Special considerations, Sample dilution, Sample seeding – Hach-Lange BODTRACK II User Manual User Manual
Page 20: Sample temperature, Toxic materials, Refer to, Refer to section, Reading. refer to, Figure 3
Figure 3 Typical curves
1 Typical with substrate variation
3 Typical with time lag
2 Typical
Special considerations
Sample dilution
Unknown sample BOD effluent is typically in the 0 to 70 mg/L range.
Unknown sample BOD influent is typically in the 0 to 700 mg/L range.
When the oxygen requirement of a sample is more than 700 mg/L, dilute
the sample with high-quality distilled or deionized water.
Calculate the results to include the additional dilution factor. Example: if
the BOD of the sample is 1000 mg/L, dilute the sample 1:1 with distilled
or deionized water. The estimated BOD is now 500 mg/L. Use the
sample volume specified in the table for the 0 to 700 mg/L range of the
selected procedure. Multiply the instrument reading result by 2. If the
Hach Standard Method procedure is used, continue with the rest of the
calculations.
Sample seeding
Some types of BOD samples do not contain sufficient bacteria to oxidize
the organic matter in the sample. Many industrial wastes are of this type.
Some sewage treatment plant effluents are chlorinated and essentially
sterile. A BOD test cannot be done in the absence of viable bacteria. To
test such samples, seed each bottle from a source known to contain a
viable bacterial population.
Settled domestic wastewater plant influent or primary clarifier effluent are
the preferred sources of seed for most samples. Mixed liquor or
undisinfected effluent can be used for seed, but it is recommended to
include a nitrification inhibitor. Commercial seed sources are sometimes
suitable. To prepare, see the instructions from the manufacturer.
Sample temperature
Standard Methods for the Examination of Water and Wastewater, 21st
Ed., 2005 5210 D recommends an incubation temperature of 20 ±1 ºC
(68 ºF) for the BOD test. Put the instrument in an incubator that is
adjusted to 20 ±1 ºC. Warm or cool samples to 20 ±1 ºC.
Instrument performance has not been validated at temperatures other
than 20 ºC.
Toxic materials
Industrial and chlorinated samples often contain toxic substances and
require special considerations when running BOD tests. Toxic materials
in the sample will cause decreased BOD values. Dilute the sample to
minimize the toxic materials or their effects. Refer to Standard Methods
for the Examination of Water and Wastewater, 21st edition, 5210 D.
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