ULTRAVIOLET DISINFECTION GUIDANCE MANUAL United States Environmental Protection Agency Office of Water ( 4601) EPA 68 C 02 026 June 2003 Draft Note on the Ultraviolet Disinfection Guidance Manual, June 2003 Draft Purpose: The purpose of this guidance manual, when finalized, is solely to provide technical information on the application of ultraviolet light for the disinfection of drinking water by public water systems. EPA is developing this manual to support two upcoming drinking water regulations: the Long Term 2 Enhanced Surface Water Treatment Rule, which would require certain systems to provide additional treatment for Cryptosporidium, and the Stage 2 Disinfection Byproducts Rule, which would place more stringent limits on certain disinfection byproducts. Chapter 1 of this manual contains additional information about these regulations.

This guidance is not a substitute for applicable legal requirements, nor is it a regulation itself. Thus, it does not impose legally binding requirements on any party, including EPA, states, or the regulated community. Interested parties are free to raise questions and objections to the guidance and the appropriateness of using it in a particular situation. Although this manual covers many aspects of implementing a UV system, it is not comprehensive in terms of all types of UV systems, design alternatives, and validation protocols that may provide satisfactory performance. The mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Authorship: This manual was developed under the direction of EPA's Office of Water, and was prepared by Malcolm Pirnie, Inc., Carollo Engineers, P. C., and The Cadmus Group, Inc. Questions concerning this document should be addressed to:

Dan Schmelling U. S. Environmental Protection Agency Mail Code 4607M 1200 Pennsylvania Avenue NW Washington, DC 20460 0001 Tel: ( 202) 564 5281 Fax: ( 202) 564 3767 Email: schmelling. dan@ epa. gov Request for comments: EPA is releasing this manual in draft form in order to solicit public review and comment. The Agency would appreciate comments on the content and organization of technical information presented in this manual. A list of topics for comment pertaining to specific chapters and appendices is provided later in this manual. Please submit any comments no later than 90 days after publication of the Long Term 2 Enhanced Surface Water Treatment Rule proposal in the Federal Register. Detailed procedures for submitting comments are stated below. Acknowledgements: The following provided valuable technical information to assist in the development of this manual:

American Water Works Association Dave Battigelli ( Clancy Environmental Consultants) William Bellamy ( CH2M Hill) Jim Bolton ( Executive Director, International Ultraviolet Association) Calgon Carbon Corporation Tom Hargy ( Clancy Environmental Consultants) Oluf Hoyer ( DVGW) Richard Hubel ( American Water) Chris McMeen ( then with Washington Department of Health) Alexander Mofidi ( Metropolitan Water District of Southern California) Ondeo Degremont Richard Sakaji ( California Department of Health Services) Severn Trent Services Regina Sommer ( University of Vienna) Paul Swaim ( CH2M Hill) Trojan Technologies Wedeco Ideal Horizons John Young ( American Water)

Procedures for submitting comments: Comments on this draft guidance manual should be submitted to EPA's Water Docket. You may submit comments electronically, by mail, or through hand delivery/ courier.

  To submit comments using EPA's electronic public docket, go directly to EPA Dockets at http:// www. epa. gov/ edocket, and follow the online instructions for submitting comments. Once in the system, select " search," and then key in Docket ID No. OW 2002 0039.

  To submit comments by e mail, send comments to OW_ Docket@ epa. gov, Attention Docket ID No. OW 2002 0039. If you send an e mail comment directly to the Docket without going through EPA's electronic public docket, EPA's e mail system automatically captures your email address, which is included as part of the comment that is placed in the official public docket.

  To submit comments on a disk or CD ROM, mail it to the address identified below. These electronic submissions will be accepted in WordPerfect or ASCII file format. Avoid the use of special characters and any form of encryption.

  To submit comments by mail, send three copies of your comments and any enclosures to: Water Docket, Environmental Protection Agency, Mail Code 4101T, 1200 Pennsylvania Ave., NW, Washington, DC, 20460, Attention Docket ID No. OW 2002 0039.

  To submit comments by hand delivery or courier, deliver your comments to: Water Docket, EPA Docket Center, Environmental Protection Agency, Room B102, 1301 Constitution Ave., NW, Washington, DC, Attention Docket ID No. OW 2002 0039. Please identify the appropriate docket identification number in the subject line on the first page of your comment. If you submit an electronic comment, please include your name, mailing address, and an e mail address or other contact information in the body of your comment. Also include this contact information on the outside of any disk or CD ROM you submit, and in any cover letter accompanying the disk or CD ROM.

For public commenters, please note that EPA's policy is that public comments, whether submitted electronically or in paper, will be made available for public viewing in EPA's electronic public docket as EPA receives them and without change, unless the comment contains copyrighted material, confidential business information, or other information whose disclosure is restricted by statute. Table of Contents Table of Contents............................................................................................................................. i List of Figures ................................................................................................................................ vi List of Tables ................................................................................................................................ vii Glossary ....................................................................................................................................... viii Acronyms and Abbreviations ...................................................................................................... xiii 1.0 Introduction.................................................................................................................... 1 1 1.1 Guidance Manual Objectives............................................................................... 1 1 1.2 Organization......................................................................................................... 1 2 1.3 Regulations Summary.......................................................................................... 1 3 1.3.1 Long Term 2 Enhanced Surface Water Treatment Rule.......................... 1 4 <IP_ADDRESS> Filtered Systems..................................................................... 1 5 <IP_ADDRESS> Unfiltered Systems................................................................. 1 6 <IP_ADDRESS> UV Requirements For Filtered And Unfiltered Systems....... 1 7 1.3.2 Stage 2 DBPR .......................................................................................... 1 9 1.4 Alternative Approaches for Disinfecting with UV Light .................................... 1 9 2.0 Overview of UV Disinfection......................................................................................... 2 1 2.1 History of UV Light for Drinking Water Disinfection ........................................ 2 1 2.2 Fundamental Aspects of UV Light ...................................................................... 2 2 2.2.1 Nature of UV Light.................................................................................. 2 2 2.2.2 Propagation of UV Light ......................................................................... 2 3 2.3 Microbial Response to UV Light......................................................................... 2 6 2.3.1 Mechanisms of Microbial Inactivation by UV Light............................... 2 6 2.3.2 Microbial Repair ...................................................................................... 2 7 2.3.3 UV Dose and Dose Distribution ............................................................ 2 10 2.3.4 Microbial Response ( UV Dose Response) ............................................ 2 11 2.3.5 Microbial Spectral Response ................................................................. 2 11 2.4 UV Reactors....................................................................................................... 2 12 2.4.1 Reactor Configuration............................................................................ 2 13 2.4.2 UV Lamps.............................................................................................. 2 14 2.4.3 Lamp Power Supply and Ballasts .......................................................... 2 17 2.4.4 Lamp Sleeves ......................................................................................... 2 17 2.4.5 Cleaning Systems................................................................................... 2 18 2.4.6 UV Intensity Sensors ............................................................................. 2 19 2.4.7 UV Transmittance Monitors .................................................................. 2 20 2.4.8 Temperature Sensors.............................................................................. 2 21 2.4.9 Monitoring UV Disinfection Performance ............................................ 2 21 UV Disinfection Guidance Manual i June 2003 Proposal Draft Table of Contents ( Continued)

UV Disinfection Guidance Manual ii June 2003 2.5 Water Quality Impacts and Byproduct Formation............................................. 2 22 2.5.1 Water Quality Impacts ........................................................................... 2 22 2.5.2 Byproducts from UV Disinfection......................................................... 2 25 3.0 Planning and Design Aspects for UV Installations ..................................................... 3 1 3.1 UV Installations Planning .................................................................................... 3 4 3.1.1 Defining UV Disinfection Goals ............................................................. 3 4 3.1.2 Identifying Potential Locations For UV Installations.............................. 3 5 <IP_ADDRESS> Combined Filter Effluent Installation .................................... 3 6 <IP_ADDRESS> Individual Filter Effluent Piping Installation......................... 3 6 <IP_ADDRESS> UV Disinfection Downstream of The Clearwell ................... 3 8 3.1.3 Defining Design Parameters .................................................................... 3 9 <IP_ADDRESS> Assessing Water Quality...................................................... 3 10 <IP_ADDRESS> Determining Design Flow Rate ........................................... 3 17 <IP_ADDRESS> Assessing Electrical Power .................................................. 3 17 3.1.4 Evaluating Potential UV Reactors ......................................................... 3 20 <IP_ADDRESS> UV Reactors......................................................................... 3 20 <IP_ADDRESS> UV Reactor Control Strategies ............................................ 3 22 <IP_ADDRESS> Equipment Validation Issues ............................................... 3 22 3.1.5 Evaluating Operational Strategies.......................................................... 3 24 3.1.6 Evaluating Hydraulics and Process Footprint........................................ 3 25 <IP_ADDRESS> Hydraulic Considerations..................................................... 3 25 <IP_ADDRESS> Process Footprint ................................................................. 3 27 3.1.7 Preparing Preliminary Costs and Selecting the UV Installation Option 3 28 3.2 Equipment Procurement Options....................................................................... 3 29 3.3 UV Installation Design Elements....................................................................... 3 30 3.3.1 UV Installation Hydraulics .................................................................... 3 30 <IP_ADDRESS> Inlet and Outlet Piping Configuration.................................. 3 31 <IP_ADDRESS> Flow Distribution, Control, and Measurement .................... 3 31 <IP_ADDRESS> Level Control ....................................................................... 3 36 <IP_ADDRESS> Air Relief and Pressure Control Valves............................... 3 36 <IP_ADDRESS> Flow Control and Isolation Valves ...................................... 3 37 <IP_ADDRESS> Intermediate Booster Pumps ................................................ 3 37 3.3.2 Operational Strategy Determination ...................................................... 3 38 3.3.3 Instrumentation and Control .................................................................. 3 38 <IP_ADDRESS> UV Reactor Start Up............................................................ 3 39 <IP_ADDRESS> UV Reactor Automation ...................................................... 3 39 <IP_ADDRESS> UV Intensity and Calculated Dose ( If Applicable).............. 3 39 <IP_ADDRESS> UV Transmittance................................................................ 3 40 <IP_ADDRESS> Flow Measurement............................................................... 3 40 <IP_ADDRESS> Lamp Age............................................................................. 3 40 <IP_ADDRESS> Lamp and Reactor Status ..................................................... 3 41 <IP_ADDRESS> Alarms and Control Systems Interlocks .............................. 3 41 Proposal Draft Table of Contents ( Continued)

UV Disinfection Guidance Manual iii June 2003 3.3.4 Electrical Power Configuration.............................................................. 3 42 <IP_ADDRESS> Power Requirements ............................................................ 3 43 <IP_ADDRESS> Backup Power Supply.......................................................... 3 43 <IP_ADDRESS> Ground Fault Interrupt and Electrical Lockout.................... 3 44 3.3.5 UV Installation Layouts......................................................................... 3 45 <IP_ADDRESS> Site Layout........................................................................... 3 45 <IP_ADDRESS> UV Installation Layout ........................................................ 3 45 3.3.6 Elements Of UV Reactor Specifications................................................ 3 47 <IP_ADDRESS> Information Provided by Manufacturer in UV Reactor Bid .......................................................................... 3 49 3.3.7 Final UV Installation Design ................................................................. 3 51 <IP_ADDRESS> Design Drawings.................................................................. 3 51 <IP_ADDRESS> Specifications....................................................................... 3 52 3.4 Reporting to the State......................................................................................... 3 52 3.4.1 Planning ................................................................................................. 3 52 3.4.2 Equipment Procurement......................................................................... 3 53 3.4.3 Drawings and Specifications.................................................................. 3 53 3.4.4 Validation Report/ Start up Confirmation .............................................. 3 53 4.0 Overview of Validation Testing .................................................................................... 4 1 4.1 LT2ESWTR UV Disinfection Requirements ...................................................... 4 1 4.2 Overview of Validation Process .......................................................................... 4 2 4.2.1 Relating the Experimental RED to Log Inactivation Credit.................... 4 4 <IP_ADDRESS> Tier 1 and Tier 2 Approaches for Establishing Inactivation Credit...................................................................................... 4 5 4.2.2 Location and Application of Validation Testing ..................................... 4 5 4.2.3 Third Party Oversight .............................................................................. 4 6 4.3 Considerations for Validation Testing ................................................................. 4 6 4.3.1 Inlet and Outlet Hydraulics...................................................................... 4 7 4.3.2 UV Equipment ......................................................................................... 4 7 <IP_ADDRESS> UV Reactor Documentation................................................... 4 7 <IP_ADDRESS> Control Strategies................................................................... 4 7 <IP_ADDRESS> UV Intensity Sensor............................................................... 4 8 <IP_ADDRESS> Lamp Aging ........................................................................... 4 8 4.3.3 Additives Used in Validation Testing...................................................... 4 8 <IP_ADDRESS> Challenge Microorganism...................................................... 4 8 <IP_ADDRESS> UV Absorbing Material ......................................................... 4 9 4.4 Validation Testing ................................................................................................ 4 9 4.4.1 Microorganism Preparation ..................................................................... 4 9 4.4.2 Collimated Beam Testing ........................................................................ 4 9 4.4.3 Biodosimetry of Full Scale Reactors..................................................... 4 10 Proposal Draft Table of Contents ( Continued)

