UV lighting for water treatment: taking reliability to the highest level

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While there is plenty of material aimed at the water and waste water (WWW) industry explaining the workings of ultraviolet (UV) disinfection water treatment systems, there is relatively little information to be found about how to ensure reliable power for UV treatment. It is of course necessary for operators of UV treatment systems to know the details of how a system operates, but it’s also important to understand how to ensure reliable power for these systems.

UV treatment is mainly used in drinking water facilities to augment or replace chlorine-based treatment. For more information on these systems and the regulations for their use, see the U.S. Environmental Protection Agency (EPA) document, “UV Disinfection Guidance Manual.”

But rather than dwell on the nature of the UV systems themselves, let’s cut right to the heart of the Secure Power issues for these systems. The key thing to understand about reliable power for these systems is that even a split second (as brief as one cycle) loss of power or a power quality issue such as voltage sag can cause the lamps to turn off.

The stickler with these systems is that lamps don’t get back to effective power very fast. To properly treat water, the UV lamps need to be at high intensity, and with some lamp systems, it can take as long as several minutes to reach effective intensity for its bacteria cleaning function.

As a result, a disruption of just a few milliseconds can cause a UV treatment system to be down for a long time period. This leads to all sorts of bad impacts, possibly even a boiled water alert for the public served by the treatment plant, and possibly, not meeting the EPA guidance requirement.

To mitigate the risk of such incidents, WWW can borrow on the same type of technology used to keep mission-critical data centers up and running: namely, uninterruptible power supply (UPS) equipment. In the event of a power outage from the utility grid, a UPS can ensure there is continuous, reliable power until transfer to power from a backup generator.

A UPS also can add a layer of power conditioning in between AC power from the grid and the UV treatment system, helping to shield the system from power quality disruptions as well as provide the ride-thru during transition to on site generators. A UPS also ensures that a system’s UV lamps stay at full power during breaker removal or other routine maintenance where generators may be out of the circuit as well. A UPS system will also help protect UV lamps from premature failures due to power outages and voltage sags that may be present in a water treatment plant.

For a detailed explanation of the power issues involved with UV treatment, Schneider Electric has an excellent technical bulletin to refer to, “Determining Power Quality and Reliability Criteria for Ultraviolet Disinfection in Drinking Water Facilities.” The bulletin includes some discussion of UPS systems, including their key purposes in UV treatment:

  • Maintaining power during power transfer (transfer time).
  • Keeping the system online until flow stops during shutdown (shutdown time).
  • Keeping the UV lamps on during breaker removal or routine maintenance (maintenance time).
  • Extending the UV lamp life


This document is a worthwhile read for those involved with water treatment, but for anyone in industry, power reliability issues with UV lighting point to a valuable lesson.We often have vulnerabilities that are overlooked in the protection of mission-critical assets. The good news is that these vulnerabilities can be mitigated with a well-designed, properly configured Secure Power solution that might also bring greater efficiency to maintenance tasks.

While UPS equipment can help solve many power protection vulnerabilities, it’s important to realize that the UPS should be properly selected and configured to meet the particular need. With UV lighting, the UPS needs to be sized to the particular system it will be protecting, and configuration issues such as specific high current inrush of UV lamps and pulses, and back up time, need to be considered. Here is where a provider such as Schneider Electric stands ready to help with its combination of industry expertise and UPS product scope and knowledge.

To find out more about Secure Power and how UPS can reduce power reliability risks in various industry settings, check out this Web page on UPS for Industry, Infrastructure and Marine. Your Schneider Electric representative can help you find out more about Secure Power solutions, and for a general backgrounder on power reliability concerns in industry, check out white paper # 7, “Maximizing Uptime in Mission Critical Facilities.”

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