UV254 and %UVT

UV254 is the absorbance of light at 254nm, a typical parameter used in water treatment to determine the amount of dissolved organic carbon (DOC) present in real time. It is also sometimes called UVA (UV Absorbance).


Many organics in raw water, such as humic substances, are aromatic and exist in relatively high concentrations. Such organics are known to be a precursor of disinfection by products (DBP). UV254 therefore provides one of the best indicators to whether organics are being removed throughout a water treatment process.


The reciprocal measurement of UV254 is %UVT. This is the same measurement but expresses the result as a in terms of how much light is transmitted through the sample relative to pure water.

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Products for this application

s::can spectro::lyser

An advanced online UV-Vis spectrophotometer for measuring multiple parameters simultaneously

s::can UV::lyser

A specialised online sensor for measuring multiple UV wavelengths

s::can i::scan

A compact UV254 and %UVT sensor for network monitoring, drinking water treatment works and wastewater treatment

Compass coagulation control system

A coagulation control system utilising differential UV-Vis spectroscopy for advanced NOM characterisation in real time

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A series of 35mm i::scan’s were setup in a grid across a network to measure UV254, TOC, colour and turbidity

Network monitoring with pipe::scan

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The pipe::scan enables utilities to better understand their network, proactively manage issues such as THM formation hotspots and prevent customer complaints before they occur.

Event detection in groundwater source monitoring

Monitoring of drinking water sources for contaminants requires an advanced event detection system based on UV-Vis spectroscopy and not just parameters. Pollution into groundwater can take many forms and by using event detection software, a flexible and intelligent system can provide the protection that is required.

Ensuring TOC removal in drinking water filtration

In this case study from s::can, the efficacy of ceramic filtration for the provision of drinking water is monitored using a 35mm i::scan sensor to simultaneously measure TOC, UV254 and turbidity.

Reduce cost of running UV disinfection systems in wastewater treatment

Energy costs of running UV disinfection systems are one of the biggest expenditures of a wastewater treatment works, accounting for up to 25% of the total energy usage. An online %UVT sensor can optimise lamp usage.

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