EFS Profiles
Sustainable solution: on-campus composting gets the right fit
Middlebury College
Middlebury, Vermont
Purpose: Greening the Campus
Please note that the copyright for this profile is retained by the institution.
After trying other options, Middlebury College chooses passively aerated windrows located on campus to compost food residuals.
To the passing jogger, the mounds of dirt with pipes stuck through them may not look like much, but they are responsible for turning 75 percent of Middlebury College's food residuals (280 tons annually) into compost for campus landscaping and herb production. After years of experimenting with different composting systems, Middlebury College in Middlebury, Vermont has found that the passively aerated windrow system (PAWS) to be most suitable for composting the food residuals of its 2,310 students. Begun in 1993, campus composting now is funded entirely through operational savings.
According to Norm Cushman, of the college's Facilities Management team, who is largely responsible for campus composting, "there is no magic" in the PAWS system. It demands little overhead, staff time, or special skills, but, he adds, may not be appropriate in some settings. The system requires at least an acre of available land with a buffer zone determined by the adjacent land uses. Middlebury College may be an atypical small college in that it owns 6,800 acres of land. "Any school with a little bit of land separate from campus could do this," says Cushman. "The recipe is not rocket science."
Diverting to Off-site Composting
In 1993, Middlebury was awarded a state grant to expand its recycling program. The college was interested in exploring methods for capturing more materials to boost its 40 percent recycling rate. An audit revealed food to be the heaviest of the components in the waste stream. As a short-term solution, the college hooked up with Agricycle, a chicken farm/composting operation in New York State.
Middlebury began its composting program with the acquisition of a self-contained, 34-cubic yard (cy) compacting roll-off container. Pre and postconsumer food residuals were separated in the cafeteria and emptied into the roll-off. With the addition of a 26-cy container, food residuals from all dining halls were collected. It cost about $30,000 to purchase and install the two roll-offs; the investment was recovered completely in 30 months. Nearly 300 tons/year of food residuals were trucked to Agricycle, where they were composted with chicken manure, grocery store residuals and paper mill sludge.
Although composting did not take place on campus at this early stage, even this simple procedure was not without problems. The roll-off boxes were prone to odors, liquid build-up from decomposition, and maggots. A year later, the college purchased an ozone generator, which greatly reduced the odor and associated maggots in one unit most of the year. The other unit had less of an odor and maggot problem.
Middlebury College switched to composting its food residuals locally in October, 1996, motivated to reduce the monetary and environmental costs of trucking from Vermont to New York and to use food residuals compost to enrich soil on campus. For one month, the college experimented with trucking the materials to the Intervale Composting Project in Burlington. However, transportation costs remained an issue, and the Intervale Project was concerned with the large volume of waxed cardboard in the loads.
Meanwhile, to explore options for on-site composting, Cushman attended a short course at the Cornell Waste Management Institute. "When I saw what was being done at Intervale and after learning from the Cornell course, I said 'we can do this at Middlebury,"' he explains. Abandoning reliance on outside facilities, the college began composting in windrows on campus. Food residuals were combined with wood chips and horse manure from the nearby University of Vermont Morgan Horse Farm. The piles were turned every few days with a bucket loader. Unpleasant odors initially plagued the operation. With an extremely wet, early winter and a difficult clay site, it was nearly impossible to stem anaerobic conditions.
Switching to the PAWS system in February, 1997 reduced or eliminated most of these earlier problems. Using pipes to passively aerate the windrows constantly (instead of turning) has been effective in reducing moisture and odor. "The traditional windrow did not work well for us," explains Cushman. "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 did not have the available labor to routinely turn the piles."
Making Compost Happen
Materials are collected from the college's two large dining halls, two smaller dining facilities, golf course and ski area, small satellite campus and special events. Preconsumer food prep scraps, postconsumer food residuals, waxed cardboard, paper towels, napkins and food prep wastepaper are placed in Toters by dining services staff. Feedstocks are collected in a new hook truck specifically designed for Middlebury. The twice daily pick up avoids the odor problems that came with two-week storage in roll-off containers. Organics are brought directly to the composting site and stored in a modified Green Mountain Technologies (GMT) Comptainer.
