Casella Organics, “Hawk Ridge” Compost Facility

GICOM “Dutch Tunnel”, In-Vessel System—George Belmont, Operator

Wednesday Afternoon – Class Scheduled Visits

Maine Compost School—2013 (Photos by John Leslie, Casella Waste Management)

This is the largest sludge compost facility in Maine.  The ingredients used include bedding from laboratory animals, wood shavings/sawdust and sludge.  An in-vessel system, known as the GICOM ‘Dutch Tunnel’ system is used.

The facility uses a large pugmill mixer to premix the ingredients which are then loaded into the tunnels.  Aeration is provided by blowing air up through slots in the floor. The facility also has a large outside curing area and a biofilter for treating exhaust gasses from the tunnels.  The finished product is primarily sold in bulk for large construction jobs.

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Receiving Area-Municipal Sewage Sludge is dumped onto a “tip-floor” in the covered pre-mix area, where it is mixed with sawdust shavings, papermill  generated short paper fiber residual, animal-bedding  from Jackson Laboratories, and some finished compost.


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Composting Area-Compost mixture is then loaded onto a conveyer system and thoroughly mixed with additional amendment to create the facility’s recipe.  The compost is then transferred to one of the six “Dutch Tunnels” where it is composted under 24/7 aeration for 7-14 days.  Exhaust air is directed through a scrubbing system to a Biofilter.

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Curing Area-Following the “Active” compost phase, compost is moved to the aerated curing area, where it is formed into windrows over perforated pipe and allowed to condition for an additional 21 days under forced air.  Finally, the finished material is screened, and sent to long-term storage where it is made available for sale.