Ultraviolet (UV) Technology
UV Disinfection Overview
The UV light disinfection process does not use chemicals.
Microorganisms, including bacteria, viruses, and algae, are inactivated within seconds of UV light disinfection, but all are not equally sensitive.
Generally, viruses and algae are more resistant to disinfection by UV light.
UV light is effective in inactivating Cryptosporidium, while at the same time decreasing chlorinated disinfection by-products.
UV disinfection is used in air and water purification, sewage treatment, protection of food and beverages, and many other disinfection and sterilization processes.
One major advantage of UV light disinfection is that it is capable of disinfecting water faster than chlorine, and without the need for retention tanks.
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Green Innovation & Practices
Today, after many years of research, we recognize that the most effective alternative air & water disinfection process available is ultraviolet light (UV). UV disinfection mimics the sun's natural behavior: that is, ultraviolet energy destroys the ability of dangerous microorganisms to multiply, rendering them harmless to humans and the environment.
Ultraviolet light is a natural component of the electromagnetic spectrum. It falls to the left of visible light with higher energy levels and wavelengths between 100 and 400 nm. One of the most effective wavelengths and the one most often used for disinfection is at 254 nm.
Physical instead of chemical disinfection
UV disinfection is a purely physical process. Micro-organisms such as bacteria, mould, viruses, yeasts, etc. that are exposed to the effective UVC radiation are inactivated within seconds.
The advantages of UV disinfection are ...
- no chemicals added
- no environmental problems
- the water retains its natural flavour and smell
- no by-products that might endanger health
- no corrosion problems
- no reaction tanks or secondary pumps
- micro-organisms inactivated within seconds
- a technology tried and tested in thousands of installations
- the process requires little maintenance and is easy to handle
- minimum operating costs
- maximum operating safety
- modular system for adaptability
UV Light Science
Ultraviolet rays have shorter wavelengths than visible light. A wavelength, the distance between the crests of two waves, is often measured in units called nanometers. A nanometer (nm) is a billionth of a meter, or about 1/25,000,000 inch. Wavelengths of visible light range from about 400 to 700 nm. Ultraviolet wavelengths range from about 1 to 400 nm and are beyond the range of visible light.
Ultraviolet rays with wavelengths shorter than 300 nm are extremely effective in killing microorganisms. The most effective sterilizing range for UV is within the C bandwidth (UVC). This range is called the germicidal bandwidth. UVC has been used in hospitals for decades to sterilize surgical instruments, water, and the air in operating rooms. Many food and drug companies use germicidal lamps to disinfect various types of products and their containers.
The cleansing mechanism of UV is a photochemical process. The contaminants that pollute the indoor environment are almost entirely based upon organic or carbon-based compounds. These compounds breakdown when exposed to high intensity UV at 240 to 280 nm. Short-wave ultraviolet light can destroy DNA in living microorganisms and breakdown organic material found in indoor air. UVC’s effectiveness is directly related to intensity and exposure time.
UV rays must strike the contaminants directly in order to penetrate the microorganism and breakdown its molecular bonds. This bond breakage translates into cellular or genetic damage with the germs rendered harmless by robbing them of the ability to reproduce.
Indoor Air Quality and Health
According to the Environmental Protection Agency (EPA), 10% of all colds are caught outdoors, 90% are caught indoors! We’ve all watched helplessly as a cold virus passed from one member of the family to another.
Perhaps you suffer from asthma or allergies and despite desperate attempts to dust more, keep the windows closed, clean your bedding, clothing, carpeting and furniture more frequently, your symptoms still persist.
The EPA states that indoor air can be up to 70 times more polluted than the outdoor environment. One reason for this is that the HVAC duct work is full of airborne germs, their particles and by products. These microbes are alive and thriving inside the furnace or air conditioning systems. The airborne germs adversely affect the air quality as they are blown past the furnace or air conditioning filter and circulated throughout the buildings.
In-duct and upper air UV air cleaners can be utilized to disinfect the indoor air.
