Question

Tertiary treatment of sewage aims at removal of-

• A. Coarse materials
• B. Nitrogen and phosphorus
• C. Pathogens
• D. Heavy metals

Hint:

Tertiary treatment is often called "nutrient removal".
High levels of nitrogen and phosphorus in discharged sewage are the leading causes of algal blooms and oxygen depletion in natural water bodies.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Wastewater or sewage treatment is performed in three distinct progressive stages to remove contaminants before discharge or reuse:
Primary treatment (physical), Secondary treatment (biological), and Tertiary treatment (advanced chemical/biological).

Step 2: Detailed Explanation:
Let us look at what each stage of treatment targets:
1. Primary treatment: Physical processes such as screening and sedimentation to remove floating, suspended, and coarse organic materials.
2. Secondary treatment: Biological processes using aerobic or anaerobic microorganisms to reduce dissolved organic matter (measured as biological oxygen demand, or BOD).
3. Tertiary treatment: This advanced stage aims to polish the effluent.
Its primary focus is the removal of plant nutrients, particularly dissolved inorganic compounds of nitrogen and phosphorus.
Removing these nutrients is crucial to prevent eutrophication in receiving aquatic ecosystems.

Step 3: Final Answer:
Tertiary treatment of sewage primarily aims at the removal of dissolved plant nutrients, specifically nitrogen and phosphorus.