November 22, 2006 | General

Mixed MSW Composting Is "Steady As She Goes"

BioCycle November 2006, Vol. 47, No. 11, p. 18
Two new facilities came on line in 2006, while one ceased operation and a second is shifting to a new technology. Annual survey identifies a total of 14 plants. Part I
Robert Spencer and Nora Goldstein

STEADY-STATE may be the best phrase to describe the status of facilities composting mixed municipal solid waste in the United States. In fact, steady-state may be the best phrase to describe solid waste composting in general since the turn of the century. Unlike the late 1980s and early to mid-1990s, when many mixed MSW composting proposals and plants came and went, the first decade of the 21st century has seen only a few new projects start up.
Two facilities opened their doors in 2006 – a 60 tons/day plant in Mariposa County, California, and a 120 tons/day plant in Delaware County, New York. The Sumter County, Florida facility, which started in 1988, ceased composting this year due to difficulty justifying the expense when landfilling is half the price. In addition, the Buena Vista County, Iowa plant, which opened in 1990, has selected a new MSW management technology. That brings the total number of mixed MSW operating plants to 14 in the United States.
Part 1 of this report includes only facilities processing a mixed (unsorted) MSW stream. Part II, to appear in the December 2006 issue of BioCycle, will report on composting of source separated municipal solid waste, where residents sort their household waste into compostables, recyclables and trash. In each case, to qualify for this survey, a composting facility has to be processing residential feedstocks other than yard trimmings only.
Table 1 lists the mixed MSW composting facilities in the United States. To the best of our knowledge, there are no mixed MSW composting plants in development at this time. That said, we welcome reader input if we have missed a project.
Pinetop-Lakeside, Arizona: The Pinetop-Lakeside Sanitary District’s (PLSD) cocomposting facility began operations 15 years ago. It processes 20 to 22 tons/day of mixed MSW and dewatered biosolids (about half and half). There are 6,700 residential and commercial customers in total. Materials are loaded into a rotary drum manufactured by A-C Equipment Services for blending, bag opening and initial processing, then transferred to aerated static piles for composting. A soil blender continues to purchase and market the finished compost. PLSD is installing a new 2-meter belt filter press to increase the solids content of the biosolids. “The smaller belt we use now gives us 10 to 12 percent solids,” explains Phil Hayes, facility manager. “We are hoping that the larger belt will yield 20 to 22 percent solids. That way, we can administer more sludge/load. Water is the limiting factor so the drier the sludge, the more we can put in.”
To reduce glass contamination in commercial loads, PLSD has begun placing recycling bins at retail businesses and offices. “We go to businesses that produce a lot of paper and carbon-based material and ask them if we can put a cardboard and paper only-container next to their garbage container,” says Hayes. “That material is collected free of charge and brought to our plant by Waste Management. Places that already had a fiber-only container, like the post office, were switched over to being serviced by the fiber-only route.” There are no nearby markets for recycled paper, so the fiber fraction is loaded into the rotary digester. “We have less reject material without the glass and other contaminants in that fraction,” he adds. “Noncompostable MSW is taken by Waste Management to the transfer station and landfill.”
Mariposa County, California: Following a grand opening in March, then receipt of its certificate of occupancy, the country’s newest MSW composting facility started accepting MSW in July 2006. The plant is designed to handle 80 tons/day, but currently is permitted for 60 tpd. Throughput in late October was about 20 tpd. The $7.5 million composting facility serves residents and businesses of Mariposa County, as well as Yosemite National Park. Colocated with a landfill and a recycling dropoff and buy-back center, the composting facility is a critical component of the county’s solid waste management system. “Mariposa County is very proud of the facility,” says Dana Hertfelder, Director of Mariposa County Department of Public Works (DPW).
Steve Engfer, the DPW’s Solid Waste and Recycling Manager, reports that eight new staff were hired to operate the facility; about half are involved with sorting recyclable and noncompostable materials out of the waste stream. The facility uses SV Composter vessels from Engineered Compost Systems. Bulk Handling Systems (BHS) supplied the front-end processing line. “We are working with the heterogeneous nature of the MSW feedstocks to learn the most appropriate amount of aeration in the vessels and recipes for moisture addition,” says Engfer. “We get such a variety of materials such as waste from Yosemite Park, horse manures, commercial MSW and residential self-haul. The composter has been working well and ECS has been good to work with in our start-up.”
