Sludge digestion temperature regimes and rates: Select the correct comprehensive statement about digestion rate, thermophilic and mesophilic ranges, and a typical mesophilic performance benchmark.

Introduction / Context:
Biological sludge stabilization rates depend strongly on temperature. Understanding mesophilic and thermophilic ranges and related performance is crucial for selecting digester type and detention time.

Given Data / Assumptions:

• Standard municipal sludge characteristics and conventional digesters.
• Mesophilic operation around 25–40°C; thermophilic around 40–60°C.
• Performance benchmarks are rule-of-thumb values for design studies.

Concept / Approach:

• Temperature effect: Within biological limits, higher temperature generally increases reaction rates and gas production.
• Thermophilic vs. mesophilic: Two common operating bands used in design.
• Benchmark: Around 30 days at ~29°C can achieve high digestion in many systems.

Step-by-Step Solution:
Assess each statement for correctness relative to standard operational knowledge.All statements are consistent with accepted descriptions of digestion behavior.Therefore, the combined option “All the above” is correct.

Verification / Alternative check:
Design handbooks present similar temperature bands and show reduced detention times at higher temperatures due to increased microbial activity.

Why Other Options Are Wrong:
Selecting only one ignores the equally correct complementary statements.

Common Pitfalls:

• Confusing the precise boundaries of temperature bands (they are approximate ranges).
• Assuming rate increases indefinitely with temperature; beyond limits, organisms are inhibited.

Final Answer:
All the above