Changes in Ultraviolet Light Technologies: Coiled Tubes Offer New Twist
By Jeff Roseman
Summary: Recent tests using coiled tubes with UV light in drinking water treatment applications show promising results for compact design and significant benefits over quartz sleeves. It’s important for dealers to recognize pre-treatment and flow rates are important factors when digesting the following results.
In a world of change, water treatment technologies offer one of the foremost changes for human health. Equipment manufacturers and suppliers are finding new and better methods to treat water more economically. Technologies such as ultraviolet (UV) light, ozone, filtration, deionization, reverse osmosis and aeration have seen dramatic changes in the last few years. Water treatment systems are becoming more reliable, compact and efficient. These changes are created because of integration of new information with previous knowledge as well as the increased awareness and needs of the consumer. Drinking water, which was once thought of as a resource of never-ending supply, has now become a resource of concern. A recent advance in UV light technologies for drinking water treatment includes use of coiled fluoropolymer tubing. These coiled tubes are proving to be successful at replacing conventional quartz sleeves that surround UV bulbs. Benefits of using fluoropolymer tubing include lower cost, ease of handling and a compact system design.
Coiled fluoropolymer tubing has been used in the Asian market, but hasn’t been as widely adapted in the American domestic marketplace. One company has introduced several types of fluoropoly-mers used in UV water treatment. They were reviewed, tested, and some of the findings are presented here.
Shedding light on tubing
Figure 1 shows UV light transparency comparisons of two types of tubing. At the wavelength of 254 nanometers (nm), there’s a 65 to 70 percent transmittance level that, under normal conditions, would be ineffective at reducing bacteria. But with coiled tubing, longer contact times are achieved and the dosage rate is multiplied drastically. The use of higher-intensity UV bulbs helps create the needed dose rate of at least 16 milliJoules per square centimeter (mJ/cm2) for public drinking water of a Class B certified system to 40 mJ/cm2 needed for Class A certification.1
The coils (see Figure 2) that were test-ed were only seven inches long but, when uncoiled, the measurement would have been over 80 inches. Many standard quartz sleeves used in under-counter drinking water systems are generally around nine-to-10 inches long. This extra length demonstrates how contact times are increased dramatically and how dosage rates are achieved in a compact area, even with a lower transmittance level.
The dosage rate for UV light is determined by light intensity multiplied by the contact time multiplied by the transmission rate of the water.2 The last is usually measured against distilled water, which has a rate of 100 percent. Turbidity, iron and other contaminants reduce UV light transmittance to a realistic rate of 85 to 90 percent. For example, a lamp with an intensity of 4 mJ/cm2 with a contact time of 10 seconds would have a theoretical dosage of 40 mJ/cm2. If multiplied by 90 percent, then the dosage rate would be 36 mJ/cm2. Values that range in the 30 to 38 mJ/cm2 are known to provide a 99.9 to 99.99 percent removal (3 to 4-log reduction) of most pathogenic microorganisms and viruses.
Study by the lake
Bacterial tests using lake water with high bacterial counts, coliforms and E. coli ran through the coiled tubes with UV bulbs of different lengths. Two types of fluoropolymers were tested to compare transmittance levels because of the physical characteristics that each possess. The first fluoropolymer has good transmittance levels as seen in Figure 1, but the other has even better clarity. They’re both resistant to heat with a maximum long-term usage temperature of 200°C and 260°C, which makes them both very favorable to UV light applications.
These tests were performed using two testing methodologies. One provided qualitative analysis and the other quantitative analysis. The presence and absence of coliforms and E. coli were tested with Aquasure Technologies Inc.’s Pro 3000™ Aqaualert™ test kit and rendered a qualitative assessment. The equipment used for quantitative analysis tested for TPC (total plate count), coliform and E. coli were Neogen Corp.’s Hygicult® TPC and E/βgur (Enterobacteriaceae/β-Glucuronidase). Both testing methods provided evidence that the coiled tubes were very effective at producing enough UV light to inactivate pathogens present in the lake water. A log reduction of 7, or 99.99999 percent, was recorded in this study.
