COD (Chemical Oxygen Demand) is the amount of oxygen required to degenerate all pollution in a chemical way (by adding oxidizing agents and heating). In general with chemical destruction you can remove more pollution than with the biological way. It is expresses in milligrams per liter(mg/l) also referred to as ppm (parts per million) which indicates the mass of oxygen consumed per liter of solution of.
As we knows that chemical oxygen demand is an indirect measurement the amount of organic matter in a sample with this test you can measure virtually all organic compounds be OD and BOD correlate with one another in virtually all samples but BOD is always lower than COD as the biochemical breakdown of organics is often not as complete and the chemical method the definition of chemical of sin demand is it is the amount of oxygen consumed during the oxidation of oxidizable organic matter in the presence of strong oxidizing is in means when we perform COD analysis the chemicals which we use to oxidize the organic matter present in the water or wastewater these chemicals oxidize the waste by chemical method and the amount of oxygen consumed in the duration of 2 RS is called chemical oxygen demand.
Importance of chemical oxygen demand
As cases of organic matter in a sample BOD and COD are critical in wastewater for determining the amount of waste in the water waste that is high in organic matter requires treatment to reduce the amount of organic waste before discharging into receiving waters water treatment facilities do not reduce organic content of wastewater before it reaches natural waters micros in the receiving water will consume the organic matter as a result these microbes will also consume the oxygen in the receiving water as part of the breakdown of organic waste this oxygen depletion along with the nutrient-rich condition is called eutrophication a condition of natural water that can lead to the death of animal.
COD Testing
COD measures how much DO is consumed by the oxidation of organic matter and inorganic compounds such as ammonia or nitrite under controlled conditions. COD testing typically involves digestion of the water sample in a sealed vial with potassium dichromate and sulfuric acid at 150C for 2 hours. Vials are read in a spectrophotometer to determine results.
Importance of Chemical Oxygen Demand:
In the COD test, a reliable oxidizing agent is used in acidic medium, and the oxygen equipment of the organic matter that can be oxidized is measured.
For the test, Potassium Dichromate (K2Cr207) is used at a high temperature & for the fast reaction, silver sulfate is added.
Before this test is carried out, the inorganic compounds (which can interfere with the test) are removed from the sample, which is used for the COD test.
On average, the COD of any sewage is always higher than its BOD because more compounds can be chemically oxidized than the compounds which get oxidized biologically.
The limiting value of COD is about 250 ppm or mg / per liter.
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