Depending on its origin, organic waste can represent a significant fraction of waste. Its recovery is possible by composting, which is a natural biological technique of aerobic fermentation.
This technique applies to household waste containing a significant part of fermentable waste, green waste and sludge from wastewater treatment plants. It can also apply to waste generated by industrial activities containing high amounts of organic material (notably waste from the food processing industry)
Certain local authorities have implemented individual composting, which is only possible in private housing areas, therefore in specific urban conditions and on a limited scale.
On an “industrial” scale, composting is facilitated by the organisation of selective waste sorting or the operation of waste drop-off centres (centralised composting). In addition to green waste generated by waste drop-off centres or public gardens, additional sludge from biological wastewater treatment plants and sometimes certain types of previously sorted household waste, can increase the amount of waste reused.
This technique makes it possible to reduce, with seasonal variations, the amount of household waste to be treated in landfills or by incineration by at least one third. It also prevents the open air burning of green waste which is sometimes practiced although often prohibited by departmental health regulations.
The compost is formed by the action of micro-organisms (bacteria, fungi etc.) and macro-organisms (earthworms, mite, woodlice etc.).
At the beginning of the composting process, only micro-organisms are active. This phase, which consumes a large amount of oxygen, results in a rise in temperature: this is the decomposition phase. The transformation of the carbonaceous material into CO2 and evaporation explain the observed reduction in volume.
The activity of micro-organisms then diminishes, the temperature drops and macro-organisms take over.
Waste should have a carbon / nitrogen ratio of around 30. Materials providing mostly carbon are wood, straw and dead leaves while green waste, vegetable peelings and paper (non printed) mostly provide nitrogen. Moisture and air are also essential elements in the transformation of materials into humus.
Appropriate aeration (stirring) prevents the emergence of anaerobic phenomena and therefore the formation of unpleasant odours.
Use of compost:
The end product is humus, which is used in soil conditioning. Organic materials therefore return to the soil while reducing the use of fertilisers.
For the marketing of the composts produced, compliance with different standards has now been made compulsory: NFU 44-051 for organic conditioners; a new version of this standard was certified in April 2006, compliance with which will shortly become compulsory; NFU 44-551 for crop support; NFU 42-001 for fertilisers.
For sludge-based composts, compliance with standard NFU 44-095 was made compulsory in 2004.
Circular of 5 January 2000 relative to the nomenclature of classified installations for environmental protection; classification of composting facilities and waste recycling banks for sorted household waste
Order of 7 January 2002 relative to the general operational requirements applicable to classified installations with a declaration obligation under section no. 2170: “Fertilisers and crop support (production of) from organic materials” and implementing an aerobic biological transformation process (composting) of organic materials