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Chemical Oxygen Demand

A measure of the amount of oxygen required for chemical oxidation of organic material in water by a strong chemical oxidant (expressed in mg/L). COD is always equal to or higher than BOD since it is the total oxygen required for complete oxidation. It is an indirect measure of the amount of organic material present in water or wastewater: the more the organic content, the more oxygen is required to chemically oxidise it (high COD). A high organic content is generally an indictor for water pollution. The COD subtracted by the BOD gives an indication of the non-biodegradable chemicals and thus the toxicity of the water. See also: COD/BOD5 Ratio

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