Hach BODTrak, Instrument Manual, Page: 45 / 63

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4.4 Sample Temperature
The American Public Health Association (APHA) recommends a
solution temperature of 20 ±1 °C (68 °F) for conducting the BOD
test. Obtain this temperature by placing the BODTrak instrument
in an appropriate incubator and adjusting the temperature until
the solution reaches 20 ±1 °C. An undercounter BOD Incubator
and a combination BOD Incubator/Refrigerator are available (see
PARTS & ACCESSORIES).
Samples should be cooled to incubation temperature. Seeding of
samples with initially high sample temperatures may also be
necessary because samples may have insufficient bacteria (see
4.3 Sample Seeding). Determine the BOD of the seed and the
BOD of the sample at the same time.
4.4.1 Other BOD Test Temperatures
The BOD test can be conducted at temperatures other than 20 °C.
Tool’s
*
results indicate that the five-day, 20 °C value can be
obtained in two and one-half days at 35 °C. Middlebrooks
†
presents nomographs for converting BOD tests to temperatures
other than 20 °C.
4.5 Industrial Wastes
Industrial and chlorinated samples often contain toxic substances
and require special considerations when running BOD tests. The
presence of toxic substances in the sample will cause decreased
BOD values. Either remove the toxic substances or eliminate
their effects by diluting the sample.
4.5.1 Chlorine
Low chlorine concentrations may be dissipated by maintaining
the sample at room temperature for 1 to 2 hours before testing.
Remove the chlorine from samples with high chlorine
concentration by adding sodium thiosulfate as described below:
* H. R. Tool, Manometric Measurement of the Biochemical Oxygen Demand,
Water and Sewage Works Journal, 114; 211-218, 1967.
† E.J. Middlebrooks, A Nomograph for Solution of the BOD Equation, Water
and Sewage Works Journal, 112; R230, 1965.
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