Biochemical Oxygen Demand (BOD₅)

(BOD₅) means a 5-day biochemical oxygen demand. The idea of the analysis is that in polluted water there is an oxygen demand caused by micro-organisms. The required oxygen demand was used to measure the extent if the pollution. Oxygen demand increases as temperature and time of reaction increases. See Figure of BOD concentration vs reaction time for various temperatures.

Different organics have different oxygen demands per gram of matter and this means that the BOD-analysis only gives an approximate estimate of the weight of oxidized organic matter.

 Details of the BOD test

Chemical Oxygen Demand (COD)

COD is a measure of the oxygen equivalent of organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. The chemical oxidants include: potassium permanganate and potassium dichromate. The COD-analysis may be carried out automatically and relatively fast (1-2 hours) and the measured COD-values give a good picture of the total content of organic matter.

Total Organic Carbon (TOC)

TOC is calculated by measuring the difference between the carbon dioxide concentration before and after oxidation. TOC is not unambiguously tied to other parameters for organic matter as it states the amount of carbin atoms, but does not say anything about their state of oxidation. Hence, it conveys no information as to how much oxygen should be used for the oxidation.

References

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