Composting and C/N balance — For rapid microbial decomposition of organic substrates, the recommended carbon-to-nitrogen (C/N) ratio is approximately:

Introduction / Context:
The carbon-to-nitrogen (C/N) ratio strongly controls composting rate and quality. Microbes require carbon (energy/building blocks) and nitrogen (proteins/enzymes). An optimal balance accelerates growth and heat generation, leading to efficient decomposition and pathogen reduction.

Given Data / Assumptions:

• Goal: rapid, aerobic composting.
• Feedstocks include high-C materials (straw, sawdust) and high-N materials (manure, green waste).
• Moisture and aeration are adequate.

Concept / Approach:
Most composting guides target an initial C/N near 25–30, allowing microbes to assimilate N without excess loss as ammonia while keeping enough carbon for energy and structure. Ratios much lower waste nitrogen; ratios much higher slow decomposition due to N limitation.

Step-by-Step Solution:

Verification / Alternative check:
Pilot piles with initial C/N ~25–30 reach thermophilic temperatures quickly and stabilize faster than piles far above or below this range.

Why Other Options Are Wrong:

• 10–20: can cause N volatilization and odor issues.
• 30–40: acceptable but not “rapid” compared to 20–30.
• 60–80: strongly N-limited; slow breakdown.

Common Pitfalls:
Not adjusting for moisture and particle size; even with ideal C/N, poor aeration stalls composting.

Final Answer:
20–30