West Yellowstone/Hebgen Basin Solid Waste District opted for mixed waste composting when area landfills closed and the round-trip haul for disposal was over 200 miles.
THE West Yellowstone/Hebgen Basin in Montana is a place like no other. Bordering Yellowstone National Park to the east, and surrounded by spectacular mountain ranges in all other directions, the area is a paradise for anyone who enjoys outdoor activities.
There are two annual peak visitor seasons in the region. During the summer months, the area's population increases dramatically when up to three million tourists visit Yellowstone National Park. In addition, each year thousands of hikers, bikers, campers, fishermen, etc. use the local forests and waterways. Winter brings the snowmobile and cross-country ski crowds to West Yellowstone.
The region's remote location and dramatic peaks in population have made waste disposal a challenge. The West Yellowstone/Hebgen Basin Solid Waste District Board governs garbage collection and disposal in the area, which includes the waste generated in Yellowstone National Park. The Waste District is part of Gallatin County, Montana, and the Board is appointed by the Gallatin County Commissioners.
FACING LANDFILL CLOSURES
In the late 1970s, discussions began to take place about closing West Yellowstone's landfill. Several key factors contributed to the need for a change in solid waste management. First, the developed landfill north of West Yellowstone was nearing capacity by 1979. The landfill was located on National Forest land through a lease agreement with the Waste District. Second, black and grizzly bears had become accustomed to feeding on garbage at the landfill. In 1973, the Interagency Grizzly Bear Study Team was initiated to study bear management in the Greater Yellowstone ecosystem, including the species' dependency upon human garbage.
Finally, the landfill's water monitoring system began to show concentrations of leachate that could threaten the water table.
In 1983, the landfill was capped and the current transfer station was built next to it. The 13-acre compound was surrounded with a buried chain-link/electric fence to keep the bears out. The Transfer Station was designed to handle approximately 1,500 tons/year (tpy) of waste from the town of West Yellowstone, Yellowstone National Park, and the surrounding Hebgen Basin region. Today, nearly 6,000 tpy are generated in the same region.
Initially trash tipped at the transfer station was hauled to an unlined landfill 50 miles away. When that landfill closed around 1990, the trash began to be hauled to the next closest landfill, 120 miles away from the transfer station. During the 1990s, growth in the area's resident population and the number of Park visitors began to increase tonnage and put a strain on the small transfer station.
GREENING THE PARK
In 1997, Yellowstone National Park celebrated its 125th anniversary and park administrators asked, “What can be done to preserve and protect Yellowstone for the next 125 years?” The result was the creation of a movement called “The Greening of Yellowstone.” This movement motivated the Park to implement a wide variety of pollution prevention, alternative fuel, recycling and waste reduction projects. Landfilling was determined to be the least favored method of waste disposal. A waste characterization study conducted in 1994 had indicated that 60 to 75 percent of the Park's waste stream was compostable, with 40 percent being food residuals. Coupled with the fact that waste was hauled up to 200 miles to landfills and transfer stations outside of the Park, it was evident that large-scale composting might be feasible.
Plans for the compost facility began to develop. The idea was that up to 50 tons/day of mixed solid waste (MSW) would be tipped at the compost facility. The organic portion of the MSW would be removed and composted. The remaining noncompostable material would be minimal and, therefore, the volume transported to the landfill would be significantly reduced. Since the cost of hauling trash to the distant landfill would be reduced, possibly the transfer station's tipping fee of $125.95/ton could be lowered for the facility's users.
The project went out for bid, and in August 2001, Engineered Compost Systems (ECS) from Seattle, Washington and Montana-based Dick Anderson Construction were awarded the contract to design, supply, and install the process equipment. The facility design was then finalized based on the specified equipment. The total project capital budget was $4.2 million, secured through Montana's State Revolving Fund Program. Dick Anderson Construction began site prep in September 2002 and, thanks to a mild winter by West Yellowstone standards, continued until completion in June 2003. The West Yellowstone Compost Facility (WYCF) officially opened on July 1, 2003, and the production of compost began.