The methodology administered was simple, but produced telling findings. The water was first tested for pathogens and a level of contamination was determined. The lake water was very high in TPC, coliforms and E. coli. The first test kit showed a presence of both coliform and E. coli, and the other tests provided evidence of a >107 or TNC (too numerous to count) concentration of these contaminants. The lake water was then run through a prototype unit that had a nine-inch UV lamp inside the coiled tubing at 2 gallons per minute (gpm). The two fluoropolymers were both used on this test and performed very well as the effluent water reduced bacteria, coliform and E. coli. The first test had a cloudy appearance, which could mean a slight presence of bacteria, since very high counts of bacteria in this test can sometimes reveal this outcome. These tests were all done without any filtration so it’s likely the high bacterial counts and turbidity caused the cloudy appearance.
Turbulence is good
The next set of tests were conducted in a similar manner except the UV reaction chamber was doubled in length and a 14-inch UV bulb was used. Again, the effluent water reduced bacteria, coliform and E. coli to non-detect levels at 7-log reduction for bacteria (TPC), coliform or E. coli. The longer contact times and clarity of the fluoropolymers provided a very good method of inactivating microorganisms. Another factor that helps with the bacterial reduction is the turbulent flow of the water caused by the coils. This turbulence, created by the coiled design, reduces shadowing that’s caused by turbidity. The qualitative test had a less cloudy appearance—which reflected better inactivation of the bacteria—because the longer contact time from the double chamber provided a higher dose rate.
A final test was conducted using filtration to see how removing particles in the water would affect the tests’ outcome. A 5-micron sediment filter was used before the UV light chamber, then a second 5-micron sediment filter, and then another UV light chamber on the final product water. This test proved to be the most effective as the water was clearer and there was no cloudy appearance in the qualitative test, which suggests removal of the particles would render a higher UV dosage, and therefore a higher reduction of bacterial organisms. The system was very compact, even when two reaction chambers and two filters were utilized, and could easily be incorporated into a tabletop design for lab use, recreational vehicle industries or other areas where space is at a premium.
In closing, these tests reveal very promising preliminary information on the uses of coiled tubing in UV water treatment applications. UV drinking water treatment applications need to address issues such as pre-treatment to reduce or prevent scaling as well as flow rates to prevent the delivery of dosages that are ineffective for microbial inactivation. These issues must be addressed whether quartz sleeves or coiled tubes are used for bulb protection. System monitors that involve timers to determine lamp life and intensity monitors that measure UV output are problems being solved with new technologies.
UV light is a method of water treatment that’s effective and affordable, and coiled tubing is another tool to help designers build more compact systems for a variety of applications where space is tight. Other uses for which these coils are being tested are water coolers, aquaculture, aquariums, beverage dispensers, icemakers as well as ozone contact chambers and dechlorination units.
The world is always in a state of change and water treatment will be industry-driven by technological advancements. Coiled fluoropolymer tubing will be at the forefront of these changes because of its ease of use, cost reduction and physical features that make them compatible in so many applications.
- Laing, Bruce, “Disinfection, Part 1: Developments in Ultraviolet Disinfection,” Water Quality Products, Vol. 8, No. 1, January 2003.
- Beauchamp, John, “Residential UV Disinfection from a Dealer’s Perspective,” WC&P, March 1998.
About the author
Jeff Roseman, CWS-I, is the owner of Aqua Ion Plus+ Technologies, of La Porte, Ind. The coiled tubing that was tested in this study are the WP-400™ and WP-510™, which are manufactured by Markel Corp. of Norristown, Pa. Roseman has a background in chemistry and physics from studying electrical engineering at Purdue University and has helped develop ionization controllers for the agriculture and greenhouse industries. He can be reached at (219) 362-7279, email: email@example.com or website: www.aquaionplus.com
What to Look for When Choosing a UV System for Your Home
By Ron Hallett, P.E.
Selecting the right water purification solution to ensure your safety is one of the most critical decisions you’ll ever make. It involves more than just deciding who has the best list of system features and functions. To be absolutely certain of your water safety, the solution you choose must meet accepted industry standards.
