Normal treatment removes how many mg/L?

• A. 2-3 mg/L
• B. 3-4 mg/L
• C. 1-2 mg/L
• D. 0.5-1 mg/L

Answer: (C)

In normal secondary wastewater treatment, the amount of a common pollutant that can be removed by standard biological processes typically falls in the 1 to 2 mg/L range. This reflects what conventional secondary treatment can achieve for many soluble, readily biodegradable substances: a meaningful reduction, but not a large one, without moving to more advanced or tertiary treatment steps. If the system were removing more than about 2 mg/L consistently, that would imply unusually efficient removal or additional processes at work; removing only about 0.5 to 1 mg/L would suggest underperformance or a pollutant much less amenable to secondary treatment. So the 1–2 mg/L range is the most representative of normal secondary removal.