Which set correctly describes the environmental conditions preferred by different microbial groups in wastewater treatment: anaerobic, aerobic, and facultative bacteria?

Introduction / Context:
Microbiology underpins sewage treatment. Understanding which organisms thrive with or without oxygen is essential when selecting unit processes (e.g., anaerobic digesters vs. activated sludge).

Given Data / Assumptions:

• Three microbial groups: anaerobic, aerobic, facultative.
• We are matching each group to its oxygen preference.

Concept / Approach:

• Anaerobic bacteria function in the absence of free dissolved oxygen (e.g., digesters, septic tanks).
• Aerobic bacteria require oxygen (e.g., aeration tanks, trickling filters).
• Facultative bacteria can live in both conditions, shifting metabolism as oxygen availability changes.

Step-by-Step Solution:
Map each group to oxygen requirement.Anaerobic → no oxygen; Aerobic → oxygen needed; Facultative → either condition.Select the option that states all three correctly.

Verification / Alternative check:
Check typical locations: anaerobic digesters (no aeration), activated sludge aeration basins (bubbled air), facultative ponds (upper aerobic layer, lower anaerobic layer).

Why Other Options Are Wrong:

• Reversing oxygen needs contradicts microbiology.
• Claiming all require oxygen ignores anaerobes.
• Sunlight is not the defining requirement for these bacteria.

Common Pitfalls:
Confusing anoxic (no dissolved oxygen, nitrate present) with anaerobic (no dissolved oxygen and no nitrate). The question refers broadly to absence/presence of oxygen.

Final Answer:
Anaerobic bacteria flourish without oxygen; aerobic bacteria flourish with oxygen; facultative bacteria can adapt to either condition.