WEF Discussion Forums
Laboratory Management and Technical Issues
Does anyone have proceedure for adding sample to bod bottles. I was always told, never add sample, ie effluent sample or seed to an empty bottle, i read standard methods and it is reverse.
Standard Methods allows you to "prepare dilutions either in graduated cylinders or volumetric glassware and then transfer to BOD bottles or prepare directly in BOD bottles".
You would measure/pipet sample volumes directly into the BOD bottles, add seed and TCMP if needed, and then fill the rest with dilution water.
You didn't say which edition of Standard Methods you are using, but it probably doesn't matter because they are all difficult to understand. For example, the 21st Edition says to never add seed directly to a sample, but for a super clean effluent where you might be analyzing 295 mL of sample, you add the seed to the sample (unless you add the buffer/nutrient pillow contents first and then say, "I didn't add the seed directly to the "sample"...but that is semantics.
I think adherence to two common sense principles will keep you out of trouble. One is never to add seed to a dry BOD bottle. The seed solution will be suddenly exposed to a dry, hostile environment which might injure or even kill many of the seed bacteria. The other is never to add the inhibitor to a small volume of sample (such as for an influent sample). The inhibitor will possibly (if not probably) inhibit not only the nitrogenous bacteria (the intended effect), but also the carbonaceous bacteria (not intended).
A third thing would be to avoid introducing the seed and, if doing a CBOD, the inhibitor as the last things in a super clean sample (i.e., ~290/295 mL of sample. The seed, and even more so, the inhibitor, might not go into solution as intended (it is already hard enough to get the inhibitor into solution when the bottle is only half full!