Advanced wastewater treatment — classifying nutrient removal processes Chemical precipitation of phosphorus in a treatment plant is typically categorized as:

Introduction / Context:
Phosphorus control is essential to prevent eutrophication in receiving waters. Plants may remove phosphorus biologically (enhanced biological phosphorus removal) or chemically by precipitation. Placing these processes correctly in the treatment train is important for design and compliance.

Given Data / Assumptions:

• Chemical precipitation uses metal salts such as alum, ferric chloride, or lime to form insoluble phosphate complexes.
• These reactions reduce effluent total phosphorus to meet stringent discharge permits.
• Such processes are considered beyond basic BOD and suspended solids removal.

Concept / Approach:
Primary treatment targets solids; secondary treatment targets BOD via biology; tertiary or advanced treatment targets nutrients (nitrogen and phosphorus), microconstituents, or fine particulates using chemical or physical-chemical processes (for example, precipitation, filtration, adsorption).

Step-by-Step Solution:
Identify the process: chemical precipitation of orthophosphate.Relate to treatment stages: nutrient polishing = tertiary/advanced treatment.Select the classification “Tertiary (advanced) treatment.”

Verification / Alternative check:
Process flow diagrams place chemical P removal as an advanced step; sometimes dosing may occur in primary or secondary basins for process reasons, but the classification remains advanced nutrient removal.

Why Other Options Are Wrong:
Primary and secondary focus on solids and BOD; phosphorus precipitation is a targeted nutrient control step.

Common Pitfalls:
Confusing point of chemical addition with treatment stage classification. Even if chemicals are dosed in primary clarifiers, the objective is tertiary nutrient removal.

Final Answer:
Tertiary (advanced) treatment.