Biological oxidation methods in wastewater treatment: Which of the following are employed as oxidation processes for treating sewage/effluents?

Introduction / Context:
Secondary treatment in wastewater engineering relies on aerobic or facultative biological oxidation to convert dissolved and suspended organics into biomass, carbon dioxide, and water. Recognizing which unit processes fall under “oxidation methods” is fundamental for plant design and exam questions.

Given Data / Assumptions:

• Oxidation ponds (waste stabilization ponds) use natural sunlight, algae, and bacteria.
• Trickling filters rely on attached biofilms over packing media with aeration.
• Contact aerators (contact stabilization/activated sludge variants) suspend biomass with aeration.

Concept / Approach:
All three are canonical biological oxidation processes transforming biochemical oxygen demand (BOD) into microbial biomass and oxidized end products. They differ in configuration (ponds vs attached growth vs suspended growth) but share the same oxidative objective: reduce BOD and pathogens through microbial respiration.

Step-by-Step Solution:
List each process and confirm it achieves aerobic oxidation of organics.Oxidation ponds: facultative or maturation stages with algal oxygenation.Trickling filters: biofilm oxidizes organics as wastewater trickles with air.Contact aerators: activated sludge contact and aeration oxidize soluble BOD.Therefore, the inclusive answer is correct.

Verification / Alternative check:
Standard design manuals classify these units under secondary treatment by biological oxidation, evidenced by BOD and COD reductions and sludge production.

Why Other Options Are Wrong:

• Single selections omit other legitimate oxidation methods.
• None of these: incorrect; all listed processes are oxidation-based treatments.

Common Pitfalls:
Confusing primary sedimentation (physical) with secondary oxidation (biological); assuming “ponds” are only for settling when they also drive oxidation via algal–bacterial symbiosis.

Final Answer:
All of these.