Annually, Middlebury College diverts over
20% of its waste stream through composting.
This low-tech composting system, technically known as a passively aerated windrow system (PAWS), has saved the College approximately $200,000 in avoided landfill disposal costs since beginning its compost initiative in 1993. The College also saves by not having to purchase soil enrichment products for campus landscaping.
Twice daily, College staff service the food waste compost bins outside its three main dining halls and several smaller dining establishments around campus. Food prep scraps and post consumer food waste (pulverized to minimize moisture, waxed cardboard and boxboard, paper towels and napkins, assorted food prep paper waste are all acceptable components as is yard and leaf debris generated by the landscaping crew. Using a special hook lift truck retrofitted with appropriate dumping features by Facilities Management staff, the food waste is delivered to the College's compost site (approximately 4 acres) at the edge of campus. There it is stored in a modified Comptainer manufactured by Vermont-based Green Mountain Technologies of Brattleboro.
The watertight unit holds a perforated plastic tank and is set below grade for easier transfer of waste. The food waste is dumped through a funnel in the top of the tank and then a cover is slid in place to minimize invitations to rodents, birds and wildlife. Sloping towards the front, leachate discharges by gravity into a line that carries it to a separate holding tank. When the leachate tank is full, the liquid is hauled to the adjacent compost pad where a hose is attached and the leachate is sprayed onto active compost piles. The food waste holding tank is also connected to a biofilter comprised of woodchips and finished compost. Air from the holding tank is pumped through the biofilter to further decrease the potential of generating unpleasant odors.
Every two weeks, internally referred to as "Dump Day," the full Comptainer is emptied. A large concrete pad provides a base for the operation. Long beds of horse manure (courtesy of nearby Morgan Horse Farm), mixed with woodchips generated from campus tree trimming, are laid out on the pad to act as a giant sponge. Waxed corrugated boxes considered as contaminants in cardboard recycling, but popular packing containers for fruits and vegetables, are placed near the bottom to aid in the absorption of excess moisture. Perforated PVC pipes are then laid perpendicular to the length of the pile. Food waste is added, followed by a covering of four to eight inches of dry horse manure that seals in the odors. The ends of the plastic pipe stick out from the pile and receive air, eliminating the need to turn the pile.
Turning the pile requires labor and releases odors." The traditional windrow did not work well for us", notes Norm Cushman of the Facilities Management team. "I knew that off-gassing of freshly turned piles would not be popular with neighbors and golfers on the college's nearby golf course. Additionally, I really didn't have the available labor to routinely turn the piles. But this system works great throughout the year".
The windrow is left to decompose for ninety days after which the pile is moved to the perimeter of the pad to cure. The College contracts with a local composting operation, Vermont Natural AG Products of Middlebury, Vermont to screen the piles. The result is a nutrient-rich, dark black soil amendment with a high humus content that is a great supplement to the rocky and clay filled soils of Addison County.
For more information, contact:
Melissa Beckwith, Supervisor Waste Management/Custodial, Middlebury College
tel: 802-443-5267
email: mbeckwith@middlebury.edu
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