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What is composting?

Composting is the biological process of transforming organic matter to obtain natural fertilizer without using any motorized system or mechanism. The main feature of organic waste is that it is biodegradable, which means that it can disintegrate quickly and transform into other organic matter, like compost. Compost can provide nutrients for the soil

The United Nations’ Food and Agriculture Organization (FAO) developed the Farmer’s Compost Handbook, which explains that composting is a controlled process that releases heat and uses oxygen, water, and humidity to break organic matter down and transform it into a useful material.

What’s the purpose of composting?

Besides utilizing organic waste, composting makes it possible to:

  • Recover contaminated and degraded soils.
  • Reduce the amount of organic matter in landfills. According to a United Nations study, approximately 11 million tons of waste are collected each year worldwide and sent to the landfill. The breakdown of the organic part of this waste contributes to about 5% of global greenhouse gas emissions.
  • Stabilize and sanitize organic waste for use as fertilizer.
  • Turn biodegradable organic matter into a biologically stable product.
  • Nurture soils, the substrate for plants. 
  • Control pest rates.

How does composting work?

Composting is similar to the natural decomposition process, but it is done in a more controlled way. In nature, organic matter like trees, leaves, stumps, animal remains, etc., slowly decompose. With the help of microorganisms present in the soil, they become an essential material for the soil, making it fertile and capable of maintaining the life cycle of vegetation.

The same happens with composting: organic waste like fruits, vegetables, leaves, vegetable fiber, etc., accumulates in an effective, organized, and controlled way to be converted into usable material. 

What are compostable materials?

Across Europe, there are laws (EU Regulations 1774/2002 and 208/2006) that establish which materials can be used for composting, specifically:

  1. Forest and agricultural waste, especially woody matter, as they have high levels of carbon, which is ideal for reaching the chemical balance needed for composting. 
  2. Manure, or livestock excretions, contain a high level of nitrogen, which is also essential for composting. 
  3. The organic materials in municipal solid waste. It’s important that organic waste is rigorously separated out to prevent other waste like plastic or glass from getting into the process, as that could impact the natural decomposition process.
  4. Wastes from the agri-food industry, such as leftovers from grains, fruits, leaves, fish remains, etc. 

However, more generally speaking and even in terms of our households, leaves, garden plants, kitchen waste (vegetables, eggshells, fruit peels, and coffee grounds), straw, and cut grass are all good organic matter for supporting the composting process. 

What are the phases of composting?

For the composting process to take place, there must be a chemical balance between the nitrogen and the carbon that comes from the waste in each of the following phases: 

  1. Preparation: the materials are collected and mixed; non-usable matter is discarded, and the nutrient levels are adjusted to reach the right carbon-nitrogen balance.
  2. Mesophilic decomposition: the process starts at room temperature (<40ºC); as the days go by, the temperature increases thanks to the microorganisms’ activity. In this phase, the goal is to reach temperatures between 50 and 70ºC.
  3. Thermophilic decomposition: microorganisms that develop starting at 45ºC, called mesophiles, disappear so that others capable of thriving at up to 100ºC – thermophiles – begin to flourish. These high temperatures sanitize the organic mixture as the decomposition process continues. The thermophilic phase can last for months, as the aim is to remove any biological contaminants.
  4. Cooling mesophilic decomposition: at this stage, it gradually returns to room temperature (<40ºC), the mesophiles reappear, and decomposition continues.
  5. Maturation: once decomposition is complete, the compost adds new microorganisms that complete the transformation of the organic matter, leading to its stabilization.

What other information is there on composting? 

  • With about 100 kg of organic garbage, you can get up to 30 kg of compost. 
  • According to the European Environment Agency, about 12 million tons of compost are generated annually in the European Union. The main countries behind this production are Austria, Belgium, Germany, Italy, and the Netherlands.

According to the Ministry for the Ecological Transition and Demographic Challenge, 65% of the organic waste produced in Spain is composted, 28.4% goes to landfills, and 6.4% is incinerated.

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