UV-Spectral Probe for Measuring Chemical Oxygen Demand, Nitrate and Nitrite in Wastewater

Optical measuring methods are widely used for analytical purposes. In the laboratory they have a long history. Various chemical compounds can be determined by forming dyes after the addition of reagents. These photometric methods also can be applied to automatic analyzers being used in online monitoring. The disadvantage of these instruments is that they require periodic replacement of chemicals and spare parts like tubes. Several wastewater relevant substances exist, that absorb light themselves, so they can be detected without the need of reagents. The range of detectable compounds can even be extended by evaluation of the ultraviolet light (UV) absorption. In the UV area of the spectrum the nitrogen parameters nitrate (NO3−) and nitrite (NO2−) can be detected directly. Even chemical oxygen demand (COD), a measure for the sum of organic compounds, is estimable in principle in wastewater since many of its pure substances absorb UV light. The quality of the correlation between these absorbances and the composite parameter COD and the discrimination from nitrate and nitrite and even the separation between nitrate und nitrite can be improved significantly by evaluating the whole spectrum instead of single wavelengths (for example the absorbance at 254 nm). Therefore important processes in the wastewater cleaning process can be monitored with a simple probe instead of a complex analyzer.