UV Health Facts
Why is UV-B harmful while UV-C (germicidal UV) is not? - The difference has to do with the ability of UV rays to penetrate body surfaces. UVC has an extremely low penetrating ability. It is nearly completely absorbed by the outer, dead layer of the skin (stratum corneum) where it does little harm. It does reach the most superficial layer of the eye where overexposure can cause irritation, but it does not penetrate to the top of the lens of the eye and can not cause cataracts. UVC is completely stopped by the ordinary eye glasses and by ordinary clothing.
How much UV exposure is considered safe? The National Institute for Occupational Safety and Health (NIOSH) has established safe exposure levels for each type of UV. These safe exposure limits are set below the levels found to cause eye irritation, eye being the body part most sensitive to UV. For germicidal UV (253.7nm) the exposure limit is less than 0.2µW/cm² over 8 hours.
How can people be certain they are not overexposed to UV? When upper room UV is first installed it must be checked with a sensitive UV meter to make sure reflected UV is less than 0.2µW/cm² at eye level. UV air cleaners must be installed well above eye level - usually 7 feet above the floor. UV tubes (lamps) within the air cleaners should not be directly visible from within 30 feet. Safety is assured if UV measurements at eye level meet NIOSH standards.
What are the symptoms and signs of UV overexposure? UV overexposure causes an eye inflammatory condition known as photokeratitis. For 6 to 12 hours after an accidental overexposure the individual may feel nothing unusual, followed by the abrupt sensation of foreign body or "sand" in the eyes, redness of the skin around the eyes, some light sensitivity, tearing, and eye pain. The acute symptoms last 6 to 24 hours and resolve completely without long-term effects. Overexposure of the skin resembles sunburn but does not result in tanning.
What precautions are needed with overhead germicidal UV? Fixtures must be turned OFF when cleaning, inspecting or changing the lamps. Persons hypersensitive to sunlight may need to wear protective glasses, clothing or use sunscreen on exposed skin. No special protection is needed for most people.
Indoor Air Pollution
Most people take the quality of indoor air for granted and assume the air is clean and safe to breathe. According to the American Medical Association 50% of all illness is caused or aggravated by polluted indoor air.
The air in today's buildings can contain different microbial contaminants such as bacteria, viruses, mold, fungi and spores. Bioaerosols are the airborne microbes, their fragments, toxins and waste products. Numerous studies have found high concentrations of such contaminants in the air handling equipment and in the air inside the places where people live and work. These indoor air pollutants can make the air quality less than desirable, may even cause unhealthy effects ranging from allergies to tuberculosis, and are actually the cause of death to an estimated 8.5 million people annually.
According to the EPA "Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands. Examples include: paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings..."
The UVC radiation itself can not destroy VOC but UVC is used as a part of a process called Photocatalytic Oxidation which can reduce or virtually eliminate VOC from the indoor air. In the Photocatalytic Oxidation process VOC are trapped by a photocatalyst - most often titanium dioxide (TiO2) - which is activated by UVC radiation. The harmful VOC are oxidized and turned into water and carbon dioxide.
Some studies state that properly designed and installed UV air cleaners will eradicate or greatly reduce the microbial contaminants from the indoor air. This is why the indoor air quality in public buildings has been addressed by specific requirements of UV installation inside the HVAC systems.
When the problem of residential indoor air quality became apparent, ultraviolet technology became the proven answer to effectively controlling airborne microbial pollutants. The artificially generated UV can reduce or virtually eliminate all DNA based air pollutants that regular filtering systems do not catch.
How UV Light Kills Germs
Germicidal ultraviolet (UVC) light kills cells by damaging their DNA. The light initiates a reaction between two molecules of thymine, one of the bases that make up DNA. UV light at this wavelength (shortwave UV or UVC) causes adjacent thymine molecules on DNA to dimerize. The resulting thymine dimer is very stable. If enough of these defects accumulate on a microorganism's DNA its replication is inhibited, thereby rendering it harmless.
Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent bases bond with each other, instead of across the "ladder". This makes a bulge, and the distorted DNA molecule does not function properly.
