Q: Is concentration or mass used?

Either works because flow cancels (assuming influent flow = effluent flow). Use concentrations for daily DMR reporting.

Question 1

What is the EPA minimum BOD removal?

Accepted Answer

85% as a 30-day average and 65% as a 7-day average under 40 CFR 133.102 Secondary Treatment standards.

Question 2

Does % removal apply to nutrients?

Accepted Answer

Only where NPDES permits require it. Some advanced plants must show ≥80% TN removal or ≥85% TP removal.

Question 3

Why is my % removal below 85% if effluent is low?

Accepted Answer

Either influent is dilute (I&I) or sampling is off. Check influent grab values; secondary treatment plants with influent BOD < 80 mg/L often qualify for the 'equivalent to secondary' less-than-85% allowance.

Question 4

Is concentration or mass used?

Accepted Answer

Either works because flow cancels (assuming influent flow = effluent flow). Use concentrations for daily DMR reporting.

Percent Removal Calculator – BOD, TSS, Nutrients