For nitrate contamination in groundwater, which remediation method is commonly used?

• A. Disinfection with chlorine.
• B. Coagulation and sedimentation.
• C. Ion exchange.
• D. Aeration.

Answer: (C)

Nitrate in groundwater is dissolved and highly mobile, so physical separation methods that target particles won’t remove it. Ion exchange works well here because it uses a resin with exchange sites that preferentially bind nitrate ions from the water while releasing another ion, usually chloride, into the water. As groundwater passes through the resin, nitrate is captured and the water exiting the bed has much lower nitrate concentration. When the resin becomes saturated, it’s regenerated with a salt solution, which releases the accumulated nitrate into a brine that must be managed. This approach directly targets dissolved nitrate and can handle typical drinking-water concentrations, though its effectiveness can be influenced by other anions present (like sulfate or bicarbonate) and water chemistry.

Disinfection with chlorine, coagulation and sedimentation, and aeration don’t remove nitrate. Chlorination targets pathogens and organic compounds, not dissolved nitrate. Coagulation and sedimentation remove suspended particles, not dissolved ions. Aeration changes volatile components; nitrate is not volatile, so it remains in the water.