Percent Removal Efficiency
Percent Removal = (Influent − Effluent) ÷ Influent × 100 — the standard way to report treatment performance.
Applied to BOD, TSS, and most other regulated parameters to demonstrate how effectively a unit process or the whole plant is treating a given pollutant.
NPDES permits often set a minimum percent removal requirement (commonly 85% for BOD and TSS) in addition to a numeric effluent limit — both need to be checked.
A dropping percent removal with stable effluent quality can still signal a problem if influent strength is falling, since removal efficiency measures performance relative to load, not absolute quality.
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