Industrial Ultraviolet Technology Overview
By Tom Schaefer
Industrial ultraviolet (UV) technology has been used for decades as a way to disinfect while reducing or eliminating chemical use. Municipal wastewater, semiconductor, pharmaceutical, beverage and aquaculture markets rely upon UV to improve water quality. Over the last couple of decades, the use of UV has expanded into dozens of new markets and applications. While it can rarely be used as a stand-alone technology, it has demonstrated great value when added to multiple processes.
How it works
UV energy is not perceptible to the human eye. The germicidal area considered valuable for disinfection is between 200-300 nanometers (nm). A bell curve of energy within this range forms a nearly instantaneous bond in the DNA of bacteria and viruses. This bond blocks the pathogens’ ability to replicate, effectively killing them. The vast majority of bacteria, viruses, yeast and mold can be relatively easily inactivated with low amounts of UV energy. However, there are a few that are very difficult to address with even high levels of UV. It is important to clarify that UV is illumination, not irradiation. UV energy is produced by lamps very similar to the fluorescent lamps in your office. Both contain a small amount of mercury. Once an electrical current is passed through the lamp, some of the liquid mercury is converted into gas, producing UV and visible light. The fluorescent lamp is made of glass, which does not allow the valuable UV energy to pass through it; additionally, it has an internal coating to provide greater luminance. A UV lamp is made of quartz, which allows UV energy to easily pass through.
Parts of the system
A typical UV system has two major components: a treatment chamber and a power/control cabinet. The treatment chamber is a large stainless steel pipe with one or more lamps mounted inside. The lamps are isolated from direct exposure to the water by quartz sleeves. These sleeves allow the lamps to operate optimally and also allow operators to replace the lamps while the pumps are on. It should be noted that big municipal wastewater systems often use large banks of external lamps in gravity-fed channels instead of pressurized piping. Water that contains high levels of organics will require a chamber with an internal cleaning mechanism. Whenever possible this should be automatic and not manual. A wiper works to remove deposits on the quartz sleeve which block the light from reaching the water. The electronic controls can be as easy or complex as the user requires. The systems are self-monitoring and self-cleaning. Annual maintenance and operational expenses are fairly limited to spare lamps, quartz sleeves and their replacement along with electrical costs.
There are primarily three types of UV lamps: low-pressure, amalgam (low-pressure high-output) and medium pressure. Low-pressure (LP) lamps are ideal for small volume applications, amalgam lamps are ideal for mid-flow applications and medium pressure (MP) are best used for large volume applications. The first two types of lamps are very similar to each other while the latter is different in several ways. The peak of the germicidal bell curve is 260-265 nm, depending on the pathogen in question. LP and amalgam lamps emit energy at one wavelength 254 nm. Being near the peak germicidal they are very efficient at producing UV energy. These lamps typically range from 6-250 Watts. The low wattage results in a lamp temperature that is not very hot. Approximately 35 percent of the electricity supplied to these lamps is emitted at 254 nm. The lamps last about one year (8,760 hours) if used continually. MP lamps are designed for large volume or high dose applications. The lamps use considerably more energy to excite the mercury in the lamp. The result is the emission of UV energy at every wavelength from 200-300 nm. The lamps are typically 500-7,000 Watts. The surface temperature of MP lamps is higher and requires water/air flow to keep them from overheating. It is common practice that the UV system is tied into a flow meter to assure optimal operation. Approximately 15 percent of the energy supplied to MP lamps is emitted in the germicidal range. These lamps are commonly rated for 4,000 hours; however, if used in a continuous flow operation, lamplife has been known to be 8,000-9,000 hours. The quartz sleeves for either lamp style should be replaced after every 20,000-25,000 hours of lamp use. This process will require the chamber to be drained and typically takes a couple of hours. The O-rings on the internal wiper should also be replaced at this time.
The amount of energy applied to the water/air is referred to as the ‘dose’ applied. The most common dose level applied for disinfection is 30mJ/cm2. This is a sufficient level of energy to reduce the viability of the vast majority of bacteria and viruses by greater than 99.9 percent. Application specific regulations sometimes require higher dose levels. A new regulation in New York will require a 40mJ/cm2 dose for a specific type of water park feature. The United States Environmental Protection Agency (U.S. EPA) recently enacted laws requiring large cities to test their drinking water sources for chlorine-resistant pathogens. If present, these pathogens need to be addressed with proven methods of alternative disinfection. UV will be used to treat 2.2 billion gallons a day (bgd) of drinking water for New York City. Higher dose levels are used for a multitude of applications.
