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.
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.
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.
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.
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.
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.
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.
Low-pressure lamps are monochromatic in nature, emitting their spectral output at a single wavelength. They can be further subdivided into three subgroups:
- Standard output (LP) UV lamps have been the “industry standard” for many years and is the reason they are still used today. They offer the best electrical efficiency (up to 40% of their electrical power is converted to UV) and their warm-up time is approximately 30 - 60 seconds. Their ambient temperature should not exceed 40°C/104°F. Low-pressure lamps operate at 425mA.
- High output (HO) UV lamps are typically used for systems in a commercial application. They operate between 600 mA to 800 mA and their output is approximately two times that of standard germicidal lamps. Their UVC output is related to ambient temperature.
- Amalgam (AM) UV lamps offer three to four times higher power density than other lamp types. They are designed for stable operation over wide ambient temperature range (4°C - 40°C). They are the preferred lamp choice for long-term applications with low or no cycles and they are usable in universal orientation applications. Due to these characteristics, amalgam lamps are typically used in municipal applications.
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. All LUMINOR lamps contain less than 10mg of mercury (including amalgam). 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.
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.
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.
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.
Overall UV Design:
The UV reactor or chamber is the component that physically houses the lamp and sleeve and is where the water is irradiated by the UV lamp. This device is a pressure vessel and should be manufactured in accordance with the ASME guidelines for pressure vessels (visit ASME atwww.asme.org). Although many UV reactors are highly polished, some use ornamental tube in their construction as opposed to A249 pressure rated tube. A proper UV pressure vessel should include both the pressure rated tube and the appropriate manufacturing techniques. Be sure to ask the manufacturer for the pressure vessel calculations if in question. Although some UV reactors are manufactured with plastic, the use of stainless steel is the correct material for UV reactor construction. Depending on the nature of the application, 304 or 316L stainless may be appropriate. Manufacturers may use different designs in their reactors, however regardless of the design (shape) of the reactor, ensure that the manufacture has done their due diligence in regards to testing the efficacy of the UV reactor (e.g. bioassay testing and/or calculations).
The ultraviolet lamps provide the necessary UV energy to facilitate the disinfection process. These mercury vapour lamps can vary in length, diameter and type (LP, LPHO & LPAM), each having their own unique power density. Regardless of the lamp chosen, they must be insulated from direct water immersion by a quartz sleeve. In addition, due to the unique operating characteristics of each individual lamp type and power rating, each UV lamp must be matched to a specific lamp driver (ballast). A single ballast design may be able to accommodate a range of lamps, however the manufacturer will perform the necessary tests to ensure this is indeed the case. The life of a UV lamp varies between 9000-12000 hours depending on the lamp type. All LUMINOR 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 contain less than 10mg of mercury (including amalgam). 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. Please refer to the lamp section above. As a final note of caution, the energy given off by a UV lamp is extremely harmful to the naked eye and one should never look directly at an illuminated UV lamp.
The controller typically houses both the ballast (for current control which controls the lamp) and electronics to control those functions of the UV system such as displays, lamp change reminders, and buzzers. The controllers should be intuitive in nature making them easy to understand and operate regardless of where the unit may be installed in the world.
Although not designed to be installed outside, exposed to the elements, the controller should be as watertight as possible (controllers with direct venting should be avoided). The controller should come with enough cable to conveniently attach to the reactor and should be provided with a method to easily install it to the wall. It is also extremely important to look for electrical certification such as CSA and CE.
- Quartz Sleeve
The quartz sleeve provides a thermal barrier between the UV lamp and the water. The UV lamp has an optimal operating temperature and the sleeve protects the lamp from the performance affecting variations in water temperature. The sleeves should be manufactured from pure quartz (100 % silica) due to the optimal transmittance characteristics of the quartz. The open end of the quartz sleeve should be fire polished to reduce stress cracking and aid in handling. Depending on the design of the UV reactor, the sleeves can be either domed on one end or open on both ends.
On some systems a UV intensity monitor may be included. This is an optical instrument that incorporates a photodiode that reads the UV light inside the reactor. The diode should be discrete in nature, reading only the 254 nm wavelength of UV and not the visible light spectrum. As the diodes all have some minor variations in their manufacture, each diode must be individually calibrated to ensure they are within specification. The UV sensors should NOT have the ability to be calibrated in the field, especially on an NSF approved system. If calibration is required, this must be done at the factory with a NIST traceable reference sensor.
The use of ultraviolet light for disinfection purposes has many advantages, some of which are as follows:
- Physical process, no addition of potentially harmful chemicals
- Virtually instantaneous disinfection, no holding tanks as in chlorination
- No change in taste, odour, pH or conductivity of water
- No handling of toxic chemicals including special storage requirements
- No disinfection by-products (e.g. THM's)
- Very low power consumption
- No removal of beneficial minerals
- Very low capital cost and reduced operational expense when compared to other technologies
- Environmentally friendly
- Universally accepted treatment process for potable & non-potable supplies
- Automatic, unattended operation
- Easy maintenance, no moving parts to wear out
- Safe to use if flowing manufacturers guidelines
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:
- UV Transmittance - 75% or greater
- Iron - less than 0.3 ppm (mg/l)
- Manganese - less than 0.05 ppm (mg/l)
- Tannins - less than 0.1 ppm (mg/l)
- Hardness - less than 7 gpg (120 mg/l)
- Turbidity - less than 1 NTU
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:
- When possible, install the UV reactor in the vertical position with the inlet at the bottom of the reactor
- Disinfect the distribution system with household bleach for a full 30 minutes to destroy any microbiological contaminants in the system and flush before use of water
- Always install a 5 micron prefilter with every UV system
- Install the UV system as your last piece of treatment equipment
- Ensure the UV is installed prior to the hot water heater and before any branch lines to ensure complete disinfection within the home
- Leave enough space to remove the lamp and/or quartz sleeve from the system
- NEVER undersize a system, always move to the next largest size if in doubt
- Install UV on a separate ground fault interrupter (GFCI) circuit
- Use unions in case the system needs to be removed from the home
- Follow the recommended pretreatment requirements to the letter!
- Do not ignore any alarms or warnings from the system
- Change your UV lamp on an annual basis
- Test your water regularly for microbiological contaminants
- Ask your manufacturer any questions if in doubt
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!