Oxygen Uptake Rates - both SOUR and DOUR - are easy tests requiring only a BOD bottle, O2 probe, and stir plate/stir bar. Completed with 5 - 10 minutes, the OUR test requires no reagents or special advanced techniques, yet provides critical information on microbial activity and growth rates.
The SOUR is simply the DOUR divided by the MLSS or MLVSS in grams - just make sure you use the same divisor each time as the oxygen uptake rate tests rely on trends rather than a single data point. As the biomass reaches a more "mature" stage - stationary or decline phase growth (all depends on system type), the SOUR decreases. Lower oxygen uptake rate values show the cells do not have excess soluble organics and are not rapidly dividing. However, if you see a high COD and still have a low OUR - it could indicate toxicity or lag phase growth. Neither condition makes for good effluent quality.
For OUR to be a powerful tool, it must be frequently run. Depending upon fluctuations in influent quality or makeup - OUR should be run anywhere from every shift to weekly. The more often it is run, the better the information provided by the test.
By running OURs, a facility can replace the use of expensive equipment such as respirometers or high cost reagent tests for daily monitoring. So remember that while the OUR test is simple and not the latest in technology, it is very useful in monitoring biomass activity.
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.
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