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With a long history in varied fields, ultraviolet now advances in OWT technology.
Though chlorine has remained the method of choice for disinfecting water over the past decades, recent studies indicate that it can damage the environment and lead to the formation of possible carcinogenic compounds, such as trihalomethanes and haloacetic acids.
The World Health Organization has stated that the “risks to health from disinfection byproducts are extremely small in comparison with inadequate disinfection.” But the above problems with chlorination have caused consulting engineers, users, and regulatory agencies to actively pursue alternatives for water disinfection. Ultraviolet (UV) light currently presents a strong alternative option for water disinfection.
As with everything else, UV light does have its downside. But for the moment, here are its main advantages:
- Fairly low energy requirements
- Few, if any, moving parts
- No formation of potentially hazardous byproducts
- Elimination of chemical use, including large-scale storage, transportation and handling, and associated possible safety risks
- A reduction in space or footprint of operations, thanks to shorter contact time and no contact basin
- Optimal performance when the lights are monitored by sensors
On the minus side is the fact that the water is now clean but has nothing to protect it from contamination as it travels through the water supply system. The water must be transported and delivered in such a way as to avoid contamination.
UV light sources are typically termed “mercury vapor lamps.” Unlike home incandescent lamps, these are in fact “arc tubes” without a filament. The sealed glasslike tube has electrodes at each end. The tubes are constructed of quartz and contain tiny amounts of liquid mercury.
Before being sealed, the tubes are filled with an inert gas, such as argon. When an electric current is applied, an arc is struck between the two electrodes, vaporizing the mercury and exciting the electrons in the mercury atoms. As the electrons change orbital states, photon energy is released at specific wavelengths in the electromagnetic spectrum, particularly in the germicidal range.
There are primarily five types of UV wave sources: low-pressure, low-pressure/high-output, low-pressure/amalgam, medium-pressure, and high-pressure arc tubes. “Pressure” refers to the internal lamp pressure (low pressure is below atmospheric pressure; medium pressure is near atmospheric; and high pressure is above atmospheric pressure).
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| Made of quartz, ultraviolet arc tubes contain small amounts of mercury. |
Getting Into UV Light
Using UV light for various treatment needs, including water, goes back longer than some may realize. The industrial use of ultraviolet light treatment for water in the US started in the late 1940s but has been around in Europe since the early 1900s, according to Charles Romary, chief executive officer with Clean Water Systems International (CWSI) in Klamath Falls, OR. Back then it was used for municipal water treatment in France.
CWSI manufactures UV monitoring controls for water, sewage, industrial, pharmaceutical, and consumer products, which it sells to other companies worldwide. Romary has been involved with UV light in wastewater applications since the early 1960s.
“UV was actually used considerably in the US until chlorine came in,” says Romary. “Chlorine was a lot less expensive, and UV also wasn’t really too good. Westinghouse and then GE were involved with UV light in those early years before smaller companies became involved. Suspended above the water, the early lamps were not particularly effective.
“Westinghouse’s early chamber systems caught on after that. Placing a quartz sleeve around the lamps and adding them directly to the water increased the efficiency of units over those hung above the water by 75% to 80%,” says Romary.
When Romary first became involved with UV, the units were expensive and unreliable, and they had to be changed and recalibrated at year’s end.
“Something new was needed, and we developed sensor systems for our own equipment, which eventually caught on for other UV light makers that we sold to as well. If you are going to sell a piece of equipment, the customer also had to know the piece of equipment was working effectively for the well-being of both the customer and the manufacturer.”
Romary fought for the idea of sensors and regular testing of equipment with NSF International, formerly the National Sanitation Foundation. Eventually Standard 55 was put through, including one for consumers and one for industrial applications. “To my mind the standards for consumers [16,000 microwatts minimum] was far too low, and that for industry [37,000 microwatts minimum] was too high,” says Romary.