The longer the exposure to UVC light, the more thymine dimers are formed in the DNA. If cellular processes are disrupted because of DNA damage, the cell cannot carry out its normal functions. If the damage is extensive and widespread, the cell will die.
The LIGHT SPECTRUM ranges from the infrared at wavelengths longer than visible light to the ultraviolet at wavelengths shorter than visible light. Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region.
UV Dosages
Please note that many variables take place in a real world environment that make actual calculating of the UV dosage very difficult (air flow, humidity, distance of microorganism to the UV light and time). However, it is proven that UV light will kill any DNA-based organism given enough UV dosage and that UV light breaks down DNA on a cumulative basis. Therefore, as air circulates through the ductwork of an HVAC system containing an UV light, the UV light continuously cleanses the air. If a microorganism is not effectively eradicated on the first pass through the ductwork, the UV light will continue to break its DNA down on subsequent passes. In addition, microorganisms typically do not sit in a static environment in HVAC systems except on coils which can be exposed to our lights also. In fact, microorganisms breed microorganisms if not controlled. The UV light helps to reduce incidences of inhaled pathogens for persons who reside or work in indoor environments.
UV Light References
The following is a list of readily available reference materials discussing the ultraviolet light and its ability to sterilize. It is not intended to be a complete list of references.
Available in the Public Library:
Britannica
Volume 12, page 118
Ultraviolet radiation…because of its bactericidal capabilities at wavelengths of 260 – 280 nm, UV is useful as both a research tool and a sterilizing technique.
Encyclopedia Americana
Deluxe Library Edition 1993
Volume 27, page 353d
A very important attribute of UV rays…is their ability to kill bacteria. For this reason UV lamps are used in hospital operating theaters, children’s nurseries, and in several manufacturing processes where sterile air is necessary.
McGraw Hill Encyclopedia of Science & Technology
Volume 19, pages 20, 21, 22
Discussion of Ultraviolet radiation, with charts showing UV’s ability to sterilize.
The World Book Encyclopedia
1997 Edition
Volume 20, page 17
Uses of ultraviolet rays
Ultraviolet rays with wavelengths shorter than 300 nm are effective in killing bacteria and viruses. Hospitals use germicidal lamps that produce these short rays to sterilize surgical instruments, water, and the air in operating rooms. Many food and drug companies use germicidal lamps to disinfect various types of products and their containers.
Physicians once used sun lamps that produce these rays to treat rickets…the lamps are used today to treat some skin disorders such as acne and psoriasis.
UV Lamps - Artificial UV Production
There are many types of lamps that artificially produce UV. There are UV lamps for tanning, for counterfeit money detection, blacklight stage lamps and lamps for mineral displays, lamps that produce Ozone and germicidal UV lamps. The focus of this document are the germicidal UV lamps, which emit shortwave UV light in the ultraviolet section of the specter also known as UVC or germicidal UV. There is more information on the nature of UV in the UV Science Facts section. Here we will discuss the artificial UV production by the different UV lamps and the specs of the different types of UV lamps. Many times people refer to the UV lamps as UV bulbs as in regular light bulb. Even though bulb is not the correct term, replacement bulb, UV bulb or bulbs are widely accepted in the industry as a reference to the UV lamps.
UV Lamps – History and Development
UV is artificially produced by mercury vapor low and medium pressure lamps. The low pressure lamps are most effective, because they emit most of the radiant energy in the germicidal wavelength of 253.7nm also known as the UVC part of the specter. This is the reason low pressure lamps are mostly used in germicidal UV applications. These lamps are sometimes called “amalgam” lamps because they contain solid amalgam “spots” (an amalgam is an alloy of mercury with another element, such as indium or gallium) that controls the mercury vapor pressure.
All lamps have secondary emissions, including small amounts of UVA, UVB, visible light (above 400nm wavelength) and heat. The blue glow of the germicidal UV lamps is not indicative to the effective germicidal output they produce – that could be only determined with a properly calibrated UV sensor and monitor.
