Which stage addresses nutrient removal such as nitrogen and phosphorus?

• A. Sewage treatment
• B. Tertiary sewage treatment
• C. Primary sewage treatment
• D. Final chemical treatment

Answer: (B)

Nutrient removal of nitrogen and phosphorus is addressed in the tertiary stage of sewage treatment. After solids are settled out in primary treatment and the organic load is reduced in secondary treatment, tertiary treatment adds polishing steps specifically to remove nutrients that can cause eutrophication in receiving waters. Nitrogen is removed through processes like nitrification and denitrification, while phosphorus can be removed by chemical precipitation or biological phosphorus removal. This stage is designed to lower nutrient levels before discharge, whereas primary treatment mainly removes solids and secondary treatment focuses on organic matter, and final chemical treatment isn’t the standard term for nutrient-focused processes.