UV Water Treatment Technology
Ultraviolet light (UV) includes the wavelengths between visible light and X-rays in the electromagnetic spectrum. UV can
be divided into the four regions: Vacuum UV (VUV), Short Wave UV (UV-C), Middle Wave UV (UV-B), and Long Wave UV
(UV-A).
UV Lamp types
UV lamps are typically tubular with an outer casing, or “envelope” which is made from quartz. Inside the quartz envelope,
electrodes emit electrons which cause an inert gas to ionize. A plasma is created and the inert gas becomes heated.
This causes mercury atoms to vaporize and collide with the high-energy plasma electrons. The mercury atoms then
fluctuate between many excited states and a ground state. During this fluctuation the mercury atoms release energy in
the form of UV light.
The most commonly used UV lamps for water purification are Low Pressure (LP) and Medium Pressure (MP). MP lamps
produce more UV energy across a broader range of wavelengths, however they require significantly more energy to
operate. Low Pressure UV lamps are considered monochromatic with approximately 82% of the ultraviolet light emitted at
253.7 nm and approximately 7% emitted at 184.9 nm. These peak wavelengths are often referred to as 254 nm and 185
nm respectively.
In general, low pressure lamps require less energy to create a given level of UV output and therefore are more efficient
than medium pressure lamps. In addition, LP lamps last longer, generate much less heat, and are less expensive to own
and operate than MP lamps.
Medium pressure lamps, with broad spectrum UV and greater UV intensity, are often used for large volume applications
(> 300 gpm), such as municipal water treatment systems where heat is less of an issue.
Disinfecting Drinking Water
UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is more commonly used in
wastewater treatment applications but is finding increased usage in drinking water treatment. It used to be thought that
UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger
pathogens which have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light.
However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism
Cryptosporidium. The findings resulted in two US patents and the use of UV radiation as a viable method to treat drinking
water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than
excystation.
UV for Ozone Creation
Ultraviolet light can be used to create ozone in air, which may be desirable for air purification applications. The creation of
ozone requires the use of a lamp which is designed to allow 185 nm to transmit through the lamp envelope. 185 nm lamps
will simultaneously create and destroy ozone. However, the ozone creation occurs at a faster rate and the net result is a
propagation of ozone in air. UV lamps are also used for creation of ozone in water, but at very low rates of production.
UV for Ozone Destruction
Germicidal ultraviolet light destroys Ozone in water very quickly. Therefore, the 254 nm wavelength produced by low-
pressure germicidal UV lamps is quite effective for ozone removal from water. The mechanism for removing ozone is
dissociation, which occurs when 254 nm UV energy “breaks” one of the oxygen bonds in an ozone molecule. As a result
of this reaction, each ozone molecule is converted into one oxygen atom and one oxygen molecule. Free oxygen atoms
will combine with each other to form oxygen molecules.
Although ozone is readily destroyed by UV, it requires more UV energy than inactivation of microorganisms (approx 90
mJ/cm² versus 30 mJ/cm²). Therefore, in order to ensure effective ozone destruction, UV systems are often sized using a
“flow-rate adjustment” of 40% the flow-rate of a disinfection system. For example, a system designed for 100 gpm
disinfection flow-rate would be required to achieve 40 gpm for ozone destruction.
Ultraviolet light (UV) includes the wavelengths between visible light and X-rays in the electromagnetic spectrum. UV can
be divided into the four regions: Vacuum UV (VUV), Short Wave UV (UV-C), Middle Wave UV (UV-B), and Long Wave UV
(UV-A).
UV Lamp types
UV lamps are typically tubular with an outer casing, or “envelope” which is made from quartz. Inside the quartz envelope,
electrodes emit electrons which cause an inert gas to ionize. A plasma is created and the inert gas becomes heated.
This causes mercury atoms to vaporize and collide with the high-energy plasma electrons. The mercury atoms then
fluctuate between many excited states and a ground state. During this fluctuation the mercury atoms release energy in
the form of UV light.
The most commonly used UV lamps for water purification are Low Pressure (LP) and Medium Pressure (MP). MP lamps
produce more UV energy across a broader range of wavelengths, however they require significantly more energy to
operate. Low Pressure UV lamps are considered monochromatic with approximately 82% of the ultraviolet light emitted at
253.7 nm and approximately 7% emitted at 184.9 nm. These peak wavelengths are often referred to as 254 nm and 185
nm respectively.
In general, low pressure lamps require less energy to create a given level of UV output and therefore are more efficient
than medium pressure lamps. In addition, LP lamps last longer, generate much less heat, and are less expensive to own
and operate than MP lamps.
Medium pressure lamps, with broad spectrum UV and greater UV intensity, are often used for large volume applications
(> 300 gpm), such as municipal water treatment systems where heat is less of an issue.
Disinfecting Drinking Water
UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is more commonly used in
wastewater treatment applications but is finding increased usage in drinking water treatment. It used to be thought that
UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger
pathogens which have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light.
However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism
Cryptosporidium. The findings resulted in two US patents and the use of UV radiation as a viable method to treat drinking
water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than
excystation.
UV for Ozone Creation
Ultraviolet light can be used to create ozone in air, which may be desirable for air purification applications. The creation of
ozone requires the use of a lamp which is designed to allow 185 nm to transmit through the lamp envelope. 185 nm lamps
will simultaneously create and destroy ozone. However, the ozone creation occurs at a faster rate and the net result is a
propagation of ozone in air. UV lamps are also used for creation of ozone in water, but at very low rates of production.
UV for Ozone Destruction
Germicidal ultraviolet light destroys Ozone in water very quickly. Therefore, the 254 nm wavelength produced by low-
pressure germicidal UV lamps is quite effective for ozone removal from water. The mechanism for removing ozone is
dissociation, which occurs when 254 nm UV energy “breaks” one of the oxygen bonds in an ozone molecule. As a result
of this reaction, each ozone molecule is converted into one oxygen atom and one oxygen molecule. Free oxygen atoms
will combine with each other to form oxygen molecules.
Although ozone is readily destroyed by UV, it requires more UV energy than inactivation of microorganisms (approx 90
mJ/cm² versus 30 mJ/cm²). Therefore, in order to ensure effective ozone destruction, UV systems are often sized using a
“flow-rate adjustment” of 40% the flow-rate of a disinfection system. For example, a system designed for 100 gpm
disinfection flow-rate would be required to achieve 40 gpm for ozone destruction.
Spartan Environmental Technologies
Air and Water Treatment
Air and Water Treatment
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Spartan Environmental
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com