As with all gas discharge lamps, the UV output of germicidal lamps is reduced when the temperature of the lamp surface deviates from the optimum. The performance data of the various lamp types and the influences of air or water cooling play an important part in an effective and reliable UV disinfection. If this is neglected it may lead to an inadequate UV installation.
For effective UV disinfection not only the temperature but the transparency of the medium for UVC (253.7nm wavelength) is of great importance. The greater the energy lost through absorption, the less energy remains to kill microbes. Tests have shown that there is a reduction in the UV lamps disinfecting performance if there is a high humidity level. For the effectiveness of UV water purification systems transmittance of the water is very important.
It is important to take the reducing factors under consideration when sizing the UV lamps for an effective UV disinfecting process.
In air stream UV irradiation reflective materials with high UVC reflection properties should be used as these materials will multiply the UV efficiency of the germicidal lamps.
Development of UV disinfection lamps started in the early forties when Westinghouse began the development of the Cold Cathode lamps in an economical production. After that UVC lamps were tried out for disinfection everywhere – surfaces, goods, water and air. The early extensive testing still applies today as a basic knowledge, underlining the UV technology.
Types UV Lamps
Cold Cathode Germicidal UV Lamps
The Cold Cathode Germicidal UV Lamps are instant-start lamps with a cylindrical cold cathode type of electrode. These lamps are available in different sizes and may be operated either from single lamp transformers or in series trough the medium of high voltage transformers.
The combination of Vycor glass tubing, used in most Cold Cathode lamps, and sturdy electrode construction make lamp life considerably longer than other types of lamps. Good ultraviolet maintenance is provided at lower temperatures and lamp life is unaffected by frequent starts.
Although the amount of radiant energy at 253.7nm wavelength emitted is the same for both high and low ozone lamps, the high ozone lamps use a special Vycor glass which transmits a controlled amount of radiation at 184.9nm, which wavelength produces ozone. Ozone has deodorizing properties and is in itself a bactericidal and fungicidal agent. However tests have shown that the Ozone has a negative health effect if used indoors so the use of Ozone producing lamps is not recommended for most applications.
The Vycor glass Cold Cathode ultraviolet germicidal lamp is the most economical type for the majority of general germicidal applications, because of its long life electrode and good glass maintenance.
Hot Cathode Germicidal UV Lamps
The Hot Cathode Germicidal UV Lamps are similar in their operation to the standard fluorescent lamps. The Hot Cathode lamp operates from a ballast or transformer and requires a device such as the glow switch starter to preheat the electrodes in order to start the lamp. The electrodes, located at the ends of the lamp, are tungsten filaments coated with emission material and, under normal operation, govern the life of the lamp. In view of the fact that the life of the electrodes is shortened by frequent starts, the lamp life is rated according to the number of times the lamp is started. Operation at refrigerator temperatures may result in excessive lamp blackening and rapid depreciation in ultraviolet output. Starting of the Hot Cathode lamps at low temperature is sometimes unreliable and may require special equipment.
Slimline Germicidal Ultraviolet Lamps
The Slimline Germicidal Ultraviolet Lamp is an instant-start lamp, similar to the Slimline fluorescent lamp. The Slimline lamps are available in low, high and very high ozone types. The lamp life is governed by the electrode life and number of starts.
Because of their high initial ultraviolet emission and good maintenance, Slimline Germicidal ultraviolet lamps are well adapted for applications such as indirect air irradiation, conveyor lines, surface sterilization and other applications which require high intensity lamps.
High Output Germicidal UV Lamps
The most recent addition to the UV lamp line of products is the type of High Output germicidal UV lamps. The HO lamps are the consequent result of constantly applied know-how and the latest lamp manufacturing processes. High UV output over a great temperature spectrum, a long life and good behavioral patterns are the pointers for the High Output UV lamps. Only high quality raw materials are used in the lamp production. A fine tuning with the automatic electronic ballasts guarantees the lowest tolerance and a maximum UV stability.
With life duration of 12,000 hours and almost linear performance degradation the high output UV lamps are setting the standards for the development of high performance UV technology.