To help with determining optimal recipes, Engfer says the DPW is going to send samples of the sorted and shredded feedstocks to a lab for further characterization of organic matter and nutrients. “We believe the character of the waste stream has changed since the original waste characterization was done several years ago,” he explains. For example, there may be more food waste than originally estimated. Mariposa County may be able to work with park concessions and other commercial operations in the county to set up source separated collection of food residuals, and dedicate one or more of the compost vessels for that material, yielding a higher quality compost to market.
“We are shifting waste from the landfill to the composting facility, and our goal is to divert at least 60 percent of the county’s estimated 14,000 tons/year from the landfill,” he says. Increasing the diversion and making an alternative daily cover product is very important to the county. “That’s a big deal for us considering the cost of purchasing dirt for the landfill is about $11/cubic yard delivered, so each cubic yard of compost produced generates at least that much savings, in addition to significantly extending the life of the landfill,” he adds. “The compost facility is also critical in assisting the county to comply with California’s AB 939 directive to divert 50 percent of waste.”
The solid waste system is set up as an enterprise zone, charging $104/ton for MSW and C&D and other materials brought to the facilities. The county also operates four small transfer stations in outlying areas. The compost, recycling and landfill facilities are open seven days per week to serve commercial haulers, and five days a week for residents.
Sumter County, Florida: After almost 18 years of operation, the Sumter County board decided to stop doing any composting at its facility that had been taking about 200 tons/day of mixed MSW and biosolids. The plant started out with an upfront hand sorting line, followed by composting in windrows. Eventually it purchased a rotary drum digester from Bedminster Bioconversion. A second digester from A-C Equipment was installed more recently. “The first digester cracked and was shut down, but the second digester was doing quite well,” says Mitch Kessler of Kessler Consulting, Inc., solid waste consultants to the county. “However the county calculated that composting was costing them over $60/ton whereas it can dispose of MSW in the low $30/ton range at a landfill 70 miles away. So the board made the decision to stop composting.” Kessler adds that the county is evaluating whether to retrofit the facility to a transfer station with some sort of recycling.
The Florida Organics Recycling Center for Excellence (FORCE) is still located at the Sumter County composting site. The newer digester had been used for research trials but none are currently underway. “FORCE is continuing to research opportunities to work with the State of Florida on its regulations to allow for an easier opportunity to compost organics in Florida,” says Miriam Zimms of Kessler Consulting, which manages FORCE. “A 7-state regulatory study and comparison was performed and is currently under review by the Florida Department of Environmental Protection. Other FORCE R&D projects are underway through the University of Florida and with Florida Department of Transportation. FORCE is continuing to keep the educational website (http://www.florida active and current with Florida organics recycling information.”
Cobb County, Georgia: Formerly the U.S’s largest MSW composting facility – now displaced by Sevierville, Tennessee (see below) – the plant’s 300 tons/day design capacity is still not being fully utilized. As reported in last year’s BioCycle survey (November 2005), the Cobb County facility is operating at around 200 tpd. No major changes have been made in terms of waste processed, or equipment, according to Lon Kennebeck, Product Quality Assurance Manager for the Cobb County Solid Waste Department. However, Kennebeck says some cost-cutting measures have been implemented, particularly in electricity usage by programming the PLC system to automatically turn the speed of the 200 hp digester drive motors to half-speed when they are not being either discharged or loaded. The facility’s odor control system, which utilizes humidification towers (scrubbers) to add moisture and reduce the temperature of exhaust air going to the biofilter, continues to work well.
Buena Vista County, Iowa: As part of a three county solid waste management program, Buena Vista County’s current MSW composting operation will be converted to pelletization of heat-dried MSW fines, and fuel production. Ellsworth Jeppeson, General Manager for the Buena Vista County Solid Waste Center in Storm Lake, described a shift away from composting to manage the fines screened out after processing to recover recyclable items. “We will still shred and screen the MSW as we do now for composting, but the wet organics and fines left after screening will be shipped to Marcus, Iowa in Cherokee County where they will be heat-dried and converted into pellets for fuel,” says Jeppeson. He adds that the Buena Vista County landfill will be closing in the next year or so, and that the Cherokee County landfill will increase its remaining life expectancy from three years to 12 years once the new pelletization facility is operating.