“But industry realizes they have much at stake in keeping things working correctly, for example, in the case of pharmaceuticals being polluted and those costs. They watch their equipment closely. The publicity alone from some disaster would be enough to do them in.
“People purchase CWSI’s monitoring controls because it’s an insurance policy that’s going to work for them. Despite costs up front, in the long run they will save a lot of money, as will their customers. We pride ourselves on the reliability, relative low cost, and the longevity—without having to be recalibrated—of our UV light monitoring systems. If the water’s too cloudy, the UV lamp hasn’t come on, or it’s malfunctioning, our monitor will tell the operator or consumer.”
Smart Technology With UV
UV Pure Technologies Inc., located in Toronto, ON, has worked in the UV light area for some nine years, five of those years in research and development, during which time the company eventually field tested and patented its UV light systems. Its “Crossfire Technologies”
pplication features a self-cleaning, smart technology with multiple sensors measuring not only lamp output but also transmittance of UV energy through the water column. Monitoring, done either onsite or remotely, can determine the effectiveness of the disinfection process at any time on a real-time basis, and the system is virtually maintenance-free, according to Rick VanSant, president and CEO of UV Pure.
“Our system goes beyond just one sensor because in the case of one sensor, all that is being looked at is whether or not there is a drop in energy,” says VanSant. “If the sensor does see a drop, it sets off an alarm; but it cannot tell an operator why there was a drop, whether it’s from water quality changed, quartz on the lamp has been fouled, or if the lamp output decreased—or even all of the above.
“But with our patented multiple-sensor system we monitor all of those things so the operator can treat the specific problem effectively, whatever it may be. They are smart systems, able to diagnose a problem as opposed to simply guessing what’s wrong.”
The water remains inside a quartz tube, which self-cleans to eliminate the need for manual cleaning. “Our lamps are in air, surrounded by elliptical reflectors, instead of in water,” says VanSant. “We receive two to three times the energy of conventional systems because we have multiple exposures of the energy, which basically bounces around inside the reflectors making it so there is no place for a bug to hide and it gets hit several times.”
The fact that the lights are in air makes changing the bulb as simple as changing one at a bedside table. No unit must be pulled apart and drained to reach the UV lamp.
Of its two product lines, the Hallett is named for Ron Hallett, the founder, vice president, and technology officer of UV Pure. The Hallett is certified to NSF55 Class A. “That is the gold standard for regulated water treatment standards,” says VanSant.
The company’s Upstream line meets the same performance standards as the Hallett, and although the Upstream is not NSF certified, it is lab validated. Upstream is a lower-cost product line than Hallett.
“Decentralized waste treatment is perhaps our fastest-growing segment right now,” says VanSant. “We’re doing many package plants going to wells, mine heads, and many other remote sites. Because of the advanced technology contained in our system, we anticipate taking on a significant share globally of the smaller water and wastewater treatment sector—for us that means less than 1 million gallons per day.
“We’re currently developing a larger system, too. But we’ll never target the million-gallons-per-day or million-gallons-per-hour applications. We will remain for smaller applications which actually form 95% of the market.”
The UV Pure lamps are from 80 to 100 watts, low-pressure/high-output or low-pressure lamps. Low-pressure lamps find use in point-of-entry locations for trailer parks, homes, schools, and decentralized water applications. These are very economical and have much longer lives, according to Ron Hallett. “The low-pressure, high-energy lamps are twice as efficient in energy use and involve flow rates of less than 100 to 300 gallons per minute. They are much more economical, last for a year, are twice as efficient as medium-pressure, and they work better.
“Low-pressure systems such as ours are easy to work with, easy to change, and lack the complexity of the medium-pressure. Our system uses two low-pressure/high-output lamps with a cost of about $100 per year, lasting for one year.”
For most smaller applications in UV water and wastewater treatment, the cost for running a medium-pressure system is much higher, including capital costs and maintenance to run the system itself, according to Hallett. “Medium-pressure systems, however, are the best for treating PPCPs and EDCs. I also have a patent on a cooling system for one of those lamps, as they’re very difficult to control the temperature on.
