YSI BODAnalyst - Manual (Page 15)

SECTION 3 SEEDING SAMPLES
3.1 WHY SEED?
Seeding is necessary when there are not enough bacteria present in the sample. A small amount
of seed material that is known to have adequate bacteria is added to the bottle along with the
aliquot and dilution water.
Seeding is most often necessary with an effluent sample that has been chlorinated. The seed
material can come from the plant's influent, from some intermediate point in the process, or from
commercially available seed packets.
If you don't seed at all, then you can ignore this section, but be sure that you do not fill in the
Seed Control Sample Name or seed Qty (ml): fields on any Sample Setup Form.
3.2 SEED CONTROL SAMPLE
In a seeded sample both the sample and the seed contribute to the depletion. Since it is the BOD
of the sample that is of interest, we must remove the effect of the seed material in our
calculations. To determine this compensation, you must run several dilutions of the seed material
itself. This is called the "seed control sample." The sample name of the seed control sample
must be indicated in the Seed control sample Name field on the sample setup form. Sometimes
the seed material is taken from a sample that is already being tested for BOD, typically the
influent. In these cases, enter Influent in the Seed control sample Name field. Sometimes there
are seeded samples for which the CBOD is to be determined, and others for which the full BOD
is to be determined. In these cases, it may be necessary to have two seed control samples of the
same material, one a CBOD and the other a full BOD.
Seed control samples cannot be pre-diluted. (Neither can blanks)
3.3 SEEDING METHODS
You may choose one of two seeding methods, adding seed material to each bottle that is to be
seeded, or adding seed material to the dilution water.
If you choose to add seed material directly to each BOD bottle, the quantity of seed material is
expressed in milliliters (ml). If you choose this method, you must put the same quantity of seed
material in each of the dilutions of the same sample. However, if you have more than one seeded
sample, each sample may have a different quantity of seed.
If you choose to add seed material to the dilution water, you must first mix the seed material with
dilution water and use the mix to dilute all of your seeded sample dilutions. Note that the amount
of seed material in each bottle depends on the amount of dilution water in the bottle. The
quantity of seed material is expressed in milliliters per liter. Typically, the same seeded dilution
water is used for all seeded samples.