Abstract :

The BOD5 and the BOD-M3 were compared using a suitably chosen test procedure. The investigation shows that clearly defined objectives are critical in comparative investigations in the analysis of waste water. A discontinuous load, in the form of a step curve with two concentration levels and a predefined ratio of these levels to each other, has proven useful in this investigation and in a calibration procedure which has resulted from it.
The results of the comparative measurement of the BOD5, as a round-robin experiment, were very scattered, as was expected. The respective laboratory averages, with a deviation of +10 to 15% , are method-dependent and are acceptable.

The measurement of the BOD-M3 in the experiment depicts the input loading as a step curve. The required stable curves are maintained. The predefined ratio of 3.0 is exceeded by 5%, the BOD-M3 is determined essentially by variations of the mixing pumps and in the oxygen measurements. The reproducibility for the detection of a biologically degradable substance is between 95 and 98%. The accuracy in reproducing the BOD-M3 cannot be achieved with the BOD5. It is therefore useful to indicate not only the BOD-M3 calibrated using the BOD5, but also the uncalibrated standard value of the BOD-M3.