UV Disinfection Guidance Manual iv June 2003 4.5 Data Analysis ..................................................................................................... 4 11 4.5.1 Developing Challenge Microorganisms Dose Response Curve............ 4 12 <IP_ADDRESS> Calculate Dose Response Data From Collimated Beam Testing.................................................................................. 4 12 <IP_ADDRESS> Fitting Dose Response Data to a Curve .............................. 4 13 4.5.2 Determining Log Inactivation from Biodosimetry Testing ................... 4 13 4.5.3 Determining the RED ............................................................................ 4 14 <IP_ADDRESS> Calculating the RED Values ................................................ 4 14 <IP_ADDRESS> Selecting the Appropriate RED for Log Inactivation Credit Determination ........................................................... 4 14 <IP_ADDRESS> Interpolating RED as a Function of Test Conditions........... 4 15 4.5.4 Determining Inactivation Credit ............................................................ 4 15 4.6 Tier 1 Criteria..................................................................................................... 4 17 4.6.1 UV Intensity Sensors ............................................................................. 4 17 4.6.2 UV Lamp Output ................................................................................... 4 19 4.6.3 Flow Measurements ............................................................................... 4 19 4.6.4 Collimated Beam Apparatus.................................................................. 4 19 4.6.5 Challenge Microorganism Dose Response............................................ 4 19 4.6.6 Medium Pressure Lamps........................................................................ 4 20 4.6.7 Biodosimetry Sampling ......................................................................... 4 21 5.0 Start Up and Operation of UV Installations ............................................................... 5 1 5.1 Start up of UV Installation................................................................................... 5 3 5.1.1 Final Inspection........................................................................................ 5 3 5.1.2 Functional Testing ................................................................................... 5 3 <IP_ADDRESS> Verification of Mechanical Operation ................................... 5 4 <IP_ADDRESS> Verification of Monitoring Equipment .................................. 5 4 <IP_ADDRESS> Verification of Instrumentation and Control Systems ........... 5 5 <IP_ADDRESS> Verification of Flow Distribution and Headloss.................... 5 6 5.1.3 Performance Testing ................................................................................ 5 7 5.1.4 Operations and Maintenance Manual ...................................................... 5 9 5.2 Operation of UV Installations............................................................................ 5 10 5.2.1 Operational Requirements ..................................................................... 5 11 5.2.2 Recommended Operational Tasks ......................................................... 5 11 5.2.3 Start up and Shutdown of UV Reactors................................................. 5 12 <IP_ADDRESS> Routine Start up ................................................................... 5 12 <IP_ADDRESS> Routine Shutdown................................................................ 5 13 <IP_ADDRESS> Winterization........................................................................ 5 13 5.3 Maintenance of UV Reactors............................................................................. 5 13 5.3.1 Summary of Recommended Maintenance Tasks................................... 5 14 5.3.2 General Guidelines for UV Reactor Maintenance ................................. 5 15 <IP_ADDRESS> UV Lamp Characteristics..................................................... 5 15 <IP_ADDRESS> UV Intensity Sensors ........................................................... 5 16 <IP_ADDRESS> Lamp Sleeves ....................................................................... 5 18 <IP_ADDRESS> Fouling ................................................................................. 5 18 Proposal Draft Table of Contents ( Continued)

UV Disinfection Guidance Manual v June 2003 <IP_ADDRESS> On line UVT Monitor Calibration ........................................ 5 20 <IP_ADDRESS> Flowmeter Calibration .......................................................... 5 20 <IP_ADDRESS> UV Reactor Temperature...................................................... 5 20 <IP_ADDRESS> Electrical Concerns ............................................................... 5 21 5.3.3 Spare Parts ............................................................................................. 5 22 5.4 Monitoring, Recording, and Reporting of UV Installation Operation............... 5 24 5.4.1 Monitoring and Recording Frequency for Compliance Parameters ...... 5 24 5.4.2 Monitoring and Recording for Other Operational Parameters .............. 5 25 5.4.3 Reporting to the State............................................................................. 5 26 5.5 Determination of Validated Operational Parameters......................................... 5 27 5.6 Operational Challenges...................................................................................... 5 32 5.6.1 Low UV Intensity or Low Calculated UV Dose.................................... 5 32 5.6.2 Low UV Transmittance.......................................................................... 5 34 5.6.3 Rapid Flow Increase or High Flow........................................................ 5 36 5.6.4 Unreliable UV Intensity Sensor Readings ............................................. 5 36 5.6.5 Power Quality Problems ........................................................................ 5 37 5.7 Staffing Issues.................................................................................................... 5 37 5.7.1 Staffing Levels....................................................................................... 5 38 5.7.2 Training.................................................................................................. 5 38 5.7.3 Safety Issues........................................................................................... 5 39 6.0 References....................................................................................................................... 6 1 Appendices Appendix A Fundamentals of UV Disinfection .......................................................... A 1 Appendix B Derivation of UV Dose Response Requirements ................................... B 1 Appendix C Validation of UV Reactors ...................................................................... C 1 Appendix D Microbiological Methods ....................................................................... D 1 Appendix E Measuring Challenge Microorganism UV Dose Response .................... E 1 Appendix F Background to the UV Reactor Validation Protocol .............................. F 1 Appendix G Issues for Unfiltered Systems ................................................................ G 1 Appendix H Issues for Ground Water Systems .......................................................... H 1 Appendix I Issues for Small Systems ......................................................................... I 1 Appendix J Pilot Scale and Demonstration Scale Testing ......................................... J 1 Appendix K Preliminary Engineering Report ............................................................ K 1 Appendix L Regulatory Timeline ............................................................................... L 1 Appendix M Compliance Forms ................................................................................. M 1 Appendix N UV Lamp Breakage Issues ..................................................................... N 1 Appendix O Case Studies [ This appendix will be included in the final draft when more information being available.] ...................................... O 1 Appendix P Validation Protocol Calculator Tool ....................................................... P 1 Proposal Draft List of Figures Figure 2.1 UV Light in the Electromagnetic Spectrum......................................................... 2 3 Figure 2.2 Refraction of Light............................................................................................... 2 4 Figure 2.3 Reflection of Light............................................................................................... 2 4 Figure 2.4 Scattering of Light ............................................................................................... 2 5 Figure 2.5 Structure of DNA and Nucleotide Sequences Within DNA................................ 2 6 Figure 2.6 UV Absorbance of Nucleotides and Nucleic Acid at pH 7 ................................ 2 7 Figure 2.7 Hypothetical Dose Distributions for Two Reactors with Differing Hydraulics............................................................................................................ 2 9 Figure 2.8 Shapes of UV Dose Response Curves............................................................... 2 11 Figure 2.9 Comparison of Microbial UV Action and DNA UV Absorbance..................... 2 12 Figure 2.10 UV Disinfection System Schematic................................................................... 2 13 Figure 2.11 Example of Closed and Open Channel Reactors ............................................... 2 14 Figure 2.12 UV Output of LP and MP Mercury Vapor Lamps ............................................ 2 16 Figure 2.13 UV Lamp Output and its Relation to the UV Absorbance of DNA .................. 2 17 Figure 2.14 UV Transmittance of Quartz that is 1 mm Thick at a Zero Degree Incidence Angle ................................................................................................. 2 18 Figure 2.15 Mechanical Wiper System and Physical Chemical Wiper System ................... 2 19 Figure 2.16 UV Intensity Sensor Viewing Lamps within a UV Reactor .............................. 2 20 Figure 2.17 UV Transmittance Monitor Design ................................................................... 2 21 Figure 3.1 Flowchart for Planning, Design, and Construction of UV Facilities................... 3 3 Figure 3.2 Schematic for UV Installation ( Upstream of Clearwell) ..................................... 3 6 Figure 3.3 Schematic of Individual Filter Effluent Piping Installation in Filter Gallery ...... 3 7 Figure 3.4 UV Disinfection Downstream of High Service Pumps ....................................... 3 8 Figure 3.5 Example CF Diagram for Three Filtered Waters............................................... 3 12 Figure 3.6 Example Flow and UV Absorbance ( at 254) Data ............................................ 3 13 Figure 3.7 Example Effect of Pre ozonation on UV Absorbance if Ozone is Quenched Prior to UV Disinfection................................................................... 3 16 Figure 3.8 Open Channel Flow Distribution Options ......................................................... 3 33 Figure 3.9 Flow Measurement and Control Options........................................................... 3 36 Figure 4.1 Steps of a Validation Process............................................................................... 4 3 Figure 4.2 Collimated Beam Test Apparatus ...................................................................... 4 10 Figure 4.3 Biodosimetry Test Components......................................................................... 4 11 Figure 4.4 Examples of UV Intensity Sensor Spectral Response Ranges........................... 4 18 Figure 4.5 Dose Response with a Shoulder ........................................................................ 4 20 Figure 4.6 Criteria for the Minimum UVT of MP UV Systems Under Tier 1.................... 4 21 Figure 5.1 Start Up and Operation Flowchart....................................................................... 5 2 Figure 5.2 Example 2 Interpoloation of Validation Data to Determine UV Intensity Setpoints............................................................................................................. 5 29 Figure 5.3 Interpolation of Validation Data to Determine UV Intensity Setpoints at Different Flows and Cryptosporidium Inactivation........................................... 5 30 Figure 5.4 Low UV Intensity of Low Calculated UV Dose Decision Chart....................... 5 33 Figure 5.5 High UV Absorbance Decision Chart................................................................ 5 35 UV Disinfection Guidance Manual vi June 2003 Proposal Draft List of Tables Table 1.1 Summary of Microbial and Disinfection Byproduct Rules ................................. 1 4 Table 1.2 Bin Requirements for Filtered Systems ............................................................... 1 6 Table 1.3 Bin Requirements for Unfiltered Systems ........................................................... 1 7 Table 1.4 UV Dose Requirements Used During Validation Testing................................... 1 7 Table 2.1 Mercury Vapor Lamp Characteristics................................................................ 2 15 Table 2.2 Mercury Vapor Lamp Comparison.................................................................... 2 15 Table 2.3 Water Quality Data and Fouling Observed for UV Disinfection Pilot and Demonstration Studies....................................................................................... 2 24 Table 3.1 Potential Method to Determine Design Flow .................................................... 3 17 Table 3.2 Start and Restart Times for LPHO and MP Lamps ........................................... 3 18 Table 3.3 UV Reactor Control Strategies .......................................................................... 3 22 Table 3.4 Summary of Recommended Hydraulic Configurations for Validation and Installation................................................................................. 3 23 Table 3.5 Potential Operational Strategies......................................................................... 3 25 Table 3.6 Potential UV Reactor Procurement Options ...................................................... 3 30 Table 3.7 Comparison of Techniques for UV Installation Flow Measurement................. 3 35 Table 3.8 Typical Alarm Conditions for UV Systems....................................................... 3 42 Table 3.9 Recommended Content for UV Reactor Specifications .................................... 3 48 Table 3.10 Recommended Information to be Provided by UV Manufacturer/ Vendor ....... 3 50 Table 4.1 Tier 1 RED Targets for UV System with LP of LPHO Lamps ......................... 4 16 Table 4.2 Tier 1 RED Targets for UV System with MP Lamps........................................ 4 16 Table 5.1 Example Monitoring During a Four Week Performance Test............................. 5 9 Table 5.2 Recommended Operational Tasks for the UV Reactor...................................... 5 11 Table 5.3 Recommended Maintenance Tasks.................................................................... 5 14 Table 5.4 Design and Guaranteed Lives of Major UV Components................................. 5 23 Table 5.5 Off Specification Operations for Each Control Strategy................................... 5 24 Table 5.6 Monitoring Parameters and Recording Frequency ............................................ 5 25 Table 5.7 Recommended Monitoring Parameters and Recording Frequency ................... 5 26 Table 5.8 UV Reactor Control Strategies .......................................................................... 5 27 Table 5.9 Example Validation Data for Variable Setpoint Operation ............................... 5 28 Table 5.10 UV Intensity Setpoint for Different Flow Ranges ............................................. 5 28 Table 5.11 Example Validation Data for Variable Setpoint Operation ............................... 5 29 Table 5.12 UV Intensity Setpoint for Different Flow Ranges ............................................. 5 30 Table 5.13 Dose Setpoints for Various Log Inactivation of Cryptosporidium.................... 5 31 Table 5.14 Factors Impacting Staffing Needs...................................................................... 5 38 UV Disinfection Guidance Manual vii June 2003 Proposal Draft Glossary The following definitions were derived from existing UV literature, standard physics textbooks, and/ or industry standards and conventions. Some concepts have more than one acceptable term or definition, but for consistency within the document, only one term is used.

Absorption   the transformation of UV light to other forms of energy as it passes through a substance.

Action Spectrum   the relative efficiency of UV energy at different wavelengths in inactivating microorganisms. Each microorganism has a unique action spectrum.

Ballast   provides the proper voltage and current required to initiate and maintain the gas discharge within the UV lamp.

