As an eco-friendly alternative to traditional plastics, the degradation performance of biodegradable bags is significantly affected by the environment. Soil and water are two common natural degradation scenarios. Due to differences in environmental conditions, the degradation process of biodegradable bags shows obvious variations. These differences not only relate to degradation efficiency but also affect the realization of their environmental value.
1. Core Driver of Degradation – Microorganisms
Soil contains a rich and diverse community of microorganisms, including bacteria, fungi, actinomycetes, etc. These microorganisms have long adapted to the complex soil environment and can secrete a variety of enzymes, such as lipases and esterases, which efficiently decompose components of biodegradable bags like polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).
In contrast, the types of microorganisms in water are relatively single, mainly aquatic bacteria. Moreover, the concentration of microorganisms in water is much lower than that in soil. Especially in clean natural water bodies, the number of microorganisms is even smaller. This results in an incomplete enzyme system for decomposing biodegradable bags, leading to relatively weak degradation capabilities.
2. Degradation Rate
In a suitable soil environment – with temperatures maintained at 25-35°C, moderate humidity, and sufficient oxygen – biodegradable bags typically show obvious degradation within 3-6 months and can be basically decomposed into small-molecule substances within 1-2 years. This is because the pores between soil particles provide sufficient oxygen for microorganisms, while the heat and water retention capabilities of soil are conducive to the activity of microorganisms.
In water, however, the degradation rate of biodegradable bags slows down significantly even under suitable temperature conditions. In natural freshwater environments, their complete degradation often takes 2-5 years; in seawater environments, due to high salinity, large temperature fluctuations, and lack of nutrients, the degradation time can be as long as 5-10 years. Additionally, the oxygen content in water is relatively low, and deep water bodies are often in an anaerobic state, which further inhibits the activity of aerobic microorganisms and delays the degradation process.
3. Degradation Products and Environmental Impacts
In soil, the small-molecule organic substances produced by the decomposition of biodegradable bags are further converted by microorganisms into carbon dioxide, water, and humus. Humus can integrate into the soil, improve soil structure, increase soil fertility, and realize a 良性 cycle (virtuous cycle) of substances.
In water, if the small-molecule substances produced by degradation cannot be promptly utilized by aquatic organisms, they may accumulate in the water body. This is particularly true in closed water bodies, where it may have a certain impact on the ecological balance of the water. At the same time, the degradation products in water may also spread with water flow, increasing the difficulty of environmental monitoring.
The factors affecting the degradation process also differ. In soil, pH value, organic matter content, and soil aeration all affect the activity of microorganisms, thereby influencing the degradation rate. For example, neutral or slightly alkaline soil is more conducive to the growth of most degrading microorganisms, while soil rich in organic matter can provide sufficient nutrients for microorganisms and accelerate the degradation process.
In water, the main influencing factors are temperature, salinity, water flow rate, and dissolved oxygen content. Higher temperatures can increase the metabolic rate of microorganisms and accelerate degradation; high salinity, however, inhibits the activity of some microorganisms and slows down degradation; a fast water flow rate is beneficial for the transport of oxygen and nutrients, promoting degradation.
In conclusion, the degradation process of biodegradable bags in soil and water differs significantly due to variations in environmental conditions. In practical applications, it is necessary to select the appropriate type of biodegradable bag according to specific scenarios and fully consider the impact of environmental factors on the degradation process. This will help give full play to their environmental role and promote the work of plastic pollution control.
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