What do changes in OUR mean?
OUR usually remains in a steady range so we become concerned when the OUR is significantly higher or lower than normal. A high OUR means there is increased soluble organics increasing microbial respiration or a chemical oxygen demand such as sulfide has created a chemical oxygen demand. A low OUR, can mean either very low organic loading rates where the biomass has moved further into decline phase growth or a toxic shock event that causes a biomass die-off. Examples of toxic shock include - phenol, cyanides, solvents, or biocides.
Can I screen influent for toxicity with a DOUR test?
Yes, you can screen influent to some extent with a DOUR. It requires taking standard influent and adding the correct percentage of the new waste stream. Add this to mixed liquor at the appropriate percentage. For a control, use the existing influent and mixed liquor at the same percentages. Add an aquarium air stone and allow to aerate/mix for at least 4 hours up to 12 hours. Run a standard DOUR and test different dilutions between influents and mixed liquor to get a uptake rate profile. (contact me if you have questions on using OUR as a toxicity screen).