We run OUR using simple equipment - a DO meter and BOD bottle which is present in most labs. No reagents or special techniques are needed. A PDF of the standard OUR & SOUR protocol is at the bottom of the post.
OUR is simply how much oxygen is consumed over a short-time period in a stirred BOD bottle. The OUR gives microbial respiration rates for the MLSS (living bacteria in the bottle). Like humans, bacteria use more oxygen when they are rapidly growing and dividing. What causes rapid growth and cell division? High levels of soluble organics that are a source of food for the microbes. So if we were to spike MLSS with sugars, we would see a rapid increase in respiration rates. A rapid decrease in OUR can be equally problematic. For instance, a shock loading of phenol, solvents, or other biocidal influent can kill many of the living organisms. There is a temporary drop in OUR due to the biocidal action. This is followed by a rapid increase in OUR as the toxicity decreases and the microbes return to steady-state populations. On the growth curve this represents low to decline phase growth where biological wastewater systems are in optimal health.