TOC Analysis How to Profit from TOC Analyzers — Reliable Monitoring of Water Quality

Author / Editor: Martin Glittenberg / Dr. Jörg Kempf

The process oriented construction of a chemical plant is one of the most important aspects to ensure high quality production. Malfunctions may lead to extensive and expensive consequences. To prevent this, the TOC (Total Organic Carbon) content is detected in the immediate proximity of the processes using an online analyser. Two success stories …

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A sample with dissolved and particulate organic carbon
A sample with dissolved and particulate organic carbon
(Picture: LAR)

An international pharma group with locations in Germany and Switzerland, monitors the inlet and outlet of its production sites for organic carbon and nitrogen. The water is characterised by a high salt concentration and frequently changing loads. On high contamination at the waste water treatment plant’s inlet, the waste water is led into a reservoir. The monitoring of the outlet is for the documentation of the successful treatment on request of the appropriate local authorities.

In order to ensure that the discharge regulations have been observed as well as for the protection of the treatment processes an online analyser is used that measures the total organic carbon in combination with nitrogen. This measuring system monitors two sample streams. The influent stream has a range of 0…1,000 mg/l C, while the effluent stream has a range of 0…100 mg/l C. Normally, the measurement values of the two streams differ by a factor of 70. The expectations of the end user were high: Besides correct measurements, no memory effects or cross contamination of the two streams were allowed. Additionally, a robust design and high availability were requested.

In order to find the best suitable system, several online analysers and methods were tested. One analyser working with the wet chemical oxidation method showed strong dependencies with the sample matrix and was not able to measure the outlet stream stably. Due to the weak oxidation power and its incomplete oxidation, a new correction factor needed to be defined very frequently. This increased maintenance, however, was only performed inadequately by the manufacturer’s representative in Germany.

Further measuring systems which worked with continuous and discontinuous catalytic thermal oxidation methods failed as well. The reasons were various. However, mostly due to the fact that the reactor could not handle salt which caused intensive maintenance and low availability.

No Expensive Catalysts

Finally, after an 8-week-trial, the end user decided to install the LAR analyser that works with the Ultra High Thermal Oxidation at 1200 °C. It is in use since then. This 2-stream-system measures the TOC in combination with TNb (Total Nitrogen bound). The high thermal oxidation potential makes the use of expensive catalysts unnecessary. The innovative robot-driven injection system handles particles very well while the complete raw sample including any particulates is injected into the reactor. After the combustion, the produced CO2 is led through the appropriate NDIR detector and the true TOC is detected. Subsequently, the nitrogen content is determined by the use of an electro chemical cell (EC-cell).

The complete digestion of all compounds of the unfiltered sample allows an accurate analysis of the required parameters. In the course of the trial, this method proved to be very reliable considering changes of the sample matrix and providing a long reactor service life. Even with high salt concentrations no problems occurred. The maintenance and service time of this system is convincingly low so that the LAR Quick TOC won the test. Now, this online analyser helps reliably to protect the waste water treatment plant from overloading as well as to observe the local discharge regulations.

For the second success story go to the next page.

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