WEF Discussion Forums
Laboratory Management and Technical Issues
Weirdest BOD Runs Ever
Let me tell you before hand I am completely stumped. I think there are gremlins in my lab.
At our lab we do our industries on a different day than the normal weekly composite samples from the plant. About a month ago our seed correction, GGA, and every sample in an industrial batch was fully depleted! Our blanks were fine with a depletion of 0.04. Since these were all unknowns we do seed every sample. I obviously pointed my finger at our seed as the culprit and wrote a corrective action determining to be more carful with seed preparation.
This is where it gets weird. The same thing happened to a batch from our weekly composites from the plant. Blanks where fine but everything else was fully depleted! The only problem is we do not seed our influent or primary clarifier effluent! So it is not the seed. We double checked the samples and our meter by performing a few winklers (fully depleted). COD was performed on all the samples with normal results. If it was the source water or the buffers we would have seen it in the blank and at least a worsening effect not full depletion randomly! Incubator is working great. We use numbered glass bottles but they are randomly selected and numbers written in the lab book so it is not the bottles. So this has happened twice with four weeks in between of passing batches and we have had two batches pass since!
What could it be?
Have you considered that it might be just that...gremlins! Well...the human kind, anyway. It wouldn't be the first time some disgruntled employee has intentionally sabotaged samples, BOD or otherwise.
Maybe your source water, or one of the nutrients, has been contaminated with some organic that is stable and will deplete when some seed material has been added (Seed material or sample).
What I would do is add to BOD bottle of source water a 300 ml Hach nutrient pillow, and fill another BOD bottle with dilution water blank, and then add just a drop or two of seed material or influent sample. This will be just a few bacteria but if there is an organic in the water it will start depletion.
You could also start over with a different source water and run comparisons to see if one source water works better than others.
I once had some mice get into the lab and was using peanut butter in traps to cacth them. They were getting into the peanut butter before I could get them so I put the small container of peanut butter into the incubator so they could not get to it. My dilution water did a similar thing as yours except did not deplete more than a couple mg/L and ruin some BOD runs.