What is the advanced treatment that removes nutrients like nitrogen and phosphorus?

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

Answer: (B)

Nutrient removal in wastewater requires an advanced polishing step called tertiary sewage treatment. Primary treatment only removes settleable solids, while secondary treatment uses biological processes to break down organic matter but leaves most nutrients behind. Tertiary treatment specifically targets nutrients like nitrogen and phosphorus to prevent eutrophication in water bodies, using methods such as nitrification-denitrification to remove nitrogen and chemical precipitation or enhanced biological phosphorus removal to reduce phosphorus. This extra stage may also include disinfection, but its primary purpose is nutrient reduction, not just solids or organic matter removal. The other stages focus on solids or organics, so the advanced nutrient-removal focus makes tertiary treatment the best answer.