November 19, 2007 | General

Mixed MSW Composting In Transition

BioCycle November 2007, Vol. 48, No. 11, p. 22
With two mixed MSW plants going source separated, and another redefining itself as “mixed waste,” the 2007 facility survey finds 13 operating plants in the U.S. Part I
Robert Spencer, Rhodes Yepsen and Nora Goldstein

WITHOUT a doubt, composting the mixed municipal solid waste stream is a “niche” business. It is an MSW management option that seems to be viable in very specific situations. In some instances, these plants were built to service tourist destinations, often in somewhat rural areas where recycling is difficult and landfills are distant. In several other cases, public agencies built plants to extend the life of an existing landfill. And in almost every case where the facilities appear to be doing well, there is a very apparent dedication to ensuring the success of the public investment in mixed waste composting.
BioCycle divides its annual survey of municipal solid waste (MSW) composting into two parts. Part I focuses on facilities that were built to process mixed (unsorted) MSW. Part II, to appear in the December 2007 issue, will report on composting of source separated MSW, 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. The first facility on the list, operated by the Pinetop-Lakeside Sanitary District in Pinetop, Arizona, is included only because it was processing mixed MSW for about half of this year. Starting in September, however, the plant completely switched over to using paper and cardboard – instead of mixed MSW – as a bulking agent for biosolids composting. Another facility on the list, Dodge County, Minnesota, is in a similar situation, having switched from composting mixed waste to composting only source separated organics during 2007. There is a new facility on the list – Z-Best Composting in Gilroy, California. However, this is not a new facility, but instead, a transfer from our list of source separated MSW composting operations. Notes Michael Gross of Z-Best, “we really fit in the mixed waste category.”
As a result, BioCycle reports a total of 13 mixed municipal solid waste composting operations in 2007. To the best of our knowledge, no new plants appear to be in planning or development.


Pinetop-Lakeside, Arizona: This small composting plant that opened in 1991 recently completed a transition from a traditional mixed MSW processing facility to one only taking in source separated loads of feedstocks – in this case paper and cardboard, and biosolids. Therefore, this is the last time Pinetop-Lakeside Sanitary District’s (PLSD) operation will appear in this mixed waste composting report.
It took almost a year to convert the 22 tons/day cocomposting facility to source separated paper and cardboard as the bulking agent for PLSD’s biosolids, incrementally backing out mixed MSW. The facility expected to screen its first batch of virtually glass-free compost the first week of November. As reported in BioCycle’s 2006 survey of MSW plants, the PLSD had started working with the region’s largest waste hauler, Waste Management (WM), to offer free front-load dumpsters and collection of paper and cardboard to willing businesses and institutions. The remote location of the resort community of Pinetop makes it financially challenging to recycle paper and cardboard since the materials have to be transported to markets a couple hundred miles south in Phoenix. Except for a few large commercial generators such as Wal-Mart, which have the quantity of cardboard to justify their own baler, most commercial haulers and their commercial and institutional customers could not justify the cost of paper and cardboard recycling programs in these mountain communities of northeast Arizona. Therefore, PLSD teamed up with WM to offer the new program. As the number of new paper customers increased, WM brought less mixed MSW to the compost plant.
The primary driver for this change was glass contamination in the compost, which for more than 15 years had been tolerated by the soil companies purchasing the facility’s product, primarily for its organic content. However, according to Phil Hayes, the compost facility manager who has been operating the plant since its start 16 years ago, the influx of new higher-end residential development and golf course communities has led to a demand for higher quality compost. “Working with Dave Smith, PLSD’s manager, we decided to morph the plant over to a source separated composting facility,” explains Hayes. “It was primarily a financial decision, due to a combination of high residue disposal costs and a decrease in the bid prices we were getting for our 2,000 cubic yards (cy) of compost each year. Our compost used to be purchased for $7/cy with several bidders, but in the last couple of years we only had one bid at $4/cy. An even bigger cost factor is residue disposal, where we used to ship one 50 cy compactor of primary trommel residue every four days to the landfill, plus one open top 40 cy container of tip floor sorted material every two weeks. Since replacing all loads of mixed MSW with paper/cardboard loads in September, we haven’t even sent out one compactor load in the last month, and only one open top container. We still get the inevitable trash that some residents, but primarily tourists, slip into the unlocked paper dumpsters scattered at about 60 locations throughout the area.”
