Preparing Several Identical Samples; Sample Seeding; Determining Bod Of Seed - Hach BODTrak Instrument Manual

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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.

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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