UV dose is an advanced calculation that takes into account lamp power, treatment chamber configuration, fluid dynamics and water quality. Water quality should be expressed in terms of UV transmission. The dose level provided should assume a realistic transmission value to the water being treated. A spectrophotometer is used to measure UV transmission. Ultrapure water would have a T-10 value of 100 percent. Standard tap water is typically around T-10 90 percent. Effluent from a wastewater treatment facility is often around T-10 60 percent. T-10 denotes that the UV transmission was analyzed using a 10 mm test curvette. Approximately three times as much energy would be required to provide the same 30mJ/cm2 dose a water with a poor T-10 60 percent transmission as it would to treat a T-10 90 percent. Whenever a UV dose is specified, a transmission value should be stated so an apples-to-apples comparison can be made.
Disinfection: The most popular use for UV is for disinfection and there are dozens of applications under this type of use. Wastewater treatment has, by and large, replaced chemical disinfection of effluent with UV disinfection. Food and beverage manufacturers use UV to disinfect ingredient water going into product ingredients, containers and the outer surface of finished product to improve quality and extend shelf life. Filters are great places for microbiological growth. Many industries use UV immediately after filtration to protect the downstream process from microbiological growth. Aquaculture uses UV to naturally reduce the risk of contamination to fish. UV lights are placed in HVAC ductwork to limit microbiological growth in warm, moist places and higher powered systems can disinfect the air moving within the duct. Low powered systems provide UV exposure to the upper air in rooms treating tuberculosis patients. UV is an irritant to the skin, eyes, plants and certain materials including plastics; exposure should be avoided. The international shipping industry is expected to require UV treatment of ballast water on ships that travel across the ocean to eliminate the threat of invasive non-native species, which will cost billions worldwide (the zebra mussel is just one example).
Advanced oxidation: UV can also be used to break down ozone and hydrogen peroxide. The later two elements are powerful oxidizers designed to treat water. Residual amount can be detrimental or even dangerous; UV naturally reduces their concentration. The bottled water industry often uses ozone to purify water. UV is used to remove any residual ozone prior to bottling. In a highly specialized process, UV is used with ozone and/or hydrogen peroxide to remediate contaminated groundwater at superfund cleanup sites.
Total organic carbon (TOC) reduction: UV is used to make super-clean, ultrapure water even cleaner. Water impurities are measured in the parts-per-billion. This water is used to rinse semiconductor chips during the manufacturing process. Even the smallest impurity can destroy the chip. UV wavelengths below 220 nm actually produce small amounts of ozone which are simultaneously broken down by UV. Hydroxyl radicals are formed in this process. These radicals are more oxidative than ozone and react many times faster, so residual levels are not a concern. It is this similar process, but on a much larger scale, which is used for the previously mentioned groundwater remediation.
Chloramine reduction and disinfection of chlorine resistant pathogens: UV is used to improve the water and air quality at indoor pools. Once chlorine binds with organic compounds in the pool water, the resulting level of combined chlorine (otherwise known as chloramines) continually rises. Chloramines are responsible for the odor and irritation associated with the indoor pool environment. Installing UV on an indoor pool will continuously reduce the chloramine concentration and dramatically improve both air and water quality. Regarding the new U.S. EPA requirement for addressing chlorine-resistant pathogens in municipal drinking water, a second benefit of using UV on a pool is protection against outbreaks of chlorine resistant pathogens. Recreational Water Illness (RWI) is becoming more of a concern for commercial pool owners and regulators. Last summer almost 4,000 attendees became ill at a water park in New York. As a result, new state regulations require similar types of facilities, among other things, to use UV.
Chlorine destruct: The pharmaceutical industry uses very high dose levels of UV to remove free chlorine from ingredient water. UV energy disassociates the bonds within compounds and reduces them to less-complex by-products.
UV is typically not a cure-all, but when combined with other technologies, it can provide dramatic benefits to a process. The number of industries and applications within them applying UV technology will continue to increase as industries continue to target chemical processes for reduction or elimination. There is a bright future for industrial UV.
About the author
Tom Schaefer is the National Sales Manager at Engineered Treatment Systems. He has an extensive background in industrial UV sales dating back to 1997. ETS represents ATG Willand for the U.S. market. He welcomes your comments and questions and can be reached at firstname.lastname@example.org or (920) 885-4628.