Bioassay   a procedure used to determine the response of a specific microorganism after exposure to UV light, usually in UV reactors. Bioassay is a term typically utilized in toxicology, describing the testing of the bio toxicity of a contaminant. Bioassay has been used in the UV disinfection literature in the same context as " biodosimetry" ( see biodosimetry).

Biodosimeter   the challenge microorganism used to measure UV inactivation and ultimately calculate the reduction equivalent dose ( RED; see UV dose) in a UV reactor.

Biodosimetry   a procedure used to determine the reduction equivalent dose ( RED) of a UV reactor. Biodosimetry involves measuring the inactivation of a challenge microorganism after exposure to UV light in a UV reactor and comparing the results to the known UV dose response curve of the challenge microorganism ( determined using collimated beam testing) to determine the RED ( see UV Dose).

Challenge Organism   a microorganism used in UV reactor biodosimetry testing.

Collimated Beam Test   a carefully controlled bench scale test that is used to determine the UV dose response of a microorganism. Both time and UV light intensity are accurately measured, resulting in a specific calculation of delivered UV dose for the microorganism being tested. Collimated beam tests are described in detail in Appendix C.

Dark Repair   an enzyme mediated microbial process that removes and regenerates a damaged section of deoxyribonucleic acid ( DNA), using an existing complimentary strand of DNA. Dark repair refers to all microbial repair processes not requiring reactivating light.

Delivered UV Dose   see UV Dose Dose Control Strategy   the technique used by a UV system to control the delivered dose that typically involves adjusting the lamp power or turning " on" or " off" banks of UV lamps to respond to changes in UV absorbance, lamp intensity, and flow. Typically, the dose control strategy is different for LP/ LPHO and MP systems.

UV Disinfection Guidance Manual viii June 2003 Proposal Draft Glossary ( Continued)

UV Disinfection Guidance Manual ix June 2003 Dose Distribution   see UV Dose, Delivered UV Dose Distribution.

Emission Spectrum   the relative light power emitted by a lamp as a function of wavelength.

Fluence   see UV Dose Fluence Rate   see UV Intensity Gas Discharge   a mixture of non excited atoms, excited atoms, cations, and free electrons formed when a sufficiently high voltage is applied across a volume of gas. Most commercial UV lamps use mercury gas discharges to generate UV light.

Germicidal Effectiveness   the relative inactivation efficiency of each UV wavelength in a polychromatic emission spectrum. This value is usually approximated by the relative absorbance of DNA at each wavelength, although individual microorganisms may respond differently. By convention, germicidal effectiveness of the 254 nm emission line by LP UV lamps is considered to be unity. The germicidal effectiveness is typically used to weight a polychromatic, MP UV lamp output to reflect the germicidal energy of that specific source.

Germicidal Range   the range of UV wavelengths responsible for microbial inactivation in water ( 200 to 300 nm).

Lamp Envelope   the exterior surface of the UV lamp, which is typically made of quartz.

Lamp Sleeve   the quartz tube that surrounds and protects the UV lamp. The exterior is in direct contact with the water being treated. There is typically an air gap ( approximately 1 cm) between the lamp envelope and the quartz sleeve.

Light Pipe   a quartz cylinder that transmits light from the interior of the UV reactor to the photodetector of a UV intensity sensor.

Lignin Sulfonate   a commercially available reagent grade chemical that can simulate the UV absorbance spectrum of natural waters and be used to adjust UV transmittance during validation testing.

Low Pressure ( LP) Lamp   a mercury vapor lamp that operates at an internal pressure of 0.001 to 0.01 torr ( 2 x 10 5 to 2 x 10 4 psi) and electrical input of 0.5 watts per centimeter. This results in essentially monochromatic light output at 254 nanometers.

Low Pressure High Output ( LPHO) Lamp   a low pressure mercury vapor lamp that operates under increased electrical input ( 1.5 to 10 W/ cm), resulting in a higher UV intensity than LP lamps. It also has essentially monochromatic light output at 254 nanometers.

Medium Pressure ( MP) Lamp   a mercury vapor lamp that operates at an internal pressure of 100 to 10,000 torr ( 2 to 200 psi) and electrical input of 50 to 150 W/ cm. This results in a polychromatic ( or broad spectrum) output of UV and visible light at multiple wavelengths, including the germicidal range.

Proposal Draft Glossary ( Continued)

UV Disinfection Guidance Manual x June 2003 Monochromatic   light output at only one wavelength. For example, because low pressure and low pressure high output lamps only significantly emit light at 254 nanometers, they are considered monochromatic UV light sources.

Monitoring Window   a quartz disc that transmits light from the interior of the UV reactor to the photodetector of a UV intensity sensor.

Offline Chemical Clean ( OCC)   a process to clean lamp sleeves where the UV reactor is taken off line and a cleaning solution ( typically an acid) is manually pumped into the reactor. After the foulant has dissolved, the reactor is drained, rinsed, and returned to service. Also called flush and rinse systems.

Online Mechanical Clean ( OMC)   a process to clean lamp sleeves where an automatic mechanical wiper ( e. g., O ring, brush) wipes the surface of the lamp sleeve at a prescribed frequency.

Petri Factor   a ratio used in collimated beam testing that is equal to the average intensity measured across the surface of a suspension in a petri dish divided by the intensity at the center of a petri dish. The petri factor is used to help calculate delivered UV dose as described in Appendix C.

Photodetector   a device that produces an electrical current proportional to the UV light intensity at the detector's surface.

Photoreactivation   a microbial repair process where enzymes activated by light in the near UV and visible range ( 310 to 490 nm) split pyrimidine dimers, thereby repairing UV induced damage. Photoreactivation requires the presence of light.

Polychromatic   light energy output at several wavelengths such as with MP lamps.

Quartz Sleeve   see lamp sleeve Radiometer   an instrument used to measure UV irradiance Reduction Equivalent Dose ( RED)   see UV Dose, RED.

Reflection   the change in direction of light propagation when deflected by an interface or surface.

Refraction   the change in direction of light propagation as it passes through one medium to another.

Scattering   the change in direction of light propagation caused by interaction with a particle.

Spectral UV Absorbance   the determination of UV Absorbance ( A) over a range of wavelengths ( e. g. 200 to 400 nm)

Proposal Draft Glossary ( Continued)

UV Disinfection Guidance Manual xi June 2003 State   the agency of the state, tribal, or federal government that has jurisdiction over public water systems.

UV absorbance ( A)   a measure of the amount of UV light that is absorbed by a substance ( e. g., water, microbial DNA, lamp envelope, quartz sleeve) at a specific wavelength ( e. g., 254 nm). This measurement accounts for absorption and scattering in the medium ( e. g., water). Typically the absorbance is measured on a per centimeter ( cm) basis in a 1 cm quartz cuvette. Standard Method 5910B details this measurement method. However, for UV disinfection applications, the sample should not be filtered or adjusted for pH as described in Standard Methods.

UV Dose   the energy per unit area incident on a surface, typically in units of mJ/ cm2 or J/ m2 ( older literature also used the units mW s/ cm2 where 1 mW s/ cm2 = 1 mJ/ cm2). The UV dose received by a waterborne microorganism in a reactor vessel accounts for the effects on UV intensity of the absorbance of the water, absorbance of the quartz sleeves, reflection and refraction of light from the water surface and reactor walls, and the germicidal effectiveness of the UV wavelengths. This guidance also uses the following terms related to UV dose:

  Delivered UV dose distribution   the probability distribution of delivered UV doses that microorganisms receive in a flow through UV reactor; typically shown as a histogram. An example is shown in Figure 2 7.

  Reduction Equivalent Dose ( RED)   a calculated dose for a flow through UV reactor that is based on biodosimetry ( i. e., measuring the level of inactivation of a challenge microorganism with a known UV dose response). The RED is set equal to the UV dose in a collimated beam test that achieves the same level of inactivation of the challenge microorganism as measured for the flow through UV reactor during biodosimetry testing.

UV Dose Response   the relationship indicating the level of inactivation of a microbe as a function of UV dose. Inactivation is often plotted as log10( N0/ N) where N0 is the number of microbes present prior to UV light exposure and N is the number of microbes present after UV light exposure. Examples are shown in Figure 2 8.

UV Installation   all of the components of the UV disinfection process, including ( but not limited to) UV reactors, control systems, piping, valves, and building or enclosure.

UV Intensity   the power per unit area passing through an area perpendicular to the direction of propagation. UV intensity is used in this guidance manual to describe the magnitude of UV light in a UV reactor and in bench scale UV experiments.

UV Intensity Sensor   a photosensitive detector used to measure the UV intensity at a point within the UV reactor.

UV Irradiance   the power per unit area incident to the direction of light propagation at all angles, including normal.

UV Light   electromagnetic radiation with wavelengths from 200 to 400 nm.

Proposal Draft Glossary ( Continued)

UV Disinfection Guidance Manual xii June 2003 UV Reactor   the vessel or chamber where exposure to UV light takes place, consisting of UV lamps, quartz sleeves, UV intensity sensors, quartz sleeve cleaning systems, and baffles or other hydraulic controls. The UV reactor also includes additional hardware for controlling UV dose; typically comprised of ( but not limited to): UV intensity sensors, UV transmittance monitors, ballasts, and control panels.

UV Reactor Validation   a process by which a UV reactor's disinfection performance is determined relative to operating parameters that can be monitored. Reactors are validated to indicate that they achieve a certain delivered UV dose for a range of flow, UV intensity, and water quality conditions ( e. g., UV transmittance). Appendix C details the protocol for validating UV reactors.

UV Transmittance ( UVT)   a measure of the fraction of incident light transmitted through the water column. The UV transmittance is the ratio of the light entering the water to that exiting the water. The UVT is usually reported for a pathlength of 1 cm. In an alternate pathlength is used, it should be specified. UVT is often represented as a percentage and is related to the UV absorbance by the following equation: % UVT = 100 x 10 A. As the UV absorbance increases, the UV transmittance decreases.

Proposal Draft List of Acronyms and Abbreviations A254 ultraviolet absorbance at 254 nanometers AC alternating current ACGIH American Conference of Governmental Industrial Hygienists ACS Automatic cleaning system ANSI American National Standards Institute AOC assimilable organic carbon APHA American Public Health Association ATCC American Type Culture Collection atm atmospheres AWWA American Water Works Association AwwaRF American Water Works Association Research Foundation BDL below detectable limits BDOC biodegradable dissolved organic carbon ° C degrees Centigrade CCPP calcium carbonate precipitation potential CF cumulative frequency CFD computational fluid dynamics CFR Code of Federal Regulations cfu colony forming unit CIP clean in place cm centimeter CPEL ceiling level permissible exposure limit CSI Construction Specifications Institute CT residual disinfectant concentration ( mg/ L) x time ( min) CWS community water system DBP disinfection byproduct DBPR disinfection byproduct rule DC direct current D/ DBP disinfectants/ disinfection by product DNA deoxyribonucleic acid DOC dissolved organic carbon DVGW Deutsche Vereinigung des Gas und Wasserfaches ( German Association for Gas and Water)

e exponent of the base of the natural logarithm EPA United States Environmental Protection Agency ° F degrees Fahrenheit ft feet g gram GAC granular activated carbon UV Disinfection Guidance Manual xiii June 2003 Proposal Draft List of Acronyms and Abbreviations ( Continued)

UV Disinfection Guidance Manual xiv June 2003 gal gallon GFI ground fault interrupt gpm gallons per minute GWR ground water rule GWUDI ground water under the direct influence [ of surface water]

h hour HAA haloacetic acid HDPE high density polyethylene HGL hydraulic grade line hp horsepower HPC heterotrophic plate count HSP high service pump Hz hertz I UV intensity IDLH Immediately Dangerous to Life or Health IDSE initial distribution system evaluation IESWTR Interim Enhanced Surface Water Treatment Rule IT UV intensity x time J joule kW kilowatt kW hr kilowatt hour ln natural logarithm LP low pressure LPHO low pressure high output LRAA locational running annual average LSI Langlier Saturation Index LT1ESWTR Long Term 1 Enhanced Surface Water Treatment Rule LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule   wavelength m meter mA milliamp MCL maximum contaminant level mg milligram mgd million gallons per day min minutes mJ millijoule mL milliliter mm millimeter MP medium pressure MS2 male specific 2 bacteriophage µ g microgram µ m micrometer, micron Proposal Draft List of Acronyms and Abbreviations ( Continued)

UV Disinfection Guidance Manual xv June 2003 NEL National Electric Code nm nanometer NIOSH National Institute for Occupational Safety and Health NIST National Institute of Standards and Technology NOM natural organic matter NSF National Science Foundation NTNCWS non transient non community water system NTU nephelometric turbidity units NWRI National Water Research Institute O& M operation and maintenance OCC offline chemical clean OMC online mechanical clean ÖNORM Österreichisches Normungsinstitut ( Austrian Standards Institute) OSHA Occupational Safety and Health Administration PAC powdered activated carbon PEL permissible exposure limit % percent PER preliminary engineering report pfu plaque forming unit pH negative logarithm of the effective hydrogen ion concentration PHA process hazard analysis PLC programmable logic controller POE point of entry psi pounds per square inch psig pounds per square inch gauge PVC polyvinyl chloride QA/ QC quality assurance/ quality control r radial distance from center r2 correlation coefficient RAA running annual average RCRA Resource Conservation and Recovery Act RED reduction equivalent dose RMS root mean square RNA ribonucleic acid rpm revolutions per minute RPZ reduced pressure zone s second SARA Superfund Amendments and Reauthorization Act SCADA supervisory control and data acquisition SDWA Safe Drinking Water Act SMCL secondary maximum contaminant level SMP standard monitoring program Proposal Draft List of Acronyms and Abbreviations ( Continued)

UV Disinfection Guidance Manual xvi June 2003 SOP standard operating procedure SSS system specific study SUVA specific ultraviolet absorbance SWTR Surface Water Treatment Rule T10 time at which ten percent of water has passed through the reactor TCLP toxic characteristic leaching procedure TCR total coliform rule TDH total dynamic head TDS total dissolved solids THM trihalo methane TLV threshold limit values TNTC too numerous to count TOC total organic carbon TOX total organic halides TSA tryptic soy agar TSB tryptic soy broth TSS total suspended solids TTHM total trihalomethane UPS uninterruptible power supply UV ultraviolet UVT ultraviolet transmittance VFD variable frequency drive W watt WTP water treatment plant Proposal Draft Requested Feedback on the UV Disinfection Guidance Manual Chapter or Appendix Title Specific Issues for Comment Glossary 1. Are there additional terms that should be defined? 2. Is each definition accurate and clearly presented?

