Question 1

Why use VSS instead of TSS?

Accepted Answer

VSS represents biologically active organic matter; TSS includes inerts. Using TSS would understate the per-cell respiration rate.

Question 2

What SOUR indicates toxicity?

Accepted Answer

A sudden drop of ≥ 30% from baseline SOUR after a discharge event indicates likely toxic shock. Some labs run a parallel SOUR with a clean control to confirm.

Question 3

Does temperature affect SOUR?

Accepted Answer

Yes — every 10 °C raises SOUR roughly 50%. Report and compare SOUR values at consistent temperature, or temperature-correct.

Question 4

What about nitrifying biomass?

Accepted Answer

Add a nitrification inhibitor (ATU) to separate carbonaceous and nitrogenous OUR. The difference is the nitrifier respiration rate.

SOUR Calculator – Specific Oxygen Uptake Rate