Composting Tunnel Grassobbio
Spurghi F.LLI Terzi SrlGrassobbio | Bergamo - Italy
- System description: Tunnel composting
- Waste processed: Organic waste, garden waste and sludge
- Plant capacity: 30,000 t/year
Tunnel composting technology is used to process organics from source-separated municipal waste and sludge from waste water treatment.
The biological process takes place inside closed reactors, consisting of tunnels made of reinforced concrete with an aeration system integrated into the fl oor.
The plant uses tunnel composting technology for biological treatment of sourceseparated organic waste in order to hygienize and stabilize it, which, after the curing phase, produces quality compost. The process takes place in three closed reactors, consisting of reinforced concrete tunnels equipped with a ventilation
system integrated in the floor. The air blown into the material through the floor is partly re-circulated inside the tunnel and partly sent to the odour control system. Air coming from the areas where waste is sorted is used as fresh process air in the tunnels, so the total volume of waste air is reduced without negatively effecting on the ventilation of the buildings.
A sophisticated collection and treatment system for leachates ensures the correct drainage of tunnels and allows re-using the liquid for moisturizing the material processed by means of nozzles set up under the ceiling of each tunnel. The material to be biologically treated is prepared by mixing source-separated organic waste, shredded green waste and recycled material deriving from the final screening of produced compost. Once the tunnel has been loaded with the wheel loader, its special door is closed and the process begins. At the end of the treatment the tunnel is emptied and a new cycle begins. A computerized control system, including visualization on PC with colour graphics, surveys the process and keeps its parameters in the preset ranges, that are different for every stage of the process. Many process parameters are measured by sensors set up in various parts of the system. For instance, material temperature, air temperature, oxygen content in the air, air pressure and air flow are continuously monitored and recorded. To control odours, the air exhausted from the tunnels, mixed with the air flow coming from the areas where waste is mechanically processed, is treated in a large biofilter. Biofiltration controls odours very efficiently because malodorous gases, absorbed by the superficial moisture of the filter media, are quickly digested through a biological process. The centralized control system also surveys the biofiltration process, which takes place after the air flow has gone through a scrubber.
After the treatment in the biotunnels, the material is moved to the curing area, which has an aerated floor.