What is UVT?

Ultraviolet Transmittance (UVT) /  UV Transmission (UV254) 

UV Transmittance, also known as UV Transmission or UV254, is a way to measure and quantify organic levels and water quality. The parameter is based on UV light passing through a water sample to a sensor, the amount of light transmitted through the sample and received by the sensor is the Ultraviolet Transmittance. At Photonic Measurements, we specialize in optimizing UVT monitoring using advanced UV254 technology that specifically targets UV light at 254nm. This is the wavelength organic chemical and biological matter are most responsive to so this parameter can be used as a surrogate for Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Organic Content (TOC). *

*As long as the content is organic.

Why measure it?

UV Transmittance UVT is a real-time measurement and is received instantly making it a very valuable unit as similar wet-chemical and reagent-based methods are costly and time consuming. Although UV is not a direct replacement for BOD5 or COD reagent tests, it is a valuable parameter for quick, instant results. There has been a steady adoption of UV Transmission equipment over the last 20 years as scientists, environmentalists and water treatment professionals realise the benefits of having real-time, reliable, instant data to improve decision making and control.

Who and where is it used?

Monitoring UV254 is beneficial in a range of applications surrounding water quality. A Water Treatment Plant (WTP) operator or MEICA/EICA engineer may use UV254 at raw water inlet and integrate the monitor with SCADA to have the water quality constantly monitored. A Wastewater Treatment Plant (WwTP) operator may need real-time measurement of water quality at Final Effluent (FE) to ensure they are compliant with bathing and discharge legislation, UV Transmission will allow them to identify any spikes immediately to ensure early rectification. UV Transmittance can be used to verify a UV disinfection process and even help to save electricity by controlling a UV dose.

Our rivers, reservoirs and coastal areas can be spot checked by environmental authorities with a portable UV254 analyser to identify a pollution event. UV 254 can also be used by companies with a risk of high COD discharges, with a constant monitoring system they can flag, alert and mitigate releasing to a water course and avoid a hefty fine.  

How to use UV Transmittance?

This continuous stream of data enables operators to closely monitor water quality, detect changes or anomalies, and make well-informed decisions regarding treatment processes. It enhances operational efficiency, helps ensure compliance with regulatory standards, and optimizes water treatment operations. UV254 can be used as a standalone measurement and will only have to be calibrated against deionized water or it can be correlated with surrogates to get real-time BOD, COD and TOC results. Simply select a monitoring solution from our list or contact us to find out more. 

The image below shows UV Transmission and Absorption Data presented on our IoT portal.

Using UVT

To use UV Transmittance UVT for continuous  water quality monitoring you will require a probe, flow cell and a controller.  These 3 parts combined and assembled make up our inline monitoring system. 

Select a controller based on how you would like to receive the UV data from the probe i.e. whether it's going to SCADA, USB or IoT Portal. Also if you wish to receive data for COD, BOD or other correlated data this will factor into your controller selection.

For on the spot measurement you can use a cuvette based UV monitor like our UV254 Go! 

Firstly set a baseline point of clean water by taking a reference using deionised water this will allow full transmittance of light and set this point as 100% transmission at the sensor. When you take a measurement of sample water the organic content will be absorbed and you will get a UV Transmission percentage based on the water quality.

Allow water to flow through the flow cell crossing the measurement path (this may require pumping). The device will take readings every 10 secs, you can customise how often you want the data reported i.e. every 5 minutes.

Ensure results are reasonable, accurate and acceptable within the expected range. You can allow the system to operate completely automatically and the only maintenance required is to clean and recalibrate the probe every 3-4 weeks using deionized water.

That's it, it's that simple! 

Check out range or ask us for more information.

Applications of UV Transmittance

UV Transmittance is used in Water Treatment Plants (WTP) , Wastewater Plants (WwTP), Industrial Trade Effluent and Environmental Monitoring.

It can be used at raw water inlet, monitoring incoming water quality for feed forward maintenance and cost saving of chemical dosing.

An analyzer can be used at final effluent to monitor discharges, report spikes, and to ensure compliance with environmental directives.

A continuous measurement device can be placed at a Combined Sewer Overflow (CSO) for event duration and quality monitoring.

UV disinfection is a very effective way of removing undesirable material from water and is used in WTP and WwTP but it is paramount to check the condition of the UV disinfection unit, this can be done continuously or spot checked. You can even measure UV254 before the disinfection to optimize the UV dose.

It can help determine the organic loads in lakes, river and reservoirs. Ensuring that water quality is known, measured and monitored is paramount for public safety.


Lisburn, BT28 2GN, GB

About us

Photonic Measurements is:
Incorporated in N.Ireland (NI622996) 
VAT registered in UK (GB192976846)
VAT registered in N.Ireland (XI192976846000)

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