Chemical Oxygen Demand (COD-cr), COD-cr
COD (Chemical Oxygen Demand) is a measure of the amount of oxygen needed for chemical oxidation of all organic compounds into their inorganic end products. Dichromate is used to oxidise the organic substances in the method called CODCr.1
CODCr is not a substance but a way of measuring organic matter and has therefore no applications.
Sources and transportation pathways
Organic matter is present naturally in water as living and dead plants and animals. However, human activity contributes to increased concentrations through for example wastewater treatment plants, industries and discharge from agriculture.2 In addition, emissions of the nutrients nitrogen and phosphorous result in increased growth of algae in water, a process termed eutrophication, which in turn results in increased COD values. The largest sources of nutrients are agriculture, municipal and industrial wastewater, forestry, road traffic and shipping.3
Effects on environment and health
Organic matter in water is degraded by aquatic microorganisms. During degradation, microorganisms consume dissolved oxygen present in the water. High levels of organic matter result in a high oxygen demand, which may create areas with oxygen deficiency. Oxygen deficiency can result in the death of for example fish.4 Humans can also be affected by high levels of organic matter in water if drinking water becomes contaminated by microorganisms.5
Extensive growth of toxic cyanobacteria (algal bloom) can occur due to high levels of nutrients in the water. These algae can be directly toxic both to aquatic organisms and to humans.6
International agreements and regulations
COD is regulated by the EU directive on Urban Waste Water Treatment (91/271/EEC) and the EU Industrial Emissions Directive (2010/75/EU).
1 http://www.matavatten.se/Mata_Vatten_3.pdf2 https://www.eea.europa.eu/data-and-maps/indicators/oxygen-consuming-substances-in-rivers/oxygen-consuming-substances-in-rivers-73 https://www.havochvatten.se/hav/fiske--fritid/miljopaverkan/overgodning.html4 http://www.wwf.se/source.php/1183906/wwf_breathless_coastal_seas_engl.pdf5 ttp://www.un.org/esa/sustdev/natlinfo/indicators/methodology_sheets/freshwater/biochemical_oxygen_demand.pdf6 http://www.wwf.se/source.php/1183906/wwf_breathless_coastal_seas_engl.pdf