A New Twist on UV-T Measurement

Aquionics offers a UV-C LED light source with a single lamp and sensor in a compact package designed for versatility.
A New Twist on UV-T Measurement
The PearlSense technology comes in a handheld unit for use in laboratories or for field grab samples.

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Monitoring UV light transmittance (UV-T) is important to control of disinfection in drinking water systems. A new offering from Aquionics is designed to provide highly stable UV-T readings under all water conditions over an extended lifetime.

The company says its PearlSense T254 unit is the first UV-T monitor to incorporate a UV-C LED light-source in place of a conventional mercury lamp. Use of a single lamp and sensor in place of multiple lamps and sensors adds consistency to readings.

The unit can be installed directly into a pipe (as in most drinking water plants) or in open channels. It can also be used offline for purposes such as grab sample testing. Dan Shaver, business development manager with Aquionics, talked about the device in an interview with Water System Operator.

WSO: Why is accurate UV-T measurement important in drinking water disinfection?

Shaver: Having the most accurate indication of changes in water quality helps a drinking water plant operate a UV disinfection system at the optimum performance, and at the most efficient UV dose. The ability to take accurate measurements enables them to make changes on more than a weekly or monthly basis. Accurate measurement translates to better results.

Getting the best performance out of a UV system and getting the best disinfection is a function of three variables. The UV transmittance of the water is one. The others are flow rate and lamp intensity. If you don’t measure those three parameters together, you’re missing out on running your system at the most cost-effective rate.

WSO: Historically, how have water systems measured UV-T?

Shaver: There are two basic ways. A lot of plants, during the design phase of their UV systems, have acquired a ballpark figure of their UV-T based on historical values. That means they would be running their system based on one value that is fixed for all time. A step up from that would be taking grab samples, having the UV-T measured in their on-site lab or in a commercial lab, and making modifications to their process based on the changes they see in those samples. That method is only as good as the frequency of sampling and measuring.

WSO: How does your device differ from other inline instruments for UV-T measurement?

Shaver: There are various instruments on the market that measure UV-T online and give real-time values for changes in water quality. They operate in various ways to deliver the most accurate UV-T readings. Most of these devices use mercury lamps or flash lamps as light sources. They’re generally programmed to look at a sample in the water about once a minute, with the light source on continuously.

We feel our instrument with a single UV LED light source simplifies the process. A big benefit of an LED is that you don’t have to run the light source continuously to get accurate readings. When you turn the LED on, it’s instantly on at full power. So you only need to turn the LED on when you’re taking a measurement. If you want to take a UV-T measurement once per minute, you only have to turn that LED on for the instant when you take the reading. Lamp life is not a factor because you’re turning the LED on when you need it and then turning it off. You can power cycle it as many times as you want. It doesn’t affect the quality of the light, and there is no warmup time.

WSO: What is the benefit of using just one lamp and one sensor in the instrument?

Shaver: We’re able to use a single lamp and a single sensor because an LED is so small and has such a stable output. With only one sensor, we don’t have to compensate for variations in sensor tolerance. It gives an accurate measurement, and it also enables us to design a product that is very compact. It fits in the palm of your hand. There is no need for, say, a large box next to the UV reactor.

WSO: How does this device function when configured for inline UV-T measurement?

Shaver: We provide adapters that allow an operator to tap the device directly into a pipe at the inlet to the UV reactor. The footprint is so small that it’s easy to tap it into a standard connection and then run the communications back to the control panel.

A 4-20 mA analog signal comes out of the instrument. Users can take that signal, tie it into their control panel, and use that to make changes in UV output based on the fluctuations they see in the water quality. If they wish, they can set up an algorithm to allow the changes to be made automatically. If they don’t have large fluctuations in water quality, they might just check it every morning and know where their system needs to be running that day. Then if there were big spikes up or down in UV-T, the system could alert them by way of an alarm.

WSO: Does this device require maintenance when mounted in inline configurations?

Shaver: It has the ability to clean itself automatically when it’s mounted in a pipe. You don’t have to take it out of the pipe to clean it. It has a wiper system so that every time the LED turns on to take a sample, a cleaning function is also performed to keep the quartz windows clear of fouling and make sure the measurements remain accurate. Also, the use of an LED means that no annual lamp replacement is required.

WSO: Is this instrument mainly for surface water systems where raw water quality is more variable?

Shaver: We think every utility should measure UV-T regardless of the water source. Yes, there will be more fluctuations in surface water than in groundwater, but if a plant runs disinfection equipment based on a historic UV-T number and they’re not able to track changes in real time or on a frequent basis, they could be missing out on energy savings by not running their system as efficiently as possible. We’ve tried to offer a very simple, plug-and-play UV-T measurement instrument so plants that may historically have thought they didn’t need to measure UV-T online will instead say, ‘Why don’t we?’ The technology is simple, the maintenance is extremely low, the footprint is small and it’s affordable. We’re trying to make it accessible to everybody.

WSO: In what circumstances might a utility use a hand-held version of this technology?

Shaver: A consultant could use a hand-held unit to go into the field and take individual samples, such as in the early stages of designing a UV system. Or they may need to take samples during the evaluation phase of a UV system installation. Some plants may opt to have the technology on hand to take measurements on grab samples and use the resulting values as a basis for running their system.


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