BioCycle August 2004, Vol. 45, No. 8, p. 43
A veteran mixed MSW composting facility manager provides insights into how economics and engineering challenges led to new ownership and a retooling of operations.
THE cocomposting facility in Marlborough, Massachusetts is a successor to a biosolids composting plant that was developed in the mid-1980s by the city of Marlborough. The covered, aerated static pile operation was successful in terms of manufacturing marketable compost, but due to neighborhood encroachment, was eventually shut down by a neighborhood lawsuit regarding nuisance odors. Nevertheless, the city was committed to composting its biosolids and issued an RFP for enclosed in-vessel technology, cocomposting biosolids with municipal solid waste.
The Bedminster Bioconversion Corporation (BBC) was awarded a contract by the city in 1995 to permit, finance, build, and operate a facility under a 20-year contract term. The composting facility, located at the city’s easterly wastewater treatment plant, was owned by one of the founders of BBC, and started operation in August 1999. For the next three years, it operated at its design capacity of 120 tons/day (tpd) of MSW and 60 wet tons/day of biosolids, producing Type I compost in accordance with Massachusetts regulations. Significantly, after some air handling upgrades, the facility demonstrated that the odor control system worked well, if properly maintained and operated. Although there were no state or local odor violations, several neighbors still were not happy with the odor situation. But from a contractual and regulatory perspective, the facility had been a success.
Unfortunately, however, the facility was an economic failure. As a consequence, the owner scaled back operations in July 2002, and while seeking a buyer, received permission from the city and state to operate as a transfer station in order to maintain contractual obligations to manage Marlborough’s MSW and biosolids. In March 2003, WeCare Environmental LLC purchased the assets from the former owner, and started investing in repairs and upgrades to the plant. In July 2004, almost two years after the facility stopped composting, the process was restarted, ramping up in three phases over a 12-month period.
An Odor Advisory Committee (OAC), comprised of one city official, one WeCare representative, two neighbors, and an at large member, is being established in accordance with the City contract. (The committee was established a number of years ago, but was reconstituted after the contract was signed with WeCare.) Phase I, which lasts for three months, allows for a maximum of 35 tpd to be loaded into the digester (only one of two digesters is running now). Before WeCare can move into Phase II, a six month period, it needs approval of the OAC and the Massachusetts Department of Environmental Protection (DEP). Air sampling is being done weekly, with measurements taken from the biofilter, the roof of the biofilter building, the property line, and a downwind location .
Once approval is received, Phase II would start in mid-October. Feedstock flow to the digesters would increase to 75 tpd. If operations during Phase II are acceptable to the OAC and the DEP, WeCare can start operating the digesters at their full capacity of 180 tpd. Currently, no biosolids are included in the composting mix. They are being managed off-site. Because all of Marlborough’s MSW is transferred through the facility, operators are pulling yard trimmings and organic-rich loads from the tip floor to process through the digester. In addition to the city’s MSW, WeCare is taking source separated commercial organics from about 15 supermarkets (see sidebar).
At the heart of the facility are two rotary Eweson digesters, each designed to process 90 tpd of solid waste and biosolids. MSW is received in an enclosed tipping building, and the dewatered biosolids are trucked into a separate building, and then pumped through pipes into the digesters, or alternatively, to transfer trailers. The two digesters span between the tipping building and the compost building, where compost is aerated and screened. All buildings are designed with odor control features, including high speed roll-up doors, odor agent sprayers around the doors, and negative air pressure. The collected air is treated through scrubbers, and an enclosed biofilter. Leachate and driveway storm water runoff are pumped to the city’s wastewater treatment plant for treatment. The facility also processes biosolids from the city’s westerly wastewater treatment plant, as well as several other plants in the region. Since the city utilizes approximately one half of the design capacity, the remaining capacity is marketed to other generators.
After two to three days in the digesters, raw compost is discharged and the material goes through a trommel screen with a 2-inch screen size. It is further processed on an aerated compost floor for at least another 21 days to meet regulatory requirements. Recently, with partial funding through a grant from the Massachusetts DEP, an Allu bucket was purchased to turn the compost on the aeration floor. A final screen is then used to make either half-inch or 3/8 inch final product.
BEDMINSTER CORPORATE STORY
During the 1990s, BBC was the leading developer of MSW composting technology in North America, with six facilities coming on line, in addition to the pioneering facilities in Big Sandy, Texas and St. Cloud, Minnesota. The lineup included Pinetop, Arizona (see accompanying article in this section); Severville, Tennessee; Cobb County, Georgia; Sumter County, Florida; Marlborough, Massachusetts; and Nantucket, Massachusetts. There were also a number of international projects, including Edmonton, Alberta, a 1,000 tpd facility with six large digesters. All are still operating.
