1. Principle of Aerobic Composting of Livestock and Poultry Manure
Aerobic composting of livestock and poultry manure refers to a treatment process where, under aerobic conditions, organic materials in the manure undergo a series of degradation and transformation facilitated by microorganisms such as bacteria, actinomycetes, and fungi in nature. Following this, the material undergoes high-temperature fermentation, resulting in the mineralization, humification, and harmless transformation of organic substances. This composting technique is essential for the production of matured fertilizer suitable for agricultural cultivation. Aerobic composting is also known as high-temperature composting, where the temperature within the compost pile generally ranges from 50 to 65°C, reaching a maximum temperature of 80 to 90°C. The high temperature effectively eliminates pathogenic microorganisms in the manure, thoroughly reduces organic matter, accelerates the decomposition of organic materials, significantly shortening the composting period. The technique boasts advantages such as high harmlessness and fertility of the compost product, making it the primary fermentation method for manure treatment.
2. Three Stages of Aerobic Composting of Livestock and Poultry Manure
A. Temperature Rising Stage: This marks the initiation of aerobic composting, usually controlling the temperature between 15 to 45°C. In this stage, the focus is on transforming easily decomposable organic matter in the compost material into organic nutrients readily absorbed by the soil.
B. High-Temperature Stage: The temperature is maintained above 45°C, representing the main phase of aerobic fermentation. During this stage, complex and less degradable substances undergo decomposition and transformation, leading to a reduction in the mass and volume of compost materials.
C. Maturation Stage: Following the high-temperature stage, the overall temperature of the compost pile gradually decreases. At this point, some less degradable lignin and humus coexist, resulting in an increase in the content of various nutrients in the compost. However, the moisture content decreases during this stage.
These principles form the basis for effective aerobic composting of livestock and poultry manure, offering a sustainable and environmentally friendly approach to waste management and fertilizer production.
Factors Affecting Aerobic Composting
1.1 Roles of Various Ingredients in Aerobic Composting
The moisture in aerobic composting primarily comes from manure, additives, or supplementary materials. It can also be separately added. Moisture softens the raw materials, dissolving organic compounds and facilitating faster decomposition. Additionally, moisture is essential for the metabolism, growth, and reproduction of microorganisms during fermentation, playing a crucial role in regulating nutrient distribution and microbial uniformity. It is also vital for temperature regulation during composting.
Livestock and Poultry Manure:
As the metabolic end product in livestock farming, manure contains a substantial amount of carbohydrates and nitrogenous compounds with putrefactive properties. During composting, it serves as a nutrient source for various microorganisms, ensuring their normal metabolic activities.
These include crop residues like straw, as well as by-products from processing such as husks, sawdust, medicinal residues, or peanut shells. Additives primarily provide a carbon source, regulate moisture and the carbon-to-nitrogen ratio. They also improve the structural condition of the compost pile, enhancing gas circulation during composting.
Exogenous microorganisms such as bacteria, actinomycetes, and fungi exhibit strong activity, rapid reproduction, and decomposition speed. Introducing these external fermentation microorganisms effectively enhances the breakdown of organic matter, accelerating the composting process and reducing the fermentation time.
2.2 Environmental Factors’ Influence
The optimal temperature for composting is maintained between 50 to 65°C. High-temperature bacteria are more efficient in degrading organic matter during composting. However, controlling the temperature is crucial. Excessive heat can lead to microbial death, while too low a temperature can delay compost maturation. Composting should be conducted continuously for at least 5 days.
Controlling the pH during composting promotes the growth and metabolic activities of microorganisms and enhances nitrogen-fixing effects. Typically, the pH should be adjusted to fall between 6.5 to 9.0 during composting.
In aerobic composting, the oxygen content directly impacts the intensity of microbial activity, affecting the speed of organic matter fermentation. If oxygen levels drop below 8%, anaerobic fermentation may occur, leading to the generation of foul odors. Therefore, the oxygen concentration during composting should not be less than 10%.
Evaluation and Influencing Factors of Compost Maturation
3.1 Methods for Assessing Compost Maturation
In practical operations, several experimental methods, including physical, chemical, and biological growth assessments, can be employed to determine the degree of compost maturation.
- Assessing the odor, color, and softness of the compost pile.
- Checking for light-yellow leachate.
- Verifying if the pile has reduced to 1/2 to 2/3 of its original size.
- Ensuring electrical conductivity is less than 1.5 ds·m^-1.
- Maintaining pH between 8 to 9, indicating weak alkalinity.
- Achieving a carbon-to-nitrogen ratio of (25 to 35):1.
- Targeting a humification coefficient around 30%.
Biological Growth Test:
- Assessing the impact of compost on plant growth.
- Unripe compost products may inhibit crop growth.
- Seed germination tests for compost fermented for over 30 days show no impact on germination rates.
3.2 Impacts of Unripe Compost
Unripe compost products may contain pathogenic bacteria that, under suitable temperature and moisture conditions, proliferate in the soil, posing risks to crops and hindering normal growth. Additionally:
- Unripe compost can undergo secondary fermentation, depleting soil oxygen, inhibiting crop growth, and generating excess heat, potentially causing plant damage or death.
- Unripe compost from flowers produces toxic gases like methane and ammonia, causing acidity in crops and hindering seed germination.
4 Common Issues and Strategies in Aerobic Composting
4.1 Failure to Reach Maturation Temperature
In practical composting, it’s common for fermentation temperature to either not rise or rise very slowly, failing to reach the required maturation temperature. Moisture content significantly influences the aerobic composting process. Ideal moisture content should be maintained around 55% to 65%. If the moisture content exceeds 65%, the compost material may compact, impeding air circulation and leading to anaerobic conditions, slowing down aerobic fermentation or causing fermentation to stop.
- Adjust moisture content by adding suitable additives or water.
- For high moisture, turn and re-stack the compost.
- Adjust moisture content to 50% to 60%.
4.2 Increased Ammonia Odor
Excessive moisture or fine particle size in composting can lead to overly compacted piles, hindering air circulation, reducing oxygen supply, causing anaerobic fermentation, and producing foul-smelling compounds like hydrogen sulfide, ammonia, and thiols.
- Adjust moisture content with larger particle additives.
- Increase aeration pump pressure or frequency to improve air circulation.
4.3 Rapid Temperature Drop After Increase
Carbon-to-nitrogen ratio directly affects microbial growth. An excessively high carbon source and low nitrogen content can result in a high carbon-to-nitrogen ratio, inhibiting microbial metabolism and causing a rapid temperature drop in the composting process.
- Monitor and adjust carbon-to-nitrogen ratio by adding organic compounds rich in carbon or nitrogen.
- Restore composting state by addressing the ratio.
In conclusion, aerobic composting effectively addresses the disposal of farm waste and surplus straw, promoting recycling and creating organic fertilizers for agricultural production. During composting, attention to aerobic fermentation conditions such as temperature, moisture, pH, and carbon-nitrogen ratio is crucial to minimize incomplete fermentation issues and enhance resource utilization efficiency.
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