Tests For: Assessing effluent and wastewater quality prior to discharge
Reagent Chemistry Used: Dichromate
Basis of Test Method: Standard Method 5220-D, ISO15705:2005, BS 6068-8.80:2002
|Test Name||Test Range (mg/L O2)||Method Detection Limit*||Limit of Quantification**|
Chemical oxygen demand is a vital test for assessing the quality of effluents and waste waters prior to discharge. The Chemical Oxygen Demand (COD) test predicts the oxygen requirement of the effluent and is used for monitoring and control of discharges, and for assessing treatment plant performance.
The impact of an effluent or wastewater discharge on the receiving water is predicted by its oxygen demand. This is because the removal of oxygen from the natural water reduces its ability to sustain aquatic life. The COD test is therefore performed as routine in laboratories of water utilities and industrial companies.
The Palintest COD method conforms to the sealed tube reflux version of the method detailed in Standard Method 5220-D. Over the range of the test, the colour changes from orange to green. The results are expressed as milligrams of oxygen consumed per litre of sample.
Effluents and wastewater samples may contain undissolved or particulate material. Such samples may be homogenised in a blender prior to the test to improve accuracy and reproducibility.
Chloride is the main potential interference in the COD test. High chloride levels may result in an apparent high COD result. The Palintest COD tests will not be significantly affected by chloride levels up to 1000 mg/L. Samples containing above this level should be diluted to reduce the concentration to 1000 mg/L or below and the test carried out on the diluted sample.
If sample dilution is not possible then it may be necessary to suppress chloride interference. The method most used in standard analytical methods is the addition of mercuric sulphate to the reagent system. The table below shows different Palintest COD mercury tests available. COD/20000/M or 2M are suitable for use with seawater samples.
|COD Tubetest||M or 2M||Amount of mercuric sulfate present (g)||COD Measuring Range (mg/L)||Maximum concentration of chloride suppressed (mg/L)|