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What are the standard methods for BOD and COD estimation in saline water?

In my coastal water quality monitoring, we've noticed significant discrepancies when applying standard APHA methods for BOD and COD to our estuarine samples. The salinity seems to interfere with microbial activity in BOD tests and the oxidation chemistry in COD tests. I need a clear, practical guide on how to properly modify these protocols or apply correction factors to get reliable data from saline matrices.

 

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By Prajwal Sharma Answered 1 year ago

This is a common and critical issue in coastal labs. I would recommend two primary adjustments. For BOD, you must use an acclimated seed microorganisms sourced from a saline environment. Inoculating with standard seed will yield falsely low results as the microbes are shocked. For COD, the chloride ion is the main interferent, consuming the dichromate oxidant. You must use the high-range method (lower sulfate concentration) and apply a chloride correction factor meticulously, as per the APHA guidelines. I have seen projects fail from neglecting this, as the reported "COD" was largely a measure of chloride concentration, not organic load.

 

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