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Approval Guidelines Ag 03 | Water Purification | Drinking Water

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Office of Drinking Water Approval Guideline ODW-AG-03 Filtration and Disinfection Log Reduction Credits PURPOSE To continue to ensure public health protection related to drinking water, Manitoba introduced regulations for the approval, design and operation of drinking water systems. These regulations, created under The Drinking Water Safety Act, are Manitoba Regulation 40/2007 Drinking Water Safety Regulation and Manitoba Regulation 41/2007 Drinking Water Quality Standards Regulation. They can
    Office of Drinking Water     Approval Guideline ODW-AG-03   Filtration and Disinfection Log Reduction Credits PURPOSE To continue to ensure public health protection related to drinking water, Manitoba introduced regulations for the approval, design and operation of drinking water systems. These regulations,created under  The Drinking Water Safety Act  , are Manitoba Regulation 40/2007 Drinking Water Safety Regulation and Manitoba Regulation 41/2007 Drinking Water Quality StandardsRegulation. They can be viewed at:www.manitoba.ca/drinkingwater .   The regulations set out requirements for public water systems including:    A permit for the construction or alteration of a water system    An operating licence for operation of a water system    A periodic assessment of a water system’s infrastructure and water source    Water quality and treatment standards This information bulletin provides guidance to water treatment system operators and consultantson procedures for determining filtration credits and CT calculations for public water systems. INTRODUCTION The treatment process for a public water system in Manitoba treating surface water or groundwater under the direct influence of surface water (GUDI) must be capable of 3-log(99.9%) reduction or inactivation of  Cryptosporidium and  Giardia , and 4-log (99.99%) reductionor inactivation of viruses that may be present in the source water. In keeping with a multi-barrier approach to drinking water treatment, the Office of Drinking Water recommends that at least 0.5-log inactivation of  Cryptosporidium and  Giardia , and 2-log inactivation of viruses be attributed to disinfection processes. Microbial standards are met using filtration (physical removal) and disinfection (inactivation). Removal and inactivation capabilities vary depending on the filtrationtechnology or disinfectant applied. Organizations such as Health Canada and the U.S.Environmental Protection Agency (EPA) have recommended procedures to determine logremoval and log inactivation credits for filtration and disinfection processes. 30 June 2010 ODW-AG-03 Page 1 of 4  30 June 2010 ODW-AG-03 Page 2 of 4 PATHOGEN INACTIVATION CREDITS (DISINFECTION CT CALCULATIONS) The effectiveness of most disinfectants including chlorine depends on the concentration of thedisinfectant (C), water temperature, pH and the amount of effective contact time (T) between thewater and the disinfectant. Manitoba’s Chlorine and Alternative Disinfectants Guidance Manual  includes an explanation of the CT (Concentration  Time) concept and tables for determining loginactivation credits for different disinfectants. The guidance manual is available on the Office of Drinking Water website at:http://www.gov.mb.ca/waterstewardship/odw/reg-info/approvals/odw_chlorine_and_alternative_disinfectants.pdf  In completing CT calculations, the following operating or design conditions must be applied todetermine the effective contact time provided at a water treatment plant:    Peak hourly flow based on raw water pump capacity or water meter records (highest pumpage hour), or estimated based on assumed water use and peaking factors (ex: HarmonPeaking Factor; Ontario Design Guidelines for Drinking-Water Systems 2008, Section 3.4)    Minimum normal operating level of the storage reservoir, clearwell or tank     Baffling factor to reduce the effective storage volume to account for potential short-circuiting    Minimum disinfectant residual (ex: typically 0.5 mg/L for free chlorine)    Minimum temperature of the water undergoing disinfection    Maximum pH of the water undergoing disinfectionBaffling factors can be determined by conducting a tracer test on an existing storage system or can be estimated using a computational fluid dynamics (CFD) computer model, otherwise, the baffling factors in Table 1 should be applied based on the water storage system configuration: Table 1. Baffling Factors for Water Storage Systems Storage System Configuration Baffling Factor (T 10 /T) Hydropneumatic tank with single inlet-outlet No contact time can beclaimedSingle, unbaffled retention tank or multiple tanks in parallel   0.1Single cell reservoir, unbaffled, inlet and outlet at opposite ends 0.2 Two storage tanks in series   0.2 Two cell reservoir, inlet and outlet in same cell 0.2 Two cell reservoir, inlet and outlet at opposite ends of separate cells 0.3 Three or more storage tanks in series 0.3-0.4Baffled tank or reservoir cell   0.3-0.6Piping 1.0 UV disinfection systems are typically tested and validated by the supplier to achieve specific loginactivation levels if operated within its validated flow and water quality (ex: UV transmittance)conditions. Additional information on validation of UV disinfection systems and log inactivationcredits can be found in the US EPA Ultraviolet Disinfection Guidance Manual:http://www.epa.gov/safewater/disinfection/lt2/pdfs/guide_lt2_uvguidance.pdf .  PATHOGEN REMOVAL CREDITS (FILTRATION) Log removal credits for filtration systems are assigned based on accepted credits determined through the ongoing use, testing and validation of various technologies. Manitoba has adopted the filtration credits included in the technical document for the Turbidity guideline issued byHealth Canada for the Guidelines for Canadian Drinking Water Quality . Filtration credits are provided in Table 2 based on filtration technology. In order to qualify for the maximum credit,the filtration system and water treatment plant must meet the following criteria:    Filter design in general conformance with the Recommended Standards of Water Works (TenState Standards)    For particulate filters, effective filter cleaning systems involving air scour and backwashing,and filter-to-waste capabilities    For particulate filters, application of pre-treatment chemicals at all times and procedures toadjust dosages in response to raw water quality conditions    For biological (slow sand) filters, maintenance of an active biological layer at all times, filter cleaning procedures and filter-to-waste capabilities    Online turbidimeters for monitoring the effluent from each operating filter that are tied into adata management system and an alarm system    Compliance with provincial turbidity standards Table 2. Log Removal Credits for Filtration Technologies Filtration Technology Log Removal Credit Cryptosporidium Log Removal Credit Giardia  Log Removal CreditViruses Conventional treatment coagulation, flocculation,clarification, filtration 3.0 3.0 2.0Direct filtration coagulation, filtration 2.5 2.5 1.0Slow sand filtration 3.0 3.0 2.0Cartridge filtration (1µmabsolute stage, certifiedto NSF Standard 53) small systems only up to 2.0 up to 2.0 0Membrane filtration 3.0+Where demonstratedthrough challengetesting and verified bydirect integrity testing3.0+Where demonstratedthrough challengetesting and verified bydirect integrity testingMF or UF: 0; 1.0 if coagulation upstreamNF or RO: demonstratedthrough challenge testingand verified by directintegrity testingNo filtration 0.0 0.0 0.0 An application can be made for alternative credits based on evidence from the supplier or documentation of credits assigned by other drinking water agencies. Such evidence must be provided for membrane filtration as the pathogen removal capabilities of these systems vary.Pressure filters are not accepted as the primary filtration barrier for the treatment of surface water or groundwater under the direct influence of surface water (GUDI), and are not eligible for logremoval credits. 30 June 2010 ODW-AG-03 Page 3 of 4  30 June 2010 ODW-AG-03 Page 4 of 4 CONTACT INFORMATION For questions on filtration credits or CT calculations, or approval requirements contact:Approvals Unit1007 Century StreetWinnipeg, MB R3H 0W4Ph: 204-945-5936 or 204-945-5949Fax: 204-945-1365Email:Kim.Barlishen@gov.mb.caor Jim.Stibbard@gov.mb.ca  For general questions on regulatory standards, monitoring or operating licence requirements,contact the regional Drinking Water Officer. Contact information is available on the Office of  Drinking Water website at:http://www.gov.mb.ca/waterstewardship/odw/reg-contacts/index.html  
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