BOD & COD testing

Bob Bentz bentz at bitstream.net
Thu Mar 20 04:51:20 EST 1997


Hello,

I am interested in understanding how the Chemical Oxygen Demand (COD) and
Biological Oxygen Demand (BOD) work, and how useful the data obtained
really is.  I have seen parts scattered throughout catalogs for these
tests, but have not found the actual method for how the tests are run.  I
am trying to put together a rough estimate of what it would cost to bring
the equipment in-house for these tests, but need to verify a few questions
I have first:

Are the BOD and COD values obtained from different test methods equivalent,
that is, the newer equipment running 'EPA approved' micro samples produce
similar results to the larger scale tests?

What are the preferred methods?  One catalog mentioned a test in the ASTM
'B' series (don't have any B series), but I don't recall ever seeing EPA
tests run based on ASTM guidelines (at least not in my D and E series).

The reagents listed in one of the tests mentioned in the Fisher catalog had
mercury.  There was mercury free reagents also for low chloride and low
nitrogen content waste water analysis, can the mercury free simply be
substituted regardless of chloride and nitrogen content (just trying to
avoid mercury disposal).  I'm really curious if someone out there has tried
both out there, and what kind of numbers popped out.

Are BOD and COD values of interest to any other part of the world, or are
these 'EPA' tests only applicable to the U.S.?  Anybody care to recommend
more useful tests that are used for most of the planet (ISO, DIN, JIT, Mil
Spec, etc.)?

Big question here:  Can biodegradeability really be determined via a ratio
between the 28-day BOD and the COD?  Some people have mentioned that if the
ration results in values 60% or higher, the product under test may be
considered biodegradeable.  Been told this is a general rule of thumb, but
nobody seems to have documentation, explanation, rhyme or reason for it. 
Worse yet, not everybody has even heard of this 'rule of thumb'.  Anybody
got any ideas on where verification of this could be as I sure haven't
found it.  TIA!!

Regarding biodegradeability testing, are there more useful and more widely
accepted methods for this type of testing?  Sure don't want to invest in
test equipment that has no real useful value other than spitting out some
numbers.

Thanks for any help you may have available on this subject!  And if you
have questions or answers you can e-mail me or call 612-429-1100.  Also,
anybody selling biodegradeable test equipment that may be monitoring, drop
a line.

Bob Bentz





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