Hach BODTrak, Instrument Manual, Page: 43 / 63

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4.2.2 Preparing Several Identical Samples
Perform a single dilution for all samples when several identical
samples are needed. After the dilution, multiply the reading by
the dilution factor.
Example:
Prepare a 1:5 dilution by multiplying the original sample volume
by 5 and adding dilution water until the new volume is obtained.
If the sample volume is 200 mL:
5 x 200 = 1000 mL
Dilute the 200-mL sample to 1000 mL using the dilution water.
Multiply the reading corresponding to the diluted sample by 5.
After sample dilution, refer to Table 5 on page 20 to select
volume and range.
4.3 Sample Seeding
4.3.1 Determining BOD of Seed
Certain types of BOD samples do not contain sufficient bacteria
to oxidize the organic matter present in the sample. Many
industrial discharges are of this type. Some sewage treatment
plant effluents are chlorinated to the extent that they are
essentially sterile, making it impossible to perform a direct BOD
test. To test such samples, seed each bottle with water known to
contain an abundant bacterial population (e.g., Polyseed
®
Inoculum, Cat. No. 24712-00, or domestic sewage).
The BOD of the seed must be known in order to determine the
BOD of the sample. To determine the BOD of the seed, follow the
same procedure used to determine the BOD of the sample. Run a
BOD test on the pure seed and sample at the same time. See
section 4.5.3 Seed Acclimatization for more information.
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