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Do You Really Have a Free Chlorine Residual?
Author(s) -
Spon Robert
Publication year - 2008
Publication title -
opflow
Language(s) - English
Resource type - Journals
eISSN - 1551-8701
pISSN - 0149-8029
DOI - 10.1002/j.1551-8701.2008.tb01993.x
Subject(s) - chlorine , residual , hypochlorous acid , chemistry , environmental science , computer science , organic chemistry , algorithm
This article begins by discussing the US Environmental Protection Agency‐accepted colorimetric N,N‐diethyl‐pphenylenediamine (DPD) method as the most commonly used procedure to determine free chlorine residuals in water. The DPD indicator immediately reacts with free available chlorine, hypochlorous acid or hypochlorite ion, to form a pink color, which is proportional to the chlorine concentration. However, some DPD test results may be misleading because monochloramine residual interferes with DPD free analysis, creating a false‐positive, phantom reading. The article provides a series of questions that will help determine if free chlorine residual is really present in the water system. Phantom residuals are discussed, along with ammonia contamination. The article provides a phantom free chlorine checklist, chlorine demand calculations, and an interpretation of a breakpoint chlorination curve.