By Tom Stoll, P.E.
Summary: Whether it’s used as a supplement to a multi-step water treatment program or by itself, UV light is beginning to take a stronghold as an effective technology in the United States. As many of you know, it has been widely used in Europe for many years. The author describes what makes UV such an attractive water treatment option.
With growing populations demanding quality public services, many countries—including less-developed ones—are searching for better ways to provide clean drinking water. There are many different purification methods from which to choose including filtration, chemical treatment, distillation and ultraviolet (UV) irradiation. Some of these methods are customarily used in conjunction with one another to provide purified water that meets certain health standards, e.g., USEPA and U.S. Public Health Guidelines. When used together, these methods remove solids, neutralize adverse chemicals, and disinfect by killing bacteria and other microorganisms.
One inexpensive and efficient way of disinfecting the water supply is by irradiating it with UV light. It’s known that UV light of wavelengths between 250 and 270 nanometers (UV-C or UVC band) is extremely effective in killing many species of bacteria, mold spores, viruses and other microorganisms. The UV light causes DNA damage to the cells of the microorganisms that leads to mutations and eventual cell death. Using UV radiation in this manner to purify water is popular among Europeans who have known about it for decades. Its use here in the United States started in the early 1990s and is becoming more prevalent especially with outbreaks of drinking water contamination by microorganisms. Those incidents include a Cryptosporidium outbreak in Milwaukee in 1993 that killed over 100 people and in Las Vegas in 1994 that killed 43 people; as well as E. coli outbreaks in upstate New York at a county fair in 1999 that killed two and in Walkerton, Ontario, Canada, in 2000 that killed seven people. In each case, hundreds and hundreds of thousands were made ill.
Typical UV water purification systems rely on the movement of water through a vessel that contains a UV lamp positioned so its axis is aligned in the same direction as the water flow. This ensures maximum exposure of the water to the UV radiation as it passes across the lamp body. Many of these types of purifiers require pressurization to assist the flow of water through the device. Some, however, don’t rely on pressurization. They use gravity instead as the primary means to move water through the system (see UV Waterworks at http://eetd.lbl.gov/iep/archive/uv). This results in a very simple design that can be easily relocated to the water supply. This is particularly important in less-developed countries where the water supply may consist of smaller sites at many different locations. The designs of these systems typically consist of a flow tank, UV (germicidal) lamp, electronic ballast, and automatic shut-off valve to prevent water flow when the lamp is inoperable. This simple design means the user now has an economical way to purify his water supply that requires very little maintenance and uses a fraction of the energy as compared to other disinfecting methods such as distillation.
Advantages of UV
A few benefits of using this type of UV water purification scheme include simplicity, portability and affordability. To help realize these benefits, the UV purification system incorporates a lamp of suitable size and wattage to generate light of the proper wavelength with an electronic ballast to operate it. The electronic ballast plays an important role in how much UV the lamp generates. Dosage is a function of UV wavelength, intensity and time. Light intensity from the lamp is proportional to the electric current flowing through it, and is also affected by the frequency at which it’s operated. Both of these parameters are controlled by the electronic ballast. Since many water purification systems are portable, they sometimes require power supplied from a battery rather than the typical AC source, i.e., 120-volt outlet. The electronic ballast must be able to accommodate applications with this requirement. Some of the other features users might expect from the electronic ballast are small physical size, long life and high efficiency.
At least one line of electronic ballasts can help meet these requirements. It can operate a wide variety of germicidal lamps from a number of different power supply voltages including both AC and DC (battery) sources. Many models are compact in size and can be easily incorporated into most designs. Probably one of the most attractive features of the product line is that nearly any model can be customized for a specific lamp to generate different levels of UV radiation. In some cases, new or specialty lamps require new ballast designs. In these instances, engineers can often create designs that meet or exceed customer needs.
As mentioned in the previous paragraph, customization could be of primary concern as different systems may require different levels of UV generation from the same lamp. This isn’t possible with most electronic ballast manufacturers since they customarily require high-volume production runs to justify any change or customization of their products. This is a good example of how a line of electronic ballasts can provide flexibility to accommodate special customer requirements. Some customers of these particular units are suppliers of UV purification products. For example, Atlantic Ultraviolet, Cannon Environmental Technologies, Photon Technologies, Sobrite Technologies, and Water Systems Integrators are all recent users of these products. Many of them use a product to generate high levels of UV radiation to purify air or water by operating a germicidal lamp from a DC power supply. This is important in remote or less-developed areas where power supplies and water quality may be more inconsistent.
In summary, UV irradiation is becoming a more viable and economical means of water purification when used in conjunction with other methods. Systems incorporating UV technology must be portable, affordable and easily maintained. Electronic ballasts can help system designers meet these requirements by offering products of small physical size, flexibility in design, and quick turnaround to help bring the system to market faster.
About the author
Tom Stoll is product engineering manager for The Bodine Co. Inc., of Collierville, Tenn. Her can be reached at (901) 854-1651, (901) 854-1630 (fax) or website: www.bodine.com