1. Introduction 1. Does this chapter provide the appropriate amount of information on the relevant regulations?

2. Overview Of UV Disinfection 1. Is the level of detail appropriate? 2. Is there additional information that should be provided?

3. Planning And Design Aspects For UV Installations 1. Is the overall UV installation design flowchart realistic? Is the chapter organization reader friendly? 2. Is the issue of off specification operation and its implications on the UV installation design clearly described? 3. Are the recommendations on developing design criteria helpful? Are there other approaches that should be discussed? 4. Is the power quality information clear? Is more information needed? 5. Are there additional planning or design issues that should be discussed?

4. Overview of Validation 1. Are the elements of validation clearly presented? 2. Is there other information from the detailed validation protocol ( Appendix C) that should be described here?

5. Start Up And Operation Of UV Installations 1. Are there other elements of the UV installation start up that should be discussed? 2. Are the organization of the chapter and presentation of information appropriate? 3. Are the operational requirements examples clearly described? 4. Are there other operation and maintenance issues that should be discussed? 5. Are the operational challenges described realistic, and are the solutions helpful?

6. References 1. Are there any references that were overlooked that should be added to help clarify any points made in the UVDGM?

UV Disinfection Guidance Manual xvii June 2003 Proposal Draft Requested Feedback on the UV Disinfection Guidance Manual UV Disinfection Guidance Manual xviii June 2003 A. Fundamentals of UV Disinfection 1. Is the level of detail appropriate? 2. Is there additional information that should be provided?

B. Derivation of UV Dose Response Requirements 1. Are there published or unpublished data available that are not included in this analysis?

C. UV Validation Protocol Testing 1. Is the description of the testing methods clear? 2. Are the distinctions between Tier 1 and 2 clearly described? 3. To provide a better assessment of the RED bias, please provide dose distributions for UV reactors you have modeled at UVTs of 95, 90, 85, and 80%. 4. Are the Tier 1 criteria acceptable? If not, please provide data and rational to support alternative criteria. 5. During validation, the uncertainty of some measurements will not be random. In particular, errors associated with measurements made by the radiometer will likely be a systematic error ( i. e., the radiometer will always read high or read low for the duration of the validation testing). Other such errors could occur with the intensity sensors or the reference sensor used to calibrate the duty sensors. Currently, the UVGM combines these sources of uncertainty with other random sources of uncertainty to define an expanded uncertainty. Because these sources of error are not random during a given validation, should the following approach be used:

If the error of a measurement during validation is constant and systematic, should the uncertainty of the measurement be used to define a bias error that is applied to the validation results? Under the current approach, this would apply to the uncertainty of the radiometer and move it from the expanded uncertainty to its own bias error. For example, if the uncertainty of the radiometer is 8 %, a safety factor of 1.08 is added to the RED bias, polychromatic bias, and expanded uncertainty. This will increase RED targets for Tier 1 and 2.

6. The expanded uncertainty is calculated for an 80 percent confidence interval to ensure at least nine out of ten cases of UV system operation meet target dose values. Should the expanded uncertainty calculation be based on a 90 or 95 percent confidence interval to ensure a higher percentage of UV systems meet requirements?

D. Validation Microbial Methods 1. The bounds provided for the MS2 and B. subtilis data come from an analysis of data published in the literature. Should these bounds be used? If not, please provide data to support using alternative bounds? Should any of the literature data used to develop these bounds not be included? If yes, please provide a rational for not including that data. 2. Are the methods for analyzing the collimated beam data and subsequent UV doseresponse curve clearly stated and appropriate? Are there other options that should be considered?

Proposal Draft Requested Feedback on the UV Disinfection Guidance Manual UV Disinfection Guidance Manual xix June 2003 E. Collimated Beam Apparatus   Measuring Challenge Microbe UV Dose Response 1. Is the collimated beam testing description clear?

F. Validation Background 1. The following is an alternate approach for monitoring dose delivery that is not included in the manual because it has not been applied or referenced.

Calculate the percent UV output from the lamp to the water based on the sensor readings using the formula:

100 ) ( '   = UVT S S P L where PL = UV output from the lamp to the water (%) S = Sensor reading S'( UVT) = Sensor reading expected with a new lamp operating with unfouled sleeves at a given UVT UVT = UVT of the water at 254 nm The calculated lamp power and measured UVT should be above setpoint values established during validation. The relation S'( UVT) is measured during validation as opposed to being calculated.

This approach has the following potential benefits:

  No requirement on sensor position   Could measure S'( UVT) with NOM and compare with LSA or coffee as an experimental approach for reducing the Polychromatic Bias to one.

Should this approach be discussed in the manual?

G. Issues for Unfiltered Systems 1. Is the level of detail appropriate? 2. Is there additional water quality related design or operational concerns for unfiltered systems that should be addressed?

H. Issues for Ground Water Systems 1. Are there design or operational issues with UV disinfection of groundwater that are not addressed?

I. Issues for Small Systems 1. Is the level of detail appropriate? 2. Are the design concerns facing small systems adequately addressed? 3. Design information is presented in Chapter 3, and this appendix only includes areas where small system design differs from the design issues discussed in Chapter 3. Is this approach effective?

Proposal Draft Requested Feedback on the UV Disinfection Guidance Manual UV Disinfection Guidance Manual xx June 2003 J. Pilot Scale and Demonstration Scale Testing 1. Is the level of detail appropriate? 2. Were all of the recommended testing methods clearly explained? 3. Are there any other example testing protocols that should be included in this appendix?

K. Preliminary Engineering Report 1. Are there any elements of this report that would benefit from more detail? 2. Is there any information missing from this report that you would like to see included in a standard template ( i. e., in this example Design Engineering Report)?

L. Regulatory Timeline 1. Is this appendix helpful for UV installation planning? 2. Are the time allocations for the tasks listed in the timeline appropriate?

M. Compliance Forms 1. Are the example compliance forms well organized and easy to complete? 2. Are there other forms that would be helpful to the utility or the State?

N. UV Lamp Breakage Issues 1. Considering available information, are the major issues surrounding lamp breakage adequately presented in this appendix? Are there additional issues or sources of information to be discussed? 2. Are there additional methods for the prevention or mitigation of on line lamp breaks that should be presented?

O. Case Studies There are no questions related to this appendix because it is not included in this draft.

P. Validation Protocol Calculator Tool There are no questions related to this appendix.

Proposal Draft 1 Throughou t this document, the terms " State" or " States" are used to refer to all types of primacy agenc ies, including U. S. Territories, Indian Tribes, and EP A Regions.

UV Disinfection Guidance Manual 1 1 June 2003 Propo sal Draft 1. Introduction There is growing interest among public water systems in using ultraviolet ( UV) light to disinfect drinking water, based on its ability to inactivate certain microorganisms without forming harmful disinfection byproducts ( DBPs). Some pathogens, such as Cryptosporidium, are resistant to commonly used disinfectants, whereas UV light has proven effective against these microorganisms.

The United States Environmental Protection Agency ( EPA) is developing the Long Term 2 Enhanced Surface Water Treatment Rule ( LT2ESWTR) to further control microbial contamination of drinking water. The rule requires additional treatment for some systems based on their source water Cryptosporidium concentrations. UV disinfection is one of the options utilities have to comply with the treatment requirements.

UV light has been widely used to disinfect effluent from wastewater treatment facilities, particularly those that reuse effluent for irrigation. Until recently, the use of UV treatment for drinking water applications was primarily limited to small ground water systems, due to the belief that it was not effective for inactivating protozoa and was not cost effective for large systems. In 1998, however, research demonstrated that UV light could effectively inactivate Cryptosporidium at low dosages ( Buhkari et al. 1998), prompting more research to better understand its potential for widespread application.

UV disinfection design, operation, and maintenance needs differ from those of traditional chemical disinfectants used in drinking water applications. EPA is therefore developing this guidance manual to familiarize States1 and utilities with these important issues as well as regulatory requirements. Areas of particular design and operational importance include hydraulic control, reliability, redundancy, lamp cleaning and replacement, and lamp breakage. Regulatory requirements are addressed through UV reactor validation, monitoring, and reporting.

1.1 Guidance Manual Objectives This manual provides guidance to utilities, States, manufacturers, and other interested parties on the disinfection of drinking water with UV light, including the regulatory requirements associated with UV disinfection. The LT2ESWTR requirements do not cover all aspects of the disinfection process. In the areas not directly addressed by the rule, the manual provides 1. Introduction UV Disinfection Guidance Manual 1 2 June 2003 Propo sal Draft recommendations to assist utilities and regulatory agencies in assessing the disinfection capability and performance of UV installations. The manual's objectives are as follows:

° Provide public water systems and designers with technical information and guidance on the selection, design, and operation of UV installations and the UV related requirements for compliance with the LT2ESWTR.

° Provide States with guidance and the necessary tools to assess UV installations at the design, start up, and routine operation phases.

° Provide manufacturers with testing and performance standards for UV components and systems for treating drinking water.

1.2 Organization This manual consists of six chapters and appendices:

° Chapter 1   Introduction. The remainder of this chapter summarizes the LT2ESWTR and Stage 2 DBPR and discusses regulatory requirements for disinfection of drinking water with UV light.

° Chapter 2   Overview of UV Disinfection. This chapter describes the principles of disinfection with UV light including inactivation mechanisms, dose response relationships, water quality impacts, and UV reactors.

° Chapter 3   Planning and Design Aspects for UV Installations. This chapter discusses the key design features for UV disinfection facilities and presents some common approaches to facility design. Key design features include treatment goals, existing infrastructure, water quality, hydraulics, and operation and control strategies.

° Chapter 4   Overview of UV Reactor Validation. This chapter describes the LT2ESWTR requirements for validating UV reactors and provides an overview of validation protocol presented in Appendix C.

° Chapter 5   Start up and Operation of UV Installations. This chapter discusses start up and operation issues of UV disinfection facilities as well as required monitoring for regulatory compliance.

