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What Oxygen Uptake Rate (OUR) test results mean for wastewater bacteria

1/28/2019

 
Picture
Standard BOD bottle used in OUR test. Photo from Wikimedia Commons.
Oxygen Uptake Rate testing is often done without much thought and we report a number, making sure it is within a specific range. Let's step back for minute and understand what the OUR number really means and how it changes in response to influent quality. 

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.
dour___sour_test.pdf
File Size: 361 kb
File Type: pdf
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    Author

    Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater  facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.

    View my profile on LinkedIn

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