Nitrogen form in well-oxidized sewage: A well-oxidized sewage contains nitrogen predominantly in which form?

Introduction / Context:Nitrogen species in wastewater evolve as treatment progresses. Understanding whether nitrogen appears as ammoniacal, organic, nitrite, or nitrate forms helps diagnose treatment performance and oxygenation status in the system.

Given Data / Assumptions:

• “Well-oxidized sewage” implies sufficient aeration and biological oxidation.
• Nitrification proceeds from ammonia → nitrite → nitrate under aerobic conditions.

Concept / Approach:In aerobic environments, nitrifying bacteria convert ammonia first to nitrite (by ammonia-oxidizing bacteria) and then to nitrate (by nitrite-oxidizing bacteria). As oxidation becomes more complete, nitrate becomes the dominant inorganic nitrogen form, indicating advanced nitrification.

Step-by-Step Solution:If oxygen present and biology active: NH3 → NO2− → NO3−.“Well-oxidized” means the terminal product of nitrification predominates.Therefore, nitrates are the main nitrogen form.

Verification / Alternative check:Process control in activated sludge systems uses low ammonia and nitrite with higher nitrate as markers of complete nitrification in aerobic zones, matching the statement.

Why Other Options Are Wrong:Nitrites: Intermediate; should be low in fully oxidized conditions.Free ammonia: Characteristic of reduced or early-stage oxidation.None/Organic nitrogen only: Inconsistent with “well-oxidized” status.

Common Pitfalls:

• Assuming elevated nitrite persists; it should be further oxidized to nitrate under stable aerobic conditions.
• Confusing nitrification (aerobic) with denitrification (anoxic), where nitrate is reduced.

Final Answer:Nitrates