DISINFECTION Stuff

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DISINFECTION Stuff

• Silver Falls
• 8 April 2008

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Some Presentation Topics(not necessarily in
order or complete)

• Residual Maint. vs. Disinfection CT
• O3-
• Chlorination calculations Questions?
• (Tracer Study Discussion, if desired)

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Purpose of Disinfection

• Inactivation of Pathogens
• Bacteria Coliforms, Campylobacter
• Viruses Norwalk, Hepatitis A/B
• Parasitic protozoa Giardia, Cryptosporidium
• Regulatory Requirements
• Residual Maintenance vs. Disinfection
• Why does your system use disinfectant?

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Waterborne Disease Outbreak Causes
From August 2006 Access AWWA
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Surface Water Treatment3-log (99.9) Giardia
Reduction

• Log Removal
• 2-log (99)
• 2.5-log (99.7)

• Log Inactivation
• 1-log (90)
• 0.5-log (68.4)

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Slight, but Significant, Distinctions in
Definitions

• Chlorination General term Add chlorine to
  system for any reason. (e.g. Fe Mn)
• Residual Maintenance Assure detectable amount
  of disinfectant (i.e. chlorine) is in your entire
  distribution at all times.
• Disinfection Add disinfectant and provide
  enough contact time to inactivate pathogens.

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Disinfection Contact Time v. Residual Maintenance

• Whats the Difference??
• Generally speaking, we require
• Disinfection with Contact Time for contaminated
  Sources.
• Residual Maintenance for Distribution.

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Chlorine Residual

• Measure record free chlorine residual daily
• Must be detectable everywhere at all times.
• High levels of iron, manganese, or turbidity will
  increase chlorine demand.
• Use DPD-type test kit (colorimeter/digital)

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Why Is Residual Maintenance NOT Disinfection?
Cl
Cl
0.2 ppm Cl residual throughout distribution system
Cl
Cl
Cl
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Why Isnt Residual Maintenance Disinfection?
Disinfection requires Contact Time
Contamination Point
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Disinfection CT Values

• Definition
• CT values are a measurement of the effectiveness
  of chlorine disinfection against bacteria,
  viruses, and protozoa.
• Concentration Time CT
• E.g. 1 ppm 6 min 6

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Groundwater CTs

• Some Groundwater WSs need CTs
• Usually initiated by sourcewater TCs.
• Groundwater Rule may increase incidence.
• CT of 6 requires 30 minutes contact time
• Do you need a Tracer Study???
• What is the pipe tank configuration?
• Alternative estimate 10 of tank volume.

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Common Disinfectants(In order of prevalence)

• CHLORINE
• Ultraviolet Light (UV)
• Ozone (O3)
• Mixed Oxidants (MIOX)
• Chloramines (Cl2 plus ammonia)

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Ozone (O3)

• Disinfection and taste/odor control
• Produced by electricity and air or pure O2
• Inactivates Cryptosporidium
• Must be generated on-site
• Leaves minimal disinfectant residual
• Costs 4 times more than conventional
  disinfection, yet cheapest LT2 option

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Onsite O3 Generation
Liquid O2
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O3 Monitor and Towers
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Ozone Towers
O2
Plasma
Cooling Water
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O3 Monitor using UV
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O3 Monitoring
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O3 O2 Ambient Safety Monitors
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Close up of O3 Monitor
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Demo SS Injection w/ Nozzles
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Questions?
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TRACER STUDIES

• What are they and why?
• Who needs to do them?
• How are they done?

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What are Tracer Studies?

• Tracer studies are tests that are done to
  determine the actual disinfection contact time
  available.

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Who Needs To Study Tracers?

• All surface water systems.
• Perhaps some groundwater systems.
• If no tracer study available, contact time is
  estimated by DWP staff.

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Basic Procedure

• Record background level of tracer (usually
  chlorine).
• Inject more.
• Record time at which 10 increase over background
  level is reached. (T10)

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Conducting Test

• Set maximum flow rate.
• Measure initial chlorine residual.
• Establish monitoring location at first user.
• Add more chlorine.
• Record T10.

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Graph Results

• Graph shows actual (or effective) disinfection
  contact time available.
• The hydraulics specifically the detention time
  determined in tracer study is used for CT
  calculations.

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Perform Test at Your Peak Hourly Flowrate
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Perform Test at Your Peak Hourly Flowrate
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How to Improve Contact Time

• Slow the flow. I.e. produce less water.
• Move point of chlorine application.
• Add additional piping (plug flow).

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Improving Contact Time (continued)

• Increase contact time in reservoirs
• Walls
• Curtains
• Flow diverters
• Separate inlet /outlet

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Disinfection CT Values

• Definition
• CT values are a measurement of the effectiveness
  of chlorine disinfection against bacteria,
  viruses, and protozoa.
• Concentration Time CT
• E.g. 1 ppm 6 min 6

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CT Calculation

• CT Cl2 residual multiplied by contact
  time
• CT mg/L X minutes
• a number (no units expressed)
• Example 0.2 mg/L times 30 minutes
• CT 6

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The Magic Number 6for Groundwater

• CT required 6
• 30 minutes 0.2 ppm Cl
• or
• 6 minutes 1 ppm Cl
• Assumptions Water Temperature 10oC (50oF)

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Required CT ValuesGW vs. SW

• Groundwater
• Minimum CT 6
• Adequate for 4-log virus inactivation
• Surface Water
• Required CT varies with pH, temp, and
  log-inactivation requirement
• Based on Giardia inactivation 67 or 90.

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Disinfection Contact Time(not to be confused
with CT Calculation)

• Determined by Tracer Study or interim estimate
• Time effective volume of contact chamber/flow
• Time minutes gal / gal/min
• Pipe flow is ideal
• I.e., 100 credit for pipe volume
• Storage tanks likely have short-circuiting

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How Do You Really Measure Contact Time? T
Vgal/Qgal/min

• Determine peak hourly demand flowrate
• Does system have an effluent flowmeter?
• Look at the configuration of system.
• Make estimate based on tank configuration
  length of pipe
• Assume 10 of tank volume if unknown.
• Calculate contact time using effective tank
  volume and effluent flowrate.

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Chlorination Concerns

• Disinfection by-products (DBPs)
• THMs and HAA5s
• DBP production encouraged by
• High chlorine levels
• Long contact time
• Warm weather
• High source water TOC