Will the BODTrak™II results match other BOD methods?

Document ID

Document ID TE3287

Version

Version 6.0

Status

Status Published

Published Date

Published Date 09/28/2018
Question
Will the BODTrak™II results match other BOD methods?
Summary
BODTrak™II versus BODTrak™ and Dilution Method
Answer

The test results for a Biochemical Oxygen Demand (BOD) test using the BODTrak™ II will not always match the results obtained when using the Dilution Method, or even the original BODTrak™.

The Respirometric Method, used by the BODTrak™ and BODTrak™ II, yields higher results than the Dilution Method due to the constant stirring and the headspace above the sample. The stirring increases the contact between microorganisms and food and accelerates the transfer of oxygen from the bottle headspace to the sample. The result is an increase in the respiration rate and oxygen consumption of the microorganisms, which creates higher BOD values.

When comparing the BODTrak™ with the BODTrak™ II, it is important to understand that the BODTrak™ was developed at a time when respirometry was not widely used as a standalone technique. The BODTrak™ was designed to allow for comparable results with the Dilution Method after a 5-day incubation period. With the acceptance of the Respirometric Method 5210 D by Standard Methods, improvements were made to the BODTrak™ II to provide greater precision and accuracy and alignment with this method.

To compare BODTrak™ II results with the BODTrak™ or Dilution Method, a correlation must be established. 

Determine the BOD of the sample using the BODTrak™ or Dilution Method. Then, follow the appropriate procedure in the BODTrak™II manual for the sample and incubate for five days. Results are graphed over time and remain on the large graphic display throughout the duration of the test. Determine the amount of incubation time that it took the BODTrak™ II to achieve the same result obtained from the comparison method. A seed correction must be applied for seeded samples.

For example, say the result was achieved in 2.45 days. For future test samples, the results shown on the BODTrak™II after 2.45 days of incubation will be comparable to the BODTrak™ or Dilution Method. Ideally,
a correlation should be determine for each type of sample tested (ex: influent, effluent, GGA).



 

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