drinking water chlorination - splash · 2017-07-20 · the chlorine revolution: water disinfection...
TRANSCRIPT
Drinking Water Chlorination
First Nations Infrastructure Conference
February 5, 2014 Marion Axmith Canadian Chlorine Chemistry Council (C4) Mary Ostrowski American Chemistry Council (ACC)
• Over 100 years ago, chlorine was first used to reduce waterborne disease outbreaks in the U.S.
• A bold step at the time due to aversion to chemicals or ‘chemophobia’
• “Chlorine” is derived from the Greek word “chloros” meaning green
Chemophobia
“Chemophobia, the fear of chemicals, was prevalent at the
turn of the 20th century & continues to be an issue”
“Chemophobia almost derailed the use of chemical disinfectants then & it often dominates discussion of
drinking water safety today”
Michael J. McGuire
The Chlorine Revolution: Water Disinfection and the Fight to Save Lives
Protecting
Public Health • Dr. Leal, physician - breaking sewer pipe-water pipe “death spiral”
• “Death spiral” – wastewater disposed of in same body of water used for drinking water perpetuated waterborne disease
Improving Water Quality • Jersey City Legal challenge
over water quality
• Dr. Leal & George Warren Fuller constructed the first water chlorination system
Illness & Death
Rates Plummeted
• Leal & Fuller presented results at 1909 American Water Works Association meeting
• Jersey City death rates from typhoid fever fell from 20 per 100,000 in 1905 to single digits by 1920
Drinking Water Chlorination
“For more than a century, the safety of Canadian drinking water supplies has been greatly improved by the addition of chlorine.”
Health Canada
It’s Your Health: Drinking Water Chlorination, 2006
Drinking Water Chlorination
is One of the Most
Significant Public Health Improvements
in History
(Data from U.S. Centers for Disease Control &
Prevention, Summary of Notifiable Diseases, 1997)
Chlorine-Based Drinking Water Disinfectants Elemental chlorine
(Cl2 gas)
Sodium hypochlorite (NaOCl liquid solution)
Calcium hypochlorite (Ca(OCl)2 solid)
On-site generation of sodium hypochlorite (NaOCl liquid solution)
Water Treatment
Steps
(Image from U.S. Environmental
Protection Agency website)
Q: Why Treat Drinking Water?
A: The
Invisible Threats!
Salmonella typhi
Vibrio cholerae
E. coli
The Concept of
“Free Chlorine”
Elemental chlorine and the hypochlorites form “free chlorine” in water
Hypochlorous acid (HOCl) and hypochlorite ion (OCl-)
pH determines which form dominates
Hypochlorous acid best penetrates pathogens
Chlorine Provides
Long-Lasting Protection
Against Waterborne
Germs
Chlorine residual helps prevent microbial re-growth in the
distribution system
Chlorination Does More
Than Destroy Waterborne
Germs
Potent germicide
Destroys most bacteria, viruses and parasites
Taste and odor control
Oxidizes disagreeable algae secretions, sulfides and reduces odors from decaying organic matter
Biological growth control
Eliminates slime bacteria, molds and algae that grow in reservoirs, water mains and storage tanks
Chlorination Does More
Than Destroy Waterborne
Germs
Chemical control
Removes hydrogen sulfide, ammonia, iron and manganese from raw water
Suitable for a wide range of water quality
Easily monitored and controlled
Cost-effective
Disinfection By-Products
or “DBPs”
• Chlorine reacts with natural organic matter
• DBPs are associated with most disinfectants
• Chlorinated DBPs are the most well-studied
• Reduced by removing natural organic matter before chlorination
Comparing Chlorine-Based
Disinfection Methods
Elemental Chlorine Lowest cost of chlorine forms
Unlimited shelf-life
Hazardous gas
Requires special handling and operator training
Transported and stored as a liquefied gas under pressure
Facilities use 100 or 150 lb cylinders or one-ton containers
Large systems use railroad tank cars or tanker trucks
Sodium Hypochlorite
(bleach) o Higher chemical cost than elemental chlorine
o Limited shelf-life
o Less hazardous than elemental chlorine
o Easier to handle but more difficult to store
o Fewer training requirements and regulations
o Higher shipment volume than elemental chlorine
Calcium Hypochlorite o Higher cost than elemental chlorine
o Long shelf-life
o Dry chemical
o Fire or explosive hazard if handled improperly
o More stable than sodium hypochlorite
o Precipitated solids formed in solution could complicate chemical feeding
o Fewer training requirements and regulations than elemental chlorine
o Typically used in small facilities
Chlorine-Based Drinking Water Disinfectants
Chloramine (NH2Cl, liquid) Chlorine Dioxide (ClO2 gas, generated onsite)
Chloramines Formed by combining chlorine and ammonia in specific ratios
Requires shipping/handling ammonia and chlorinating compounds
Weak primary disinfectant; well-suited as a secondary disinfectant
Reduced formation of DBPs
Very stable residual
Good control of coliform bacteria and biofilm growth
Lower taste and odor than free chlorine
Must be removed for kidney dialysis
Must be removed for aquarium water
Chlorine Dioxide Dissolved gas generated onsite from mixing
sodium chlorite and elemental chlorine in solution
High operating cost
Strong disinfectant
Effective against Cryptosporidium and Giardia
Does not form chlorinated DBPs
Very volatile residual
Treats some taste and odor problems
Requires on-site generation equipment
Requires high-level technical competence
From Hubbs, S., “Disinfec4on Source Water Quality Drives Treatment Selec4on,” Opflow, April 2013.
Comparing Disinfectants: Including Energy Efficiency and Greenhouse Gas Emissions
Chlorine: A Public Health Chemistry for
100 Years and Running…
Most water systems use some type of chlorine-based process
No “one size fits all”
Every water system is unique
Industry is committed to safe, sustainable use of chlorine-based disinfectants
We Welcome Your Inquiries!
Marion Axmith ⎜416.456.4619
Canadian Chlorine Chemistry Council www.cfour.org
Mary Ostrowski ⎜202.249.6705
American Chemistry Council www.americanchemistry.com/chlorine
The Chlorine Institute ⎜703.894.4140 www.cl2.org