Oxygen Uptake Rate (OUR)

I think the subject of oxygen uptake rate testing is so valuable and so important that I have this topic as one of the main sections of this website. Measuring the OUR of a mixed liquor suspended solids sample, and analyzing the data, has become one of my favorite techniques for evaluating the operating condition of an activated sludge biological reactor. This simple, though potentially somewhat time-consuming, test can reveal more about the condition of the microorganisms in a bioreactor than just about any other laboratory test you might conduct.

What Does the OUR Tell Us?

The OUR indicates the biological performance or the health of the microorganisms in an activated sludge wastewater treatment system. The OUR is easily obtained by performing a series of dissolved oxygen measurements over a period of time (≤ 15 minutes) and is reported as mg O2/L/min or mg O2/L/hr.

The oxygen uptake rate test reveals:

  • The general health of the microorganisms (Level 1 testing),
  • Organic overload (Level 1),
  • The presence of inhibitory or toxic compounds (Level 1),
  • Whether or not biological treatment is complete and aeration capacity is sufficient (Level 2 testing), and
  • The oxygen consumption of various waste streams or chemical compounds (Level 3 testing).

I consider there to be three “levels” or three different approaches that can be taken in conducting the OUR test. We’ll discuss each level of OUR testing in more detail on the associated pages. Just click on a Level in the graphic below to get started.

Three Levels of OUR Testing

Some humor

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