What is the maximum value in the breakpoint range for secondary wastewater?

• A. 25
• B. 150
• C. 75
• D. 300

Answer: (B)

Breakpoint chlorination shows the dose at which all the reducing substances in the wastewater (like ammonia and organics) have been consumed and any additional chlorine appears as free chlorine. For secondary wastewater, the chlorine demand can be substantial, and reference charts used in practice show the breakpoint doses extending up to about 150 mg/L. Therefore, the maximum value in the breakpoint range for secondary wastewater is 150. The smaller numbers are simply lower points on the same curve, and a value like 300 mg/L would be beyond the typical range used for this context.