Biothermal drying (composting) is a natural process in which living organisms (bacteria, fungi, protozoa, etc.) convert fresh organic matter under controlled conditions and in the presence of oxygen into homogeneous, stable and humus-rich (organic matter) compost.
In Flanders animal manure is usually composted in closed systems on manure processing companies with hygienisation as the main goal. After composting, the product still contains a lot of phosphorus and is therefore exported outside Flanders.

Compost from fruit and vegetable household waste, on the other hand, have a low phosphorus content and is therefore an interesting product for the Flemish arable farmer.