Wastewater math

Percent Removal Formula for Wastewater Operators

How much of a pollutant a process removes, from influent and effluent.

The formula

Formulas

Find percent removal
% removal = (influent − effluent) ÷ influent × 100
WPI Formula/Conversion Table (2023), Printed page 5 of 10, Removal, %: (In − Out) ÷ In × 100%
Find effluent
effluent = influent × (1 − removal decimal)
WPI Formula/Conversion Table (2023), Printed page 5 of 10, Removal, %: (In − Out) ÷ In × 100%

Worked example

Influent TSS is 280 mg/L and effluent TSS is 42 mg/L. What is the percent removal?

Known Values
Influent TSS is 280 mg/L and effluent TSS is 42 mg/L.
Find
Find the percent removed.
Check Your Units
Both values use mg/L, so they can be compared directly.
Find What Was Removed
280 minus 42 = 238 mg/L removed.
Build the Comparison
Removed amount divided by influent = 238 divided by 280.
Calculate the Percent
0.85 times 100 = 85%.
Check the Answer
The effluent is lower than the influent, and 85% of the entering concentration was removed.
Answer
85%

Answer: 85%

Practice

Practice this math in the Math Center, with hints and worked steps.

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