In-Vessel Composting or Bio-Drying is a natural biological process which takes place in a series of long concrete rooms known as tunnels.
- After waste has been mechanically sorted, the resulting fine material is transferred to a tunnel.
- The entire floor space (approximately 150 square metres) is covered to a height of up to four metres.
- The tunnel is then sealed at both ends.
- The tunnel has a perforated floor allowing warm air, driven by fans, to circulate
- Over the next two to three weeks, this warm air helps compost the material, releasing carbon dioxide and water vapour
- This reduces the mass of the material by about 30%.
The final product is a stable compost-like material which can be easily landfilled or used as a fuel source.