° Chapter 6   References. This chapter lists the full references from Chapters 1 5. 1. Introduction UV Disinfection Guidance Manual 1 3 June 2003 Propo sal Draft ° The appendices and their titles follow:

Appendix A. Fundamentals of UV Disinfection Appendix B. Derivation of UV Dose Response Requirements Appendix C. Validation of UV Reactors Appendix D. Microbiological Methods Appendix E. Collimated Beam Apparatus: Measuring Challenge Microorganism UV Dose Response Appendix F. Background to the UV Reactor Validation Protocol Appendix G. Issues for Unfiltered Systems Appendix H. Issues for Ground Water Systems Appendix I. Issues for Small Systems Appendix J. Pilot Scale and Demonstration Scale Testing Appendix K. Preliminary Engineering Report Appendix L. Regulatory Time Line Appendix M. Compliance Forms Appendix N. UV Lamp Breakage Issues Appendix O. Case Studies [ This appendix will be included in the final draft at which time EPA anticipates more information being available.] Appendix P. Validation Protocol Calculator Tool 1.3 Regulations Summary This section summarizes the drinking water regulations for microbial and DBP control. The Stage 2 Disinfectants and Disinfection Byproduct Rule ( DBPR) aims to reduce peak DBP concentrations in the distribution system by modifying the Stage 1 DBPR monitoring requirements and procedures for compliance determination. The LT2ESWTR and Stage 2 DBPR are to be promulgated together to address the risk risk trade off between microbial disinfection and the byproducts formed by commonly used disinfectants. Consequently, when a utility assesses its disinfection strategy, not only the disinfection of target pathogens is important, but also the DBP formation from each disinfectant. Table 1.1 summarizes the microbial treatment requirements and DBP maximum contaminant levels ( MCLs) from the Surface Water Treatment Rule ( SWTR), Interim Enhanced Surface Water Treatment Rule ( IESWTR), Long Term 1 Enhanced Surface Water Treatment Rule ( LT1ESWTR), LT2ESWTR, Stage 1 DBPR, and Stage 2 DBPR. 1. Introduction UV Disinfection Guidance Manual 1 4 June 2003 Propo sal Draft Table 1.1 Summary of Microbial and Disinfection Byproduct Rules Surface W ater Treatmen t Rules  Minim um Trea tment Req uirements Regulation Giard ia Virus Cryptosporidium SWTR 3 log removal and inactivation 4 log removal and inactivation Not addressed IESWTR and LT1ESWTR No change from SWTR 2 log removal LT2ESWTR No change from SWTR 0 2.5 log additional treatment1 2 3 log treatment2 Disinfection Byproduct Rules  MCLs Based on Run ning Annual Averages ( RAAs)

Regulation Trihalomethanes ( TTHM) ( µ g/ L) Haloacetic Acids ( HAA5) ( µ g/ L) Bromate ( µ g/ L) Chlorite ( µ g/ L)

Stage 1 DBPR 80 as RAA 60 as RAA 10 1000 Stage 2A DBPR3 120 as LRAA 100 as LRAA No change from Stage 1 Stage 2B DBPR4 80 as LRAA 60 as LRAA No change from Stage 1 1Requirement for filtered systems is in addition to removal achieved by conventional treatment complying with the IESWTR and LT1ESWTR. Specific requirements for each plant depend on source water monitoring results ( 40 CFR 141.720). 2Unfiltered systems must provide 2 3 log inactivation; specific requirements for each plant depend on source water monitoring results ( 40 CFR 141.721( b)). 3Stage 2A bases compliance on a locational running annual average ( LRAA) at the Stage 1 monitoring locations. Stage 1 RAAs must still be met during this time. Stage 2A begins [ 3 years after rule promulgation] for all systems. 4Stage 2B bases compliance on an LRAAs at revised monitoring locations identified during the Initial Distribution System Evaluation. Stage 2B begins [ 6 years after rule promulgation] for large systems and [ 7.5 8.5 years after rule promulgation] for small systems dependent on their LT2ESWTR requirements.

1.3.1 Long Term 2 Enhanced Surface Water Treatment Rule The LT2ESWTR applies to all public water systems that use surface water or ground water under the direct influence of surface water ( GWUDI), except those that purchase all their surface and GWUDI water. It builds on the SWTR, IESWTR, and the LT1ESWTR by improving control of microbial pathogens, specifically the contaminant Cryptosporidium. Unlike the previous rules, the LT2ESWTR bases treatment requirements on a system's source water Cryptosporidium concentration and type of treatment provided. This section describes the rule requirements for filtered and unfiltered systems. 1. Introduction UV Disinfection Guidance Manual 1 5 June 2003 Propo sal Draft <IP_ADDRESS> Filtered Systems The LT2ESWTR requires systems that use a surface water or GWUDI source ( referred to collectively in this manual as surface water systems) to conduct source water monitoring to determine average Cryptosporidium concentrations, unless they have historical Cryptosporidium data equivalent to what is required under the LT2ESWTR ( 40 CFR 141.701( a)). Based on its average source water Cryptosporidium concentration, filtered systems will be classified in one of four possible bins. A system's bin assignment determines the extent of any additional Cryptosporidium treatment requirements. The rule requires systems to comply with additional treatment requirements by using one or more management or treatment techniques from a toolbox of options ( 40 CFR 141.720( b)). The process is described in more detail below; the full monitoring requirements are described in the Source Water Monitoring Guidance Manual for Public Water Systems for the Long Term 2 Enhanced Surface Water Treatment Rule ( USEPA 2003).

Bin Classification Table 1.2 presents the bin classifications and their corresponding additional treatment requirements for all filtered systems ( 40 CFR 141.709 and 40 CFR 141.720). Systems with average Cryptosporidium concentrations of less than 0.075 oocysts per liter are placed in Bin 1, for which no additional treatment is required. For concentrations of 0.075 or more, additional treatment is required on top of that required by existing rules. The additional treatment required for each bin, specified in terms of log removal, depends on the type of treatment already in place by the system. 1. Introduction UV Disinfection Guidance Manual 1 6 June 2003 Propo sal Draft Table 1.2 Bin Requirements for Filtered Systems1 If your Cryptosporidium concentration ( oocy sts/ L) is... Your bin classification is... And if yo u use the follo wing filtration tre atment in full compliance w ith existing re gulations , then you r additional treatm ent req uirem ents ar e...

Conventional Filtration Treatment ( includes softening) Direct Filtration Slow Sand or Diatomaceous Earth Filtration Alternative Filtration Technologies < 0.075 1 No additional treatment No additional treatment No additional treatment No additional treatment > 0.075 an d < 1.0 2 1 log treatment2 1.5 log treatment2 1 log treatment2 As determined by the State 2,4 > 1.0 and < 3.0 3 2 log treatment3 2.5 log treatment3 2 log treatment3 As determined by the State 3,5 > 3.0 4 2.5 log treatment3 3 log treatment3 2.5 log treatment3 As determined by the State 3,6 1 ( 40 CFR 141.709 and 40 CFR 141.720) 2 Systems may use any technology or combination of technologies from the microbial toolbox.

3 Systems must achieve at least 1 log of the required treatment using ozone, chlorine dioxide, UV disinfection, membranes, bag/ cartridge filters, or bank filtration. 4 Total Cryptosporidium treatment must be at least 4.0 log. 5 Total Cryptosporidium treatment must be at least 5.0 log. 6 Total Cryptosporidium treatment must be at least 5.5 log.

<IP_ADDRESS> Unfiltered Systems All existing requirements for unfiltered systems under the SWTR ( 40 CFR 141.71 and 141.72( a)) remain in effect. This includes disinfection to achieve at least 3 log inactivation of Giardia and 4 log inactivation of viruses and to maintain a disinfectant residual in the distribution system ( e. g., free chlorine or chloramines). The IESWTR and LT1ESWTR did not change the disinfection requirements for unfiltered systems. The LT2ESWTR requires 2 log or 3 log inactivation of Cryptosporidium, depending on the source water concentration of Cryptosporidium ( 40 CFR 141.721( b)).

The arithmetic mean concentration of all Cryptosporidium samples taken is used to determine the amount of treatment required, as shown in Table 1.3 ( 40 CFR 141.721( a)). If the mean concentration is less than or equal to 0.01 oocysts/ L, the system must provide 2 log inactivation of Cryptosporidium ( 40 CFR 141.721( b)). If the mean concentration of Cryptosporidium exceeds 0.01 oocysts/ L, the system must provide at least 3 log inactivation of Cryptosporidium ( 40 CFR 141.721( b)). 1. Introduction UV Disinfection Guidance Manual 1 7 June 2003 Propo sal Draft Table 1.3 Bin Requirements for Unfiltered Systems Bin Number Average Cryptosporidium Concentration ( oocysts/ liter) Additional Cryptosporidium inactivation requirements 1 < 0.01 2 log1 2 > 0.01 3 log1 1 Overall disinfection requirements must be met with a minimum of two disinfectants ( 40 CFR 141.721( d)).

<IP_ADDRESS> UV Disinfection Requirements for Filtered and Unfiltered Systems To receive disinfection credit for a UV reactor, the LT2ESWTR requires utilities to demonstrate through validation testing that the reactor can deliver the required UV dose ( 40 CFR 141, Subpart W, Appendix D). EPA developed dose requirements for Cryptosporidium, Giardia, and virus as presented in Table 1.4 and described in Appendix B of this guidance manual. These dose requirements account for uncertainty associated with the dose response of the microorganisms in controlled experimental conditions. In practical application, other sources of uncertainty are introduced due to the hydraulic effects of the UV installation, UV reactor equipment, and monitoring approach ( e. g., UV intensity sensors). Therefore, the validation protocol ( described in Chapter 4 and Appendix C of this guidance manual) applies a safety factor to the Table 1.4 dose requirements to account for these areas of uncertainty and variability.

Table 1.4 UV Dose Requirements Used During Validation Testing1 Log Inactivation 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Cryptosporidium 1.6 2.5 3.9 5.8 8.5 12

Giard ia 1.5 2.1 3.0 5.2 7.7 11

Virus 39 58 79 100 121 143 163 186 1 40 CFR 141.729( d)

The LT2ESWTR ( 40 CFR 141, Subpart W, Appendix D) specifies the following with respect to reactor validation:

C Validation testing must determine a range of operating conditions that can be monitored by the system and under which the reactor delivers the required UV dose.

C Operating conditions must include flowrate, UV intensity, and lamp status, at a minimum. 1. Introduction UV Disinfection Guidance Manual 1 8 June 2003 Propo sal Draft C Validated conditions determined by testing must account for UV absorbance of the water, lamp fouling and aging, measurement uncertainty of on line UV intensity sensors, UV dose distributions arising from the velocity profiles through the reactor, failure of UV lamps or other critical installation components, and inlet and outlet piping or channel configurations of the UV reactor.

Using the above requirements as a basis, Appendix C provides guidance for several possible approaches to reactor validation. States may approve modifications to these approaches or alternative approaches at their discretion.

Monitoring Requirements ( 40 CFR 141.729( d))

The LT2ESWTR requires utilities to monitor their reactors to demonstrate that they are operating within the range of conditions that were validated for the required UV dose. At a minimum, utilities must monitor each reactor for flowrate, lamp outage, UV intensity as measured by a UV intensity sensor, and any other parameters required by the State. UV absorbance should also be measured where it used in a dose control strategy. Systems must check the calibration of UV intensity sensors and must recalibrate sensors in accordance with a protocol approved by the State. The LT2ESWTR does not specify monitoring frequency ( section 5.4 of this guidance describes the monitoring requirements with recommended frequencies).

Reporting Requirements ( 40 CFR 141.730)

The LT2ESWTR requires utilities to report the following items:

° Initial reporting  Validation test results demonstrating operating conditions that achieve the UV dose required for the inactivation credit desired for compliance with the LT2ESWTR.

° Routine reporting  Volume of water entering the distribution system that was not treated by the UV reactors operating under validated conditions on a monthly basis.

For the purposes of this guidance manual, when a UV reactor is operating outside of its validated limits, it is considered " off specification."

Additional Requirement for Unfiltered Systems ( 40 CFR 141.721( c)( 2))

For unfiltered systems using UV disinfection to meet the LT2ESWTR requirements, the required Cryptosporidium log inactivation by UV disinfection must be achieved in at least 95 percent of the water delivered to the public during each calendar month. 1. Introduction UV Disinfection Guidance Manual 1 9 June 2003 Propo sal Draft 1.3.2 Stage 2 DBPR The requirements of the Stage 2 DBPR will apply to all community water systems ( CWSs) and nontransient noncommunity water systems ( NTNCWSs)   both ground and surface water systems   that add a disinfectant other than UV light, or that deliver water that has been treated with a disinfectant other than UV light.

Initial Distribution System Evaluations The Stage 2 DBPR is designed to reduce DBP occurrence peaks in the distribution system by changing compliance monitoring requirements. Compliance monitoring will be preceded by an initial distribution system evaluation ( IDSE) to identify compliance monitoring locations that represent high TTHM and HAA5 levels. The IDSE consists of either a standard monitoring program ( SMP) or a system specific study ( SSS). NTNCWSs serving fewer than 10,000 people are not required to perform an IDSE, and other systems may receive waivers from the IDSE requirement.

Compliance Determination and Schedule The Stage 2 DBPR changes the way sampling results are averaged to determine compliance. The determination for the Stage 2 DBPR is based on a LRAA ( i. e., compliance must be met at each monitoring location) instead of the system wide RAA used under the Stage 1 DBPR.

The Stage 2 DBPR will be implemented in two phases, Stage 2A and Stage 2B. Under Stage 2A, all systems must comply with TTHM/ HAA5 MCLs of 120/ 100 µ g/ L measured as LRAAs at each Stage 1 DBPR monitoring site, while continuing to comply with the Stage 1 DBPR MCLs of 80/ 60 µ g/ L measured as RAAs. Under Stage 2B, systems must comply with TTHM/ HAA5 MCLs of 80/ 60 µ g/ L at locations identified under the IDSE.

Significant Excursion Evaluations Because Stage 2 DBPR MCL compliance is based on an annual average of DBP measurements, a system could from time to time have DBP levels significantly higher than the MCL ( referred to as a significant excursion) while still being in compliance. This is because the high concentration could be averaged with lower concentrations at a given location. If a significant excursion occurs, a system must conduct a significant excursion evaluation and discuss the evaluation with the State no later than the next sanitary survey.

