Why are CBOD results lower than BOD results when testing a BOD standard solution formulated from GGA?

Document ID

Document ID TE170

Version

Version 4.0

Status

Status Published

Published Date

Published Date 08/28/2018
Question
Why are CBOD results lower than BOD results when testing a BOD standard solution formulated from GGA?
Summary
Differences between CBOD and BOD results using a BOD standard
Answer
It is common for the results of Carbonaceous Biochemical Oxygen Demand (CBOD) to be lower then Biochemical Oxygen Demand (BOD) when testing Glucose and Glutamic Acid (GGA) standards for BOD.

The structures of Glucose and Glutamic Acid are shown below. Glutamic Acid contains a nitrogen group, which will contribute to the nitrogenous demand of the BOD measurement. During a CBOD test, nitrification inhibitor is added, which prevents the oxidation of the nitrogen group in Glutamic Acid to nitrite or nitrate.

Per Standard Methods, one would adjust (increase) the amount of seed, even with CBOD, to get within the specified result of 198 +/- 30.5 mg/L.


 
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