Composting is a biochemical degradation process where microorganisms act on organic waste, playing a crucial role in the composting process. The primary sources of composting microorganisms are twofold: the inherent microbial populations within the organic waste, such as bacteria in urban waste which typically range from $10^{14}$ to $10^{16}$ per kilogram, and specially introduced microbial strains. These added strains possess characteristics such as high activity, rapid reproduction, and efficient organic matter decomposition, which can accelerate the composting process and reduce composting time. This article outlines the specific functions and types of composting microorganisms.
Main Microorganisms in Composting
The microorganisms involved in composting primarily include bacteria, actinomycetes, fungi, and protozoa. As the composting process progresses and organic matter is gradually decomposed, the populations and quantities of composting microorganisms also change.
Bacteria
Role of Bacteria: Bacteria are the smallest and most numerous microorganisms in composting, responsible for decomposing most of the organic matter and generating heat.
Types and Characteristics: Bacteria are unicellular organisms that can be rod-shaped, spherical, or spiral. Some are motile. In the early stages of composting, mesophilic bacteria dominate at temperatures below 40°C. As the temperature rises above 40°C, thermophilic bacteria, primarily rod-shaped, become dominant. When temperatures exceed 60°C, the differences between bacterial species reduce. When environmental conditions are unfavorable, bacteria survive by forming spores. Spores are highly resistant to heat, cold, drying, and nutrient scarcity, reactivating when conditions improve.
Actinomycetes
Role and Characteristics: The characteristic earthy smell of finished compost is due to actinomycetes. They play a crucial role in decomposing complex organic materials such as cellulose, lignin, keratin, and proteins. Enzymes produced by actinomycetes help break down tough organic substances like bark and newspaper.
Fungi
Role and Characteristics: Fungi become increasingly important in the later stages of composting. Unlike bacteria, fungi can tolerate lower temperatures and require less nitrogen, allowing them to decompose lignin, which bacteria cannot.
Microfauna
Role and Types: Microfauna such as rotifers, nematodes, springtails, woodlice, beetles, and earthworms also play significant roles in composting. By moving through and ingesting compost, they help break down organic waste and increase the surface area for microbial activity.
Research Advancements in Composting Microorganisms
Experts have isolated and identified various microbial groups during the composting process:
- Mesophilic Bacteria: 57 strains were isolated, with 12 strains undergoing further identification.
- Thermophilic Bacteria: 32 strains were isolated, with 7 strains undergoing further identification.
- Enzymatic Activity Studies: The protease, amylase, pectinase, and cellulase activities of various strains were measured, along with studying the effect of temperature on enzyme activity. It was found that during the thermophilic phase, the reaction rates of thermophilic microorganisms’ enzymes are significantly higher than those of mesophilic microorganisms, with an optimal physiological temperature of 70°C.
Conclusion
In-depth research into composting microorganisms can further optimize the composting process, improving efficiency, shortening composting time, and enhancing compost quality. Understanding the roles and optimal conditions for different microorganisms, particularly bacteria, is essential for refining composting practices and achieving better composting outcomes.
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