UV Water Treatment
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UV Water Treatment
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UV Water Treatment
Solids / Turbidity reduce UV light
Transmission thus reducing the effectiveness
of the treatment it is therefore common to
install filters upstream from the UV system
to remove fine silt/rust present in the water.
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Ultraviolet systems (UV)
– Disrupts bacteria/pathogen “life cycle”
Advantages
•
Automatic
•
Low contact time
•
Low cost to operate
•
Compact and easy to maintain
•
No taste or odor
Disadvantages
•
Not effective in turbid water (cloudy)
•
Blub housing can become coated, less light penetration
•
Bulbs wear out
•
No way to test effectiveness (i.e., can’t test for residual
chlorine levels)
•
No Residual property
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UV Systems
Not just fit and forget they should be monitored
• New UV systems should measure UV intensity, Bulb
operational hours and should have an alarm to indicate
bulb failure. Bulbs should be changed once intensity
figures have dropped out of spec or after running a set
number of hours.
• The Quartz glass housings will require regular cleaning.
Newer models are fitted with rubber wipe blades.
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How Does UV Disinfect ?
UV light penetrates and permanently alters the DNA of the
microorganisms in a process called
thymine dimerization.
The microorganisms are “inactivated” and rendered unable to reproduce
or infect.
Analogy: a broken zipper.
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Certain wavelength of UV light more effective than others
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Certain wavelength of UV light more effective than others
LP, LPHO lamp Output Spectrum
Approximately 90% of UV output is at 254nm and 5-7% is at 185nm
254nm wavelength is well suited to microbial disinfection
Low Pressure Lamp UV Output
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Medium Pressure Lamp UV Output
Medium Pressure Lamp UV Output
Broad spectrum of UV
output (<200 to >600
nm) is characterized as
polychromatic
Though less efficient,
medium pressure
lamps emit
significantly more UV
energy - allowing very
compact treatment
systems capable of
treating large flows
Medium Pressure Lamp UV Output
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UV light will also remove Free Chlorine !
A strong enough UV lamp emitting the right wavelengths will remove free chlorine
Between the wavelengths 180 and 400 nm, UV light produces photochemical reactions that
dissociate free chlorine to form hydrochloric acid.
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Effects of Iron on UV Transmittance
UV are affected by various
compounds that are able to
absorb UV, including iron,
tannins.
Fine particles will also reduce
UV effectiveness through light
scatter.
Iron and hardness are often a
factor in sleeve fouling
UV Dose Influencing Factors
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Sleeve Fouling
The deposition of minerals on the sleeve protecting the UV lamp
LAMP
Quartz Sleeve
Scale Coating
Reduces the intensity of light getting into the water
Iron and hardness are often a factor in sleeve fouling
Pretreatment and/or an appropriate cleaning schedule allow for the use of
UV where iron and hardness are factors
Effect of Hardness and Iron on UV Dose
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UV Dose Influencing Factors
UV Transmittance (UVT)
UVT is a measure of how well the water is able to transmit UV light
(water clarity). It affects the intensity of light reaching pathogens.
Less UV light
getting through
the water
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Ultraviolet systems (UV)
Major
Disadvantage
• UV light does not provide residual protection because
bacterium will persist in biofilms where UV light cannot
penetrate. Thus, UV light is unsuitable as the only
control measure for an entire water system;
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Ultraviolet systems a requirement for Norwegian
sector
• Giardia Lamblia outbreak in Bergen 2004-05
• Caused by presence of Giardia cysts in drinking water supply
• Around 2500 people were treated for Giardiasis during the
outbreak. Contamination though to come from Lake
Svartediket
which supplied water to 60,000 of Bergen’s
250,000 population at that time.
• Chlorine only partially effective against Giardia cysts cold
water reduces chlorine disinfection speed.
• Bergen water supply not protected by UV systems.
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Ultraviolet systems (UV)
Mini UV filters sometimes used at point of use
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