Enter your DO decline and solids. You'll get specific oxygen uptake rate both ways — the process control value against MLVSS, and the 40 CFR Part 503 value against total solids, corrected to 20°C.
This is the distinction the calculator exists to make. Same sample, same DO decline, two different numbers:
| Process control | 40 CFR 503 | |
|---|---|---|
| Denominator | MLVSS (volatile) | Total solids (dry weight) |
| Temperature | Reported at test temperature | At or corrected to 20 °C |
| Test duration | 10 min common practice | 15 min per Standard Methods |
| Pass/fail | None — trend against your baseline | ≤ 1.5 mg O₂/hr/g TS |
Because volatile solids are a fraction of total solids, the process control number is always the larger of the two. Reporting it against the 1.5 limit means submitting the wrong figure.
Procedure, both calculations, the EPA temperature example that turns a pass into a fail, interpretation against your own baseline, and thirteen common errors — sourced to 40 CFR Part 503 and Standard Methods 2710 B.
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