What Are The Phases Of Composting

During composting, biological and biochemical processes run side by side and successively under optimal conditions (temperature, moisture, etc., e.g., in the composting plant). In principle, three phases of composting can be distinguished, although there are different methods of composting.

Phase 1 Pre-rotting, degradation or hot rotting phase

Important for the course of composting is the C:N ratio, the ratio of the elements carbon (C) and nitrogen (N) in the starting material to each other. For the microorganisms, which are significantly involved in composting, a C:N ratio of about 25:1 is quite favorable (range 15-30 parts carbon to one part nitrogen). This means that for every 25 parts of carbon, there is one part of nitrogen. At higher carbon ratios, the process of composting takes much longer. The microorganisms can then not optimally influence the rotting process.

If the proportion of nitrogen is too high, the rotting process takes place too quickly. The nitrogen becomes gaseous and is thus no longer available as a nutrient in the soil or for plants.

To ensure optimal rotting in the compost, low-nitrogen and high-nitrogen organic waste should therefore be mixed well together during composting (at the plant and privately), and only a small amount of tree and shrub cuttings (C:N ratio 150:1) and other organic waste such as sawdust (C:N ratio 200:1-500:1) or paper and cardboard (C:N ratio 350:1-1000:1) should be added.

At the beginning of composting, a large number of microorganisms (e.g. bacteria, fungi) are active. They initially feed on easily degradable proteins and sugars and multiply rapidly in the compost material. During decomposition, for example of carbohydrate molecules, excess energy is produced. This energy is released in the form of heat.

If the material to be composted is well chopped up beforehand, decomposition is accelerated because the surface area for the microorganisms to attack is increased.

After one week, temperatures of about 40°C are reached in the compost material. Due to a rapid conversion of easily degradable substances as a result of well-shredded material, the pH value in the compost drops somewhat as a result of an accumulation of organic acids. This period is sometimes referred to as the first phase of composting, so that the process of composting is variously described as four-phase.

From the second to about the twelfth week, the temperature in the compost can rise to over 60°C under optimal conditions (hot rotting). At these temperatures, wild weed seeds and germs are killed. The pH value increases because organic acids are broken down again.

Alkali metals and alkaline earth metals, on the other hand, are released. The increased temperature causes the microorganisms of the first phase to die. When the temperature reaches 50 to 65°C, heat-loving fungi and radiation fungi appear. In this phase, fungi degrade not only easily degradable substances but also components of the plant cell walls that are difficult to degrade (cellulose, pectin).

Fats are degraded by bacteria during this phase. At the end of hot rotting (after 3-6 months), hygienized fresh or raw compost is obtained, which can be applied to beds as mulch and long-term organic fertilizer.

Phase 2 Conversion phase or main rotting

From the twelfth week (approximately), the temperature in the compost gradually drops again to about 40 to 45°C. The existing lignin is broken down by fungi, the work of other microorganisms slows down and decreases, humus substances are built up. The pH value settles around pH 7.0.

Phase 3 Post-rotting

In this phase, the compost material undergoes the post-rotting process with temperatures of about 40° to 30°C, possibly below 20°C. During this process, substances in the compost that are difficult to degrade are mineralized and partly converted into valuable humus substances (humic acids).

Depending on the process, post-composting can take place in open, covered or closed heaps. After about four to six weeks (depending on the process), the compost is considered finished compost and can be screened.

Composting plant and garden

In principle, all of these processes occur both at the composting plant and with compost in the private garden. In the garden, however, the temperatures of the hot rotting phase are hardly reached in the composting plant. For this purpose, the compost piles in the garden are usually too small and, moreover, are only filled gradually. Hygienization therefore hardly takes place in private compost.

On the other hand, worms, insects, isopods and arachnids migrate into the compost in the garden, especially towards the end of the rotting process (and sometimes even before). Their feeding, excreting and burrowing activities primarily influence the physical and chemical properties of the compost. The soil animals mix organic and mineral components and thus contribute to the buildup of stable humus for

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