Bedminster’s strategy was to sign long-term operating contracts with municipally owned facilities such as Sevierville and Cobb, as well as develop privately owned plants under municipal contracts, such as Marlborough and Nantucket. Such 20-year contracts were apparently attractive to banks and other investors, and BBC was successful in raising money to keep the company afloat while it marketed the technology. In 2000, BBC’s owners decided to close its office in Marietta, Georgia, lay off most of its employees, and sell the technology licenses to Bedminster AB, a Swedish company. That company eventually failed, and the licenses were sold to an Irish company, Bedminster International.
One unfortunate consequence of the Bedminster corporate demise was the loss of a formal mechanism for operating facilities using the same technology to share information. Through corporate Bedminster, there had been an umbrella company which occasionally organized operator conferences to exchange knowledge. In the meantime, the only two privately owned and operated Bedminster plants, Marlborough and Nantucket, were going through their first year of operation, without the corporate engineering and marketing support originally expected by the two licensees.
At the Marlborough facility, several major, faulty financial and engineering assumptions eventually revealed themselves during 2000, the first full year of operation. These included the percentage of facility residue, final screen processing capacity, compost quality, and total operating costs.
At the Marlborough facility, residue is generated at the tipping floor (8 to 10 percent of all residue), off the primary trommel screen (close to 70 percent of total), and off the final screen (5 to10 percent). This material must be disposed in a landfill or incinerator. The residue from the city’s solid waste was sorted several times to determine its composition. By weight, the facility residue was comprised mostly of film plastic (30 percent), metal (17 percent), and textiles (15 percent). Any material that went into the digesters picked up considerable weight due to moisture added from biosolids, as well as entrained compost.
Marlborough’s residential MSW was determined to have a residue rate of approximately 50 percent, even though the financial pro forma’s had estimated a maximum of 40 percent. The total facility residue production had been estimated at 14,000 tons/year, but was 18,000 tons/year. Exacerbating that miscalculation was the higher cost of landfill disposal than originally estimated. The company had financed the project based on $45/ton residue disposal costs, on the assumption that the residue could go to a transfer station right across the road. Unfortunately, due to a pungent odor associated with residue that came out of the digesters, the transfer station had to stop taking the material, thus it was hauled to distant landfills at greater cost. The financial impact of this miscalculation is evident considering 18,000 tons of residue per year at an additional $10/ton disposal cost, or $180,000/per year.
Moving to the issue of compost quality, it was learned early on that it was very difficult to make a saleable compost out of residential solid waste due to the presence of glass and plastic, as well as poor performance of the final screening system. The Marlborough facility was successful in attaining a DEP Type 1 classification for unrestricted distribution of the compost, in accordance with the Commonwealth’s biosolids composting requirements (there are no MSW compost regulations) and no inert material standard). However, the marketplace set the inert standard, and because the Marlborough compost had small pieces of glass and plastic, as well as some odor, the owner spent between $5 to $22/ton to move compost out of the facility. In 2001, the last year of full production before shutting down in 2002, the facility produced 24,000 tons of compost. Most was beneficially utilized for gravel pit and mined land reclamation, as well as for landfill closure projects. These outlets all charged a tip fee, in addition to the cost of transportation. Taking an average disposal cost of $10/ton, that was almost $250,000 of added expense!
One reason the compost had excessive physical contaminants was the inability of the aeration floor to reduce the moisture content of the compost to a target of 40 percent or less before final screening. At higher moisture concentrations, the final screening system (a Bivitec vibrating deck screen and a destoner) could not operate efficiently. Contaminants remained in the compost – and compost was carried over into the screen tailings. Excessive moisture content also caused the final screening system to clog, or break down. Trommel screens were leased as needed. The resulting bottleneck led to higher piles of compost on the aeration floor, making it even more difficult to get air through the piles, turn them, and drive off moisture. Several times during the first three years of operation, compost had to be purged from the facility and used as landfill cover, at considerable expense.
Another major problem with the Marlborough compost prior to the 2002 shutdown, was that it was immature. Once taken off-site and piled up, it became anaerobic and generated nuisance odors. This was due to the fact that insufficient degradation occurred on the aeration floor, and once the compost was piled up at an off-site location, it continued to reheat and generate odor. Even though another party had been paid to take the material, and technically “owned it,” it was still a problem for the Marlborough facility. This in turn generated added costs since company employees would be sent to the site to apply costly, but effective, odor control agents, in order to maintain use of the site.
