Nutrient Removal

Nutrient removal in wastewater treatment is the process of removing nutrients such as nitrogen (N) and phosphorus (P) from wastewater before it is discharged into the environment. The goal is to prevent water pollution, especially the phenomenon of eutrophication, which is an explosion of algae growth that can reduce dissolved oxygen levels and damage aquatic ecosystems.

Types of Nutrients Removed

1. Nitrogen (N)

   • Forms in wastewater: ammonia (NH₄⁺), nitrite (NO₂-), nitrate (NO₃-), organic-N compounds.

   • Impact: toxic to aquatic organisms, can cause "blue baby syndrome" when contaminating drinking water.

   • Removal process:

     • Nitrification → converts ammonia to nitrate (by nitrifying bacteria).

     • Denitrification → converts nitrate to nitrogen gas (N₂) which escapes into the air.

2. Phosphorus (P)

   • Forms in wastewater: orthophosphate (PO₄³-), polyphosphate, organic-P.

   • Impact: triggers eutrophication in waters.

   • Removal process:

     • Chemical precipitation → addition of iron/aluminum/calcium salts to bind phosphate.

     • Biological phosphorus removal (EBPR) → certain microorganisms absorb excess phosphorus in their cells.

Nutrient Removal Methods

1. Biological Process

   • Rely on microorganisms to break down nitrogen and phosphorus.

   • Example: Activated sludge with anaerobic, anoxic, and aerobic zones.

2. Chemical Process

   • Addition of chemicals (e.g. alum, FeCl₃, lime) to bind phosphate.

   • Usually used when phosphorus levels are very high or when biological processes are not sufficient.

3. Combined Process (Biological-Chemical)

   • Combines both methods to be more efficient and stable.

Benefits of Nutrient Removal

• Protects the water quality of rivers, lakes and the ocean.

• Prevents eutrophication and algae blooms.

• Maintain aquatic biodiversity.

• Ensures the safety of drinking water sources.