Integrated UV Disinfection Strategies

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Integrated UV Disinfection Strategies

• November 24, 2005
• Kananaskis Researcher Retreat

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Overall Goal

• Improve the process of drinking water
  disinfection through optimization of UV and
  multiple disinfectant strategies

• Key Participants

• 16 HQPs Graduate students, Post-Docs, Research
  assistants

University of Toronto
Dalhousie University
University of Waterloo
University of Ottawa
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Key Challenges/Goals

• Investigate impact of combined UV/chemical
  disinfection on biofilms
• Investigate AOP disinfectant by-product formation
  and potential genotoxicity of UV/AOP and
  chemically treated water
• Develop optimized integrated multiple barrier
  disinfection strategy that minimizes DBPs
• Examine UV for mitigation of taste and odour
  compounds
• Examine impact of particles on effectiveness of
  UV and UV/chemical disinfection

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Relevant State-of-The-Research

• UV rapidly gaining popularity impact on other
  treatment processes not well known
• Combined use of UV and chemical disinfectants has
  good potential to reduce pathogens, DBPs and
  taste odour
• Opportunity for integrated disinfection approach
  to enhance public health and reduce
  capital/operating costs

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Approach

• Annular reactors used to model both bulk water
  and biofilm in distribution systems (various
  materials)
• Pilot and bench-scale examination of effect of
  UV/AOP on DBP formation
• Literature review bench scale experiments to
  develop integrated disinfection strategies for
  various water types

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Stage of Research

• Integrated Disinfection Project started September
  2004
• CWN project to be completed September 2006
• CWN project has led to several major research
  initiatives (AwwaRF, etc.) being created/allied

Key Concepts/Observations

• Investigation of the impact of combined
  UV/chemical disinfection on biofilms
• Annular reactors used to simulate distribution
  systems

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Laboratory Set-up

• HRT 6.0 hours
• Rotational Speed 50 rpm
• Shear Stress 0.25 N/m2
• Pipe Velocity 0.30 m/s (100-mm dia)

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Key Concepts/Observations

• Investigation of impact of combined UV/chemical
  disinfection on biofilms
• Annular reactors used to simulate distribution
  systems
• Consistently observed that disinfection improved
  when chemical disinfection follows UV
• Based on lab and field data (Florida, Nova
  Scotia, California)
• Attempting to discern selective versus
  synergistic disinfection

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E. coli Spiking
Post-UV
GAC/ BAC Water
Pre-UV

GAC/ BAC Water
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Key Concepts/Observations

• Potential genotoxicity of UV/AOP and chemically
  treated water
• Goal to create a database of potential
  genotoxicity produced by various treatment
  scenarios, for several water types
• Development of optimized integrated multiple
  barrier disinfection strategy
• Use existing data and DBP models to develop a
  holistic strategy that provides redundancy,
  minimizes disinfectant use and DBP formation
  (ie. UV
  and minimal chlorination)

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Key Concepts/Observations

• UV/H2O2 Advanced Oxidation Characterization of
  DBP formation, TO
• Hypothesis UV/AOP may alter DBP precursors.
• Preliminary pilot-scale results observed
  increase in THM HAA formation, decrease in TO

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Insights on Knowledge Transfer

• Impact of UV on the distribution system should be
  considered in addition to disinfection credit at
  the plant
• 0.2 mg/L chlorine residual may be more realistic
  for systems applying UV
• May need to develop new distribution system rules

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Opportunities

• Ottawa and Dalhousie have identified potential
  limitations of coliform detection
• Chlorine may interfere with commercial kits
• Significant long-term challenge for industry that
  may need to be addressed

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Collaborative Interests

• Confirm work with annular reactors at full scale
• Halifax Regional Water Commission
• Gagnon, Andrews, Hofmann
• Developing disinfection plan, as part of
  long-term pilot assessment
• key question will be defining synergies between
  UV and chloramines
• Numerous other collaborative projects initiated
  through CWN project