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BD 600_GB_1 08/2015
6 Determining the BOD
WARNING! Observe the SAFETY INSTRUCTIONS at the beginning of the manual. DANGERS
can arise from the sample, the KOH, and the nitrification inhibitor!
6.1 Selection of sample volume
The BOD value of the sample to be expected determines the volume used. A BOD measurement
range (without dilution of the sample) from 0 – 4000 mg/l arises from this.
BOD range
in mg/l
Sample volume
in ml
Nitrification
inhibitor ATH
dosage
0 – 40
428
10 drops
0 – 80
360
10 drops
0 – 200
244
5 drops
0 – 400
157
5 drops
0 – 800
94
3 drops
0 – 2000
56
3 drops
0 – 4000
21,7
1 drops
The measurement range should be chosen such that the results to be expected are in the upper half
of the measurement range. If the BOD value to be expected is unknown, it can be assumed for the
household waste water that the BOD5 value to be expected corresponds to approximately 80% of
the COD value.
6.2 Preparation of the water sample
1. Test the pH value of the waste water sample. The ideal pH value lies between pH 6.5 and 7.5. Any
greater deviation provides a lower BOD value. If a pH value is too high, it can be neutralised with
diluted hydrochloric acid (1 molar) or diluted sulphuric acid (1 molar), and if the pH value is too
low, it can be neutralised with a sodium hydroxide solution (1 molar).
2. Depending on the specifications, the water sample must be mixed well, briefly allowed to settle,
and filtered or homogenised.
3. Measure the exact necessary sample quantity (see 6.1) with the appropriate overflow volumetric
flask and add to the test bottle (use a funnel as necessary). Specified sample volumes must be filled
very precisely. Otherwise major measurement errors can occur. IN the process, ensure the even dis-
tribution of particulate matter. We recommend performing a double or triple test for each sample.
Different results can be expected for the same samples with different shares of particulate matter.
The measurements should be repeated if there are greater variations.