Qualitative measurements in combined sewer systems lead to high demands on the measurement equipment. This paper describes the application of a newly developed measuring device for continuous measurements in combined sewer systems. First results with a prototype tested in municipal waste water show a very good representation and correlation of the physical parameters measured by the online-probe and the chemical analysis of samples in the laboratory. Measurements in industrial waste water with varying colors and concentrations made it necessary to develop a specialized calibration model. Finally, the paper describes an improved version of the measuring device, that was developed during a research project. In the future, this device will be used for continuous measurements of the parameters COD, SS and SAC in a stormwater overflow.

To obtain a further appreciable reduction of discharges in the area of sewage disposal, besides waste water purification at our treatment plants, discharge of wastewater through the sewer system has to be taken into account. Today, control strategies pursuing this aim are mainly based on hydraulic conditions like level or flow rate. They all neglect the wastewater organic load as an essential parameter. The main reasons are the expensive methods used to continuously measure traditional organic sum parameters like COD or TOC. A meaningful alternative to those parameters is the spectral absorption coefficient at lambda = 254 nm (SAC), defined in DIN 38402 by the German Institute for Standardisation. As a purely physical parameter, the SAC shows a good correlation to organic sum parameters like COD and TOC, especially if municipal wastewater is considered. By using an UV-process probe, it is possible to measure the SAC and infer the organic load of raw wastewater continuously without any sample pre-treatment. By the use of this instrument numerous possibilities arise, in order to control the sewers discharge load depend.