illuminating technologies for life
Home

LUMINOR UV Education - 101

UV 101

History

Sun

Many of us have heard of the term “ultraviolet”, however the likelihood was that it was in reference to exposure to the sun rather than its disinfection capabilities of drinking water and other fluids! As early as 1877, two British researchers, Downes & Blunt discovered the dramatic ability of sunlight to destroy and provide for an effective means of treating bacterial infections. In 1901, Cooper-Hewit's mercury arc invention was unveiled to the world, followed by the Quartz-Burner as the first intensive UV source by Mich in 1906. The first fused silica quartz arc tube was developed by a pair of Germans, Kuch & Retschinsky in 1906. They managed to get more light output from a quartz glass tube as compared to standard glass because the quartz glass tube could endure the higher operating temperature associated with a higher tube pressure that was required to generate more light output. Quartz was also the ideal choice of material because it was less chemically reactive to the hot chemicals and gases encountered within the lit arc tube. This ultimately led to the first full-scale UV disinfection apparatus by Henri and coworkers in France in 1910.

Today, UV technology is used in virtually every country around the world and is considered the best available technology for treating waterborne microbiological contamination.

Disinfection

The term disinfection is the process of destroying or preventing the growth of disease carrying microorganisms. But what does this really mean? There are two main types of disinfection; chemical and physical. Chemical disinfection is when a chemical is added to a substance, depending on the substance being disinfected, whereas with physical disinfection no chemical is added.

Drinking Water

One of the most popular chemical disinfectants is chlorine. Most drinking water facilities use chlorine in order to control microorganisms in the water that is being distributed to the public. It is applied by adding a known concentration of the chemical to a volume of water and then mixing throughout. The chlorine immediately targets the microorganisms killing them, however there is free chlorine remaining in the water that was not used. This free chlorine can then bond with other compounds that may be present in the water, like organics. The water now has the potential to smell different, taste different, the pH can change and various compounds could possibly have been formed due to reactions happening in the water. In other words chlorine is very effective at treating microorganisms in water however it can cause a great deal of change to the water that is being treated.

Physical disinfection is when the microorganisms only are being targeted. Various forms of physical disinfection are filtration, the boiling of water and ultraviolet disinfection. None of these various forms listed will cause changes to the water, only the inactivation or removal of microorganism. The water will taste the same, smell the same and no new compounds will be formed. The water will simply become free of microorganism contamination. For our interests UV disinfection is a form of physical disinfection.

Electromagnetic Spectrum

For water treatment, the power of the sun artificially lies inside a mercury vapour lamp. Similar to a fluorescent light tube, a mercury vapour lamp (UV lamp) emits its spectral output at 253.7 nm, a wavelength that is very close to the 265 nm wavelength that is considered the optimal for microbiological inactivation.

EM Spectrum diagram

To understand the functionality of a UV lamp, one must first understand the electromagnetic spectrum. The electromagnetic spectrum (ES) is a range of all possible frequencies of electromagnetic radiation and extend from low frequencies used for modern radio, to gamma radiation at the short-wavelength end, covering wavelengths from thousands of kilometers down to a fraction of the size of an atom. The long wavelength limit is essentially the size of the universe!

Ultraviolet light is electromagnetic radiation that lies between visible light and x-rays and is comprised of four basic segments. The shorter the wavelength, the higher the energy and as a result, vacuum UV (UVV) lies in the 100-200 nm wavelength. On the opposite end of the UV scale lies long wave UV(UVA) which has the lowest energy output and lies between 315-400 nm. Almost 99% of the sun's output is in the form of UVA energy. Middle wave UV (UVB) have wavelengths between 280-315 nm and have more energy than long wave UV. For disinfection purposes, it is the short wave UV (UVC) that we are most interested in as its wavelength covers 100 - 280 nm which covers the 265 nm optimal wavelength mentioned earlier for microbiological inactivation.

UV Process

DNA

At the 254 nm wavelength, UV light alters the microorganisms' DNA. As we all know, DNA is a form of genetic coding that all of us have. Within each DNA strand there are different sequence codes, with each sequence coding for different characteristics. The DNA strand of a microorganism is very simple with the major coding being for replication. UV light is absorbed quite readily at this one spot in the DNA strand causing it to break the bond. This then causes the microorganism to become sterile, no longer able to replicate.

Within a properly designed UV system, the process of disinfection occurs very rapidly within the system. As water runs through a UV reactor it is exposed to the UV light that the lamp gives off causing a genetic change in the microorganisms that are present in the water. This genetic change causes the microorganisms to no longer have the ability to replicate and produce colonies. Keep in mind that the only thing that microorganisms do in life is replicate and make colonies, this is why we get sick if we consume them in large amounts through our drinking water, so microorganisms that cannot replicate are ones that we do not have to be concerned with. These organisms can enter our system and will pass right through without causing any sickness or ailment.

