Coagulation and pH adjustment are often needed to treat which group?

• A. Priority pollutants
• B. Nutrients
• C. Total suspended solids
• D. Dissolved oxygen

Answer: (A)

Coagulation paired with pH adjustment is used to make dissolved or fine colloidal contaminants form larger particles that can be settled out or filtered. For priority pollutants, many contaminants are metals that are present as ions in wastewater. By raising the pH, these metals precipitate as insoluble metal hydroxides, and the coagulant helps gather the resulting particles into flocs that are easy to remove. This combination is a common and effective way to meet strict limits for these troublesome pollutants.

Nutrients are typically handled mainly by biological processes or specific chemical precipitation for phosphorus, not primarily by coagulation to the same extent. Dissolved oxygen isn’t removed by coagulation at all, since it’s a gas managed by aeration and biological activity. Total suspended solids removal does involve coagulation, but the question targets the contaminant group most often addressed with this chemical approach, which points to priority pollutants.