Ultraviolet (UV) disinfection has only in recent years been recognized as one of the most effective, least complicated and least expensive technologies to use for effective water treatment. It’s gained supporters due to distinct advantages, i.e., no chemical by-products but powerful disinfection properties. Now, recent innovations in UV technologies and system design for rural residential, commercial and small community water treatment applications are dramatically improving UV water disinfection effectiveness and safety over conventional systems.
The advances in UV treatment that have emerged differ dramatically from conventional UV system design. By turning existing UV system design inside out, water is pumped inside the quartz tube for treatment instead of outside the tube. UV lamps are now mounted outside the quartz tube in the air. Shadowing is drastically reduced since the UV light enters the water chamber from 360 degrees.
Below is a list of things to look for when choosing your system:
New levels of UV efficacy—The technique of mounting the lamps outside the quartz tube has proven to be a very efficient use of UV light. Using two lamps in conjunction with elliptical reflectors provides a higher UV dose than is obtained with only one lamp. UV light is used far more effectively with this design since 95 percent of the UV light will reflect back into the quartz tube for a second or third time. A comparison of efficiencies between the two technologies shows more than double the UV dose for each watt of electrical power consumed.
New lamp location eliminates overheating—Having lamps mounted outside the quartz tube ensures lamp output isn’t dependent on water temperature. Lamps are cooled by natural convection, resulting in the water always being treated at the maximum UV dose from the first glass in the morning until the last one at night. Lamp changing becomes a quick two-minute task requiring only a screwdriver, and the system doesn’t have to be drained simply to change a bulb.
Eliminating quartz fouling—Automatic quartz cleaning devices have been introduced to minimize and, in most cases, eliminate quartz fouling. The unique advantages of passing the water inside the quartz tube make the automatic cleaning device both affordable and effective. By using a built-in mechanical device consisting of a simple central turning shaft and stainless steel wiping blades, the necessity for complicated reciprocating motion used in some conventional systems is eliminated.
Alarms and fail-safe shutoff—A pivotal innovation in UV system design includes the use of multiple sensors capable of monitoring both UV lamp output and water UV transmittance separately. UV sensors are also mounted in air to prevent fouling and the need for high-pressure housings. UV transmittance can be calculated with assistance of a microprocessor to compare sensor readings of one UV lamp out-put with output of the second lamp sensor readings as seen through the water and quartz tube.
Any UV system that’s used to protect people from drinking contaminated water must have a method to detect when the water isn’t being treated with sufficient UV dose. Preferably, the system should incorporate a normally closed electric solenoid valve that shuts off the water if a problem occurs with the UV system. A normally closed valve is one that closes on loss of power. This is called a “fail-safe” valve since its mode of failure is in the safe condition.
Safety first—The dramatic advancements in UV technology described here have made these systems some of the safest and most reliable in the world. They have been tested and certified so their dose and UV sensors meet NSF Standard 55A-Ultraviolet Microbiological Water Treatment Systems.1 In fact, 22 of 54 products listed under Standard 55 have passed the Class A requirements.
Today, UV is the only technology certifiable for microbiological water disinfection. One of the reasons is its effective output is verifiable (via sensors) in real time. Choosing the right system for you and your family is a critical decision. Don’t settle for less.
- Hallett 13, ANSI/NSF Standard 55–Disinfection Performance, Class A (Rated at 13.3 GPM), NSF International, Nov. 12, 2001.
About the author
Ron Hallett, founder of UV Pure Technologies Inc., of Toronto, Canada, is a professional engineer and holds a bachelor’s degree from the University of Waterloo, Canada, in mechanical engineering. He holds memberships in the American Society of Industrial Engineers, the Association of Professional Engineers in Ontario, the American Water Works Association and serves on the NSF-55 Task Force with NSF International, a global certification authority for drinking water safety systems. He can be reached at (416) 208-9884, (416) 208-5808 (fax), email: firstname.lastname@example.org or website: www.uvpure.com