Marlborough, Massachusetts: This MSW and biosolids composting facility has two rotary drums. Like other such plants, problems with cracks in the drum shells has hampered operations. For WeCare Environmental, LLC, the company that purchased the plant from Bedminster Marlborough LLC in 2003, problems with the drums have delayed ramp-up to full capacity. In 2006, Bedminster International purchased 50 percent of the Marlborough plant.
Chris Ravenscroft, WeCare Environmental’s President, is looking forward to completion of repairs to both of the rotary drums, with installation of a new sleeve around the shell cracks on the second digester, as well as a new pinion gear before the end of the year. A sleeve was installed around the shell of the other digester earlier this year. This has allowed the plant to process up to 100 ton/day of MSW and biosolids, with the biosolids accounting for approximately 40 percent of that mix.
Once both digester repairs are completed WeCare plans to increase throughput to approximately 120 tons/day of MSW plus biosolids. Once the plant is operated successfully at design capacity during the first quarter of next year, WeCare will seek approval from the City of Marlborough to leave its phased in restart schedule, and operate at full capacity. This will be the first time the plant will have been operated at full capacity since being shut down by Bedminster in August 2002.
Brian Fleury, Sales Manager for WeCare Organics, LLC, marketing arm for its sister company, reports that markets for the finished compost include topdressing athletic fields and lawns, manufactured topsoil, and golf course blends. “We feel that we now have a compost that can service many different sectors of the market, including the higher end golf course and athletic field markets,” says Fleury.
Nantucket, Massachusetts: In its seventh year of operation, this rotary drum composting facility on an island off the coast of Cape Cod – jointly owned by Waste Options, Inc. and Bedminster International – has been operating status quo according to Whitney Hall, President of Waste Options. For Hall, that means processing between 30 to 125 tons/day, depending on the season. The solid waste facility includes a resident drop-off area and a swap shop, as well as a Materials Recovery Facility. Fiber and commingled containers are sorted and bales of paper, cardboard, metal, and plastic are shipped off the island to markets. Other items separated for recycling include mattresses and electronic equipment. The site also has a C&D processing building where clean wood is separated for recycling into mulch. Mixed C&D is shipped off the island to a processing facility. An adjacent yard trimmings composting facility also grinds brush to use as a bulking agent for curing the MSW compost. A new lined landfill cell is used to dispose of baled residue from the compost plant. An ongoing project during the slower winter waste season is mining of the unlined landfill.
Ron Alexander of R. Alexander Associates has been working with Waste Options for over a year to improve compost markets, an effort that Hall says has paid off. “We have made major strides in compost marketing, and are making topsoil out of stump and brush dirt blended with the MSW compost and yard waste compost,” he says. “Almost 800 cy of this blend has been sold at an average price of $24/cy, with 50 percent of revenues going to the Town of Nantucket.”
Hall adds that his operators are paying more attention to the final screening process, which uses a BiviTek with destoners to remove glass and other inert materials. After mixing the MSW compost with brush and yard trimmings for further curing, it is processed through a McCloskey trommel screen with three-eighth inch holes.
Dodge County, Minnesota: After two years of composting about 3,000 tons/year in six Nature Tech in-vessel containers, Mark Gamm, Dodge County Environmental Quality Director reports that the county recently screened its first windrow, “and initial test results of the compost are better than we expected.” As with a number of other mixed MSW composters in the U.S., Gamm says the county is converting the facility to composting source separated commercial organic materials. “We will continue to remove the low Btu materials from the MSW, but send it to the landfill rather than composting it in our vessels. That way we can use the vessels for food waste from supermarkets and other commercial generators.” The compost system was designed to process wet organic materials screened from MSW that is shipped to a waste-to-energy facility. The remaining wet organics contain glass, bottle caps, and other inert material that restricts compost use to on-site landfill cover.
Truman, Minnesota: Like Nantucket, the Prairieland solid waste composting facility in Truman reports that operations are status quo. In response to questions from BioCycle, Prairieland Solid Waste Commission Director Mark Baumann reports that there is nothing new at the 65 tons/day facility in terms of operations or compost markets in 2006. The plant, which utilizes the OTVD agitated bay composting system, began operating in 1991.
West Yellowstone, Montana: The remote, high elevation location of this 2,000 cubic yards/year enclosed composting facility is presenting a challenge in terms of marketing compost, reports Kathy O’Hern, manager of the West Yellowstone/Hebgen Basin Solid Waste District. “There is no agricultural market up here and not much gardening due to our short summer season,” she says. “So we are trying to market our compost to land reclamation projects, but the answer may be in bagging of our compost.” The in-vessel system supplied by Engineered Compost Systems is “working nicely and in general we have had good luck with the system,” she adds.
