To maintain aerobic biological activity during composting of municipal organic wastes, the moisture content of the composting mass should be maintained approximately at what level?

Introduction / Context:
Composting efficiency depends on moisture content: too dry halts microbial activity; too wet limits air diffusion and causes anaerobic conditions. Designers therefore target an optimal moisture band for aerobic composting.

Given Data / Assumptions:

• Organic municipal waste with typical bulking agents.
• Aerobic process desired (odor control, faster stabilization).
• Temperature and aeration are adequate if moisture is in the recommended range.

Concept / Approach:
Aerobic microbes thrive when water films enable transport of nutrients but pore air is preserved. Empirical practice sets an optimum moisture around mid-50% by mass for MSW windrows with bulking.

Step-by-Step Solution:
Step 1: Identify standard moisture band for aerobic composting: roughly 50%–60%.Step 2: Choose the mid-range value commonly recommended for control: 55%.Step 3: Confirm that at 55% moisture, porosity and oxygen transfer remain adequate with periodic turning.

Verification / Alternative check:
Field guidance for windrow and aerated static pile composting frequently targets 50–60%, with 55% a commonly cited setpoint.

Why Other Options Are Wrong:

• 45%–50%: Often too dry; activity slows and dusting increases.
• 60%–65%: Risk of anaerobic pockets, odors, and leachate.

Common Pitfalls:
Not re-wetting dry feed or over-wetting with leachate recirculation; neglecting bulking agents that maintain structure at target moisture.

Final Answer:
55%