COMPOST FACILITY DESIGN
The WYCF was designed to receive and separate up to 50 tons/day of MSW. The 30 percent of projected noncompostables would be diverted to the adjacent transfer station, and the balance, after being mixed with amendments, would be sent to the compost vessels for primary composting. The compost would be cured in an indoor aerated static pile, and passed through a multistep material refining process to make the end product.
Several constraints influenced the facility design: The selected site at the existing transfer station was on National Forest land and the lease agreement between the National Forest and the Solid Waste District did not allow for expanding the site, All composting activities needed to be conducted indoors because of extreme winter conditions, A particular processing drum had been preselected to provide the mechanical separation of incoming feedstocks, and The facility needed to be operated with a minimum number of staff.
ECS's in-vessel system met these constraints. Carrying out active composting in a low-headspace, in-vessel system (as opposed to an open headspace, in-building system) greatly reduced the need for air changes. The concrete vessels are adjacent to each other and share interior walls, only the vessel loading doors are accessible from inside the building, which reduced the size of the building that houses the compost piles.
The labor burden was minimized with an integrated conveyor system used to transport the raw compost from the mixer to inside the vessels. This system also limits worker exposure to the raw MSW.
THE EQUIPMENT AND OPERATION
MSW is tipped out of packer trucks in the receiving area up to seven days a week during the busy summer season. Operators do a coarse floor sort and load the pit conveyor. The MSW is carried on a lifting conveyor to the Seerdrum Waste Processing Drum. The rotating drum is 40 feet in length and 10 feet in diameter. Water is sprayed on incoming material to soften and pulverize the drier components of MSW. There is a 5-inch screen plate inside the drum, the 5-inch minus fraction is conveyed to the compost mixer. The overs, which include items such as PET bottles, film plastic, cans, clothing, etc., are conveyed to a 40-yard roll-off box, which is tipped at the adjacent transfer station when full.
The Luck/Now Mixer from Helm Welding is loaded with the MSW, woodchips, manure, biosolids from the Park's wastewater treatment plants, and seasonal lawn clippings/leaves in predetermined ratios. The on-board scale and posted “recipe” assure that each batch is consistent. Once the desired weight of 8,700 lbs/batch has been achieved, the operator starts the mixer/conveyor system.
After three minutes of mixing, the operator opens the mixer door and the raw compost is conveyed to the first of two auger-type conveyors. The incline conveyor moves the compost to the second conveyor, which runs along the front of the vessels. This conveyor drops the material via a motor-controlled chute on to the vessel-loading conveyor (VLC) that has been prepositioned in the vessel to be filled. The VLC travels back and forth to evenly distribute the mix inside of the vessel. Loading vessels in this manner has several advantages over using front-end loaders including: reducing labor hours, better control of pile height, less pile compaction, and reduced overhead clearance requirements.
Primary composting takes place in the seven concrete vessels (each 10-feet by 10-feet by 60-feet), a vessel holds up-to 175 cubic yards of raw compost. The integral aeration floor and nonconcrete interior surfaces are constructed of stainless steel. The aeration and control room is located along the rear of the vessels.
At the end of each loading day, the VLC is retracted, temperature probes are inserted into the compost media, and the vessel door is shut. The operator then initiates the automated control of the aeration system. The system provides reversing and recirculating airflow. Make-up air is drawn from the receiving area, and the corresponding exhaust air is scrubbed in a biofilter. The aeration floor includes a clog resistant drain system.
ECS' CompTroller, an automated compost control and monitoring system, enables the operator to track and optimize process conditions (e.g., it has variable frequency drives to control blower speeds), and collect data required for regulatory compliance. Temperatures are monitored near the top and bottom of the compost pile, recorded temperatures are logged and provide feedback for the automated control of both the volume and the direction of aeration.
After a minimum of 14 days, the partially stabilized compost is removed from the vessels using a front-end loader and placed in aerated static piles for curing. The piles are negatively aerated at a low rate, and the air is filtered through a separate biofilter. The material is rewet and turned periodically for six to ten weeks to achieve final stability.
