What are the scientific principles behind composting?

In a corner of your garden or farm, a seemingly ordinary pile of fallen leaves, vegetable scraps, and kitchen waste is quietly hosting one of Earth’s oldest and most exquisite life cycles. This process—composting—is not mere decay but a grand biological transformation project orchestrated by billions of microorganisms. It magically converts discarded organic matter into “black gold”—humus, which not only nourishes plants but also improves soil. Understanding the science behind composting is to understand the wisdom of natural cycles, enabling us to more efficiently mimic and optimize this process, turning waste into treasure. First Movement: The Four-Season Symphony of Microorganisms If the composting process is likened to a symphony, then different types of microorganisms are the musicians, appearing on stage in strict sequence according to the “score,” collaborating to complete this movement of life. Spring Overture: The Mesophilic Phase When organic materials are mixed and piled, the “pioneer troops”—mesophilic bacteria and fungi (e.g., Bacillus, yeasts)—rapidly multiply. They prefer “fast food,” prioritizing the decomposition of simple organic compounds like sugars, starches, and proteins. Like lighting a bonfire, their rapid metabolism releases heat, raising the pile temperature from ambient to 40-50°C within 1-2 days. This phase primarily involves rapid energy release and breakdown of basic substances. Summer Climax: The Thermophilic Phase Temperatures exceeding 55°C mark the climax of the movement. The “specialist team”—thermophilic bacteria and actinomycetes—take the lead. They can break down the “tough bones” in plant fibers like cellulose and hemicellulose. This phase maintains high temperatures of 55-70°C for 5-7 days, ensuring the safety of the compost. The heat acts like natural pasteurization, effectively killing pathogens, parasite eggs, and weed seeds, achieving waste sanitization. Simultaneously, complex organic matter is further dismantled. Autumn Settlement: The Cooling Phase As the “tough bones” are largely consumed and food diminishes, thermophilic activity wanes, and the temperature begins to drop below 40°C. At this point, another group of mesophilic microorganisms returns, starting to process the most stubborn remaining substances like lignin, and using simple compounds produced earlier as “building blocks” to synthesize precursors of humus—a critical turning point from “dismantling” to “rebuilding.”

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