The basic principle and process of composting

The basic principle and process of composting
The basic principle and process of composting

Basic principles of composting

There are many microorganisms in nature that have the ability to oxidize and decompose organic matter.

Microorganisms are used to biochemically degrade organic waste under certain temperature, humidity, and pH conditions to form an organic substance similar to humus soil for use as fertilizer and soil improvement.

This method of using microorganisms to degrade organic waste is called biological treatment and is generally called composting treatment.

Organic waste is the material condition for the survival and reproduction of microorganisms in compost because some microorganisms need oxygen when they live, and some do not need oxygen;

Therefore, according to the different oxygen requirements of the microorganisms acting in the treatment process, the composting treatment of organic waste can be divided into two types: aerobic composting (high temperature composting) and anaerobic composting.

The former is to degrade organic matter through aerobic microbial activities under aeration conditions. Since the temperature of aerobic composting is generally 50-60 degrees, and the highest can reach 70-80 degrees, it is also called high-temperature composting.

The latter is the process of making fertilizer using anaerobic microbial fermentation.

Aerobic composting

Aerobic composting is carried out under aerobic conditions with the help of aerobic microorganisms.

In the composting process, the soluble organic matter in the organic waste penetrates the cell wall and cell membrane of the microorganism to be absorbed by the microorganism. The solid and colloidal organic matter first adheres to the body of the microorganism, and the extracellular enzyme secreted by the microorganism is decomposed into the soluble matter. Then infiltrate the cells.

Through their own life activities-oxidation, reduction, and synthesis processes, microorganisms oxidize part of organic matter into simple inorganic matter, release the energy required for life activities, and convert part of the organic matter into nutrients necessary for organisms to synthesize new cell material, so the microorganisms gradually grow and multiply to produce more organisms.

Generally, the temperature change of compost is used as the evaluation index of the composting process.

A complete composting process consists of four composting stages, namely the low-temperature stage, medium temperature stage, high-temperature stage, and cooling stage.

Each stage has different bacteria, actinomycetes, fungi, and protozoa. These microorganisms use the organic matter in the waste as a source of food and energy until a stable humus material is formed.

Anaerobic composting

Anaerobic composting is carried out with the help of anaerobic microorganisms under anaerobic conditions.

When organic matter decomposes anaerobic, it mainly undergoes two stages of acid fermentation and alkaline fermentation.

The decomposition products in the microbial activities at the initial stage of decomposition are mainly organic acids, alcohols, carbon dioxide, phosphine, and so on.

At this stage, due to the accumulation of a large number of organic acids, the PH value of the fermented material gradually decreases.

With the reduction of easily decomposable organic substances and the reduction of oxidation-reduction potential, another group of microorganisms called methane bacteria began to decompose organic acids and alcohols, and the main products are methane and carbon dioxide.

With the reproduction of methane bacteria, organic acids are rapidly decomposed and the PH value rises rapidly. This stage is called the alkaline fermentation stage.

Because the product after anaerobic fermentation is liquid, sometimes still contains a small number of pathogenic bacteria and emits an odor, it must be sterilized and sprayed with a special biogas slurry spreading machine before application in the farmland. The land area of the fertilization field should also be large. So this method is more suitable for large farms.

Composting process and parameters

The traditional composting technology uses an anaerobic field accumulation method, which not only covers a large area, long accumulation time but also has a low degree of harmlessness.

Modern compost production generally adopts an aerobic composting process, which has the advantages of a high degree of mechanization, large processing capacity, fast compost fermentation speed, a high degree of harmlessness, and easy clean production.

The aerobic composting of livestock and poultry manure usually consists of pre-treatment, primary fermentation (main treatment or main fermentation), secondary fermentation (post-mature fermentation), and subsequent processing and storage.


Because the moisture content in livestock manure is large (the moisture content is usually 70% to 90%), if moisture is not adjusted, the compost temperature will rise slowly, the amount of odor will be large, and the transportation and mixing will be inconvenient due to poor ventilation.

Therefore, the main task of pretreatment is to adjust moisture content, material permeability, and C/N.

At the same time, you can also remove impurities such as iron wire, bricks, stones, plastic film, ropes, and other impurities that are not suitable for composting, by the way, otherwise, it will affect the subsequent mixing and aeration processes.

One-time fermentation

The primary fermentation of livestock manure is usually carried out in a specific fermentation place (tank, pond, etc.) or device. During the composting process, oxygen is introduced into the compost through stirring and forced ventilation to promote aerobic microbial activity.

Due to the existence of a large number of various microorganisms in the compost raw materials, air, and soil, it will soon enter the fermentation stage.

First, microorganisms use easily decomposable organic matter to reproduce, produce water dioxide, and at the same time generate heat to heat up the compost.

In the initial stage of fermentation, the decomposition of organic matter is mainly carried out by medium-temperature microorganisms (30-40 degrees). As the temperature rises, the thermophilic bacteria that are most suitable for living at 45-65 degrees gradually replace the medium-temperature microorganisms.

At this temperature, various pathogens, parasite eggs, weed seeds, etc. can be killed.

Generally, the stage from the temperature rising to the temperature falling is called the primary fermentation stage.

In order to improve the detoxification effect, this stage should be maintained for at least 10 days.

Under normal circumstances, cow manure at this stage is about 4 to 5 weeks, pig manure for 3 to 4 weeks, and chicken manure for about 2 to 3 weeks.

Secondary fermentation

Send the compost after the primary fermentation to the secondary fermentation site for further composting, so that the easily decomposable and harder-to-decompose organic substances that have not been completely decomposed in the primary fermentation will continue to decompose and gradually convert into relatively stable and mature compost.

Generally, the requirements for secondary fermentation are not as strict as those for primary fermentation, and the stacking height can be 1~2m, as long as there are rainproof and ventilation measures.

Turn the pile every 1 to 2 weeks during the accumulation process. The length of the secondary fermentation depends on the various types of livestock and poultry manure and the nature of the added moisture adjustment materials;

Generally, when the internal temperature of the compost drops below 40 degrees, the secondary fermentation is complete, and the compost can be air-dried and processed;

Generally, the secondary fermentation of pure livestock manure composting takes about 1 month, and the secondary fermentation takes about 2 to 3 months when other straw materials are added;

In the case of adding wood materials such as sawdust, bark, etc., the secondary fermentation takes more than 6 months.

Addition of microorganisms

The addition of microorganisms in the compost can accelerate the rapid decomposition and maturity of livestock manure and straw materials, greatly improving production efficiency.

However, if the conditions required for composting are not met, no matter how many microorganisms are added, the fermentation effect will not be achieved.

Title: The basic principle and process of composting
Source: ThumbGarden
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