Unveiling Vegetable Composting: Where Does the Odor Come From, and Who Controls Fermentation?

As a major vegetable producer, China generates over 245 million tons of vegetable waste annually. Improper handling of discarded tomato stalks, cabbage leaves, and similar waste not only occupies space but also produces complex volatile organic compounds (VOCs) during composting, emitting unpleasant odors. A recent study on the co-composting of tomato stalks and cow manure systematically revealed, for the first time, the 58 different VOCs produced during this process and tracked the succession of microbial communities driving the fermentation. This research not only explains the source of compost odors but also provides scientific basis for optimizing composting processes and reducing environmental pollution. I. The “Odor Map” in Composting: A Symphony of 58 Chemical Compounds During the 40-day composting cycle, researchers detected a surprising 58 volatile organic compounds. These substances form a complex chemical symphony, including nine major categories: sulfur-containing compounds, alcohols, esters, aldehydes, ketones, halogenated hydrocarbons, aromatic hydrocarbons, alkanes, and alkenes. Who are the main “culprits”? Not all detected compounds produce noticeable odors. The study showed that seven substances exceeded the human olfactory threshold: methyl sulfide, ethanol, n-butanol, ethyl acetate, acetaldehyde, butyraldehyde, and α-pinene. Additionally, ammonia (NH₃) was a significant odor contributor. Methyl Sulfide—This substance, smelling like rotten cabbage, is one of the most important sulfurous odor components in compost. The study found its concentration peaked around day 20 (0.1926 mg/m³). Interestingly, its production is closely related to the presence of anoxic zones within the compost pile. When turning frequency decreases, anaerobic microenvironments easily form inside the pile, promoting methyl sulfide generation. Ammonia—Persists throughout the composting process as a byproduct of nitrogen transformation. Its production is directly related to the efficiency of nitrogen loss in composting. Unexpected Discoveries The study also detected a large number of aromatic hydrocarbons (18 types), likely related to the added cow manure. Aromatic compound precursors in cow manure are converted into these volatile substances by microbial action. Although various alkanes (17 types) were detected, their concentrations were low, contributing little to the overall odor.

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