NIST: UV Sensor for Water Disinfection Monitoring

UV Sensor for Water Disinfection Monitoring

Figure 1. NIST UV sensor for water disinfection monitoring facility.		NIST is participating in a project of American Water Works Association Research Foundation (AwwaRF) in collaboration with Carollo Engineers (Boise, ID), CDM (Denver, CO), and the University of Veterinary Medicine (Vienna, Austria) to develop guidelines for UV sensors to monitor UV disinfection in water treatment facilities. NIST is studying characteristics of various UV sensors currently used for this purpose by measuring their spectral responsivity, linearity, angular responsivity, temperature dependence, etc., and develop plans for calibration scheme and establishing traceability, which will be included in the guidelines.
Introduction Ultraviolet (UV) radiation 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 UV radiation for disinfection of drinking water, replacing standard chemical treatment. Typically, low-pressure mercury (LPM) and medium-pressure mercury (MPM) lamps are used in the UV reactors at the facilities. In these reactors, water flowing at a given rate should receive an appropriate UV dose. UV sensors mounted on the wall of the UV reactor or inserted into the water flow monitor the dose level by measuring the irradiance from the lamps. The UV sensors currently in use have a variety of designs and performance characteristics. Austria and Germany have developed or are developing standards for the sensor design and performance to be used to validate new facilities and for their maintenance. These two standards differ in their requirements and do not address many of the problems associated with the UV monitors. Furthermore, there are already many water plants employing UV sensor systems consistent with one or the other standard. American Water Works Association Research Foundation (AwwaRF) decided to develop new guidelines for UV monitors. NIST is participating in this project in collaboration with Carollo Engineers (Boise, ID), CDM (Denver, CO), and the University of Veterinary Medicine (Vienna, Austria). The current UV water disinfection standards, ÖNORM M5873-1 and M5873-2 (Austria), and DVGW W294-3 (Germany), on the requirements for UV sensors for LPM and MPM lamp systems were studied. Pertinent to the study, the characteristics of various types of UV sensors were measured at NIST. This information will aid in the development of new guidelines which will address issues such as sensor requirements, calibration methods, uncertainty, and traceability. NIST measured 10 different UV sensors from 6 manufacturers used for water disinfection, for relative spectral responsivity in the 200 nm to 400 nm region, absolute irradiance responsivity at 254 nm, linearity, temperature dependence, and angular responsivity. Many of these sensors have very low sensitivity in order to measure very high irradiance levels, thus spectral responsivity measurements using a monochromator system was very difficult. We used the tunable-laser based spectral calibration facility (SIRCUS).

Figure 2. Examples of UV sensors for water disinfection monitoring.

The physical quantity to be measured is the microbicidal irradiance, defined as the total irradiance (W/m²) weighted by the microbicidal action spectrum s_mik,rel(λ) as shown in figure 3. According to ÖNORM M5873-1, M5873-2, and DVGW W294-3, UV sensors for both LPM and MPM systems are calibrated for irradiance responsivity against an LPM lamp (254 nm line emission). Since the relative spectral responsivity of the sensors deviate from the action spectrum, there can be serious measurement errors when measuring radiation from MPM lamps. NIST is proposing to intoduce a new calibration method and traceability scheme to calibrate reference sensors for responsivity for LPM or MPM lamps depending on which system the sensors are used.

Figure 3. The microbicidal action spectrum, plotted with an example of UV sensor responsivity and spectral distribution of low and medium pressure mercury lamps.

NIST References

T.C. Larason and Y. Ohno, Calibration and Characterization of UV Sensors for Water Disinfection (388 kB) , Metrologia 43, S151-S156 (2006).

T.C. Larason and Y. Ohno, Y., Calibration and Standardization Issues of UV Sensors for Water Disinfection (744 kB) , in Proc. 2005 NCSLI Workshop and Symposium, CD-ROM (2005).

T.C. Larason, S.W. Brown, G.P. Eppeldauer, and K.R. Lykke, Responsivity calibration methods for 365 nm irradiance meters, IEEE Trans. Instrum. Meas. 50, 474-477 (2001).

T.C. Larason, S.S. Bruce, and A.C. Parr, Spectroradiometric Detector Measurements: Part I - Ultraviolet Detectors and Part II - Visible to Near-Infrared Detectors (11 MB) , NIST Special Publications 250-41 (U.S. Government Printing Office, Washington, D.C., 1998).

Y. Ohno and A.E. Thompson, Photometry - the CIE V(λ) Function and What Can be Learned from Photometry (46 kB) , Measurements of Optical Radiation Hazards - A Reference Book Based on Presentations Given by Health and Safety Experts on Optical Radiation Hazards, September 1-3, 1998 Gaithersburg, MD, ICNIRP 6/98, CIEx016-1998, 445-453 (1998).

Other References

ÖNORM M5873-1, "Plants for the Disinfection of Water using Ultraviolet Radiation: Requirements and Testing Low Pressure Mercury Lamp Plants," (2001).

ÖNORM M5873-2, "Plants for the Disinfection of Water using Ultraviolet Radiation: Requirements and Testing Medium Pressure Mercury Lamp Plants," 2003.

DVGW W294-3, "UV Disinfection Devices for Drinking Water Supply - Requirements and Testing," 2003.

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For technical information or questions, contact:
Tom Larason Phone: (301)-975-2334 Fax: (301)-840-8551 Email: tlarason@nist.gov	Yoshi Ohno Phone: (301)-975-2321 Fax: (301)-840-8551 Email: ohno@nist.gov

UV Sensor for Water Disinfection Monitoring

Introduction

NIST References

Other References