Organic waste is all the waste that can be degraded by micro-organisms. We find there:
Animal products: blood, meat, milk, …
Vegetables and food leftovers
Gardening waste: cut grass, remains of pruning …
Sludge from the wastewater recycling process
Why recycle organic waste?
Organic waste constitutes 30% of the waste rejected by the average household, as well as most of the waste of the Agrifood Industry. These wastes are therefore present in large quantities, and recycling them makes it possible to reduce the volumes treated by the conventional incinerator.
In addition, these wastes can pose several problems if they are poorly managed:
How does it work?
The green waste is sent to special centers where a quick manual sorting tries to remove the non-degradable elements such as stones, glass, etc. From there, green waste can follow two distinct paths: anaerobic digestion or industrial composting.
The waste is crushed, mixed with chips to ensure good ventilation and finally stacked in the open air in the form of huge piles. They are then left there for six to ten months. Every month, a construction machine is used to return the piles (composting needs aeration). Bacteria, worms, and fungi will colonize the mass of biodegradable waste and feed on the nitrogen and carbon present. Such biological activity can raise the temperature in the center of the pile up a bunch.
An example of industrial composting
The rainwater that falls on these mountains of decomposing waste is reprocessed (see treatment of wastewater) because they come out too loaded with nitrogen.
At the end of the process, the compost looks like a black earth, heavy and granular. This material is meant to obtain a perfectly homogeneous material that will be resold.
Beautifully called “anaerobic digestion” by professionals, this process is less common than composting. Unlike the latter which requires dry elements to avoid rotting, methanation works perfectly with liquids or very wet, poor in structuring elements.