Tunnel Composting

Static Pile Systems and Tunnel Composting

• Tunnel composting is a type of static pile composting system. These systems continually place compost in a receptacle until the receptacle is full and then let the material decompose with only occasional agitation and, often, forced aeration and temperature controls.This lack of agitation slows down the physical breakdown of material; therefore, tunnel systems often integrate another type of composting system in the final phases to speed things along.

Tunnel Composting Equipment

• Basic tunnel composting system equipment is fairly simple. It requires a tunnel, a forced aeration system, a biofilter and mechanisms to load and unload the organic material. The tunnels themselves are long receptacles that vary greatly in size, depending on where and how they will be used. However, they are usually between 120 to 180 feet long and 12 to 15 feet high. Large systems require multiple tunnels to handle high volumes of waste.

Typical Uses

• Tunnel composting systems are typically used to decompose feedstocks of similar consistency and homogeneity and biosolids, according to the Compost Council of Canada. Some compost processing facilities also use tunnel systems to decompose source-separated organic waste and mixed solid waste -- like food, yard scraps and paper. However, to create a usable and stable product, like humus, additional steps are usually required.

Other Uses

• Some institutions and facilities are beginning to integrate tunnel composting systems into their everyday practices. For instance, Colby College diverts the majority of its dining hall food wastes to a third-party company that uses tunnel composting. Despite costs associated with an additional truck, additional staff wages and composting fees, the school still saves over $10,000 annually in sewer and water bills, primarily because it no longer needs many of its dining hall garbage disposals.