Active composting starts on "Dump Day," when the full comptainer is emptied onto a concrete pad, and the contents mixed with the manure and chips. Any obvious contaminants are pulled from the mixture.
The PAWS windrows are then formed. A bed of manure and wood chips is laid down to sponge up any moisture leaking to the bottom of the pile. Perforated PVC pipe, similar to the drainage pipe used in home foundations, is laid out over the manure and wood chips perpendicular to windrow direction. The food residuals mixture is then placed on top, and the entire pile is covered in a six-inch layer of dry manure that seals in odors. The ends of pipe stick out and receive air. The mixture demands little attention other than weekly temperature monitoring.
After 12 to 16 weeks, the compost is moved nearby to an eight- to 12-foot-high curing pile. To determine whether the material is finished, a handful of wetted compost is placed in a bag and sealed for a week. If the compost gives off a pleasant earthy odor, it is ready for application. If it smells like ammonia, the compost remains piled. The finished compost is then ready to be screened.
Savings and Benefits
Compost is applied as a soil amendment for campus landscaping. It also is being used experimentally for growing herbs in the dining halls as a full-circle demonstration-from food to compost to food.
Middlebury College has saved an estimated $102,000 since 1993. The average cost for the college to dispose of wastes in a landfill is $135/ton, while the average cost for composting is $39/ton. Start-up costs were low. The college already owned most of the equipment and the system elements are relatively low tech. "We get a good soil amendment, and we are also saving money, so the payback is huge," says Cushman. "When the recycling market for paper is down, when the tin market is down, composting is the winner."
Composting food residuals also serves as a vehicle for education. Students have the opportunity to learn about composting and use it in their research projects. Benefits to the outside community include reduced stress on the county's water treatment plant, since a large volume of residuals are being diverted from the sewer.
Improvements and Plans
Throughout this five-year process, Middlebury experienced most of the typical problems with large-scale composting, and through trial and error has decreased or eliminated most of them. Contamination with plastics and metals has been reduced to .5 percent through training workers, educating students, fostering employee interest and screening the mixture before building windrows. Early odor and the associated maggot problems in the roll-offs have been solved through replacing them with a Toter system and twice daily collection. Moisture content in the mixture has decreased with the addition of paper towels and waxed cardboard, running postconsumer scraps through a dewatering pulper, and increasing the ratio of wood chips to food residuals. Paying attention to wind direction on pile-building days has eliminated complaints about odor.
A variety of recent changes have eliminated odor problems, including a GMT biofilter and a tank for leachate in the Comptainer, which is sprayed on windrows that need moisture. The college also is considering renting a trommel to screen the finished compost. "Now that we know it is a huge success and a huge money saver, we are investing more money in composting, instead of staying with our original shoestring budget," explains Cushman.
A new direction involves a pilot partnership with Addison County Solid Waste Management District, which will deliver food residuals from restaurants, grocery stores and public schools in the region to the Middlebury site. The program will have no upfront costs for the county because the college will provide the necessary facilities and technology in return for gaining increased amounts of soil replenishment for its 6,800 acres. The project is in the permitting process. "What has been a winner for Middlebury will also be a winner for Addison County," says Cushman. "Composting is sensible and profitable. This new project enables the college to meet both its goals for environmental stewardship and its goals for community service."
[Editor's note: This information originally appeared in an article written by Amy Seif and published in the journal BioCycle. The publisher, JG Press, Inc. in Emmaus, Pennsylvania, should be contacted before this material is copied or distributed.]
For additional information:
This project was presented as a poster developed for Second Nature's 1999 Northeast Regional Workshop, "Shaping a Sustainable Future: Best Practices in Higher Education," although the content varied somewhat.
Middlebury Recycles
BioCycle: Journal of Composting and Recycling
Amy Seif
Environmental Coordinator
Middlebury College
226 Sunderland
Tel. 802-443-5043
Email: aseif@middlebury.edu
Norm Cushman
Maintenance and Operations
Service Building
Middlebury College
Middlebury VT 05753
Email: cushman@middlebury.edu
© 2005 Second Nature, Inc.