The PLSD composting facility is processing (on a weekly basis) about 12.5 tons of paper and cardboard in a 1:1 blend of wood chips and around 34.5 wet tons of dewatered biosolids. It has taken some trial and error to get the optimal recipes. A belt press installed last year dewaters sludge to 17 percent solids (compared to nine percent solids with the old press). The higher solids, combined with the paper/cardboard that absorbs more moisture than the mixed MSW, enables more biosolids to be processed through the rotary drum. “My recipe is basically three to six times more paper/cardboard, by weight, than biosolids, plus an equal volume of wood chips per volume of biosolids,” he explains. Regarding food waste, Hayes said they tried to work with some restaurants and the high school cafeteria but had problems with contaminants, plus the high moisture content cut into the amount of biosolids that could be processed.
PLSD does not get paid by WM to take the paper/cardboard, but has offset the loss of tip fees with much lower residue disposal costs, and higher quality compost. Hayes now has the Blue Ridge High School participating in the paper recycling program, something that was not happening previously, and has painted a sign on the recycling trailer to give visibility to the program. He also reports that the hospital, police station and other schools are participating. A new aspect of the program is confidential document destruction, with 25 law offices and the school system regularly bringing discarded files to the facility, and witnessing their papers going up the conveyor and dropping into the rotary vessels’ steaming brew of biosolids. “We even took out an ad in the paper to promote confidential document destruction, and our users have found that they do not have to use a shredder in the office, and they can leave the material in three-ring binders and paper clips since our screening system removes those contaminants,” says Hayes.
Gilroy, California: The Z-Best Composting site south of Gilroy was permitted in 1998 to accept up to 1,300 tons/day of curbside collected yard trimmings. In 2001, Z-Best was permitted to process municipal solid waste at the site as well. A sorting line was installed at the facility, which included hand sorting stations, as well as a BHS debagger, disc screen and a shredder. Materials passing through the 3-inch minus shredder were composted in Ag Bags. The company targeted “organics-rich” compactors, primarily from its commercial collection routes as well some residential. In addition to the compactor loads, the facility takes in screenings from a dirty MRF in Sunnyvale operated by a sister company, Zanker Material Processing Facility. “We receive about 280 tons/day of mixed waste, including the dirty MRF screenings, MSW from residential sources and commingled garbage and yard waste,” says Michael Gross of Z-Best Composting.
Z-Best is in the process of changing its operations at several of its recycling facilities in the San Jose region. As a result, it is dismantling the front-end processing plant at the Gilroy site. “All materials will go through our new MSW MRF in San Jose,” adds Gross. “Processed material that has been cleaned will be hauled to Gilroy for composting. This way, we won’t have to haul residuals back to our landfill. It is a better use of that composting site.”
Mariposa County, California: The Mariposa County mixed waste composting plant began operating in the summer of 2006. The facility is designed to process 60 tons/day of material from residents and businesses in Mariposa County, as well as Yosemite National Park. Finished compost is used for daily cover at the county’s landfill. Equipment at the plant includes a Bulk Handling Systems sorting line (including a debagger) and SV Composter vessels from Engineered Compost Systems (ECS). In the fall of 2006, there were some odor complaints that needed to be addressed. Part of the problemwas traced to the biofilter, which wasn’t functioning properly. ECS rewetted and reformed the media, added additional material and put an exhaust air humidifier that had been installed initially but wasn’tin operation at that time, back in service. Odor emissions were significantly reduced both in frequency and severity, reports ECS.
Cobb County, Georgia: The Cobb County mixed waste composting plant opened in 1996 to process 300 tons/day of mixed waste with 100 tons/day of biosolids. As reported in last year’s BioCycle, the facility is operating at 200 tons/day. Operations have not changed much during 2007. The compost is a mixture of MSW and treated sewage sludge, which enters rotating drums for three days, and then is screened and placed in aerated windrows for 28 days. After a second and final screening, its Bio-Blend compost is offered free to residents for individual use, and is available for commercial sales by appointment.
Marlborough, Massachusetts: Starting its eighth year of operation this fall, this 120 tons/day rotary drum cocomposting facility processed 34,000 tons of mixed MSW, 12,000 tons of biosolids and 8,000 tons of source separated organics. According to Chris Ravenscroft, President of WeCare Environmental, owner and operator of the facility under contract to the City of Marlborough to process its MSW, it had to reduce the quantity of biosolids processed through the facility and have continued to identify new, clean sources of organic wastes, such as supermarkets.
