OUR measures how fast the biomass uses oxygen. A sudden drop can signal toxicity.
Oxygen Uptake Rate (OUR)
Formula
OUR, mg/L/h = (Starting DO - Ending DO) / minutes x 60
Inputs used
- Starting DO (mg/L)
- Ending DO (mg/L)
- Elapsed time (min)
Worked example (White River WRRF, fictional)
- OUR = (6.8 - 2.3) / 10 x 60 = 27.0 mg/L/h
Tips
- Start with DO near 6 to 8 mg/L and record until about 1 to 2 mg/L.
- Use the straight line part of the DO drop.
Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.
This calculator also appears on ActivatedSludge.com, our consulting site. Results are for training and operator use; always follow your plant’s procedures.