Typical pH of oxidized (stabilized) sewage After adequate aeration and biological oxidation, the pH of treated sewage is generally around which value?

Introduction / Context:
pH is a key control parameter in wastewater treatment. During biological oxidation (secondary treatment), acids formed initially are buffered and consumed, and the effluent typically trends toward neutral to slightly alkaline values, depending on alkalinity and process conditions.

Given Data / Assumptions:

• “Oxidized sewage” implies stabilized effluent post-aeration/secondary treatment.
• Municipal sewage has natural alkalinity; nitrification can slightly acidify unless alkalinity is adequate.
• We seek the most representative pH value of treated effluent.

Concept / Approach:
Typical secondary effluent pH lies close to neutral. Values near 7.0–7.5 are common when alkalinity buffers acids and the process is well operated. Extremely acidic (≈2) or strongly alkaline (≈13) conditions are incompatible with biological treatment and regulatory discharge norms.

Step-by-Step Solution:

Verification / Alternative check:
Design manuals show typical effluent pH between 6.5 and 8.5; 7.3 sits in the middle of this band.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming influent pH carries through; biological processes and buffering shift pH toward neutrality in well-run systems.

Final Answer:
7.3