The facility produces approximately 30,000 cy of compost per year, with 15 percent sold for $4 to $8/cy, and the balance distributed at the cost of transportation. Compost is used for topdressing existing lawns and athletic fields, as well as to manufacture topsoil. The compost is screened through a 3/8-inch McCloskey trommel screen. “We find that the markets have a very low tolerance for contamination,” says Ravenscroft. The residue rate from material processed through the composting system is approximately 35 percent.
Nantucket, Massachusetts: On the Island of Nantucket off the coast of Cape Cod, Waste Options, Inc. continues to operate the 125 tons/day MSW and biosolids cocomposting facility under a 25-year contract with the Town of Nantucket. The last two years have focused on compost marketing, and Whitney Hall, President of Waste Options, reports that demand for the compost and organic topsoil continues to grow. “Landscapers who bring in yard waste are our largest customers, and we sell more topsoil than straight compost,” he says. “We also have some distributors who take bulk deliveries and market the product.”
The MSW compost is refined with a bivi-TEC screen and a destoner to remove glass, and then blended with ground yard trimmings for further curing. One modification to the blending recipe has been to cut back on the amount of chipped wood and brush and use more leaves and wood fines. Hall explains that this results in less wood and sticks to screen out of the final product. “Instead of using a 3/8-inch screen in the McCloskey trommel, we are using a one-half inch screen,” he notes. Waste Options has a sliding scale price for the organic topsoil, with discounts for larger quantities – 1-6 cy is $35/cy; 7-16 cy is $30/cy; and >16 cy is $25/cy. Fifty percent of compost sales revenues go to the Town.
As for possible changes at the facility, Hall says Waste Options is investigating the use of pyrolyis, a high temperature process that would extract combustible gas from the compost facility residuals, and construction and demolition debris. The gas would be used to generate electricity to power the plant. “I have looked at two operating pyrolysis facilities and have discussed it with the Town and the Massachusetts Department of Environmental Protection (DEP),” he says. “It appears that the process could be permitted by the DEP. A quick look at the economics indicates that it could be viable, so the Town is forming a committee and hiring a consultant to assist with a feasibility study.”
Dodge County, Minnesota: The Dodge County Transfer and MSW Compost Facility in Mantorville switched from processing mixed waste in its Nature Tech composting vessels in 2007 to only source separated organics from grocery stores and other commercial sources. The facility still has a permit from the Minnesota Pollution Control Agency to compost MSW. The site currently produces 1,500 tons of compost a year, which is being stockpiled until tests are complete. Tipping fees are $45/ton for source separated organics and $86/ton for garbage at the transfer station. Screening is contracted to an outside company, using a 3/4-inch screen.
Truman, Minnesota: The Prairieland Solid Waste District steadily processes 65 tons/day in its OTVD agitated bay composting system, with no plans to expand capacity. A portion of the residuals from the process are burned as refuse-derived fuel (RDF). According to the facility’s director, Mark Bauman, if demand for RDF expands, the District might install an additional shredder to produce more fuel. It still produces 3,000 tons/year of compost, and will land spread it for no charge. A fee for trucking is charged to haul compost to farmers, and eventually, when demand increases, a small fee will be charged for the compost. In the last year, there has been growing demand for the end product to use in animal mortality composting, particularly with the swine industry. Pork producers use the compost as an amendment to process piglet mortalities, and the occasional sow.
The facility’s tipping fee is currently $75/ton. A bivi-TEC is used to screen the compost to five millimeters. Due to fluctuating levels of lead, the District’s compost is usually Class 2. “We landfill some residuals that could be used for fuel, but just don’t have capacity in area to burn it at this time,” says Bauman.
West Yellowstone, Montana: The West Yellowstone Compost Facility, operated by the Hebgen/West Yellowstone Refuse District, is designed processes 3,000 tons/year of mixed MSW. It uses an in-vessel composting system supplied by Engineered Compost Systems. “We accept mixed MSW from Yellowstone National Park only,” explains Kathy O’Hern, facility manager. “The Park’s waste stream includes a small amount of residential material. The remaining waste stream consists of waste generated in campgrounds, concessionaire restaurants and hotels, roadside bins and the Park’s trade shops, e.g., electrical, plumbing and woodshops.”
The plant opened in July 2003. Initially, it also accepted biosolids from the park. “The only change we made to our operations in 2007 was to stop accepting biosolids,” adds O’Hern. “Although we are permitted to handle biosolids, we found that this material does not work well in our incline coreless auger conveyor.” During 2008, the facility is planning to add a road kill composting program for the bison hit on local highways.
