Chemical Oxygen Demand

Topics: Sewage treatment, Water pollution, Sulfur Pages: 2 (544 words) Published: February 25, 2014

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Chemical Oxygen Demand (COD)Introduction:The Chemical Oxygen Demand (COD) test is the standard method for measuring the amount of pollution in a sample that is unable to be oxidised biologically.Oxidation takes place on both the organic and inorganic component but as the organic component is more dominant, it is of more significant interest.In the COD test, the amount of oxidation that takes place depends on sample COD concentration, digestion time and reagent strength. It gives a measurement for the total organic carbon present in the sample.The open reflux test can be used for a large range of wastes, but results in hazardous wastes such as mercury and sulphuric acidbeing produced. These quantities can be reduced by the use of the closed reflux method. The aim ofthis experiment is to determine the COD value for a given sample using the closed reflux method.

Procedure: Apparatus:Digestion VesselIncubator preheated to 150 ̊C, with holes for holding digestion vesselsMicroburetSilver Sulphate Sulphuric Acid (AgSO4)Potassium Dichromate MixTest SampleSpectrophotometerFigure 1-SpectrophotometerFigure 2-IncubatorFigure 3-Absolute Value Solutions

Methodology:1.To ensure no contamination of sample occurs, cleanthe culture tubes and caps using 20% silver sulphate sulphuric acid (AgSO4)2.Insert 3.5ml of AgSO4, 1.5ml of potassium dichromate mixand 2.5ml of test sample into digestion vessel using the microburet. Provide a duplicate sample so as to minimise any error that may occur.3.Insert sample tube into incubator preheated to 150 ̊C and leave for 2 hours. Remove and allow sample to cool to room temperature.4.Set spectrometer...

References: iely, G. (1997)Environmental Engineering.Mcgraw-HillClesceri. C, Greenberg. S & Eaton. D (1998) Standards and methods for Examination of Water and Wastewater. 20thEdition
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