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

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Monitoring of Cooling Water and Waste Water with One TOC Analyzer

At an international chemical group located in Western Germany, cooling water and waste water is produced during the production processes. Cooling water may be discharged into the river Rhine provided that the local regulations are respected. If the threshold value is exceeded, the discharge will be prohibited. Additionally, organic solvents may enter the cooling water during production processes. These purgeable organic carbons are a real challenge for analyses.

The waste water is characterised by a high salt concentration of 100 g/l. By now, the company used in both applications two TOC online analysers that worked with the catalytical high temperature method at 680 °C. Despite the use of an dilution unit, the analysers could not reach a higher reactor service time than seven days. Additionally, these installed analysers work with the NPOC or direct method and determine the parameter only insufficiently.

In the first step of this method, the total inorganic carbon (TIC) is stripped out by adding acid. However, during this process also the volatile and purgeable organic carbons are removed resulting in the so called non purgeable organic carbon (NPOC). However, this NPOC is claimed to be the TOC. As this method did not correspond to the operators’ requirements, different methods were tested in order to find a better solution.

The trial started in spring 2008. Among the tested analysers there was one with the wet chemical method and one with the non-catalytical Ultra High Temperature combustion at 1200 °C. The wet chemical device, nevertheless, proved itself as inappropriate due to its low recovery rates of several substances and its strong dependency on the sample composition. Furthermore, neither the wet chemical method nor the installed catalytical combustion were able to determine both water qualities without any cross contamination.

The non-catalytical TOC analyzer, however, convinced through its innovative oxidation method, its robust design as well as the long service time of its reactor. This system determines the TOC by difference, whereby in the first step, the inorganic and organic carbon compounds are completely and verifiably combusted. The CO₂ produced is detected by an infrared detector (NDIR). This first step results in the value of the total carbon (TC). Afterwards, a separate determination of the TIC takes place. The TC less TIC results in TOC including the POC and VOC.

Two in One Measuring without Cross Contamination

In summer 2010 both analyzers have been replaced by one Quick TOC. The TOC analyzer, now quickly determines any exceeding of threshold values ensuring counter measures in time. With the two-stream feature the analyzer measures both waters, the cooling water as well as waste water, without any cross contamination. Using only one device the operators saved not only high costs of investment, but also costs for operating and maintenance. Additionally, by the use of the new technique the availability of measurements was significantly increased.

The analyzers’ block-building system provides optimal adaptation to different applications. Various requirements are solved easily with specific features such as the combination with the TN_b measurement or the multi-stream option. Since their installations, these online analyzers optimally control the processes. High maintenance costs due to technical shortcomings or analytical inaccuracy and operational costs due to the purchase of expensive catalysts or chemicals are saved.

* The author is an employee at LAR Process Analysers AG, Berlin/Germany.

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