The screen line includes a shaker screen and air separation system to remove the contaminants. Aggregates Equipment, Inc. supplied the feed hopper, conveyors, and Bivi-Tec vibrating deck screen system with a three-eighth-inch sized screen. After the larger materials are screened out, a conveyor moves the compost to a Forsberg air-classifying destoner that separates the small pieces of broken glass, rocks and metals. Each tunnel batch generates about 3,000 pounds of broken glass. The screen overs and heavies, approximately 30 percent by volume, are taken to the transfer station, the remainder is the finished compost.
TWEAKING THE SYSTEM
Once the WYCF began production in 2003, it became clear some issues needed to be dealt with immediately. First was the idea that a single equipment operator could conduct the initial floor sort while loading the MSW onto the pit conveyor. Both a front-end loader and a Bobcat were tested, but the operator was in and out of the equipment to the extent that production was slowed to a crawl. Having a dedicated sorter on the tip floor to assist the equipment operator was considered, but decided to be too dangerous to allow. However, the incoming MSW contained many items that needed removal. This problem was solved by the purchase of a rubber track mini-excavator with a bucket/thumb mechanism. Now one operator can effectively sort nonorganics and load the conveyor simultaneously.
Next were apparent flaws in the translation of the waste stream analysis that had been conducted for the project. The initial analysis reported that the average unsorted waste stream consisted of 35 percent recyclable material. Once the recyclable component was removed, the remaining material would consist of 70 percent compostable material and 30 percent inorganics. The project's budget was built on these optimistic assumptions, including that the entire 35 percent of recyclable material would be removed from the MSW once the compost project began. In reality, a large percentage of recyclable items, and other contaminants to the compost process, remained in the waste stream. This translated into many more loads being hauled to the landfill than initially planned for, and a scramble to acquire the truck/trailer combinations to accommodate the increased loads.
Another unexpected discovery in the waste stream was the large volume of plastic can liners used in Yellowstone National Park. This was tracked back to the Park's bear management practices, which include double-bagging trash being placed in the Park's dumpsters to prevent leakage that would potentially attract bears. These plastic liners increased the percentage of the inorganic portion of the MSW tipped at the compost facility, thus more weight and bulk sent to the landfill via the transfer station. The Park has discontinued the practice of double bagging and replaced a portion of the plastic bags used with paper bags.
Despite these and other challenges, the facility has moved forward and steadily improved many processes. Recycling in the region and the Park consist of a series of drop-off receptacles that are serviced by Headwaters Cooperative Recycling. Although drop-off programs generally have a lower recovery rate than curbside programs, the addition of recycling bins, sites, and education have translated to an increase in recycling rates.
Yellowstone National Park, WYCF's largest supplier, has made a huge commitment to change its waste stream, which has been a tremendous help. Some changes the Park and its concessionaires have implemented are: Eliminate doubling plastic liners, Distribute kraft paper bags to residents for compostable material, Reduce roadside trash containers to eliminate a percentage of plastic liners, Expand recycling program within the National Park, Initiate a mini-propane canister recycling program, Provide education about waste management to residents and visitors, and Use a dual color bag program for organics/inorganics in Park kitchens.
The small West Yellowstone Compost Facility has produced more than 3,500 yards of compost that has tested well in laboratory analyses. The compost is priced at $15/cubic yard and is sold in bulk only, although discussions are taking place about acquiring bagging equipment. West Yellowstone's compost has been used in Yellowstone National Park's developed landscape projects, a LEEDS-certified duplex built by Yellowstone's concessionaire, Xanterra Parks and Resorts, and by many local gardeners in the surrounding region.
The Waste District's composting project would not be possible without the strong support of the many project partners, listed after this article. The ultimate goal of the compost project is to continue in all efforts to reduce the volume of trash being hauled to the landfill.
Kathleen O'Hern is Compost Facility Manager at the West Yellowstone Compost Facility in West Yellowstone, Montana. Tim O'Neill is President of Engineered Compost Systems. Project Partners: Yellowstone National Park, Montana Department of Natural Resources &, Conservation, Montana Department of Environmental Quality, Gallatin County, Headwaters Cooperative Recycling, Dick Anderson Construction, Engineered Compost Systems, BFI, Allied Engineering, Dorsey &, Whitney, D.A. Davidson and Gallatin National Forest. Individuals: Larry Watson, Bill Emerson, Anna Miller, Mae Nan Ellington and Chris Budeski.