Traditionally, ultraviolet (UV) disinfection technologies available for use in wastewater, drinking water and water reuse applications have used mercury UV lamps containing electrodes for the generation of UV radiation to meet disinfection needs. These electrodes are delicately constructed and their deterioration is the primary source of disinfection system failures.
A groundbreaking development in UV disinfection is the use of microwave energy to power electrodeless, high-output UV lamps integrated with advanced system designs to meet ever more stringent disinfection requirements. Microwave-powered UV systems utilize microwave energy generated by a magnetron and directed through a waveguide into quartz lamps. These microwave-powered electrodeless lamps produce predominantly monochromatic UV light, with the majority of the UV output optimized at a 254 nm disinfection wavelength.
Two distinct types of commercially available, microwave-powered UV disinfection systems are available: modular, vertical open-channel configurations for large-flow-rate wastewater applications; and modular, closed-vessel configurations for low-flow-rate wastewater and drinking water applications. Both large- and low-flow-rate MicroDynamics™ systems were launched in June 2007 by Severn Trent Services.
Microwave-powered UV disinfection systems allow quick start-up, longer lamp life, less fouling and higher overall reliability, coupled with increased efficiency, safety and flexibility in design.
Within the MicroDynamics system, the electrodeless lamps warm up quickly and produce full disinfection capability within 12 seconds. This often negates the requirement for expensive uninterruptible power supply standby electrical generation, as the microwave lamps re-strike the instant that power is available.
Without electrodes to fail or deteriorate, UV lamp life is extended beyond three years in MicroDynamics systems, resulting in both operational and cost advantages by requiring less frequent lamp changes. Additionally, savings are achieved because without electrical connections between the microwave generator and the lamps, components can be changed quickly, reducing labor-related maintenance costs.
The MicroDynamics electrodeless lamps can be turned on and off as often as required without affecting lamp life. Therefore, the system is ideal for flow pacing and other applications that experience changes to flow rates, such as instances with varying weather conditions and flow patterns, since power consumption can be accurately matched to disinfection requirements. Moreover, the MicroDynamics system can operate in a partially-filled wastewater channel without deterioration.
Unlike an electroded lamp, which requires space at the top and bottom for the electrodes, the gas discharge fills the entire lamp column in an electrodeless lamp. Radiation is, therefore, more efficiently produced through the entire length of the lamp.
Improved safety is inherent in the MicroDynamics system, as the electrodeless lamp has very low residual radiation of energy and thus an almost instant shut-off capability. Eliminating the need for electrical connections in the water produces greater operational safety, with high-tension wiring contained within the magnetron head.
For more than 100 years, UV disinfection has proven highly effective on waterborne pathogens and viruses, offering low capital and operating costs compared to alternative treatment methods. The new microwave-powered, electrodeless UV disinfection systems offer significantly improved reliability and lamp life compared to traditional electroded UV lamps, resulting in lower overall operational cost and maintenance requirements. In a net present value comparison of microwave-powered and traditional UV disinfection systems, the operational and maintenance benefits of a microwave-powered system can produce significant operational cost savings for a utility.
For more information, e-mail info@severntrentservices.com.
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