“The ability to monitor the performance of systems both onsite and remotely is a very important developing trend,” adds Hallett. “Rather than requiring certified operators onsite or continually visiting sites, remote monitoring enables systems to be monitored efficiently with a PLC controller by only one certified operator and all of our systems have this capability.”
UV Pure also has a wireless monitor able to be read within by a modem or by Internet hookup. The company feels that the market is heading toward “intelligent” systems.
“In a nutshell, our focus is on deactivating the pathogens in water systems and doing that better than any other systems, with more efficiency, the least maintenance, lowest cost, and the smartest reporting.”
Detecting Efficiency
Aquionics Inc. had some interesting early years. In the 1940s, the company used its UV light sources to disinfect wounds of returning soldiers. Eventually drug technology advanced to the point where UV became obsolete in treating wounds.
“Since those days we’ve re-focused on disinfection—for water. That’s where we started making quality, lasting equipment to treat municipal drinking water,” says Jon McClean, president of Aquionics. McClean has been with the Erlander, KY–based company for 20 years.
Aquionics specializes in medium-pressure and amalgam technologies. It now serves many sectors, including drinking water, wastewater, industrial process water (food, beverage, and brewing), high-purity water (pharmaceutical and semiconductor manufacture), and also water reuse from agricultural applications. It opened up its product to the North American market starting in 1982. “Since low-pressure lamps eventually proved too unwieldy for us (many lamps in the water eventually started to break), we’ve made our way into the medium-pressure UV lamps, our biggest area of sales now.”
The company also leads the world in UV systems enclosed in piping and closed vessels, also known as in-line systems. “We developed our patented equipment ourselves,” says McClean. Ours sits on the side on the interior of the pipes within a quartz sleeve. Several of our research programs are also looking into light-emitting diodes [LEDs]; but the limitation with these presently is that the power is very low. Delivering the UV light into the water is the difficult part. LEDs are a long way from being commercially up-scalable—but I think they’ll get there.”
Aquionics also supplies monitoring camera equipment with its lamps, so the amount of UV energy coming off the lamps is always known. This is all done remotely and automatically.
Three years ago, in the city of Thornton, Aquionics supplied UV equipment for Colorado’s first-ever UV light, medium-pressure treatment application. It is also among the first of the EPA’s mandated sites for use of UV for killing Cryptosporidium in a municipal drinking water application.
“We also do a lot of work where we use our medium-pressure UV lamps to remove endocrine disruptors in the wastewater instead of the drinking water,” says McClean.
R&D Pushes to Improve UV Pulse Lamp
Raymond Schaefer, president of Phoenix Science and Technology (PS&T) has three patents and one pending on a very intense UV pulse-lamp light source using a rare gas discharge, such as xenon, which can generate very high UV efficiencies. Also, there isn’t any mercury in the light system—a major reason the EPA funded the program. The high intensity of the pulsing has led to some enhanced treatment rates as well.
“We’ve demonstrated the efficacy of the lamp,” says Schaefer. “We’ve gotten some very high rates in some of the more difficult-to-treat microorganisms.
We’ve received grants from the EPA for drinking water and from the National Science Foundation for the remediation of organic contaminants. The UV from our lamp is good for any water treatment application.”
While its lamp works very well, it has to increase the lifetime to make it practical. This is the one technical hurdle PS&T is working on presently. “We let our lamps pulse to test them in systems, take samples after a certain number of pulses, and get the inactivation rates, similar to what is done with mercury lamps,” says Schaefer. “In fact, when we run our tests we have both low- and medium-pressure mercury lamps in our laboratories, so we’re doing a real apples-to-apples comparison with our pulse lamp. We are doing some of the science to prove in a quantitative way what the pulsing actually does. The EPA is interested in this as well.