The most important factor in using germicidal UV lamp technology is the knowledge about their behavior under real working conditions (e.g. the effect of air stream cooling). It is definitely not just the lamp performance under laboratory conditions that count. Only in gaining this knowledge high quality disinfecting technology can be achieved.
Taking the example of air stream cooling the High Output lamps do show their real advantage. While classic UV lamps heavily depreciate under real working conditions inside an air duct, this is not the case with the High Output UV lamps.
Light Emitting Diodes (LED) UV Lamps
Recently a completely new technology for UV production started to emerge. This is the UV Light Emitting Diodes or UV LED lamps. The UV LEDs are the next generation UV producing devises that will compete with the established UV lamps. Some researchers claim that the UV LEDs have better characteristics surpassing the regular UV lamps. However at this time there is no UV LED equipment that can compete with the high output UV lamps in real world production conditions.
Lamp Shapes and Lamp Connectors
There are many lamp shapes: cylindrical lamps - like a glass tube, circular tube, multi-coiled tube lamps, U-shaped lamps, double tubes or by-axial lamps. The UV LED lamps are much smaller than the regular lamps and can be installed in spaces that do not permit installation of regular lamps.
All lamps are powered by ballasts that provide the starting electrical voltage to ionize the gas in the UV lamp and then limiting the current to the nominal level. Lamp ballasts can be either magnetic or electronic. The LED UV lamps do not require ballasts for their operation.
The lamps have different types of connectors at one or both ceramic ends. The connectors can be single-pin, double-pin or four-pin. The single and double pin connectors are located on both ends of the lamps, while the four-pin connectors are single connectors at one end of the lamp.
UV Lamps Aging
The decrease in UV lamp output over the typical lifespan of 8,000 - 12,000 hours can vary between 15-40%. The manufacturer should be consulted for information on the end-of-life output of UV lamps. The decrease in UV output should be accounted for in the design phase such that the lamp output does not decrease to a point where the air treatment system becomes ineffective. The most conservative approach is to size the system based on the end-of-life of the lamp UV output. Selecting lamps based on end-of-life UV output will avoid the lamps aging problem.
The lamps should be kept clean and free of dust at all times. If dust accumulates on the lamp it will absorb the UV and convert it to heat, therefore lowering the effectiveness of the UV lamp. Appropriate filtration of the air prior to the UV lamps is recommended.
UV Water Purification
Canadian Air & Water offers UV water disinfection systems for a variety of water purification applications. Water is being used for practically everything therefore ultraviolet water purification can be applied to a vast number of diverse applications. Water treatment professionals have used ultraviolet water disinfection for over 60 years and the technology is steadily advancing.
UV offers a very economical and environmentally friendly water disinfection solutions for the following applications:
Swimming pools
Installation of UV water purifiers reduces the use of chlorine as primary disinfectant for swimming pools and ensures hygienically pure water, free of chemical residue and by-products. UV for swimming pools »
Drinking water
UV water purification can reduce, and in some cases replace, chlorine as primary drinking water disinfectant. Water sterilized with UV meets microbiological requirements according to drinking water regulations. UV water purification applications range from municipal to domestic water supplies and Vending machines water. UV is also used for preventing bacterial growth in water collection systems applicable in domestic rainwater collection systems. UV for drinking water purification »
Process / ultra-pure water
Process water for medical, pharmaceutical industries and electronics and semiconductors - process water disinfection and TOC (Total Organic Carbon) reduction is a quality control measure for ultrapure water applications in cosmetic, pharmaceutical and electronics industries and hospitals requiring exacting pure water standards for clinical applications and pharmaceutical manufacturing. UV for ultrapure water »
Warm water systems
UV water purification systems are also used for sterilizing water in air-conditioning systems and preventing infection due to microorganisms in air humidifying systems. UV is used for control of Legionella with applications in hospitals, office buildings and large residential buildings.
