Potent Against Parasites

A closed-vessel UV disinfection system effectively neutralizes Cryptosporidium and Giardia while avoiding chlorine byproducts and conserving energy.
Potent Against Parasites
Xylem’s WEDECO Spektron e series closed-vessel UV disinfection system

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The danger of parasites in water supplies came to the forefront with the outbreak of Cryptosporidium in Milwaukee in 1993. Organisms like Cryptosporidium and Giardia resist traditional disinfection and remain a concern for water utilities drawing from surface sources such as lakes, rivers and reservoirs.

Alternative disinfection technologies have proliferated since the Milwaukee outbreak, and they include disinfection using ultraviolet (UV) light. At the AWWA ACE12 Annual Conference and Exposition in June, Xylem introduced the WEDECO Spektron e series closed-vessel UV disinfection system.

The units are designed to deliver highly effective treatment with low energy consumption. Jay Jordan, disinfection and oxidation market manager for Xylem's WEDECO brand in the United States, spoke about the systems in an interview with Water System Operator.

WSO: What drove the need to develop this product series?

Jordan: The U.S. EPA Long Term 2 Enhanced Surface Water Treatment Rule (LT 2) requires municipal water systems, and in fact private water systems as well, to monitor for Cryptosporidium and Giardia if they draw water from a reservoir or lake. And if they find either of those two organisms in their source water, they have to provide adequate disinfection to keep them from harming public health. These units are specifically designed to target those organisms.

WSO: Ozone disinfection has often been specified for treatment of parasites. What are the merits of UV disinfection versus ozone?

Jordan: UV actually does a bit better job of neutralizing Cryptosporidium and Giardia, and does it more economically. Ozone will treat both those organisms, there's no question about it. If you need ozone for other reasons, such as odor, taste or color, then ozone is a good solution. But if your water is clear and clean enough that you don't have to treat it for those issues, then UV has a smaller carbon footprint and can treat a lot more water for the dollar.

WSO: What about the merits of UV disinfection versus various levels of membrane filtration?

Jordan: If you're using reverse osmosis, you probably would not need to add UV disinfection on the end, but if you're using even microfiltration, some organisms can get through, and therefore we would suggest a multi-barrier approach, where you would add UV disinfection to the end of that train.

Of course, for drinking water, you need to add a small dose of chlorine to the water before it goes out into the distribution system to keep it safe while it's being transported to the customers.

WSO: How does UV light destroy pathogens?

Jordan: It doesn't kill them directly — it deactivates them. UV light in 200 to 280 nanometer wavelengths (UV-C) alters the organisms' DNA so that when the organism tries to replicate, it dies. Once you break that replication cycle, you in effect kill the organisms. Our system renders more than 99.99 percent of all pathogens harmless in seconds. UV disinfection has an added advantage over chlorine in that it is a chemical-free treatment that does not carry the risk of forming harmful byproducts, such as trihalomethanes and chloramines.

WSO: Is closed-vessel disinfection the norm for drinking water?

Jordan: Yes. It provides a very secure place for the water. With an open-channel system, contaminants can get into the water while it's being treated. A closed vessel prevents that from happening.

WSO: What accounts for the efficiency of the Spektron e units?

Jordan: They are designed with a J-style vessel configuration. Water comes into the vessel and then leaves at a right angle — we've found that's a very efficient design. It helps to prevent any type of dead spots or eddies inside the unit.

Along with that, we have an OptiCone diverter, which takes the incoming water and distributes it evenly across the UV lamps, so that as it moves through the vessel, all of the water spends approximately the same amount of time in front of the lamps. This means you get a very even UV dose and so highly effective treatment.

WSO: Is there any automated control associated with these systems?

Jordan: We have a feature called dose vario or dose control. In real time, it measures the UV lamp intensity, the UV transmittance (UVT) of the water, and the flow rate. It actually sets the power going into the vessel based on those parameters. For example, a 75 percent UVT water would require a lot more UV light to kill the organisms than a 90 percent UVT water.

So, when you have a lot of water coming through the vessel, the power is automatically turned up to provide proper disinfection. On the other hand, when the water slows down, or the water quality improves, the power is dialed back on the UV lamps, so you save energy while still enjoying confidence that the water is being disinfected properly. It's a very adaptive system with low cost of operation and ownership.

WSO: Is there anything different about the UV lamps in this series?

Jordan: The Spektron e series uses ECORAY lamps and ballasts developed at WEDECO over the past few years. We see an average 20 percent energy savings over previous lamp and ballast technology. We use a special gas mixture and a special mercury amalgam in the lamps.

In addition, the lamps contain only about 15 to 20 percent as much mercury as the previous version. With less mercury, there's less risk to the environment if a customer should fail to dispose of used lamps properly. We have a program where if a customer sends the lamps back to us, we recycle them at no charge, and the mercury is reclaimed and reused.

WSO: How are these systems protected against fouling?

Jordan: We have an automatic cleaning system that runs continuously to help prevent any contaminants from sticking to the lamps. The system can be adjusted based on the level of constituents in the water. If you're getting some fouling on the quartz sleeves, you can adjust the mechanism to wipe more often. It works in a manner similar to the windshield wipers on a car. It keeps the quartz sleeves very clear and clean so that the UV light can get into the water and have the desired effect.

WSO: Is there a target facility size for this series?

Jordan: These units are designed for small and medium-sized water treatment facilities, up to about 15 mgd. For facilities larger than that, we have other offerings.

WSO: How has the performance of these systems been validated?

Jordan: We have both domestic and international validation certificates. The units are certified under the Austrian ONORM and German DVGW directives. The four largest units, which are the ones designed for municipal treatment plants, have been tested and validated under the U.S. EPA UV Disinfection Guidance Manual (UVDGM). So we have certifications from independent third-party engineers that these units do exactly what we say they will do.


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