Key reaction in biochemical treatment of sewage effluents Which fundamental process best describes the main transformation occurring in secondary (biological) wastewater treatment?

Introduction / Context:
Secondary wastewater treatment relies on microbial communities to convert dissolved and colloidal organic matter into stable products. Understanding the core biochemical pathway helps in selecting and operating activated sludge, trickling filters, and aerated lagoons.

Given Data / Assumptions:

• “Biochemical treatment” here refers to conventional secondary treatment in public works (activated sludge, trickling filters).
• Influent contains biodegradable organics measured as BOD/COD.
• Aeration or passive oxygen transfer is available in aerobic systems.

Concept / Approach:
The principal reaction in aerobic biological treatment is oxidation of organic carbon to CO2 and water, with a fraction assimilated into new biomass. While some systems include anoxic/anaerobic zones (denitrification or digesters), the mainstream carbon removal step is oxidative. “Fermentation” is part of anaerobic digestion and occurs without oxygen, but typical secondary treatment for municipal sewage emphasizes aerobic oxidation.

Step-by-Step Solution:

Verification / Alternative check:
Plant operation targets sufficient dissolved oxygen and aeration capacity, directly reflecting an oxidative process.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing anaerobic digestion of sludge with the aerobic secondary treatment of the liquid stream.

Final Answer:
Oxidation