“The science is still being sorted out as to what the real advantages are for pulsed lamps. Generally the main advantages remain the fact that it’s mercury-free, has enhanced treatment rates, and is more efficient, meaning less electrical consumption.”
When this product is available on the market, the upfront cost will be more, according to Schaefer, but the lower power cost over the life cycle of the product should cancel that out. Fortunately, PS&T was recently notified by the National Science Foundation that it will be receiving a grant to develop the lamp. The goal is to demonstrate this feature and then get the lamps out in the field soon afterwards.
PS&T is currently working with Trojan Technologies to develop a marketable product. “They are interested in placing our lamps in their products,” says Schaefer. “But we do have to demonstrate an effective lifetime for the product first.”
Using UV Where It Fits
Trojan Technologies Inc. of London, ON, has 30 years of experience working with UV light applications. It has done extensive research on a great many contaminants in different water qualities. Trojan also does modeling of the attributes of different contaminants. From treating wastewater for disinfection, the company has broadened its focus to include industrial applications, processing waste treatment, and residential and municipal water, eventually crossing over into the treatment of environmental contaminants.
“In terms of drinking water, we are currently using UV/oxidation for a whole variety of different applications, including the treatment of pesticides, taste and odor, or industrial contaminants,” says Adam Festger, communications coordinator with Trojan. “All these systems are also providing a barrier to endocrine disruptors and personal care products.”
Indirect potable reuse is generally Trojan’s largest market segment. Wastewater is placed in an advanced treatment train with micro-filtration and reverse osmosis—with UV light and hydrogen peroxide as a final step.
“For effectively treating nitrosamines, whose main source is as a disinfection byproduct, UV light must be used,” says Festger. “UV light also provides superior disinfection of Cryptosporidium; it’s less expensive, more effective, and not affected by water temperature. Additionally, UV light is able to treat nitrosamines, whereas ozone cannot. Nitrosamines have been identified as strong carcinogens.”
Trojan plans on continuing expansion of UV light in drinking water applications and sees in the future many more facilities using UV to treat contaminants while simultaneously disinfecting. “In sites where disinfection only is the goal, UV light is far more cost-effective than treating with ozone, in any size plant,” says Festger.
“In terms of oxidizing pharmaceuticals, UV will also be cost-competitive at any size plant as well. But when all is said and done, at least on the municipal side of things, there are a variety of targeted contaminants that we deal with, and we simply don’t worry about the other ones.”
IUVA Raises Awareness Globally—It Hopes
The International UV Association’s (IUVA’s) Executive Director Jim Bolton notes that there are many cases in which treatment with UV and ozone can give an operation a much bigger advantage than having either one alone. The two in combination can lead to a much more economical system. During the treatment of drinking water, if ozone is used before disinfection treatment with UV, the water can be cleared up and made more transparent, thus raising the efficiency of the UV system.
Regarding the PPCP issue, Bolton points to a large facility in the Netherlands. “This installation in Holland is treating what we call the ‘micropollutants’ with UV light and hydrogen peroxide and is having great results,” says Bolton.
Also, certain organisms are resistant to UV light but very sensitive to ozone and vice versa. In those cases, use of the two treatments offers a multi-barrier approach.
One of the most promising areas of development when it comes to UV light treatment in water applications, according to Bolton, is in the area of deep UV LEDs. “These can now be manufactured to emit in the deep ultraviolet region,” says Bolton. “As they raise efficiencies with these devices, this could be quite a development in terms of the UV technology on the horizon.”
Eventually these could replace UV lamps, according to Bolton. “The advantages of UV LEDs are that they could be placed virtually anywhere and they last forever,” says Bolton. “They are semiconductor, solid state devices that could cover the whole side of a wastewater treatment reactor.
“Lots of companies are looking into this technology, but it remains at the research level for the moment. This is something quite exciting. It could offer much more flexibility in the design of the reactors. Because they last so long, replacement costs would drop dramatically.”
Henry Vere writes extensively on engineering and scientific subjects.
OW - March/April 2007 |