1.4 Alternative Approaches for Disinfecting with UV Light This manual provides technical information about using UV disinfection for drinking water treatment. Although it covers many aspects of implementing a UV installation, from design and validation to operation, it is not comprehensive in terms of all types of UV installations, design alternatives, and validation protocols that may provide satisfactory 1. Introduction UV Disinfection Guidance Manual 1 10 June 2003 Propo sal Draft performance. For example, pulsed UV and eximer lamps are two types of UV technologies not included in this manual, but they may provide effective disinfection. Currently, a significant level of research is being conducted surrounding UV disinfection and its applications in various industries. As more information becomes available, other UV equipment or methods of operation, design, and validation will evolve. States may recognize alternatives in UV installation design, operation, and validation that are not described in this manual. 2. Overview of UV Disinfection Chapter 2 provides an overview of UV disinfection. The material ranges from an explanation of the process in terms of basic chemical and physical principles to a description of the components of a UV installation and performance monitoring. Appendix A, Fundamentals of UV Disinfection, serves as a companion to this chapter by providing more detailed information on each of the topics discussed. The corresponding appendix sections are noted throughout the text. The organization of this chapter is presented below, including the key question each section addresses.

  What are the fundamental characteristics of UV light, and what happens to UV light as it propagates through water? .................................. Section 2.2   How does UV light inactivate microorganisms? ....................................... Section 2.3.1   Can microorganisms undergo repair and become infectious after inactivation by UV light? .................................................................. Section 2.3.2   How are UV dose and microbial response determined? .............................................................................. Sections 2.3.3 and 2.3.4   How does UV dose vary in a UV reactor? ................................................. Section 2.3.3   What affects a microorganism's response to UV light? .................................................................................. Sections 2.3.4 and 2.3.5   What do UV reactors look like and how do the key components function? .................................................................................. Section 2.4   What are the differences between low pressure and medium pressure lamps?........................................................................................... Section 2.4.2   How do the utility and the State know the UV reactor is delivering the required UV dose? ............................................................... Section 2.4.9   How does water quality affect UV reactor performance? .......................... Section 2.5.1   Do any disinfection byproducts form as a result of UV disinfection?................................................................................................ Section 2.5.2 2.1 History of UV Light for Drinking Water Disinfection UV disinfection is an established technology supported by decades of fundamental and applied research and practice in North America and Europe. Downes and Blunt ( 1887) discovered the germicidal properties of sunlight. The development of mercury lamps as artificial UV light sources in 1901 and the use of quartz as a UV transmitting material in 1906 was soon UV Disinfection Guidance Manual 2 1 June 2003 Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 2 June 2003 followed by the first drinking water disinfection application in Marseilles, France in 1910. In 1929, Gates identified a link between UV disinfection and absorption of UV light by nucleic acid. The development of the fluorescent lamp in the 1930s led to the production of germicidal tubular lamps. Considerable research on the mechanisms of UV disinfection and the inactivation of microorganisms occurred during the 1950s ( Dulbecco 1950; Kelner 1950; Powell 1959; Brandt and Giese 1956).

While there was substantial research on UV disinfection during the first half of the 20th century, the low cost of chlorine and operational problems with early UV disinfection systems limited the growth of UV disinfection as a drinking water treatment technology. The first reliable applications of UV light for disinfecting municipal drinking water occurred in Switzerland and Austria in 1955 ( Kruithof and van der Leer 1990). By 1985, the number of installations in these countries had risen to approximately 500 and 600, respectively. With the discovery of chlorinated disinfection byproducts ( DBPs), UV disinfection became popular in Norway and the Netherlands with the first installations occurring in 1975 and 1980, respectively.

As of 1996, there were over 2000 UV disinfection systems treating drinking water in Europe ( USEPA 1996), primarily treating flows less than 1 million gallons per day ( MGD). A survey conducted in 2000 found that UV disinfection is currently being used to treat larger flows, including two installations treating a combined flow of 76 MGD in Helsinki, Finland ( Toivanen 2000), and that the number of installations is increasing ( USEPA 2000). Several large installations across the United States are currently under design. Because of the susceptibility of Cryptosporidium to UV disinfection and the emphasis in recent regulations on controlling Cryptosporidium, the number of utilities using UV disinfection is expected to increase significantly over the next decade.

2.2 Fundamental Aspects of UV Light The use of UV light to disinfect drinking water involves ( 1) the generation of UV light with the desired germicidal properties and ( 2) the delivery ( or transmission) of that light to pathogens. This section provides a basic description of how UV light is generated and the environmental conditions that affect its delivery to pathogens.

2.2.1 Nature of UV Light UV light is the region of the electromagnetic spectrum that lies between x rays and visible light ( Figure 2.1). The UV spectrum is divided into four regions as shown in Figure 2.1: vacuum UV ( 100 to 200 nm), UV C ( 200 to 280 nm), UV B ( 280 to 315 nm), and UV A ( 315 to 400 nm) ( Meulemans 1986). UV disinfection occurs due to the germicidal action of UV B and UV C with microorganisms. The germicidal action of UV A is small relative to UV B and UV C and therefore needs very long exposure times to be effective as a disinfectant. Light in the vacuum UV range is very effective in disinfecting microorganisms ( Munakata et al. 1991). However, it is impractical for water disinfection applications because it rapidly attenuates over very short distances in water. For the purposes of this manual, the practical germicidal wavelength for UV light ranges between 200 and 300 nm.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 3 June 2003 Figure 2.1 UV Light in the Electromagnetic Spectrum 254 nm 100 nm 400 nm 100 nm 200 nm 300 nm 400 nm 315 nm 280 nm X ray Gamma Rays UV Visible Infrared Vacuum UV UV C UV B UV A Typically, UV light is generated by applying a voltage across a gas mixture, resulting in a discharge of photons. The specific wavelengths of light emitted from photon discharge depend on the elemental composition of the gas and the power level of the lamp ( section A. 1.1). Nearly all UV lamps designed for water treatment use a gas mixture containing mercury vapor. Mercury is an advantageous gas for UV disinfection applications because it emits light in the germicidal wavelength range, as discussed in section 2.3.5. The light output depends on the concentration of mercury atoms, which is directly related to the mercury vapor pressure. Mercury at low vapor pressure ( near vacuum; 0.001 to 0.01 torr, 2 x 10 5 to 2 x 10 3 psi) and moderate temperature ( 40 º C) produces essentially monochromatic UV light at 253.7 nm. At higher vapor pressures ( 100 to 10,000 torr, 2 to 200 psi) and higher operating temperatures ( 600 to 900 º C), the frequency of collisions between mercury atoms increases, producing UV light over a broad spectrum ( polychromatic) with an overall higher intensity. Mercury vapor pressure between 0.01 and 100 torr does not efficiently produce UV light.

2.2.2 Propagation of UV Light As UV light propagates from its source, it interacts with the materials it encounters through absorption, reflection, refraction, and scattering. In disinfection applications, these phenomena result from interactions between the emitted UV light and UV reactor components ( i. e., lamp envelopes, lamp sleeves, and reactor walls) and also the water being treated. When assessing water quality, UV absorbance or UV transmittance is the parameter that incorporates the impact of absorption and scattering. This section briefly describes both the phenomena that influence light propagation and measurement techniques to quantify UV light propagation. More detailed information is provided in sections A. 1.2.1 through A. 1.2.5.

Absorption is the transformation of light to other forms of energy as it passes through a substance. UV absorption of a substance will vary with the wavelength of the light. The components of the reactor and the water passing through the reactor all absorb UV light to varying degrees, depending on their material composition. When UV light is absorbed, it is no longer available to disinfect microorganisms.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 4 June 2003 Unlike absorption, the phenomena of refraction, reflection, and scattering change the direction of UV light, but the UV light is still available to disinfect microorganisms.

Refraction ( Figure 2.2) is the change in the direction of light propagation as it passes from one medium to another. In UV reactors, refraction occurs when light passes from the UV lamp through an air gap, through the lamp sleeve, and through the water. These changes alter the angle that UV light strikes target pathogens.

Figure 2.2 Refraction of Light Incident Light from UV Lamp Air Gap Quartz Sleeve Water Refracted Light  A  Q  W  A >  W >  Q Reflection is the change in direction of light propagation when it is deflected by a surface ( Figure 2.3). Reflection may be classified as specular or diffuse. Specular reflection occurs from smooth polished surfaces and follows the Law of Reflection ( the angle of incidence is equal to the angle of reflection). Diffuse reflection occurs from rough surfaces and scatters light in all directions with little dependence on the incident angle. In UV reactors, reflection will take place at interfaces that do not transmit UV light ( e. g., the reactor wall) and also at UV transmitting interfaces ( e. g., the inside of a lamp sleeve). The type of reflection observed and intensity of light reflected from a surface depends on the material of the surface.

Figure 2.3 Reflection of Light Specular Reflection Reflected Light Incident Light Diffuse Reflection Incident Light  1  1 Reflected Light Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 5 June 2003 Scattering of light is the change in direction of light propagation caused by interaction with a particle ( Figure 2.4). Particles can cause scattering in all directions, including towards the incident light source ( back scattering). Scattering of light caused by particles smaller than the wavelength of the light is called Rayleigh scattering ( section A. 1.2.4). Particles larger than the wavelength of light scatter more light in the forward direction but also cause some backscattering. Rayleigh scattering depends inversely on wavelength to the fourth power ( 1/  4) and thus is more prominent at shorter wavelengths. Scattering by particles larger that the wavelength of the light is relatively independent of wavelength.

Figure 2.4 Scattering of Light Incident Light Target Pathogens Forward Scattered Light 90 ° Scattered Light Back Scattered Light Incident Light Target Pathogens Forward Scattered Light 90 ° Scattered Light Back Scattered Light UV absorbance ( A254) is a commonly used water quality parameter that characterizes the decrease in the amount of incident light as it passes through a water sample over a specified distance or pathlength. Various procedures call for filtering the sample through a 0.45 µ m membrane before measuring the absorbance. If the measurement is made according to a modified version of Standard Method 5910B ( APHA et al. 1998), the water sample is not pH adjusted or filtered. Since most particles in drinking water are strong absorbers of UV light, it is recommended that absorbance measurements be made without filtering the sample. Therefore, the modified measurement accounts for scattering and some absorption from particles in the water sample that may interfere with UV disinfection. Although Standard Methods identifies this measurement as UV absorption, this manual will refer to it as absorbance since the latter term is widely used in the water treatment industry.

The term UV transmittance ( UVT) has also been used extensively in the literature when describing the behavior of UV light. UVT is the percentage of light passing through a water sample over a specified distance and is related to UV absorbance by Equation 2.1:

254 10 100 % A UVT     = Equation 2.1 where UVT = UV transmittance at specified wavelength ( e. g., 254 nm) and pathlength ( e. g., 1 cm) A254 = UV absorbance at specified wavelength, based on 1 cm pathlength ( unitless; UV absorption as measured by Standard Method 5910B)

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 6 June 2003 2.3 Microbial Response to UV Light The mechanism of disinfection by UV light differs considerably from chemical disinfectants such as chlorine and ozone. Chemical disinfectants inactivate microorganisms by destroying or damaging cellular structures, interfering with metabolism, and hindering biosynthesis and growth ( Snowball and Hornsey 1988). UV light inactivates microorganisms by damaging their nucleic acid, thereby preventing the microorganism from replicating. A microorganism that cannot replicate cannot infect a host.

When studying UV disinfection effectiveness, it is important to use microbial assays that measure infectivity, not viability. Until recently, viability assays such as excystation and vital dyes were used to determine inactivation. However, these assays do not evaluate changes in the ability of a microorganism to reproduce and infest a host. The importance of using assays that measure inactivation is highlighted by the history of UV disinfection for Cryptosporidium. It was believed that UV disinfection was not effective for Cryptosporidium inactivation because results of early Cryptosporidium inactivation studies were based on viability assays. The ability of UV light to inactivate Cryptosporidium at low doses was revealed when infectivity was assessed by inoculating mice with UV treated water, which showed greater than 4 log inactivation of Cryptosporidium at doses less than 20 mJ/ cm2 ( Bukhari et al. 1999).

This section discusses the damage that causes microbial inactivation, the ability of microorganisms to repair the damage, methods for determining microbial inactivation, and how wavelength of UV light affects inactivation.

2.3.1 Mechanisms of Microbial Inactivation by UV Light UV light inactivates microorganisms by damaging deoxyribonucleic acid ( DNA) or ribonucleic acid ( RNA), thereby interfering with replication of the microorganism ( section A. 2.2). In normal DNA replication, the double helix strand separates allowing the single strands to serve as a template for reconstructing the opposite strand of nucleotides: adenine bonds to thymine and guanine bonds to cytosine ( Figure 2.5).

Figure 2.5 Structure of DNA and Nucleotide Sequences Within DNA DNA STRUCTURE Sugar Phosphate Backbone DNA SEQUENCE A = Adenine C = Cytosine T = Thymine G = Guanine   A   T   G   C   G   A   T   C     T   A   C   G   C   T   A   G   Hydrogen Bonded Nitrogenous Base Pairs ( A, T, G, C)

Purines Pyrimidines | | | | | | | |

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 7 June 2003 Light that is absorbed by a system can induce a chemical reaction. As shown in Figure 2.6, each of the nucleotides absorbs UV light from 200 to 300 nm ( section A. 2.2). The UV absorption of DNA results from the combination of nucleotides and has a peak near 260 nm and a local minimum near 230 nm. DNA absorbs light in the wavelength range emitted by UV lamps, enabling photobiological effects that lead to nucleic acid damage.

