Which chemical used for oxidizing iron and manganese will react with hydrogen sulfide, cyanides, phenols, and other taste and odor compounds and will not form trihalomethanes?

• A. chlorine dioxide
• B. potassium permanganate
• C. ozone
• D. chlorine

Answer: (D)

Oxidants chosen for this purpose must both remove metals like iron and manganese and also react with compounds that cause taste and odor, all while minimizing disinfection byproducts. Chlorine is widely used as a pre-oxidant because it effectively converts soluble iron and manganese to forms that can be filtered out, and it readily oxidizes reduced sulfur compounds (like hydrogen sulfide) as well as various organics such as cyanides and phenols that contribute off flavors and odors. This broad reactivity means one chemical can address metal removal and odor/taste concerns in a single step, with the added benefit of providing a residual disinfectant.

Among the other options, those alternatives either don’t cover all these targets as effectively or have different byproduct profiles. Chlorine dioxide and ozone are powerful for taste-and-odor control and for oxidizing organics, but chlorine remains the most common choice for iron and manganese oxidation with strong compatibility to subsequent filtration and disinfection steps. Potassium permanganate is excellent for manganese oxidation but less versatile for the full set of taste-and-odor compounds. So, given the combination of metal oxidation and broad reactivity with odor-causing compounds, chlorine is the best fit in this context.