There are various fermentation methods in fertilizer production. The following are some common fermentation methods:

1. Aerobic Fermentation

Principle
Aerobic fermentation is the process of decomposing and transforming organic materials by aerobic microorganisms (such as bacteria, fungi, etc.) in an aerobic environment. Under aerobic conditions, these microorganisms break down carbohydrates, proteins, etc. in the organic materials into simple substances such as carbon dioxide, water, and ammonia through respiration, while releasing energy for their own growth and reproduction. During this process, microorganisms multiply in large numbers, enabling the fermentation process to continue until the organic materials are finally converted into stable products such as humus.
Process
Material Pretreatment: Firstly, the fermentation materials need to be pretreated, including adjusting the particle size, water content, and carbon-nitrogen ratio (C/N) of the materials. For example, the organic wastes are crushed into an appropriate particle size. Generally, the smaller the particle size, the larger the contact area between the microorganisms and the materials, which is more conducive to fermentation. Meanwhile, the water content is adjusted to about 50% – 60%. The appropriate water content can ensure the activity of microorganisms. The carbon-nitrogen ratio is usually adjusted to 25 – 30:1, which can provide a suitable nutritional environment for microorganisms.
Aeration and Turning: During the fermentation process, sufficient oxygen supply must be ensured. This can be achieved by regular turning or using aeration equipment. Turning can make the materials fully contact with the air. Generally, the materials are turned once every 1 – 3 days. Aeration equipment such as ventilation pipes can deliver air to the interior of the material pile to maintain the aerobic environment required by microorganisms.
Temperature Control: Heat is generated during the aerobic fermentation process, causing the temperature of the material pile to rise. Generally, the temperature will rise to 50 – 70°C within a few days. This high-temperature stage is beneficial for killing harmful organisms such as pathogenic bacteria and weed seeds in the materials. However, if the temperature is too high, it may inhibit the growth of microorganisms. Therefore, the temperature needs to be monitored and controlled. When the temperature is too high, it can be lowered by turning or increasing the aeration volume.
Completion of Fermentation: After a period of fermentation, the properties of the materials will change significantly. The originally loose organic materials will gradually become compact, the color will change from light to dark, and the smell will change from the pungent raw material smell to the earthy smell of humus. When the temperature of the materials drops close to the ambient temperature and their physical and chemical properties are stable, it indicates that the fermentation is basically completed. Generally, it takes about 2 – 4 weeks.

2. Anaerobic Fermentation

Principle
Anaerobic fermentation is the process of decomposing organic materials by anaerobic microorganisms in an anaerobic or hypoxic environment. Under anaerobic conditions, anaerobic microorganisms break down the complex organic substances in the organic materials into products such as organic acids, methane, and carbon dioxide. During this process, microorganisms utilize the chemical energy in the organic materials for metabolic activities, and the methane and other gases produced can be collected and utilized as energy sources.
Process
Material Preparation and Sealing: Similar to aerobic fermentation, the materials need to be pretreated, but the requirements for particle size and air permeability are relatively low. After the materials are prepared, they are placed in a sealed container or fermentation tank to create an anaerobic environment. For example, in a biogas fermentation tank, organic wastes (such as livestock and poultry manure, crop straws, etc.) are mixed with water and then loaded into the tank, and then the tank mouth is sealed.
Fermentation Stages: The anaerobic fermentation process is usually divided into, namely the acid production stage and the gas production stage. In the acid production stage, anaerobic microorganisms break down the organic substances into organic acids (such as acetic acid, propionic acid, etc.) and carbon dioxide, etc. This stage usually lasts for several days to several weeks. Then it enters the gas production stage, where methanogens and other microorganisms further convert the organic acids into methane and carbon dioxide. The gas production stage may last for several weeks or even months, depending on the type of materials, temperature, and fermentation conditions.
Product Utilization and Post-treatment: The methane produced by fermentation can be used as fuel for power generation, heating, etc. The res