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What are the differences between Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD)?

Ask the expert: What are the differences between Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD)?

Answer: Both COD and BOD test methods aim to give an indication of the amount of pollution in a water sample. COD is the amount of oxygen required to chemically breakdown the pollutants. Whereas BOD is the amount of oxygen required to do this biologically through micro-organisms. There is a strong correlation between COD and BOD, however COD analysis is a much faster and more accurate method.

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BOD Analysis

BOD analysis is performed to determine what effect dirty water, containing bacteria and organic materials, will have on animal and plant life when released into a stream or lake. Bacteria will need to take in oxygen in order to break down the organic materials (pollution) in the water. The test measures the potential of the incoming water to deplete the oxygen of the receiving waters due to the bacterial activity.

If there are high levels of organic waste and bacteria in the water it will have a detrimental effect on the surrounding ecosystem. Low levels of organic waste and fewer bacteria present mean the BOD will be lower and the dissolved oxygen levels higher. The BOD test involves taking an initial dissolved oxygen (DO) reading and a second reading after five days of incubation at 20°C.

COD Analysis

COD analysis on the other hand is a measurement of the oxygen-depletion capacity of a water sample contaminated with organic waste matter. Specifically, it measures the equivalent amount of oxygen required to chemically oxidize organic compounds in water. Thus removing the pollution. COD is an integral part of all water quality management programmes.

Traditional COD measurement methods use potassium dichromate and mercury. We have compiled a handy bundle of all of the equipment needed to get you started with perform COD measurements here.

For more information on the COD and BOD products available from Camlab in the UK or the rest of the world please fill in the form below. Or you can call us on 01954 233 120 to discuss your options with our technical support team.