approval guidelines ag 03

7/27/2019 Approval Guidelines Ag 03

1/4

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 introducedregulations for the approval, design and operation of drinking water systems. These regulations,

created underThe 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 systems infrastructure and water source

Water quality and treatment standards

This information bulletin provides guidance to water treatment system operators and consultants

on 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 orgroundwater under the direct influence of surface water (GUDI) must be capable of 3-log

(99.9%) reduction or inactivation ofCryptosporidium andGiardia, and 4-log (99.99%) reduction

or 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 ofCryptosporidium andGiardia, 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 filtration

technology or disinfectant applied. Organizations such as Health Canada and the U.S.Environmental Protection Agency (EPA) have recommended procedures to determine log

removal and log inactivation credits for filtration and disinfection processes.

30 June 2010 ODW-AG-03 Page 1 of 4
http://www.manitoba.ca/drinkingwaterhttp://www.manitoba.ca/drinkingwater


2/4


PATHOGEN INACTIVATION CREDITS (DISINFECTION CT CALCULATIONS)

The effectiveness of most disinfectants including chlorine depends on the concentration of the

disinfectant (C), water temperature, pH and the amount of effective contact time (T) between thewater and the disinfectant. Manitobas Chlorine and Alternative Disinfectants Guidance Manual

includes an explanation of the CT (Concentration Time) concept and tables for determining log

inactivation credits for different disinfectants. The guidance manual is available on the Office ofDrinking 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 to

determine the effective contact time provided at a water treatment plant:

Peak hourly flow based on raw water pump capacity or water meter records (highestpumpage hour), or estimated based on assumed water use and peaking factors (ex: Harmon

Peaking 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 disinfection

Baffling 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(T10/T)

Hydropneumatic tank with single inlet-outlet No contact time can beclaimed

Single, 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 0.2Two cell reservoir, inlet and outlet in same cell 0.2Two cell reservoir, inlet and outlet at opposite ends of separate cells 0.3Three 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 log

inactivation 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.
http://www.gov.mb.ca/waterstewardship/odw/reg-info/approvals/odw_chlorine_and_alternative_disinfectants.pdfhttp://www.gov.mb.ca/waterstewardship/odw/reg-info/approvals/odw_chlorine_and_alternative_disinfectants.pdfhttp://www.gov.mb.ca/waterstewardship/odw/reg-info/approvals/odw_chlorine_and_alternative_disinfectants.pdfhttp://www.epa.gov/safewater/disinfection/lt2/pdfs/guide_lt2_uvguidance.pdfhttp://www.epa.gov/safewater/disinfection/lt2/pdfs/guide_lt2_uvguidance.pdfhttp://www.gov.mb.ca/waterstewardship/odw/reg-info/approvals/odw_chlorine_and_alternative_disinfectants.pdfhttp://www.gov.mb.ca/waterstewardship/odw/reg-info/approvals/odw_chlorine_and_alternative_disinfectants.pdf


3/4

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 by

Health Canada for the Guidelines for Canadian Drinking Water Quality. Filtration credits areprovided 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, filtercleaning 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 CreditCryptosporidium

Log Removal CreditGiardia

Log Removal CreditViruses

Conventional treatmentcoagulation, flocculation,clarification, filtration

3.0 3.0 2.0

Direct filtrationcoagulation, filtration

2.5 2.5 1.0

Slow sand filtration 3.0 3.0 2.0Cartridge filtration (1mabsolute stage, certifiedto NSF Standard 53)small systems only

up to 2.0 up to 2.0 0

Membrane filtration 3.0+Where demonstrated

through challengetesting and verified bydirect integrity testing

3.0+Where demonstrated

through challengetesting and verified bydirect integrity testing

MF or UF: 0; 1.0 ifcoagulation upstream

NF or RO: demonstratedthrough challenge testing

and verified by directintegrity testing

No 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 log

removal credits.



4/4


CONTACT INFORMATION

For questions on filtration credits or CT calculations, or approval requirements contact:

Approvals Unit

1007 Century Street

Winnipeg, MB R3H 0W4Ph: 204-945-5936 or 204-945-5949

Fax: 204-945-1365Email: [email protected] [email protected]

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
mailto:[email protected]:[email protected]://www.gov.mb.ca/waterstewardship/odw/reg-contacts/index.htmlhttp://www.gov.mb.ca/waterstewardship/odw/reg-contacts/index.htmlmailto:[email protected]:[email protected]

approval guidelines ag 03

Documents