In water quality analysis, COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand), TOC (Total Organic Carbon), and KMnO4 value (permanganate index) all measure different aspects of organic matter present, with COD representing the total oxidizable organic matter, BOD indicating the biodegradable organic matter, TOC measuring the total carbon content, and KMnO4 value reflecting the readily oxidizable organic matter; essentially, COD is the most comprehensive measure, followed by BOD, then KMnO4 value, while TOC provides a different perspective on organic content by directly measuring carbon atoms.
Key points about the relationships:
COD is always greater than or equal to BOD:
Since COD measures all oxidizable organic matter, including non-biodegradable components, its value will always be higher than BOD, which only measures the biodegradable organic matter that bacteria can consume.
COD and BOD can be used to estimate the biodegradability of organic matter:
A high COD/BOD ratio indicates a large proportion of non-biodegradable organic matter present in the water sample.
TOC provides a different perspective:
While COD and BOD measure oxygen demand based on oxidation, TOC directly measures the total carbon content in a sample, which can be useful for specific applications.
KMnO4 value is a quick indicator:
KMnO4 value, measured by the amount of potassium permanganate consumed by a water sample, is a rapid test to estimate readily oxidizable organic matter, often used as a preliminary screening tool.
Important considerations:
Site-specific correlations:
The exact relationships between COD, BOD, TOC, and KMnO4 value can vary depending on the water source and the types of organic compounds present.
Analytical methods:
Each parameter is measured using different analytical methods, which can affect the results.
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