TURNING TRASH INTO TOPSOIL
The Waste Options Nantucket co-composting facility went on line in December 1999 at the Town of Nantucket’s landfill site.
The technology used at the Waste Options' facility recycles organics by processing municipal solid waste (MSW) and sewage sludge together and utilizing natural biological processes to create a compost end product. Non-compostable materials are separated from the compost by a series of screens.
The plant consists of three buildings and a steel drum digester. MSW and sewage sludge are delivered to the Tipping Building by waste haulers. Utilizing rolling stock, plant operators visually inspect loads of MSW to remove unacceptable materials. MSW is delivered in clear bags to allow the contents to be viewed. Unacceptable waste will be rejected. Acceptable waste and sewage sludge are loaded into the digester by conveyor. A hydraulic ram loads the MSW and sludge into the digester.
The digester is a multi-compartment steel drum 12’-6” in diameter and 185 feet long. The drum rotates at a variable speed between 0.5 and 1.0 rotations per minute. Air and water are added to the digester, as required, to optimize the biological digestion. Material remains in the digester for 3 days.
After three days, material is discharged from the digester and conveyed to a
trommel screen. Undersized material (less than 1-inch), or unders, passes through the screen for processing as compost. Oversized material, or overs, is conveyed to a baler for landfill disposal.
The compost is removed from the trommel screen area by front-end loader and placed on the floor of the Maturation Building. A computer based control system regulates airflow through the compost material based on temperature measurements and controls moisture through a spray system operated by a timer. Material will remain on the maturation floor for several weeks and will be turned daily by using a front-end loader.
Following its period on the maturation floor, the material is then moved to the final screening area. The material is loaded into a hopper, which feeds a belt conveyor. The belt conveyor discharges materials onto a vibrating screen. The screen overs (greater than 3/8-inch) are conveyed to a compactor. The compacted material is transported to the landfill.
The vibrating screen unders are conveyed to a destoner to remove glass, stone and other heavy particles. The light fraction is sent to a compost container for removal and use. The heavy fraction is sent to a container and is either landfilled or reintroduced to the digester.
Odor control is an essential component of the processing facility. Odor is controlled by a biofilter. The biofilter is located in a separate building adjacent to the Aeration Building. The Tipping Building and Aeration Building are maintained at a slightly negative pressure to prevent the escape of odors from the plant.
High-grade compost can be blended with sand, peat, bark, and other select horticultural products for use in nurseries, greenhouses, and other purposes. All soil products are carefully tested for quality to meet state and federal regulations.
Here are some of the advantages that the Waste Options co-composting
facility brings to the Nantucket landfill:
Co-composting, in combination with the recycling of plastic, glass, steel, aluminum, construction and demolition waste, and tires, maximizes material recovery and minimizes the amount of material added to the landfill. This reduction of material deposited into the landfill is up to 80 percent. The only material then landfilled has been sanitized and will not create leachate or methane.
The system is pollutant free; there are no foul air emissions or ash disposal problems. The only material remaining to be landfilled is a clean, non-putrescent residue primarily comprised of plastic.
There is no shredding of the municipal solid waste, so there is control of the ingredients going into the compost end product. This process produces a high quality organic compost that will be marketed for landscaping and gardening uses.
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