What is it?

Composting is the way to turn bio-waste, which makes up 53 % of all urban waste, into a fertilizing product. It is an aerobic (with air) and thermophilic (with rising temperatures) process in which natural decomposing organisms and microorganisms are involved. It requires mixing kitchen and garden waste with dry and woody pruning remains, sawdust and leaves to produce a high-quality amendment: compost. For every 100 kilos of organic matter, we can obtain 10 kilos of compost.

The Plan Revitaliza of the Deputación de Pontevedra promotes composting as a global waste management scheme, treating organic waste in the same place where it is produced (kilometre zero) through community composting centres, individual composting and local plants.

Advantages of composting

No more landfills or incineration

No more landfills or incineration

Organic waste is treated in the same place where it is produced (kilometre zero) and doesn't need to be stored in a landfill or incinerated in certain facilities.

Savings in waste collection

Savings in waste collection

organic waste doesn't need to be collected or transported, which eliminates the need to use lorries and other machinery and the corresponding costs.

Savings in waste management

Savings in waste management

Composting through community centres, individual composting and local plants is more affordable than schemes currently used if implemented globally.

Reduction of CO2 emissions

Reduction of CO2 emissions

Since organic waste is neither transported nor incinerated, each person that composts stops releasing 155 kilos of CO2 to the atmosphere per year.

A natural fertilizer

A natural fertilizer

Composting organic urban waste generates compost, which can be used to improve the quality of soils avoiding the costs of chemical fertilizers.

Better recycling

Better recycling

When people separate organic waste correctly, they also increase their plastic, cardboard and glass separation ratios.

Compostable materials

Compostable materials:

Kitchen waste (both cooked and uncooked):

  • Fruit and vegetables
  • Rice and pasta
  • Meat and fish
  • Bread and eggs
  • Yogurts
  • Coffee grounds and filters
  • Tea grounds and teabags (without staples)
  • Undyed paper napkins and paper towels

Garden waste:

  • Leaves, flowers and green or dry plants
  • Grass
  • Crushed pruning remains
  • Natural wood ash and sawdust
  • Crops remains
  • Over-ripe fruit
  • Hay

Non-compostable materials:

  • Treated wood ash
  • Disposable diapers
  • Magazines or colour-printed paper
  • Swept up or vacuumed dirt
  • Cigarette filters
  • Synthetic fabrics
  • Any inorganic and non-biodegradable material 


During the composting process, crushed or broken, preferably ligneous, dry vegetal must be mixed in with the humid bio-waste (food scraps and green plants) to obtain compost.

These dry, carbon-rich materials are called bulking materials and their main function is to "bulk up" the material that is being composted. They allow for air circulation and regulate moisture.

Some materials that can be used as bulking include crushed pruning remains, dry leaves, sawdust, natural wood shavings, hay or dry grass.

If you have a vegetable garden or a garden you can use pruning remains and dry leaves. If you do not have any or enough of those materials, you must contact your town council or master composter so they can provide them to you.

Remember that adding bulking material is one of the basic rules of proper composting.

Composting stages

Stage 1

Stage 1

Food scraps, plant residues and bulking material deposited in the individual or community composter start degrading by bacterial activity. The pile starts heating up and emanating water vapour from the top.

Stage 2

Stage 2

After the first occurrence of bacteria, other organisms that act at even higher temperatures appear, producing a faster degradation and ensuring sanitation and elimination of possible pathogens. Between a week and two months later, biological activity diminishes and the materials become stable.

Stage 3

Stage 3

The material is subjected to a slow fermentation process that can last for several months. The temperature of the pile progressively decreases and microorganisms that help degrade the less biodegradable parts start working. At the end of the maturing process compost is obtained.

Problems and solutions

The material is very dry: mix it with kitchen waste or water lightly and turn.

The material is very humid: turn it. If it doesn't work, add bulking material and turn.

There are many fruit flies: turn and cover it with bulking material.

It smells like ammonia: turn and cover it with bulking material.

It smells rotten: turn it. If it doesn't work, add bulking material and turn.

Other experiences

Chicken composting

The Deputación de Pontevedra is installing composting facilities with chickens linked to urban vegetable gardens or public parks. Composting made with chickens needs a henhouse with an open part with free-range chickens and a closed part with three composting modules.

In the first module, citizens deposit their organic waste and bulking materials are added. The chickens act as natural mixers, turners and oxygenators.

Once the first module is full, the material must be transferred to the second module. The second module must be closed and covered to prevent the animals from accessing it so that the composting process can continue without any microbial contamination.

In the third module, the material is treated with worms, promoting the colonization of the waste and bulking material mix, for the last transformation and final maturity.


Vermicomposting is the organic matter decomposing process produced by the activity of certain earthworm species, particularly of the genus Eisenia. It can be carried out in any private house or community composing centre using organic waste generated at home.

Through their digestive tubes, earthworms work with the combined action of various microorganisms that transform organic matter into a product called vermicompost or humus. This type of compost has a very good structure and contains a great amount of nutrients.

In some of the Plan Revitaliza community composting centres, earthworms are being introduced by master composters in a fully controlled manner to further improve the quality of the compost.