Which of the following conditions most directly improves anaerobic sludge digestion performance?
- AHigh dissolved oxygen concentration in digester
- BContinuous removal of all volatile solids before digestion
- CStable temperature and adequate retention timeCorrect
- DExtremely low pH to suppress microbial activity
Solution
Concept
Optimal conditions for anaerobic digestion
Formula
NONE
Step-by-step solution
1. Anaerobic digestion stabilizes sludge through methane-forming archaea (methanogens). 2. Methanogens are obligate anaerobes with slow growth rates and high sensitivity to temperature fluctuations. 3. Digesters require stable temperature (typically 35°C) and sufficient solids retention time (15-30 days) to prevent failure. 4. Therefore, stable temperature and adequate retention time directly improve digestion. Answer: C
Explanation
Anaerobic sludge digestion requires syntrophic activity between acid-forming bacteria and methanogenic archaea. Methanogens are obligate anaerobes with slow metabolic rates that are highly sensitive to environmental fluctuations, demanding strict temperature stability (typically 35°C) and adequate retention time (15-30 days) to prevent digester failure.
Why the other options are wrong
A) Dissolved oxygen is toxic to obligate anaerobic methanogens. B) Volatile solids are the essential substrate converted into biogas. D) Low pH creates acidic sour conditions that inhibit methanogenesis.
Shortcut
Anaerobic digestion thrives on: No Oxygen, Near-neutral pH, Stable Temp, and Ample Retention Time.
Common mistake
Confusing aerobic aeration needs (high DO) with anaerobic digestion requirements.
Correct answer: C) Stable temperature and adequate retention time