3. Water & Environmental / Water Analysers

Where can the WTW reagent free COD method be used? How does reagent free COD compare to standard methods?

WTW has developed an innovative reagent free system to measure COD, Nitrate and Nitrite without the need for vials.

The OptRF system is built in to some of their spectrophotometers, and provides calculation of the results based only on absorbances in the UV wavelength range.

However, this system is only applicable to some samples and should be evaluated before changing from traditional COD vials methods. We have explored the details of the OptRF system below.

PhotoLab 7600 spec by WTW
The PhotoLab 7600 Spectrophotometer is one of the models with the reagent free COD, Nitrate and Nitrite measuring system OptRF built in

How does reagent free COD, Nitrate and Nitrite analysis work?

The technology evaluates COD, Nitrate or Nitrite levels by photometric analysis. It is built in to some of WTW’s advanced spectrophotometers, including the PhotoLab 7600 model.

The unit scans the sample from 200 to 390 nm, over the UV range. The absorbance seen is then used to calculate the result in mg/L which can be displayed instantly.

The calculation is based on a multitude of real measured samples which have been measured by traditional COD vial methods.


What samples can be tested in this way?

This new method is currently designed for the effluent of wastewater treatment plants. It is only suitable in applications where there are few particles, as these can interfere with the measurement.

Even in this type of environment, the specific matrix of substances present will vary from site to site, so an internal calibration and comparison to traditional methods should be conducted to assess if it is suitable. Camlab can assist and advise on this if required.


How do the results compare to traditional vial test methods?

The technology has been implemented in the municipal wastewater treatment plants in Muhlbachl (Tyrol, Austria) and Adelsorf (Bavaria, Germany) and showed good correlation against traditional methods.

For example, the results from Adelsorf in Germany showed;

  • COD with OptRF = 30.8 mg/L
  • COD with OptRF with site calibration = 28.0 mg/L
  • COD with traditional vial testing = 28.1 mg/L
  • Nitrate with OptRF = 0.91 mg/L
  • Nitrate with OptRF with site calibration = 0.71 mg/L
  • Nitrate with traditional vial testing = 0.70 mg/L
  • Nitrite with OptRF = 0.17 mg/L
  • Nitrite with OptRF with site calibration = 0.10 mg/L
  • Nitrite with traditional vial testing = 0.11 mg/L


To find out more about reagent free COD, Nitrate and Nitrite testing, follow the links above or contact us with your questions or to find out if the technology would be suitable for your site;