Delaware County, New York: Doors opened for business at Delaware County’s solid waste processing facility in May 2006. The plant is designed to process 35,000 tons/year of mixed MSW and 6,500 tons/year of biosolids. A full-length feature article – based on a recent tour of the plant – accompanies the project updates in this 2006 MSW Composting Report.
West Wendover, Nevada: The City of West Wendover built its composting facility as an alternative to a $1 million Class I landfill to service 5,000 residents. It installed two used cement kilns that operate as rotary drums. Problems with the gear drive systems have been one of the operating challenges for the city. “Everything was gong fine with our used cement kilns when all of a sudden we had trouble with the gear reduction drives,” says Bryce Kimber of the Department of Public Works. Repairs have been made, and the city has resumed loading 5-10 tons of MSW into one of the two rotary drums daily, and unloading the other drum every other day. “We mix the MSW in the drums for two to three days at the most, then screen the discharged material through a trommel, aerate the unders, then process through a second trommel screen,” explains Kimber.
To improve compost quality, a destoner was recently added. “We have not had much compost sales due primarily to a glass problem in the compost, so we installed the destoner in order to improve the consistency of the compost quality,” he adds.
Medina, Ohio: The Medina County Central Processing Facility receives 550 tons/day of MSW. The material traverses on conveyors through sorting and screening equipment and picking stations to recover recyclables. After the first sorting phase for fibers, plastic and cans, material passes through a trommel screen with 2-inch holes. The 2-inch minus fraction – about 45 tons/day – is mixed with yard trimmings and wood and composted in windrows. The compost generated is only used in several applications in landfills; the main application is as a substitute for daily cover.
Rapid City, South Dakota: News out of the Rapid City Department of Public Works is that the composting facility is “going great guns.” The plant composts 200-plus tons/ day of mixed MSW with about 10 dry tons of biosolids. Initial results have been positive amending soils with compost for landscaping projects at the regional airport. The one major operational problem reported was a crack in one of the two rotary Dano drums, which was welded and back in service in just 10 days.
Sevierville, Tennessee: With the addition of a fifth rotary drum digester, the Sevierville composting facility is now processing 245 tons/day of MSW, plus 40 tpd of biosolids, for a total of almost 300 tpd – making it the largest MSW composting facility in the country. (Cobb County has the same design capacity but is operated at 200 tpd as explained above). Sevier Solid Waste, Inc. (SSWI) made a $5.2 million investment in two new rotary drums in 2006, one to replace Digester #3, and a new Digester #5, increasing composting capacity by 100 tpd. Both rotary drums were designed and manufactured by A-C Equipment Services, and are larger than the original drums at 14 feet in diameter and 185 feet in length. They are rated at 75 tpd of MSW, plus another 30 tpd of biosolids. Both drums have just one internal stainless steel baffle, located near the discharge end of the drum, instead of several baffles as in the earlier drums.
Tom Leonard of SSWI explains that this design change is based on the crack-free operation of Digester #4, from which he removed all but the last baffle six years ago. The one baffle serves to meter flow of material out of the drum, something that Leonard feels is important compared to not having any baffles. Another design change was the use of a Marathon compactor as the hydraulic feed ram to the new drum. “There is significantly less leakage around the seals than we have with the other hydraulic ram systems initially installed. This saves lots of clean-up labor, and reduces associated odor,” he says.
SSWI recently approved $1.5 million to purchase and install a new, corrosion-resistant aeration building. The new building will replace the original metal building, which is not only too small for the expanded composting capacity, but seriously corroded. Leonard recently attended the In-Vessel Users meeting at the solid waste composting facility on Nantucket, and came away impressed with how two Universal Fabric buildings used to house the aeration process, as well as the biofilter, are holding up after seven years (see “Building Longevity Into Composting Buildings,” September 2006). “We have not yet selected the type of building, but it will be corrosion-resistant,” he notes.
Columbia County, Wisconsin: The Columbia County Recycling and Waste Processing Facility, which has been operating since 1992, continues to process between 70 and 80 tons/day of MSW. Bill Casey, manager of the facility, says everything is status quo at the plant. The facility shuts down one of its two rotary drums each February for repair. The MSW compost is provided to area farmers at no charge.

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