Alexander Szabo and Oscar Engle - Svenskt Vatten

BOD analyzes were carried out using a BOD incubator (Hach, model 205) which is especially
designed for BOD tests. The sampling bottles are connected with a tube (for oxygen
measurements) and put in a compartment that keeps the temperature at 20 °C. A computer
records the oxygen consumption over time. The procedure was performed according to the
product manual. One benefit of the BOD incubator is that it allows reading of the oxygen
consumption (BOD) continuously (instead of only a final measurement after 5 days as the
“manual” procedure described above). For calculations of the k-value (Appendix E) readings
were recorded with 0.5 days intervals (Appendix F).
One full testing event with the BOD incubator was successful. Other testing events failed due to
technical problems with the BOD incubator or lack of available storage space in the fridge where
the incubator was.
Manual method
The “manual” measuring of BOD 5 is done with the following procedure:
‐ Filing 300 ml airtight bottles with diluted waste water (The purpose of diluting the
samples was to reach a DO above 7 mg O 2 / liter, which may be necessary for a
successful BOD reading after 5 days, as the DO must be above 2 mg O 2 / liter at final
reading. Dilution 1:1 with distilled water was enough for this purpose).
‐ Measuring the initial DO level in the samples with a DO meter.
‐ Storing the bottles in a refrigerator at 20 °C for 5 days.
‐ Measuring the final DO with a DO meter.
The BOD 5 was calculated as the decrease of DO per liter of water.
This method was considered as slightly unreliable as the reading of the DO meters was difficult.
The DO measured DO concentration was not stable over time, hence making it difficult to
measure the final DO.
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