Introduction to the Principles of Agricultural Solid Waste Composting

Composting is "a controlled process of aerobic biological decomposition of organic matter to form a stable product known as compost; essentially similar to natural degradation, but differing in that composting also promotes microbial growth by mixing organic waste with other components, thereby enhancing and accelerating the decomposition process." Waste materials are transformed through the composting system into a usable resource with stable organic matter, high carbon content, and free of pathogens, parasite eggs, and weed seeds. Its physical properties are distinctly different from the original raw materials. Compost products can serve as soil amendments or fertilizers, and can also be used to create growing substrates or soil coverings.

2. Introduction to Aerobic Composting Technology

Aerobic composting is conducted under aerobic conditions with the action of aerobic microorganisms (primarily aerobic bacteria). During the composting process, soluble organic matter from agricultural solid waste is absorbed by microorganisms through their cell walls and membranes. Solid and gel-like organic substances first adhere to the exterior of microbial cells, where they are broken down into soluble substances by extracellular enzymes secreted by the microorganisms before infiltrating the cells. Through their life activities—oxidation, reduction, and synthesis—microorganisms oxidize some of the absorbed organic matter into simple inorganic compounds, releasing energy necessary for microbial growth and activity. Additionally, microorganisms can transform some organic matter into nutrients for themselves, synthesizing new cellular material. As a result, microorganisms gradually grow and multiply, producing more biomass. Therefore, the material transformation in aerobic composting primarily involves two processes: the decomposition of organic matter and the synthesis of humus.

During the biochemical degradation of organic matter, heat is generated. In the composting process, this heat does not dissipate entirely into the environment, inevitably causing a rise in the temperature of the compost material. This leads to the death of thermosensitive microorganisms and the rapid proliferation of heat-resistant bacteria. Ecodynamic studies indicate that the primary role in aerobic decomposition is played by thermophilic bacterial communities with large, active bacterial cells. These bacteria oxidize and decompose organic matter in the presence of abundant oxygen molecules while releasing significant amounts of energy. Consequently, the aerobic composting process can be divided into three stages: the initial heating phase, the high-temperature phase, and the maturation (cooling) phase, with two heating processes. Overall, aerobic composting offers advantages such as relatively thorough waste decomposition, shorter composting cycles, reduced odor production, and the capability for large-scale mechanical processing.

3. Summary

"Greeen, environmentally friendly," and "circular development" are the goals of agricultural development both domestically and internationally. Composting plays a crucial role in the sustainable development of agricultural ecosystems and serves as an effective means of resource utilization for agricultural solid waste. Through aerobic fermentation, agricultural solid waste can be transformed into stable fertilizers or soil amendments, enhancing the level of waste-to-fertilizer utilization and laying the foundation for its broader applications.