Which treatment sequence is used to greatly reduce EPA priority pollutants?

• A. Lime coagulation, mixed media filtration, and activated carbon filtration
• B. Disinfection with chlorine only
• C. Boiling and distillation
• D. Sedimentation without filtration

Answer: (A)

Removing EPA priority pollutants effectively relies on a sequence that first targets particulates and dissolved metals, then removes suspended solids, and finally adsorbs remaining dissolved organics. Starting with lime coagulation helps raise the water’s pH and promotes the formation of larger flocs by destabilizing particles and precipitating certain inorganic contaminants as insoluble solids. This step makes it easier to trap contaminants in the subsequent solids removal stage.

Following coagulation, a mixed-media filter captures the formed flocs and remaining particulates, reducing turbidity and preparing the water for downstream treatment. Clean filtration also enhances the efficiency of the next step by reducing the amount of organic matter and particles that could interfere with adsorption.

The final stage uses activated carbon filtration to adsorb dissolved organic compounds, including many EPA priority pollutants such as volatile organics and pesticides. Activated carbon has a large surface area and affinity for these dissolved contaminants, pulling them out of solution rather than just passing them through.

Disinfection with chlorine alone mostly targets microorganisms and does not reliably remove many chemical pollutants; boiling and distillation are energy-intensive and not practical for large-scale treatment to remove a broad range of priority pollutants; and sedimentation without filtration leaves dissolved contaminants in the water. So the combination of lime coagulation, filtration, and activated carbon filtration provides a comprehensive approach to greatly reduce EPA priority pollutants.