What is the daily maximum limit for chlorine (CL2) in mg/L?

• A. 0.019 mg/L
• B. 0.11 mg/L
• C. 0.5 mg/L
• D. 1.0 mg/L

Answer: (A)

Residual chlorine in treated wastewater is tightly limited to protect aquatic life and meet discharge permits. The daily maximum is the highest concentration allowed in a single day's effluent sample, so facilities must keep the chlorine residual at or below that level every day. A value of 0.019 mg/L is very low because chlorine can be toxic to aquatic organisms even in small amounts, so plants often use dechlorination or precise dosing to stay under this limit. The other options—0.11, 0.5, and 1.0 mg/L—represent higher chlorine levels that would not satisfy typical daily maximum limits for effluent discharges. Keeping chlorine within this small limit helps ensure the treated water won’t harm downstream ecosystems.