Biological treatment fundamentals: Which of the following statements correctly describe aerobic bacteria relevant to sewage treatment?
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AThey flourish in the presence of dissolved (free) oxygen
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BThey consume organic matter as a food/energy source
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CThey oxidize organic matter in sewage to stable end products
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DAll of the above
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ENone of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:
Aerobic biological processes are central to secondary wastewater treatment (e.g., activated sludge, trickling filters). Understanding how aerobic microbes function helps in process control (DO setpoints, sludge age, nutrient balance).
Given Data / Assumptions:
- Bacteria require oxygen, nutrients, and suitable environmental conditions.
- Influent sewage contains biodegradable organics.
Concept / Approach:
Aerobic bacteria oxidize biodegradable organics into carbon dioxide, water, and new biomass in the presence of adequate dissolved oxygen. Process design ensures oxygen transfer (aeration), mixing, and solids retention time to sustain these microorganisms.
Step-by-Step Solution:
Identify oxygen requirement: aerobic microbes thrive at DO typically 1.5–3.0 mg/L in aeration tanks.Confirm substrate utilization: they consume organic matter (measured as BOD/COD) for energy and growth.Recognize end products: oxidation yields CO2, H2O, nitrified forms (if ammonia is present), and biomass.Verification / Alternative check:
Process schematics for activated sludge clearly depict aeration providing oxygen so bacteria oxidize organics, confirming all statements apply.
Why Other Options Are Wrong:
- Choosing any single statement ignores the complete biological picture; therefore “All of the above” is correct.
- “None of the above” contradicts standard treatment biology.
Common Pitfalls:
- Confusing aerobic with anaerobic processes (which occur without oxygen and produce methane/CO2).
Final Answer:
All of the above