Monitoring the effluent of an industrial waste water treatment plant

A german special chemical manufacturer with production sites all over the world, monitors the waste water effluent of its site in western Germany for the total organic carbon (TOC) and nitrogen compounds (TN). The waste water is characterised by a very high salt concentration and strongly varying compositions. After treatment, the waste water may be discharged into the river Rhein. If the effluent is high contaminated, the waste water will be led into a reservoir.

Due to ensure local legal regulations, an analyser that measures TOC in combination with TN_b (Total Nitrogen bound) is now used. The requirements on such an online system are high accuracy, a robust design as well as an exceptional availability. To find out the best analysers suitable for this application, the operators tested several systems and methods.

During the first trial one analyser that used a wet chemical oxidation method showed a high dependency on the sample matrix resulting in a bad recovery rate. Additionally, various substances of the resin production were only recovered by 40% which was not sufficient for the operators. Apart these analytical shortcomings technical malfunctions occurred. A valve in the inlet of the reactor was blocked very frequently causing an increased need of maintenance. The next system tested, worked with a catalytic thermal combustion by 800°C. The sample taking system of this analyser was blocked every few days causing fall outs of measurements and the expensive Chemolumineszenz Detector was defective. Plant operators' requirements were not met and both analysers failed the test.

After that another third trial started. This time an analyser based on the Ultra High Temperature method at 1,200°C was tested. This system determines the TOC and TN_b by thermal combustion without the need of any expensive catalysts. The innovative XY-injection system injects a part of the homogenised sample into the reactor where it is combusted completely, without filtration. The so produced CO₂ is detected by the NDIR detector (non dispersive infrared) resulting as TOC. Finally, the nitrogen shown as TNb is determined by use of an electro chemical cell (EC-cell). The complete digestion of the ingredients including particulates ensures the accurate analysis of the requested parameters. In the course of the trial, this analyser proved to be a very reliable measurement system. It considered fluctuations of the sample composition, had no problems with high salt concentrations and provided an exceptionally long service life of the reactor.

LAR's QuickTOC_ultra won the test and now it helps to optimally monitor the effluent of this industrial waste water treatment plant. By reliably monitoring the organic contamination in combination with nitrogen the discharge of the waste water is optimally controlled observing the local discharge regulations.