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On-line Chemical Oxygen Demand Monitoring and Analysis

Redox Titration

The usual method for determining chemical oxygen demand involves reacting a sample with dichromate under acidic conditions. In this reaction, pollutants in the sample are oxidised and the dichromate is reduced to the chromic ion. The unreacted dichromate is titrated with iron(II) ammonium sulphate to determine the amount that was used.

This procedure can be performed automatically by an Applikon on-line analyser in 125 minutes with an accuracy of ± < 5.0% FSR.

UV Absorption

The Lange UV process probe for chemical oxygen demand measurement has a flashlight photometer with a cuvette formed by a gap (aperture) in the probe housing. The UV extinction of the immersion medium around the probe is measured across the width of this measuring aperture. A wiper in the aperture prevents fouling of the measuring window. The effect of turbidity on UV absorption is compensated by a reference measurement.

The benefits of this method are:

High Temperature Oxidation

The QuickCOD from LAR oxidises samples at over 1200°C without the aid of expensive catalysts. Therefore, difficult to combust compounds are oxidized effectively and rapidly, regardless of their composition. Since the complete sample is injected into the furnace, no solvents can evaporate, and the QuickCOD is able to measure methanol, ethanol, and other volatile C-sources exactly. Results are available in 1 minute.

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