Figure 2.6 UV Absorbance of Nucleotides ( left) and Nucleic Acid ( right) at pH 7 ( adapted from Jagger 1967)

200 260 300 Wavelength ( nm) UV absorbance ( Relative Scale)

Adenine Guanine Thymine Cytosine 220 240 280 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 DNA 200 260 300 Wavelength ( nm) 220 240 280 UV absorbance ( Relative Scale)

Damage to nucleic acid does not prevent the cell from undergoing metabolism and other cell functions. Although the microbial cell is alive after exposure to UV light, it cannot reproduce, and therefore it is incapable of infecting a host. To kill the microbial cell, the UV dose would need to be increased by orders of magnitude as compared to the UV dose needed to prevent replication.

Variations in DNA content cause microorganisms to absorb UV light differently, thereby contributing to the differences in microorganism susceptibility to UV disinfection. There can be significant disparity in the susceptibility of different strains of bacteria and viruses to UV disinfection ( section A. 2.7). Among the pathogens of interest in drinking water, viruses are most resistant to UV disinfection followed by bacteria and Cryptosporidium oocysts and Giardia cysts. Appendix B provides statistical evaluations for dose response data of Giardia cysts, Cryptosporidium oocysts, and viruses, and Chapter 1 contains the regulatory requirements for inactivating these pathogens.

2.3.2 Microbial Repair Because microorganisms that have been exposed to UV light still retain metabolic functions, some are able to repair the damage done by UV light to a limited degree as described in section A. 2.3. In some cases, the microorganism regains infectivity. These microorganisms have evolved enzyme mediated mechanisms for reversing UV damage. Repair of UV lightinduced DNA damage includes photoreactivation and dark repair ( Knudson 1985). In photoreactivation ( or photorepair), enzymes energized by exposure to light between 310 and 490 Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 8 June 2003 nm ( near and in the visible range) repair damaged sections of DNA. Photoreactivation needs the presence of reactivating light. Dark repair is defined as when a repair process does not need reactivating light. The term is somewhat misleading because dark repair can occur in the presence of light, and therefore does not need dark conditions. Excision repair, a form of dark repair, is an enzyme mediated process where the damaged section of DNA is removed and regenerated using the existing complimentary strand of DNA.

Knudson ( 1985) found that bacteria are able to repair in light and dark conditions, suggesting that bacteria may have the enzymes necessary for photorepair and dark repair. Viral DNA lacks the necessary enzymes for repair, but can repair using the enzymes of a host cell ( Rauth 1965). Linden et al. ( 2002a) did not observe photoreactivation or dark repair of Giardia at UV doses typical for UV disinfection applications ( 16 and 40 mJ/ cm2). However, unpublished data from the same study show Giardia reactivation in light and dark conditions at very low UV doses ( 0.5 mJ/ cm2; Linden 2002). Shin et al. ( 2001) reported Cryptosporidium does not regain infectivity after inactivation by UV light. One study has shown that Cryptosporidium contains the capability to undergo some DNA repair ( Oguma et al. 2001). However, even though the DNA is repaired, infectivity is not restored.

Knudson ( 1985) demonstrated that photorepair can be overcome by increasing the damage to the DNA through higher UV doses. However, it is unknown if higher UV doses can reduce dark repair because it is more difficult to study experimentally. Research is continuing to evaluate this phenomenon. At the doses typically used in UV disinfection, microbial repair can be controlled and accounted for as discussed in section 3.1.1.

2.3.3 UV Dose and Dose Distribution UV dose is a measurement of the energy per unit area that is incident on a surface. UV dose is the product of the average intensity acting on a microorganism from all directions and the exposure time. Units commonly used for UV dose are J/ m2, mJ/ cm2, and mWs/ cm2 ( 10 J/ m2 = 1 mJ/ cm2 = 1 mWs/ cm2) with mJ/ cm2 being the most common units in North America and J/ m2 being the most common in Europe.

In a batch system such as a bench scale collimated beam test ( described in Appendix E), the average intensity is determined mathematically. For collimated beam tests using a lowpressure lamp, the UV intensity measured by a radiometer, the UV absorbance of the water, the thickness of the water layer, the distribution of light across the water surface, and the reflection and refraction of light from the water surface all are considered in calculating the average intensity. The UV dose can be determined in a batch system by multiplying the calculated average intensity by the specific exposure time.

When using polychromatic light sources ( e. g., medium pressure lamps), UV dose calculations in batch, bench scale experiments also incorporate the same parameters as a lowpressure lamp collimated beam test. In addition, the intensity at each wavelength in the germicidal range and the germicidal effectiveness at the associated UV wavelengths are also considered because microorganisms absorb different amounts of UV light at different wavelengths. The UV dose response measured with polychromatic lamps will match the UV Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 9 June 2003 dose response of monochromatic lamps when the UV dose delivered by the polychromatic source is properly calculated ( Cabaj et al. 2001; section A. 2.4.1).

Dose delivery in a continuous flow UV reactor is subject to hydrodynamic irregularities and a variable UV intensity distribution and is a function of the UV absorbance of the water, the flowrate through the reactor, the UV output from the lamps, and the hydraulic characteristics within the reactor. As such, it is difficult to calculate directly UV dose within a UV reactor. If the reactor has plug flow with complete mixing perpendicular to that flow, all microorganisms leaving the reactor receive the same dose, and the reactor would be termed an " ideal" reactor. However, these ideal conditions do not generally do not exist in continuous flow UV reactors. As such, microorganisms passing through a UV reactor are exposed to different doses. The difference in UV doses experienced by microorganisms in a flowing reactor is best characterized by a dose distribution.

A dose distribution is the probability distribution of UV doses that microorganisms receive in a flow through UV reactor; typically shown as a histogram ( Figure 2.7). Some microorganisms travel close to the UV lamps and experience a higher dose while others that travel close to the reactor walls may experience a lower dose. Some microorganisms move through the reactor quickly while others travel a more circuitous path. A narrow dose distribution ( Figure 2.7a) indicates more ideal hydrodynamic conditions. A wider distribution ( Figure 2.7b) indicates less efficient reactor performance and results in a greater degree of " overdosing" to ensure that the minimum desired dose is achieved for the microorganisms at the lower end of the dose distribution.

Figure 2.7 Hypothetical Dose Distributions for Two Reactors with Differing Hydraulics 0.1 0.2 0.3 0.4 0.5 0.6 UV Dose ( mJ/ cm2) Occurrence Probability a. Narrow Dose Distribution ( Better Hydraulic Conditions)

0 15 30 45 75 90 0.0 Occurrence Probability b. Wide Dose Distribution ( Worse Hydraulic Conditions)

0.1 0.2 0.3 0.4 0.5 0.6 0.0 UV Dose ( mJ/ cm2) 0 15 30 45 75 90 There are currently no methods to measure directly the dose distribution in a continuous flow UV reactor, but mathematical models can help to characterize dose distribution. Therefore, the UV dose in a UV reactor is estimated as the reduction equivalent dose ( RED). The RED is a calculated dose for a flow through UV reactor that is based on biodosimetry ( i. e., measuring the level of inactivation of a challenge microorganism with a known UV dose response). The RED is set equal to the UV dose in a collimated beam test that achieves the same level of inactivation Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 10 June 2003 of the challenge microorganism as measured for the flow through UV reactor during biodosimetry testing. Methods for collimated beam testing and biodosimetry are in Appendix E section 4.2, respectively.

2.3.4 Microbial Response ( UV Dose Response)

The response of microorganisms to UV light is calculated by determining the concentration of infectious microorganisms before and after exposure to a measured UV dose and applying Equation 2.2.

N N on Inactivati Log 0 10 log = Equation 2.2 Where N0 = Concentration of infectious microorganisms before exposure to UV light N = Concentration of infectious microorganisms after exposure to UV light UV dose response relationships can be expressed as either the proportion of microorganisms inactivated ( log inactivation, results in a dose response curve with a positive slope) or the proportion of microorganisms remaining ( log survival, results in a dose response curve with a negative slope) as a function of UV dose. The proportion of microorganisms remaining and the log inactivation are typically shown on a logarithmic ( base 10) scale, while the UV dose is typically shown on a linear scale. This manual will present microbial response as log inactivation since the terminology is widely accepted in the industry. Therefore, all doseresponse curves presented will have a positive slope.

Although several approaches may be used to measure microbial dose response, the bench scale collimated beam test has evolved as the customary method because it has carefully controlled conditions, allowing for accurate and repeatable determination of UV dose. Accurate determination of UV dose is beneficial for developing meaningful relationships between UV dose and microbial response.

Figure 2.8 presents examples of UV dose response curves. In general, the UV doseresponse of disperse microorganisms follows first order inactivation ( Figure 2.8, E. coli curve; section A. 2.5.1). However, some microorganisms are slower to respond, producing a shoulder at low UV doses followed by near linear inactivation ( Figure 2.8, B. subtilis curve; section A. 2.5.2). UV dose response is generally independent of how the germicidal UV light is produced ( i. e., low pressure or medium pressure UV light), UV absorbance, temperature, and pH.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 11 June 2003 Figure 2.8 Shapes of UV Dose Response Curves ( adapted from Chang et al. 1985)

0 1 2 3 4 5 6 0 20 40 60 80 100 UV Dose ( mJ/ cm2) Log Inactivation E. coli B. subtilis spores Total coliform wastewater Rotavirus UV dose response is affected by particle association and clumping of microorganisms. Solids present in wastewater samples can cause a tailing or flattening of the dose response curve at higher inactivation levels ( Figure 2.8, total coliform curve; section A. 2.5.3) because clumping or particle association shields a fraction of the microorganisms from UV light. In these wastewater experiments, the microorganisms are present in the treated water at very high concentrations so that any particle association with turbidity reflects the impact of upstream treatment processes.

Research by Linden et al. ( 2002b) indicated that the UV dose response of microorganisms added to filtered drinking waters is not altered by variation in turbidity that meets regulatory requirements ( 40 CFR 141.73). For unfiltered waters, Passantino and Malley ( 2001) found that source water turbidity up to 10 NTU does not impact the UV dose response of separately added ( seeded) microorganisms. In these experiments, however, microorganisms were added to waters containing various levels of treated or natural turbidity. Therefore, it was not possible to examine microorganisms associated directly with particles in their natural or treated states. Consequently, these drinking water studies can only suggest the impact of turbidity on dose response as it relates to the impact of UV light scattering by particles, rather than particle association or clumping of microorganisms.

2.3.5 Microbial Spectral Response The action spectrum ( also called UV action) of a microorganism is a measure of inactivation effectiveness as a function of wavelength. Figure 2.9 illustrates the UV action for three microbial species and also the UV absorbance of DNA as a function of wavelength. Because of the similarity between UV action and DNA absorbance, and because DNA absorbance is easier to measure than UV action, the DNA absorbance spectrum of a microorganism is often used as a surrogate for its UV action spectrum. The scale of the y axis Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 12 June 2003 represents the ratio of inactivation effectiveness at a given wavelength to the inactivation effectiveness at 254 nm. For most microorganisms, the UV action peaks at or near 260 nm, has a local minimum near 230 nm, and drops to zero near 300 nm. Although the sensitivity of the organism often increases below 230 nm, the strong absorption of UV light by components in natural water at these wavelengths offsets the increased organism sensitivity in this region. Nevertheless, an operating definition of the effective germicidal range for UV light in water includes wavelengths from 200 to 300 nm.

Figure 2.9 Comparison of Microbial UV Action and DNA UV Absorbance ( adapted from Rauth 1965 and Linden et al. 2001)

0.0 0.5 1.0 1.5 2.0 200 300 Wavelength ( nm) UV Action or DNA Absorbance Relative to 254 nm DNA Cryptosporidium MS2 Herpes simplex virus 220 240 260 280 2.4 UV Reactors The goal in designing UV reactors for drinking water disinfection is to deliver efficiently the necessary dose to inactivate pathogenic microorganisms. An example UV reactor is shown in Figure 2.10. Commercial UV reactors consist of open or closed channel vessels containing UV lamps, lamp sleeves, UV intensity sensors, lamp sleeve wipers, and temperature sensors. UV lamps are housed within the lamp sleeves, which protect and insulate the lamps. Some reactors include automatic cleaning mechanisms to keep the lamp sleeves free of deposits that may form due to contact with the water. UV intensity sensors, flow meters, and in some cases, UVT monitors are used to monitor dose delivery by the reactor. This section briefly describes UV reactor components. A more detailed discussion of these components is provided in section A. 3.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 13 June 2003 Figure 2.10 UV Disinfection System Schematic ( courtesy of Severn Trent Services)

Influent Pipe UV Transmittance Monitor Control Panel UV Lamp Housed in Quartz Sleeve UV Intensity Sensor UV Intensity Sensor Reactor Casing Temperature Sensor Electrical Connection to Lamp Effluent Pipe Quartz Sleeve Wiper Wiper Motor 2.4.1 Reactor Configuration UV reactors are typically classified as either open or closed channel. Water flows under pressure ( i. e., no free surface) in closed channel reactors ( Figure 2.11a). Drinking water UV applications have used only closed reactors to date. Open channel reactors ( Figure 2.11b) are open basins with channels containing racks of UV lamps. Open channel reactors are most commonly used in wastewater applications.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 14 June 2003 Figure 2.11 Example of Closed ( a) and Open ( b) Channel Reactors ( courtesy of Trojan Technologies)

a. Closed Channel Reactor b. Open Channel Reactor Reactors are designed to optimize dose delivery, and the reactor hydrodynamics play an important role in design. Lamp placement, inlet and outlet conditions, and baffles all affect mixing within a reactor. Improvements to the hydraulic behavior of a reactor are often obtained at the expense of headloss. Individual reactor designs employ various methods to optimize dose delivery ( e. g., higher lamp output versus lower lamp output and improved hydrodynamics through increased headloss).