About 2,000 cy/year of compost are produced. It is sold in bulk for $15/cy. The facility has a bivi-TEC screen and a Forsberg destoner to remove contaminants from the compost. “About 95 percent of the contaminants are removed,” she says. “The final compost continues to contain small flecks of colorful plastic picnic ware.” Overall, residue from operations accounts for about 50 percent of the total incoming waste stream. “We receive a large amount of recyclable materials that cannot be recovered with our existing system,” adds O’Hern. Tipping fee at the facility is $207/ton; cost to operate, including loan repayment, is $200/ton.
West Wendover, Nevada: The city of West Wendover’s composting facility accepts up to 25 tons/day of garbage, which is mechanically sorted and combined with up to 5 tons/day of biosolids (generated by the nearby wastewater reclamation facility). The compostable mix is then loaded into cement kilns, which operate as rotary drums. The end result is 14 tons/day of compost, and 6 tons/day of noncompostable garbage such as glass and C&D debris, which is hauled to the landfill for disposal. By combining the MSW and biosolids, West Wendover is achieving a 70 percent recycling rate, notes a statement on its website.
Delaware County, New York: “This year has been a good one for our compost facility, and I have to say we are successfully producing a quality product with minimum down time,” reports Susan McIntyre, Solid Waste Director for the Delaware County Department of Public Works. The facility, which is owned by the county, came on line in May 2006. Its processing line includes a Conporec rotary drum and Siemens/IPS agitated bays (14 in total). The plant is processing 24,000 tons/year of MSW, 6,500 tons of biosolids and 2,800 tons of select commercial/industrial organics from local dairy plants.
McIntyre describes a number of minor changes made in the plant over the last year as part of fine-tuning the operation. “We made some adjustments to the bioreactor’s interior for better waste tumbling and mechanical separation,” she says. “We also added chains and paddles to the trommel screen interior to improve organics separation and screen cleaning. A leveling bar was added to the infeed conveyor to the pulverizer that crushes glass in the final compost product.” The county instituted a two-week preventive maintenance shut down, a practice it plans to continue.
Operationally, the most significant change has been a more aggressive effort to divert problematic waste items such as hose, tubing, strapping, carpet and other bulky objects that contribute to generation of large “hair balls” inside the drum. “We are working with the private haulers who collect the MSW, and are making progress,” adds McIntyre. “Our crane operators have gotten more skilled at removing these materials from the tip floor prior to loading into the bioreactor. Once the operators extract a few hair balls out of the discharge end they tend to get more discriminate as to what they load in the front end!” To help with removing the hair balls that still are created, the county installed a permanent winch with custom designed logging grapples to hook onto the balls and pull them out.
Total residuals from the composting facility are 38 percent by weight, and 20 percent by volume, a more important number to Delaware County since all residuals go to its adjacent lined landfill. Landfill staff has found that disposal of wet residuals (about 55 percent moisture) has advantages over the drier MSW they used to bury since it is easier to handle and has less wind-blown litter. Recyclable materials are diverted through a separate MRF prior to MSW being delivered to the composting facility. The MRF is located on the same site. The facility does not charge a tipping fee, but McIntyre reports that operating costs and debt service are in the low to mid $50/ton. The County sold approximately 7,500 cy of compost in the first three quarters of 2007. Most is sold to a broker on a profit share basis, with limited direct sales from the facility. Testing has repeatedly shown that the compost contains less than one percent foreign particles by dry weight. “We have a dedicated staff that is committed to what we are doing, and believe in it, and that is an important contribution to our success thus far,” says McIntyre.
On the regulatory front, the New York State Department of Environmental Conservation recently determined that the facility must register as a minor air emission source due to its biofilter. Using data from comparable composting facilities and their biofilters, the county was able to demonstrate that the facility is in the state’s lowest regulatory threshold for emissions of NOx and SOx. As for odor complaints, McIntyre says that when the occasional complaint comes in it is usually the adjacent landfill. “It’s a different odor from the composter, and we can recognize it too,” she says.
Medina, Ohio: Medina County has operated a mixed municipal solid waste processing facility (“dirty MRF”) since 1993. Between 140,000 and 150,000 tons/year of MSW is tipped at its Central Processing Facility. Recyclables are removed via manual and automated sorting. Screened two-inch minus fines (the mixed organic waste fraction) are composted with yard trimmings and wood. Compost is used for various landfill applications. Recently, the facility began producing refuse derived fuel pellets from shredded paper and film plastic.
