CBOD Blank is too High

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First, despite what anyone has told you, nitrification inhibitor should not be added to a blank. The nitrification, whether ATU or TCMP, will have an oxygen demand in water if there is nothing else in the water besides it for food. It is essential that if a regulator requires that CBOD be done, that the regulator also understands that Standard Methods very clearly identifies the blank as nutrients and source water, and THAT IS IT! There is really nothing that can be done to removet the effects of this as a food source.

Other than the nitrification inhibitor, it is also possible that the blank is bad all by itself. If a normal blank is not run then it is a good idea to run one. That way, it can be determined whether or not the problem is the nitrification inhibitor or the rest of the reagents in the BOD test.


  • Stop using nitrification inhibitor in the blank (if your regulator will permit it).
  • Follow the same procedures that are recommend for My Blank is too High.


1. American Public Health Association (2005) Standard Methods for the Examination of Water and Wastewater "Part 5210B, ΒΆ6c: 5-day Biochemical Oxygen Demand, 21st Edition" Edited by A. D., Eaton, L. S. Clesceri, E. W. Rice, and A. E. Greenberg.

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