2.4.2 UV Lamps UV light can be produced by the following variety of lamps:

  Low pressure ( LP) mercury vapor lamps   Low pressure high output ( LPHO) mercury vapor lamps   Medium pressure ( MP) mercury vapor lamps   Electrode less mercury vapor lamps   Metal halide lamps   Xenon lamps ( pulsed UV)

  Eximer lamps   UV lasers Full scale drinking water applications generally use LP, LPHO, or MP lamps. As such, the subsequent discussions in this manual are limited to these UV lamp technologies. Table 2.1 Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 15 June 2003 lists characteristics associated with these lamps, and Table 2.2 lists operational advantages and disadvantages of the lamp types.

Table 2.1 Mercury Vapor Lamp Characteristics Parameter Low pressure Low pressure high output Medium pressure Germicidal UV light Monochromatic at 254 nm Monochromatic at 254 nm Polychromatic, including germicidal range ( 200 to 300 nm)

Mercury Vapor Pressure ( torr) Optimal at 0.007 0.76 300   30,000 Operating Temperature ( ° C) Optimal at 40 130   200 600   900 Electrical Input ( W/ cm) 0.5 1.5   10 50   250 Germicidal UV Output ( W/ cm) 0.2 0.5   3.5 5   30 Electrical to Germicidal UV Conversion Efficiency (%) 35   38 30   40 10   20 Arc length ( cm) 10   150 10   150 5   120 Relative Number of Lamps Needed for a Given Dose High Intermediate Low Lifetime ( hrs) 8,000   10,000 8,000   12,000 4,000   8,000 Table 2.2 Mercury Vapor Lamp Comparison Low pressure Medium pressure Comparative Advantages   Higher germicidal efficiency; nearly all output at 254 nm   Smaller power draw per lamp ( less reduction in dose if lamp fails)   Longer lamp life   Higher power output   Fewer lamps for a given application   Smaller reactors   Smaller footprint Comparative Disadvantages   More lamps needed for a given application   Larger footprint   Higher operating temperature can accelerate fouling ( section 2.5.1)   Shorter lamp life   Lower electrical to germicidal UV conversion efficiency The light emitted by LP and LPHO lamps is essentially monochromatic at 253.7 nm ( Figure 2.12a) and is near the maximum of the microbial action spectrum. MP lamps emit at a wide range of wavelengths across the action spectra ( Figure 2.12b). Therefore, LPHO lamps convert power to germicidal light more efficiently. In either lamp type, power not converted to light is primarily lost as heat.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 16 June 2003 Figure 2.12 UV Output of LP ( a) and MP ( b) Mercury Vapor Lamps ( Sharpless and Linden 2001)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 200 250 300 350 400 Wavelength ( nm) Relative Lamp Output Lamp Output Relative to Maximum Output in Range b. Medium Pressure Lamp 0.0 0.2 0.4 0.6 0.8 1.0 1.2 200 250 300 350 400 Wavelength ( nm) Relative Lamp Output Lamp Output Relative to Maximum Output in Range a. Low Pressure Lamp Figure 2.13 shows the output of LP and MP lamps superimposed with the DNA absorption spectrum. In Figure 2.13, the DNA absorbance is plotted relative to the maximum absorbance in the range ( 260 nm). The lamp outputs are also presented on a relative scale. However, in absolute terms, there is a significant difference in the intensity and power of LP and MP lamps ( see Table 2.1 for more information on lamp operating characteristics).

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 17 June 2003 Figure 2.13 UV Lamp Output and its Relation to the UV Absorbance of DNA ( courtesy of Bolton Photosciences, Inc.)

200 250 300 Wavelength ( nm) Lamp Output Relative to Maximum Output in Range DNA Absorbance MP Output

LP Output

DNA Absorbance Relative to Maximum Absorbance in Range 0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 UV lamps may be oriented parallel, perpendicular, or diagonal to flow or ground. Orienting MP lamps horizontally relative to the ground prevents differential heating of the lamps and reduces the potential for lamp breakage. Lamp breakage is discussed further in Appendix N.

UV lamps degrade as they age resulting in a reduction in output ( section A. 3.1.6). MP lamps may have a shift in spectral output as well. Lamp degradation will impact dose delivery over time.

2.4.3 Lamp Power Supply And Ballasts Ballasts supply the UV lamps with the appropriate power to energize and operate the UV lamps. Ballasts use inductance ( coil or transformer), capacitance, and a starting circuit. Power supplies and ballasts are available in many different configurations and are tailored to a unique lamp type and application. UV reactors may use electronic ballasts, magnetic ballasts, or transformers. The various ballast types and their differences are detailed in section A. 3.2.

2.4.4 Lamp Sleeves UV lamps are housed within lamp sleeves to help keep the lamp at optimal operating temperature and to protect the lamp from breaking. Lamp sleeves are tubes of quartz ( or vitreous silica). The sleeve length is sufficient to include the lamp and associated electrical connections. The sleeve diameter is typically 2.5 cm for LP lamps and 5 to 10 cm for MP lamps. The distance between the exterior of the lamp and interior of the lamp sleeve is approximately 1 cm. Sleeve walls are typically 2 to 3 mm thick and absorb some UV light ( Figure 2.14). UV lamps are usually centered radially within lamp sleeves using spacers.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 18 June 2003 Figure 2.14 UV Transmittance of Quartz that is 1 mm Thick at a Zero Degree Incidence Angle ( GE Quartz 2001)

50 60 70 80 90 100 200 220 240 260 280 300 320 340 360 380 400 Wavelength ( nm) UV Transmittance (%)

Lamp sleeves can fracture and foul, and their transmittance will decrease as they age. Fractures can occur from internal stress and external mechanical forces such as wiper jams, water hammer, resonant vibration, and impact by objects. Microscopic fractures may also occur if lamp sleeves are not handled properly when removed for manual cleaning. If the sleeve fractures while in service, water can enter the sleeve, making the lamp vulnerable to breakage as a result of temperature differences between the lamp and the water. Lamp breakage is undesirable due to potential for mercury release. Appendix N discusses the potential effects of lamp breakage and possible response plans.

Fouling on the internal lamp sleeve surface arises from the deposition of material from components within the lamp or sleeve due to temperature and exposure to UV light. The UV reactor manufacturer can control internal lamp sleeve fouling through appropriate material selection. Fouling on external surfaces is caused by the reaction of compounds in the water with the lamp sleeve surface. Compounds that contribute to fouling are discussed in section 2.5.1. External fouling must be removed by cleaning. In addition, exposure of quartz contaminated with metal cations can cause solarization as lamp sleeves age. Both fouling and solarization can decrease the UV transmittance of the sleeve.

2.4.5 Cleaning Systems UV reactor manufacturers have developed different approaches for cleaning lamp sleeves, depending on the application. These approaches include both off line chemical cleaning ( OCC) and on line mechanical cleaning ( OMC) methods.

In OCC systems, the reactor is shut down, drained, and flushed with a cleaning solution. Solutions used to clean lamp sleeves include citric acid, phosphoric acid, or a food grade Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 19 June 2003 proprietary solution provided by the UV reactor manufacturer. The reactor is rinsed and returned to operation after sufficient time to dissolve the substances fouling the sleeves is allowed. LPHO systems typically use OCC systems.

OMC systems are built in UV reactor components that consist of wipers that are driven by either screws attached to electric motors or pneumatic pistons. There are two types of wipers used in OMC systems: mechanical wipers and physical chemical wipers. Mechanical wipers may consist of stainless steel brush collars or Teflon ® rings that move along the lamp sleeve ( Figure 2.15a). Physical chemical wipers have a collar filled with cleaning solution that moves along the lamp sleeve ( Figure 2.15b). The wiper physically removes fouling on the lamp sleeve surface while the cleaning solution within the collar dissolves fouling materials. The use of mechanical and physical chemical wipers does not necessitate that the UV reactor be drained. Therefore, the reactor can remain on line while the lamp sleeves are cleaned. MP systems typically use OMC systems because the higher lamp temperatures can accelerate fouling under certain water qualities.

Figure 2.15 ( a) Mechanical Wiper System ( courtesy of Calgon Carbon Corporation), ( b) Physical Chemical Wiper System ( courtesy of Trojan Technologies)

a b 2.4.6 UV Intensity Sensors UV intensity sensors are photosensitive detectors that measure the UV intensity at a point within the UV reactor ( Figure 2.16). Sensors are used to indicate dose delivery by providing information related to UV intensity at different points in the reactor. The measurement responds to changes in lamp output due to lamp power setting, lamp aging, lamp sleeve aging, and lamp sleeve fouling. Depending on sensor position, UV intensity sensors may also respond to changes in UV absorbance of the water being treated ( section A. 3.8.2). UV intensity sensors are composed of optical components, a photodetector, an amplifier, a housing, and an electrical connector. The optical components may include monitoring windows, light pipes, diffusers, apertures, and filters. Monitoring windows and light pipes are designed to deliver light to the Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 20 June 2003 photodetector. Diffusers and apertures are designed to reduce the amount of UV light reaching the photodetector, thereby reducing sensor degradation that is caused by UV energy. Optical filters are used to modify the spectral response such that the sensor only responds to germicidal wavelengths ( i. e., 200 to 300 nm). At the time of publication, sensors are specific to each manufacturer and are subject to validation as described in sections <IP_ADDRESS> and C. 4.7.

Figure 2.16 UV Intensity Sensor Viewing Lamps within a UV Reactor ( courtesy of Severn Trent Services)

UV intensity sensors can be classified as wet or dry. Dry sensors monitor UV light through a monitoring window, whereas wet UV intensity sensors are in direct contact with the water flowing through the reactor. Monitoring windows and the wetted ends of wet sensors can foul over time and need cleaning similar to lamp sleeves.

2.4.7 UV Transmittance Monitors As stated previously, UVT is an important parameter in determining the efficiency of UV disinfection. Therefore, monitoring UV transmittance ( or UV absorbance to calculate UVT) is critical to ensure the success of a UV disinfection application. UVT can be determined either through grab samples with a laboratory instrument or on line. Several commercial UV reactors use the measurement of UVT to help monitor and control the calculated UV dose in the reactor.

In general, commercial on line UVT monitors calculate UVT by measuring the UV intensity at various distances from a lamp. One such monitor is schematically displayed in Figure 2.17. In this monitor, a stream of water passes through a cavity containing a LP lamp with three UV intensity sensors located at various distances from the lamp. The difference in sensor readings is used to calculate UVT.

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 21 June 2003 Figure 2.17 UV Transmittance Monitor Design ( courtesy of Severn Trent Services)

UV Lamp UV Intensity Sensor Inlet Outlet A B C UV Lamp UV Intensity Sensor Inlet Outlet A B C UV Lamp UV Intensity Sensor Inlet Outlet A B C 2.4.8 Temperature Sensors Energy input per unit volume is relatively high for a UV reactor. The water flowing through a reactor efficiently absorbs the wasted heat and maintains operating temperatures within a desirable range. Nevertheless, temperatures can become elevated under the following circumstances:

  Water level in the reactor drops and lamps are exposed to air.

  Water stops flowing in the reactor.

UV reactors are equipped with temperature sensors that monitor the water temperature within the reactor. If the temperature is above the recommended operating temperature range, the reactor will shut off to minimize the potential for the lamps overheating.

2.4.9 Monitoring UV Disinfection Performance The performance of an operating UV disinfection system must be monitored to demonstrate that adequate disinfection is being achieved ( 40 CFR 141, Subpart W, Appendix D). Because the concentration of pathogenic organisms cannot be measured continuously in the UVtreated water and the dose distribution cannot be measured directly in real time, various strategies have been developed to monitor dose delivery. Any dose monitoring method must be evaluated during reactor validation ( as described in section <IP_ADDRESS>), and the outputs measured during validation will be part of the monitoring requirements described in section 5.4.1 ( 40 CFR 141.729( d)).

Proposal Draft 2. Overview of UV Disinfection UV Disinfection Guidance Manual 2 22 June 2003 Currently, there are three fundamental approaches to monitor UV disinfection performance in a UV reactor:

1. UV Intensity Setpoint Approach. In this approach, measurements made by the UV intensity sensor are used to control the UV reactor. The UV intensity sensor is located in a position that allows it to properly respond to both changes in UV intensity output of the lamps and also UVT of the water. The UV intensity sensor output and the flowrate are used to monitor dose delivery. The setpoint value for UV intensity over a range of flowrates is determined during validation.