Development of a utility-based strategy for achieving microbiologically safe drinking water

Transcription

1 National Conference on Drinking Water Canadian Water & Wastewater Association Health Canada October 29 th, 2014 Development of a utility-based strategy for achieving microbiologically safe drinking water Ian Douglas, P.Eng. City of Ottawa Drinking Water Services University of Toronto Dept. of Civil Engineering

2 Acknowledgements Will Robertson ( retired microbiologist)

3 Water Treatment Process City of Ottawa Britannia & Lemieux Island WPPs 11 billion? = # of Giardia cyst s t hat ent er t he p lant each year Anthracite Raw water Coagulation & Flocculation Sedimentation Sand Dual-media Filtration CT Disinfection (Clearwell) ph Adjustment & Chemical Mixing How m any leave t he plant?

4 the challenge To supply safe drinking water for the promotion and protection of public health microbial hazards are invisible to our measurement tools pathogens are transient & difficult to detect operators rely on indirect measurements (eg. turbidity, chlorine) relationship between operating data & pathogen risk is fuzzy how do we know if we re achieving our goal?

5 Normalized PDF Probability Distribution for annual health risk (DALYs) risk level (Health Canada) E-15 1.E-14 1.E-13 1.E-12 1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 Cryptosporidium Giardia Rotavirus Campylobacter E. Coli O157

6 How can we effectively control pathogens to achieve safe drinking water?

7 How to control microbial risks in a drinking water supply? Operations Engineering & design Management & Regulatory

8 10 Elements: Drinking Water Safety Plan (World Health Organization, 2011)

9 12 Elements: Australian Framework for Management of Drinking Water Quality (Australian Drinking Water Guidelines, 2011)

10 21 Elements: Ontario DWQMS (Drinking Water Quality Management System)

11 Microbiological guidelines Health Canada GCDWQ (Total coliforms, E.coli, Protozoa, Enteric viruses, Emerging pathogens, Boil Water Advisories, etc.)

12 ? Which ones do we really need in our tool-kit?

13 Development of a utility-based strategy for City of Ottawa: Idea: short (1-2 yrs), medium (2-4 yrs), & long-term (5-10 yrs) action items based on risk management concepts largely in place for Canadian utilities borrow selected elements from existing management systems include other critical pieces from operational experience written for a surface water, source-to-tap system use of clear language for operators, engineers, & managers

14 Development of a utility-based strategy for City of Ottawa: Idea: short (1-2 yrs), medium (2-4 yrs), & long-term (5-10 yrs) action items [17] [9] [4] based on risk management concepts largely in place for Canadian utilities borrow selected elements from existing management systems include other critical pieces from operational experience written for a surface water, source-to-tap system use of clear language for operators, engineers, & managers

15 Short term actions (1-2 years) 1) minimum level of treatment - ensure barriers are in operation at all times 2) primary disinfection targets: ensure CT-disinfection levels met at all times 3) process control measures: chemical feed, redundancy, analyzers, trends, alarms 4) coagulation dosage map : dosing strategy for all raw water conditions 5) operator core technical skills & knowledge: jar testing procedure to determine optimum dose pump draw-down & manual dosage calc s analyzer, bench-scale, & lab measurements QA/QC measures to verify accuracy of readings calculate level of CT disinfection being achieved dosage & residual targets to achieve CT in all seasons

16 Short term actions (1-2 years) 6) source water characterization physical (turbidity/ph/uv254) seasonal variation & patterns 7) filter optimization turbidity <0.1 NTU, backwash strategy, ripen-to-waste, sub-fluidization 8) bulk chemical quality method to verify identity & purity of delivered chemicals 9) critical control limits develop CCLs for treatment process 10) response to treatment failures develop & practice response procedures (eg. purge) 11) public health trigger levels criteria, communications, critical customers, etc.

17 Short term actions (1-2 years) 12) bacti testing for high risk areas verify water quality in potential problem areas 13) distribution field practices review to minimize impact on microbial water quality 14) inspection of hatches & vents annual check for animal intrusion (tanks & reservoirs) 15) emergency valve isolation identify major valves to isolate portions of distribution system 16) flushing plans for areas with high risk of depressurization (eg. closed zones) 17) continuous pressure monitoring focus on closed pressure zones, high elevations

18 Medium term measures (2-4 years) 1) operator competency testing comprehensive training, site-specific, test, skills test 2) source water pathogens pathogen concentrations, weather, correlations, etc. 3) physical log-removal evaluate actual performance of treatment plant 4) CT disinfection tracer studies to verify contact time, mixing 5) QMRA analysis assess microbial risk during normal & upset conditions 6) process optimization optimize for particle & organic removal 7) public health surveillance tools develop sensitive indicators of community health 8) distribution system hot spots widespread survey of water quality in problem areas 9) cross-connection control program risk based, evaluate reverse flow reports

19 Long term measures (5-10 years) 1) source water protection and control implement source water protection initiatives 2) research & optimization universities, research partners, process analysis, workshops, conferences 3) network of water utilities share operating experiences, emergency help, watershed basis 4) peer review 5yr formal review of operating strategy; utility peers / academics / consultants

20 Review cycle annual review by Water Quality or Quality Management representative report on progress / gaps / resources needed staff & senior management recommend joint review with Public Health staff review microbial risk events & identify corrective actions

21 A few examples: City of Ottawa Public health list of criteria for drinking water advisories (microbial=11, chemical=9) raw water characterization pathogen removal studies QMRA analysis Operator training (4 days annually; days for 4 staff) QA/QC measures coagulation dose map draw-down & manual dosage calc s for chemical feed every 2 weeks research & optimization

22 Self-assessment: how is City of Ottawa doing? Short term actions City of Ottawa Medium term actions City of Ottawa minimum level of treatment operator competency testing primary disinfection targets source water pathogen levels process control measures evaluate physical log removal coagulation dosage map CT disinfection tracer operator core skills QMRA analysis source water characterization process optimization filter optimization <0.1 NTU public health surveillance tools bulk chemical quality distribution water quality hot spots critical control limits cross-connection control program response to treatment failures public health trigger levels bacti testing in high risk areas Long term actions City of Ottawa distribution field procedures source water protection & control inspect tank hatches/vents research & optimization emergency valve isolation network of water utilities flushing plans peer review pressure monitoring

23 How many of these actions are covered by DWQMS & O.Reg.170/03? Short term actions minimum level of treatment primary disinfection targets process control measures coagulation dosage map operator core skills source water characterization filter optimization <0.1 NTU bulk chemical quality critical control limits Medium term actions operator competency testing source water pathogen levels evaluate physical log removal CT disinfection tracer QMRA analysis process optimization public health surveillance tools distribution water quality hot spots cross-connection control program response to treatment failures public health trigger levels bacti testing in high risk areas distribution field procedures inspect tank hatches/vents emergency valve isolation flushing plans pressure monitoring Long term actions source water protection & control research & optimization network of water utilities peer review

24 Water Treatment Process City of Ottawa Britannia & Lemieux Island WPPs 11 billion? = est im at ed # of Giardia t hat ent er t he p lant each year Anthracite Raw water Coagulation & Flocculation Sedimentation Sand Dual-media Filtration CT Disinfection (Clearwell) ph Adjustment & Chemical Mixing How m any leave t he plant? 7.5-log r educt ion = 348

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26 The pursuit of safe drinking water continues to be a noble, challenging, and important task one that directly contributes to our quality of life.

27 Thank you & Questions