An engineering design assumption that proved to be incorrect and expensive, was that unsealed metal buildings can adequately contain odors when kept under negative pressure. During the first year of operations, occasional odor complaints were traced to air leaks along the seams of the buildings when down drafts of wind would pull odors out of the building, overpowering the negative pressure gradient. Considerable cost was incurred to seal seams of the three waste handling buildings, which largely corrected the problem.
MUNICIPAL RECYCLING PARTNERSHIP
In a show of commitment to the cocomposting facility, the city of Marlborough supported the sale to WeCare Environmental LLC. A key element of the renegotiation was a recognition that both parties would take steps to improve the city’s dropoff and curbside recycling programs, with a goal of making the residential MSW more compatible with composting. By diverting recyclables to the curbside collection program, the city can save on avoided tipping fees at the plant. The primary benefit to the WeCare composting facility is that less inorganic contaminants are contained in the MSW, and there is a reduction in total tons of residue for disposal.
To this end, the City established a new Recycling Committee, and WeCare is an active participant. The City Council also voted to hire a part-time recycling coordinator to work on boosting the curbside recycling rate up from approximately 13 percent. WeCare also operates the dropoff facility and has made a number of improvements.
WeCare Environmental is confident that the Marlborough cocomposting facility will be both technically and financially successful for a number of reasons. From a financial perspective, it has significantly less debt service than Bedminster Marlborough. On the cash flow side, regional tipping fees for both MSW and biosolids continue to rise as a result of diminishing landfill space in New England, allowing WeCare to charge higher rates for waste from other sources.
Another important difference is that WeCare, through its various sister companies, is internalizing construction, hauling, and compost marketing costs rather than outsourcing them. Capital improvements are being made at the facility, including the aeration floor operation. The company’s management style is also very hands on, with the owners involved on a daily basis – a stark contrast from the absentee owner style of the previous owner. Several key employees of the former company are working for WeCare, making the transition relatively smooth.
Finally, greater emphasis on processing high organics waste is already improving compost quality. Marlborough’s commitment to improving curbside recycling rates, as well as the availability of source separated commercial organics, are key differences from two or three years ago. Given these and other factors, WeCare’s Marlborough cocomposting facility is writing an exciting new chapter in the City of Marlborough’s composting journey.
Robert Spencer is Compliance Manager and Director of Technical Services for WeCare Environmental, and was formerly Regional Manager for Bedminster Marlborough. WeCare Environmental is a subsidiary of WeCare Holdings, based in Weedsport, New York.
TARGETING HIGH ORGANICS WASTE STREAMS
THE Massachusetts Department of Environmental Protection has been working with the state’s grocery industry for many years to encourage and facilitate source separation of its waste stream in order to make the organic fraction more compatible with composting. Participating grocery stores have benefited from reduced disposal costs as well the positive public relations associated with improved recycling rates. The results of the DEP’s initiatives have been a significant contribution to the WeCare facility’s current operations, and its goal of manufacturing a saleable compost product. The plant has about 70 tons/day of capacity to process “high organics waste,” defined by the company as having at least 90 percent organic material. In addition to grocery stores, WeCare is targeting food processors.
Three supermarket chains currently send compactor loads to the plant (Hannaford Brothers, Roche Brothers, and Whole Foods). Acceptable organics include waxed corrugated cardboard and wet/dirty paper products, which are a significant component of the organic waste stream in a supermarket. Most departments in the participating supermarkets utilize two containers, with the organic barrels lined with biodegradable polymer bags. The following residuals are typical: Meat rendering, floral, fish, bakery, delicatessen and produce. Generators are told that no glass or other sharps are permissible.
After each load is dumped on the tipping floor, it is inspected, and digital photographs of inorganic contaminants in the loads are sent immediately to the store manager, with a list of the contaminants discovered. All of the currently participating supermarkets utilize compactors, one for organics, and one for trash. Sometimes there is a third compactor for cardboard. With two or three compactors located on the backside of each supermarket, WeCare had to manage a logistics issue with contract hauling companies in order to ensure that the proper compactor was emptied. Accordingly, the words “Organics” and “Trash” were stenciled on the ends of the containers, as well as the walls next to the compactors.
Recently, WeCare participated in a media event at a Whole Foods Market in Bellingham, Massachusetts that highlighted the store’s participation in recycling and composting programs. Whole Foods noted that the first load from its new compost dumpster delivered to WeCare weighed in at about seven tons – versus the less than 3-ton load of noncompostable trash.
August 15, 2004 | General
AN MSW COMPOSTING JOURNEY
BioCycle August 2004, Vol. 45, No. 8, p. 43