Lamp Technology

As mentioned earlier, current UV systems use mercury vapour lamps in order to create UV energy. These lamps can be divided into two sub-categories, the low-pressure (LP) lamps and the medium-pressure (MP) lamps.

UV Lamp

Low-pressure lamps are monochromatic in nature, emitting their spectral output at a single wavelength. They can be further subdivided into three subgroups:

Medium-pressure (MPUV) lamps offer the highest power density currently available in the market. Unfortunately, this high power density is also coupled with the worst electrical efficiency (approximately 12% of their electrical power is converted to UV). Additionally, the operating temperatures of a typical MPUV system range from 600°C - 750°C (1112°F - 1382°F) which make them typically suited to UV curing or water applications requiring high constant flows and/or extremely compact footprints.

At LUMINOR, all three low pressure lamp technologies are used. In addition, all our lamps are manufactured with a proprietary Long-Life+™ coating which provides a consistent UV output over the life of the lamp. Additionally, all LUMINOR lamps are the most environmentally friendly UV lamps on the market as each lamp contains less than 10mg of mercury (including amalgam) which is up to 30% less than leading competitors. These lamps fall under the Toxicity Characteristic Leaching Procedure (TCLP) requirements which falls under the Resource Conservation and Recovery Act (RCRA) established under U.S. Federal laws for the disposal of wastes.

Dose

The term UV Dose, or more simply Dose, is the total amount of radiant energy products by a UV light source inside a system. It is the product of Intensity “I”, (expressed as energy per unit surface area) and “T”; the residence time. Dose can be shown in many units, however the most common are in mJ/cm² or W/m². As dose is a product (multiplication) of two units, one can easily see how the adjustment of one of these variables will adjust the corresponding dose. This is why many UV systems are rated at different dose levels depending upon the stated flow rate (the “T” portion or residence time). Dose levels required are typically represented at three distinct levels. The first is based on an old US Public Health document outlining a UV dose of 16,000 µWsec/cm² (or 16 mJ/cm² under the newer units where 1000 µWsec/cm² equals 1 mJ/cm²). Over the past many years, a UV dose of 30 mJ/cm² has become the industry standard used by many UV manufacturers, including LUMINOR. A UV dose of 40 mJ/cm² has been adopted by NSF and consequently by many US states as the new “standard” for dose levels. Whatever dose level you may choose for your system, it is important to remember that this can be achieved by simply controlling the flow of the unit with an optional flow restrictor.

Microorganisms

As there are many different kinds of microorganisms that can be found in drinking water there are different levels of UV energy (dose) required to inactivate each one.

E. Coli
E. Coli
B. Subtilis
B. Subtilis
Cryptosporidium
Cryptosporidium
Legionella
Legionella
Giardia lamblia
Giardia lamblia

For example, E.coli will require a slightly different dose of UV light to inactivate than Cryptosporidium as they are genetically different. The good news is that typical bacteriological contaminants that are found in water are all easily inactivated using UV light. E. coli for example is inactivated at a dose of 6.6 mJ/cm² and both Giardia lamblia and Cryptosporidium are eradicated at dose levels less than 10 mJ/cm². Although UV is effective against all forms of bacteriological contaminants, viruses typically require the highest dose level for complete destruction. In some cases, such as Adenovirus, a UV dose of 165 mJ/cm² is required for inactivation. As this dose is typically much higher than what traditional UV systems are rated for, a multi-barrier approach (using chlorine or chloramine in addition to UV) is typically used to address the virus inactivation (typically used in municipal applications). Please see the Microbiological Destruction Chart for a complete listing of UV dose levels required for inactivation.

Design

The overall design of a UV system encompasses four basic components:

Advantages

The use of ultraviolet light for disinfection purposes has many advantages, some of which are as follows:

Water Issues

Water Quality

UV is an extremely effective treatment technology, however for the proper functioning of a UV system, water quality plays a very important role. LUMINOR recommends the following when it comes to pretreatment:

Installation

Install icon

One may purchase the best UV system available on the market today, however if it is not installed correctly, or misapplied, then all is for nothing! Modern UV systems are designed for years of trouble free operation; however one must remember that the system is treating your water in your specific application. If you do not follow the Manufacturer's Installation & Maintenance Instructions exactly, then how can the product work as it was designed? The following are some installation tips and suggestions for a trouble-free operation:

The Future

Install icon

UV is the fastest growing segment in the water treatment industry today. It is universally accepted around the globe for the treatment of microbiologically contaminated waters and happens to be the most cost effective method. As a manufacturer, LUMINOR is poised to adapt and utilize any new technologies as they relate to UV or disinfection in general. We work closely with others in the industry who are developing new technologies such as those in the LED industry. LUMINOR is committed to providing their customers with the latest technological innovations at the most economical price. The future is definitely bright!