Removing iron and manganese from water—identify the ineffective method Which listed method alone cannot reliably remove dissolved iron and manganese from raw water to meet potable standards?

Introduction / Context:
Groundwaters often contain ferrous iron (Fe^2+) and manganous manganese (Mn^2+). These cause staining, taste issues, and distribution problems. Treatment typically oxidizes dissolved species to insoluble oxides then removes them physically, or exchanges them on selective media.

Given Data / Assumptions:

• Dissolved iron and manganese are initially in reduced soluble states.
• Final goal is compliance with drinking-water limits and aesthetic standards.
• Single-step chlorination is considered without filtration.

Concept / Approach:
Oxidation converts Fe^2+ to Fe(OH)3/Fe2O3 and Mn^2+ to MnO2 (often requiring higher pH or stronger oxidants). These particulates must then be removed by settling/filtration. Ion exchange or manganese-oxide coated media also remove these ions. Chlorination alone may oxidize but does not remove precipitated solids; without clarification/filtration, water remains non-compliant.

Step-by-Step Solution:

Verification / Alternative check:
Water treatment practice uses filters (e.g., greensand, MnO2 media) post-oxidation; residual particulates are not acceptable in finished water.

Why Other Options Are Wrong:

• Ion exchange: effective with pretreatment to prevent fouling.
• Oxidation + filtration: standard and effective.
• Lime-soda or Mn zeolite: proven technologies for Fe/Mn control.

Common Pitfalls:
Assuming a disinfectant automatically removes metals; oxidation must be followed by solids capture.

Final Answer:
Chlorination (alone, without subsequent removal steps)