UV for warm water »
Fish Farming and Aquaculture
Aquariums, Zoos, Aquaculture and Fish farms, Ornamental Ponds and Koi Ponds to control algae - Fish Farming/Aquaculture industry, to protect fish larvae from disease in hatcheries, to disinfect incoming water to the site and effluent from the farms. UV for fish farms, ponds and aquariums »
Beverage & Bottled Water
Ultraviolet equipment provides an economical means of water disinfection for beverage and bottled water manufacturing facilities. Beverage UV systems »
Municipal wastewater
UV is installed for disinfecting biologically treated wastewater in final effluent channels before discharge to the environment. The UV treatment of wastewater for re-use ensures that treated water meets the USEPA, EU or other wastewater disinfection standards. UV for municipal wastewater »
UV Definitions and Terminology
As the UV air, surface and water sterilization technology becomes widely popular, the need of uniform terminology becomes more and more apparent. The following UV abbreviations and definitions represent the most common UV terminology used in association with UV and germicidal UV technology systems. The germicidal UV definitions and terminology were developed by the IUVA and published in the UV Standards and Guidelines. A member of IUVA, American Air & Water intends to contribute for further development and establishment of uniformed UV terminology and definitions.
BPF: Building Protection Factor
Building Protection Factor (BPF): A rating systems that defines the effectiveness of the building in purging itself of airborne microbiological contaminants.
Design Basis Attack Scenario: A bioweapon or biocontaminant release scenario which produces 99% casualties (infections or fatalities) in a building that has 15% outside air and no filtration or other air treatment. Used as the basis for evaluating the effectiveness of air treatment systems.
Fluence Rate: The UV fluence across a surface, typically in units of µJ/cm². This is the technically correct term that describes UV irradiance on non-flat surfaces.
ID50: Infectious Dose 50% - the dose of a pathogen that produces infections in 50% of the population.
ID99: Infectious Dose 99% - the dose of a pathogen that produces infections in 99% of the population.
Kill Rate: The percent of a population removed of disinfected by an air treatment system. The complement of survival in percent.
LD50: Lethal Dose 50% - the dose of a pathogen that produces fatalities in 50% of the population.
LD99: Lethal Dose 99% - the dose of a pathogen that produces fatalities in 99% of the population.
MERV: Minimum Efficiency Reporting Value. An ASHRAE test method for rating filters.
Overload Attack Scenario: The use of a quantity of a bioweapon in excess of that need to cause 100% casualties.
Rate Constant: The rate constant k in the decay equation lnS=-kD where S=survival and D=dose. Defines the slope in a log plot of survival.
Scenario A: Gradual release of a bioweapon agent inside the air handling unit. Used as one basis for evaluating the Building Protection Factor.
Scenario B: Gradual release of a bioweapon agent in the general area or first floor of a building. Used as one basis for evaluating the Building Protection Factor.
Scenario C: Sudden release of a bioweapon agent in the outside air intakes. Used as one basis for evaluating the Building Protection Factor.
Ultraviolet: Electromagnetic radiation with wavelengths shorter than the wavelengths of visible light and longer than those of X rays; situated beyond the visible spectrum at its violet end.
URV: UVGI Rating Value. A scale for rating UVGI air treatment systems based on the UV fluence or UV dose produced.
UV: Ultraviolet
UVA: Ultraviolet light in the range 315-400 nm. Has a minor disinfecting effect.
UVB: Ultraviolet light in the range 280-315 nm. Has a minor disinfecting effect.
UVC: Ultraviolet light in the range 200-280 nm. Has a major disinfecting effect.
UVGI: Ultraviolet Germicidal Irradiation.
UV Dose: The amount of UV irradiation absorbed by an exposed population of microbes, typically in units of µJ/cm² (µJ/cm² = µW/cm² per second). Often assumed to implicitly represent total absorbed dose.
UV Fluence: The total radiant energy incident on an infinitesimal sphere. Technically, this term is more accurate than the more commonly used term “UV dose.”
UV Intensity: An indefinite term often used to describe the irradiance field of a UVGI system. Virtually synonymous with the preferred term UV irradiance.
UV Irradiance: The total radiant energy incident on some surface from all directions.
Z: The Z value, which is sometimes used in place of the rate constant for UV applications. Sometimes written Zeff and defined as Zeff = k.
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