method • Future Work Note: This talk was presented at the 6th UVNet Workshop on Ultraviolet Radiation Measurements, 21 October 2005 in Davos, Switzerland and published in Metrologia43 (2006) S151-S156.

3. Background Ultraviolet radiation (UV) effectively inactivates common pathogens found in ground and surface waters such as Cryptosporidium, Giardia, and most bacterial pathogens (e.g., E. coli). Water treatment facilities recently started using ultraviolet radiation for disinfection of drinking water, replacing standard chemical treatment.

4. Increasing use of UV for Drinking Water Disinfection Municipalities like Vancouver, BC and New York, NY are planning water treatment facilities that incorporate UV light in the water disinfection process. Vancouver (2008 construction complete ) 12 UV Reactors: 480 million gallons / day Wash. DC Suburbs (2007 installation begins) 12 UV Reactors: 300 million gallons / day New York City (2011 operational) 56 UV Reactors: 2.4 billion gallons / day UV Reactor From Greater Vancouver Regional District document: SCFPOverview.pdf Update: UV water disinfection is coming to Montgomery and Prince Georges counties in Maryland. http://www.gvrd.bc.ca/water/pdfs/SCFPOverview.pdf

5. Example UV Reactor Vessel There are many different designs for the reactor vessels and lamp placement inside the vessels. UV Sensor design and configuration varies with manufacturer. Illustrations courtesy of Severn Trent Services from US EPA document 815-D-03-007 June 2003 Draft http://www.epa.gov/safewater/lt2/guides.html

6. Example UV Sensors

7. Measurement Quantity: Microbicidal Irradiance The physical quantity to be measured is the microbicidally weighted irradiance (microbicidal irradiance): [unit: W/m2] E(λ): spectral irradiance (e.g., W/m2/nm) smik,rel(λ)

8. American Water Works Association Research Foundation (AwwaRF) NIST is participating in AwwaRF Project 2977: Design and Performance Guidelines for UV Sensor Systems collaborating with • Carollo Engineers, Boise, ID • Camp Dresser and McKee, Denver, CO • Institute of Medical Physics and Biostatistics at the University of Veterinary Medicine, Vienna, Austria In this project, NIST is responsible for Task 3. Methods Development and Lab Studies 3.1 Methods Development 3.2 UV Sensor Testing

9. NIST Measurements of the UV Sensors We have tested several UV sensors (reference and duty) used to monitor UV reaction chambers in water treatment facilities for several characteristics: • Absolute irradiance calibration at 254 nm • Relative spectral responsivity, 200 nm to 400 nm • Linearity of response • Temperature dependence • Angular responsivity Some problems have been identified on the absolute calibration of these UV sensors.

10. UV Spectral Comparator Facility (UV SCF) UV Working Standards Test UV Sensor

11. UV SCF Measurement Setup Photo of UV SCF Measurement Setup UV SCF Working Standards UV Sensor

12. Spectral Irradiance and Radiance Calibrations using Uniform Sources (SIRCUS) Facility Radiance and Irradiance Responsivity SIRCUS uses tunable lasers from 200 nm to 1800 nm Laser Intensity Stabilizer Spectrum Analyzer Wavemeter Test Meter Transfer Standard Computer Translation Stages Exit Port Lens Integrating Sphere Monitor Photodiode Galvo-driven Oscillating Mirror or Optical Fiber and Ultrasonic Bath

13. SIRCUS Facility Measurement Setup Diffuser plate was used to increase the irradiance levels Irradiance Standard Detector – Trap and Precision Aperture UV Sensors Frosted glass diffuser plate

14. Relative Spectral Responsivities of the UV Sensors

15. Irradiance Responsivity Linearity (Limited Range)

16. Temperature Dependence Measurement Setup Photo of variable temperature chamber used for UV sensor characterization Test Chamber Entrance Port Radiator Coils circulating water for temperature control Twin-tube 35 W LPM lamp with intensity monitor Water Bath, set water temperatures, 10 °C to 35 °C UV Sensor Position

17. Temperature Dependence of the Irradiance Responsivity

18. Angular Dependence Measurement Setup Set up for angular responsivity measurement (top view)

19. Angular Responsivities of the UV Sensors

20. Proposed Calibration Method for Sensors used with MPM Lamp Systems Calibrate the sensors used for MPM lamp systems, against irradiance by a MPM lamp (strict substitution). Typical MPM Lamp Spectrum (or LPM lamp) Responsivity for MPM lamp: [A/(W/m2)]

21. Future Work • NIST will measure the absolute spectral responsivity of the 10 test sensors after UV exposure testing by the Institute of Medical Physics and Biostatistics at the University of Veterinary Medicine. • NIST has a plan to develop a new facility and calibration service to establish traceability for the UV sensors used by the water disinfection community.

22. Acknowledgements This work is part of AwwaRF-funded Project 2977. We thank AwwaRF for their support and the technical discussions with the project advisory committee members. We thank the project members for their valuable technical discussions and providing data: • Harold Wright of Carollo Engineers, • Christopher Schulz of Camp Dresser and McKee, • Alexander Cabaj of the Institute of Medical Physics and Biostatistics at the University of Veterinary Medicine We also thank the vendors of the UV sensors and water disinfection facilities who provided the project with the sample UV sensors. And lastly, our NIST colleagues, Keith Lykke, Steve Brown, and Yuqin Zong for their assistance in taking data.