Hach BODTrak, Instrument Manual, Page: 46 / 63

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1. Add 10 mL of 0.02 N Sulfuric Acid Standard Solution and 10
mL of 100 mg/L Potassium Iodide Solution to a 100-mL
portion of sample in a 250-mL erlenmeyer flask.
2. Add three droppers of Starch Indicator Solution and swirl
to mix.
3. Titrate from dark blue to colorless with 0.025 N Sodium
Thiosulfate Standard Solution.
4. Calculate the amount of Sodium Thiosulfate Standard
Solution necessary to dechlorinate the remaining sample:
5. Add the required amount of 0.025 N Sodium Thiosulfate
Standard Solution to the sample and mix thoroughly. Wait 10
to 20 minutes before running the BOD test.
4.5.2 Other Toxic Materials
Determine the concentrations of other toxic materials such as
phenols, heavy metals, and cyanides.
NOTE: To determine the concentrations of these and other materials,
see the Hach “Water Analysis Handbook.”
Dilute the sample with distilled water to eliminate the effect of
these materials. The correct BOD is obtained when two
successive dilutions result in the same sample BOD value.
4.5.3 Seed Acclimatization
Domestic sewage or Polyseed Inoculum can provide seed for
most samples. Polyseed Inoculum is ideally suited for domestic
and industrial wastewater because it provides a constant seed
source and is free of nitrifying microorganisms.
Pour the contents of one polyseed capsule into dilution water to
rehydrate (refer to the procedure packaged with the Polyseed).
Aerate and stir for 1 hour. Use enough of this solution so that it
makes up 10 to 30% of the overall sample volume. The exact
percentage of seed must be determined for each sample type.
mL of Sodium Thiosulfate
mL used
( )
mL sample to be dechlorinated
( )
100
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