Removal of radionuclides from contaminated water Radioactive substances present in a polluted water stream can most effectively be removed by which treatment method?

Introduction / Context:
Water streams contaminated with radionuclides require specialised treatment because radioactive ions pose long-term health and environmental risks even at very low concentrations. Environmental engineers choose processes that selectively remove ionic species with high efficiency, allow safe handling, and minimise secondary waste volume. Understanding which unit operation is best suited for dissolved radioactive ions is essential for plant design and emergency response.

Given Data / Assumptions:

• Dissolved radioactive species are primarily in ionic form (e.g., Cs+, Sr2+, Co2− complexes).
• Target is polished removal to very low residual levels.
• Normal water temperatures and pH within treatable ranges.

Concept / Approach:
Ion exchange uses solid media with fixed functional groups that swap harmless counter-ions for target radionuclides. Resins or inorganic exchangers (e.g., zeolitic media) provide high selectivity, allowing very low effluent concentrations. The process is compact, controllable, and widely proven at nuclear facilities, research labs, and hospitals. In contrast, conventional coagulation/filtration removes particulates and some colloids but is far less selective for dissolved ions. Biological oxygen treatment is designed for biodegradable organics, not for ionic species. Air stripping works for volatile compounds, not for nonvolatile metal/radionuclide ions.

Step-by-Step Solution:

Verification / Alternative check:
Decontamination factors achieved by properly selected ion exchange media are significantly higher than those from generic physical separation methods; many nuclear effluent standards rely on this step for compliance.

Why Other Options Are Wrong:

• Biological oxygen treatment: Targets BOD and nutrients; ineffective for radionuclide ions.
• Coagulation and filtration: Limited for dissolved ions unless converted to insoluble forms first.
• Air stripping: Works on volatile organics/ammonia; not applicable to nonvolatile radionuclides.
• None of these: Incorrect because ion exchange is suitable and standard.

Common Pitfalls:
Assuming that any “advanced” unit (membranes, coagulation aids) will equal ion exchange selectivity; overlooking resin fouling by iron or organics without pretreatment; forgetting to plan for spent resin disposal per radiation safety rules.

Final Answer:
Adsorption using ion exchange materials