Rapid City, South Dakota: The mixed waste composting plant in Rapid City will celebrate its fifth year of operation next May. The plant has two rotary drums, followed by a nine-bay Siemens/IPS composting system. “We currently process 180 tons of MSW/day, down from 200 tons/day last year,” says Mike Oyler, plant manager. “Our goal is to get a better breakdown of the organic fraction by putting less material through the drums. We are finding that by not overloading the drums, we are getting better separation of the MSW as it has more room to tumble.” The facility cocomposts the MSW with about 12,000 gallons/day of biosolids. Retention time in the bays is 28 days, followed by secondary composting in aerated piles in an adjacent building. “We decreased the height of these piles, as well as piles of finished compost outside, to 6-feet,” adds Oyler. “That eliminated a lot of odors. We think the piles were going anaerobic.” On occasion, material is put back through the bays for a total retention time of 56 days. “That compost is much darker in color and when we screen it, it looks like wet coffee grounds.”
The media in the biofilter was changed earlier this year; staff decided to use compost screen overs instead of wood chips only. In addition, the biofilter sprinklers were changed from a rotating head with a 30-foot pattern to umbrella head sprinklers that cover a 10-foot area, providing better overall coverage. In addition, operators are building a screen to further refine the finished compost. “We’ve designed a small vibration unit with a 1/8-inch screen,” says Oyler. “We’d like to market this compost for use on golf courses and to topdress lawns.” Roughly 40 to 50 tons/day of compost is produced using a 1/8-inch screen. Finished compost is given away. “We are getting great testimonials from area residents who are using the compost on their lawns and gardens,” he adds.
Sevierville, Tennessee: Sevier Solid Waste Inc.’s 15 year-old MSW cocomposting facility, the largest operating plant in the U.S. in 2006, burned to the ground on May 31, 2007, completely destroying the 102,000 square foot building that housed the tip floor and compost hall. As fully described in the accompanying article, the five rotary drum compost vessels and their hydraulic rams were saved by the Pigeon Forge Fire Department. Pending final terms of the insurance settlement, Sevier Solid Waste Inc. plans to rebuild the facility, expanding it to 180,000 square feet and making significant changes to the materials flow process.
Prior to the fire, the facility was processing 250 tons/day of MSW and 50 tons/day of biosolids. A new Backhus windrow turner had been purchased and was being used to turn and aerate the compost piles; the forced aeration system had been turned off. According to Tom Leonard, Solid Waste Director, the aeration trenches had been a continual maintenance challenge due to clogging of the specially manufactured plastic grates developed by Bedminster Bioconversion when it built the facility. The grates were also prone to being dislodged by the loader bucket as it was turning the piles, and had to be continually replaced.
All of the residential and commercial MSW generated in Sevier County was being processed at the facility, with 60 percent of the total tons converted to compost. The remaining 40 percent residue, mostly plastic, glass and metal, goes to an unlined demolition debris landfill operated on an adjoining parcel of land, thereby diverting the residue from a lined landfill. There is no upfront sort line for recyclables, and after discharge from the digesters the recyclables are too dirty for marketing. In the early years, the facility utilized a belt magnet to pull metals off the residuals, as well as an eddy current separator to extract aluminum. Both streams were shredded and screened to remove dirt. However, neither metal product was sufficiently clean for recycling markets. In 2006, notes Leonard, the facility produced almost 30,000 tons of 1/4-inch screened compost. All of it was sold to a company that markets the materials for soil blending, topdressing and erosion control. The tip fee at the facility is $40/ton, with total costs to process MSW and biosolids, as well as dispose of residue, estimated at $25.34/ton.
Columbia County, Wisconsin: The Columbia County Recycling and Waste Processing Facility has been operating since 1992, and continues to process between 70 and 80 tons/day, although the flow is a bit higher in the summer. There are two rotary drums, each loaded with five yards of material at a time, with a daily capacity of 40 tons (maximum capacity of 250 tons per drum). After five days in the drum, the compost goes through a 15-foot long screen with 3/4-inch holes. The compost is then put into windrows for eight weeks, and is finally screened to 3/8-inch. About 3,000 tons/year of compost is produced. It is given away at no cost to local farmers.
According to Bill Casey, the facility manager, national waste companies have been purchasing the independent haulers in the county, including those servicing municipalities. These companies also own the landfills, and with an inside market, they are able to undercut the $34/ton tip fee at the MSW composting facility, making it increasingly difficult to maintain the throughput. “We had to go out and do our own collection; we offer curbside collection in certain areas,” says Casey.

Sign up