Chemical Oxygen Demand (COD-cr), COD-cr
Chemical oxygen demand (COD) is used to measure the total quantity of oxygen-consuming substances in the complete chemical breakdown of organic substances in water.
Chemical oxygen demand is an important parameter in measuring quality and determining what organic load is present in the water.
All aquatic plants and animals contribute to chemical oxygen demand through their metabolism and excretion of waste products. Dissolution of dead organisms also contributes to the organic carbon, as well as surrounding humus and peat. Anthropogenic dispersal includes all organic substances released into the environment.
A high COD-Cr load in water may signify oxygen deficiency, and fish and other aquatic species are consequently repelled. COD-Cr cannot become a global problem, but regionally there are examples of very serious consequences of COD-Cr. The phenomenon can arise naturally, principally in deep lakes. The ratio between chemical oxygen demand and biochemical oxygen demand can be used in some contexts as a measure of whether the water contains toxic substances.
Source: European Pollutant Emission Register (EPER) and Nationalencyclopedin 2010