Expensive devices are now mostly used for COD, BOD, TOC determination. These devices are not only expensive in terms of initial outlay, but also in their maintenance. The part ranges captured, however, are not identical, which means that each of these measured values has a different significance. For this reason, every operator chooses a different values from which he believes he can best control his plant, i.e. the sum parameter he believes to have the greatest significance for his system.
SAC is the Spectral Absorption Coefficient measured at 254 nm, its unit is 1/m and his value is a sum parameter that represents a guide value for organic load in wastewater. The SAC value enables the creation of a direct relationship to COD or TOC using correlation in municipal sewage treatment plants, providing a significant sum parameter for dissolved organic contents.
The measuring principle of the sensor is based on the UV light absorption of organic substances. The water sample is exposed to UV light and the transmitted light is deflected to photo receivers using an optical system of mirrors and lenses; a reference measurement compensates for the absorption created by turbidity.
Tests at various sewage treatment plants show that there is good correlation in the outflow between COD and SAC and between TOC and SAC; the running costs of the SAC measurement system are also significantly lower than conventional TOC or COD analysers because the measurement process, is a direct physical SAC measurement which does not require chemicals or other materials. In addition, the sensor does not require pumps or other moving mechanical components which are subject to wear.
The CSS 70 SAC probe can be used wherever correlation factors need to be determined between TOC (total organic carbon) or COD (chemical oxygen demand) parameters.
It is important that there are no significant fluctuations in the composition of the wastewater. Applications in which different types of wastewater are used for different production processes should therefore be avoided, since correlation between TOC and COD is not ideal here. Typical applications are the monitoring of the inflow and outflow of municipal sewage treatment plants.