What is a common method for measuring chlorine residual in wastewater?

What is a common method for measuring chlorine residual in wastewater?

• A. DPD colorimetric test or an online amperometric chlorine analyzer.
• B. pH meter
• C. Turbidity meter
• D. Conductivity meter

Answer: (A)

Measuring chlorine residual relies on methods that directly detect chlorine or its active oxidant form. The most common approach is a colorimetric test using the DPD reagent, which reacts with chlorine to produce a pink color whose intensity is proportional to the residual chlorine concentration. This can be done in the lab with a colorimeter or comparator, or continuously with an online amperometric chlorine analyzer that uses an electrode to measure free chlorine in real time. Other options don’t measure chlorine residual: a pH meter checks acidity, not chlorine; a turbidity meter measures suspended solids; and a conductivity meter gauges overall ionic content.

Measuring chlorine residual relies on methods that directly detect chlorine or its active oxidant form. The most common approach is a colorimetric test using the DPD reagent, which reacts with chlorine to produce a pink color whose intensity is proportional to the residual chlorine concentration. This can be done in the lab with a colorimeter or comparator, or continuously with an online amperometric chlorine analyzer that uses an electrode to measure free chlorine in real time. Other options don’t measure chlorine residual: a pH meter checks acidity, not chlorine; a turbidity meter measures suspended solids; and a conductivity meter gauges overall ionic content.