Reagent-Free Measurement of COD, Nitrate and Nitrite

The revolutionary new optical reagent-free measurement procedure (OptRF) allows measurement of COD, Nitrate and Nitrite in the discharge of municipal wastewater plants photometrically, yet without the need for any photometric reagents. The optical procedure is well-proven in online measurement  and has now been adapted by Xylem WTW for laboratory use with the photoLab 7600 UV-VIS spectrophoto­meter.

To perform an optical reagent-free measurement, the sample is pipetted directly into a 10 mm quarz cuvette. Upon selection of the method from the menu, a UV range spectrum of the sample is measured. The concentration of the parameter is calculated by complex algorithms taking into account the whole spectrum, and the result is displayed directly as a concentration in mg/l.

The evaluation models are matrix, i.e. sample dependent. As each wastewater treatment plant shows a specific sample composition (matrix), the OptRF method can be adapted and optimized for the respective plant. This is done by a reference measurement with common standard-complying procedures, e.g. the COD cuvette test permitted for self-control. The COD cuvette test requires smaller reagent volumes than the DIN standard procedure, but it is still time-consuming and still employs the health hazardous substances potassium dichromate and mercury sulphate. Potassium dichromate has been included in appendix XIV of the REACH regulation for substances of very high concern (SVHC).

The results of reagent tests, online measurements and OptRF procedures show excellent consistence, especially when taking into account the tolerance ranges of COD cuvette tests and COD standards. Hence, the reagent-free measurement lends itself e.g. for quick controls of preliminary tests of the expected measurment ranges of test sets.

The OptRF procedure offers enormous advantages compared to the usual reagent procedures: Faster than any digestion, Cost-savings at reagents, Cutback of environmentally hazardous reagents, and Improvement of ocucpational health and safety (no harmful substances).