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Comparison of manometric and disolve oxygen method of BOD
Antonios Eleftherianos
Posted: Thursday, March 15, 2012 3:49 AM
Joined: 3/15/2012
Posts: 4


Hello, checking the available BOD5 methods in Standard Methods for Examination of Water and Wastewater i notice that the two different methods give for the same concentration of standard (150 mg/l glucose and 150mg/l glutamic acid) diferent expected results: For the method using oxygen meter the expected BOD5 for this standard is 198±30,5 mg/l while for the respirometric method the expected result is 260±30 mg/l. Which is the explanation for this difference? Thank you very much.

Charlie_2
Posted: Sunday, March 25, 2012 4:57 PM
Joined: 8/15/2011
Posts: 5


I agree.  An error must have been made in the respirometric BOD method.  We should wait and see if Perry Brake has an explanation for these different GGA target concentrations between 5210 B and 5210 D.
Perry Brake
Posted: Tuesday, March 27, 2012 9:41 AM
Joined: 12/17/2010
Posts: 23


Perry doesn't have an answer for this one.  In each test, the same bugs work on the same organic material (GGA) for the same length of time so one would expect the two methods to give comparable results.  Standard Methods 5210B says how the 198 mg/L goal was derived...from a nationwide study.  But 5210D doesn't say how the 260 mg/L was derived.  I suspect a faulty study resulted in that number, but if not, it would be nice if the BOD Committee of Standard Methods would explain the difference.
Charlie_2
Posted: Tuesday, March 27, 2012 5:00 PM
Joined: 8/15/2011
Posts: 5


I asked Standard Methods why there was this difference in the depletion targets for the two methods.  They forwarded my Query to experts within AWWA and this is their response, "In 5210B, oxygen depletes to near stasis conditions for aerobic organisms; in the respirometric test, oxygen is not limited, because air is renewed periodically keeping oxygen levels in a higher range throughout the test.  I don't know of any lab that ever gets consistent GGA results above 220 with 5210B." This answer is quite logical. It does contradict my experience. We used Oxtitops in the past to avoid week-end work.  Our GGA results were higher than the dilution method by a few mg/L but no where near 260 mg/L.