September 12, 2007 | General

Commingled Organics At Yard Trimmings Composting Site

BioCycle September 2007, Vol. 48, No. 9, p. 23
Minnesota project evaluates both regulatory implications and how overall economics are improved by adding food waste and soiled paper to yard trimmings composting operation.

UNDER Minnesota legislation, there are essentially two types of composting facilities – yard trimmings and solid waste. The former are not allowed to accept source separated organics (SSO), since they are considered part of mixed municipal solid waste (MSW), and the latter are expensive and time consuming to permit, construct and operate. This is due to restrictive regulatory requirements.
A demonstration project in Carver County, Minnesota is showing how commingled source separated organics (food waste and soiled paper) can be collected in trucks used for yard trimmings, and processed at a yard trimmings compost site. Project goals of a grant received last year from the Minnesota Pollution Control Agency are to demonstrate that: 1) Commingled collection and processing of this material will improve the overall economics of SSO management; and 2) Processing the organic feedstocks at a yard trimmings compost site can be accomplished without any significant environmental impacts and with only minimal changes in the design and operation of the site.
Findings of this project could lead to greater opportunities for the collection and composting of SSO from both residential and commercial sources. To accomplish this, however, current rules and regulations related to the management of SSO would need to be changed, perhaps with its own designated category.
Under Minnesota Statute, 115A.03, Subd. 21(a) Mixed Municipal Solid Waste is defined as: “…garbage refuse, and other solid waste from residential, commercial, industrial, and community activities that the generator of the waste aggregates for collection, except as provided in paragraph (b).”
Paragraph (b) of that same citation reads: “Mixed municipal solid waste does not include auto hulks, street sweepings, ash, construction debris, mining waste, sludges, tree and agricultural wastes, tires, lead acid batteries, motor and vehicle fluids and filters, and other materials collected, processed, and disposed of as separate waste streams, but does include source separated compostable materials.”
A definition of source separated compostable materials is also provided in the statutes (MN Stat., 115A.03 Subd. 32a) and for all practical intents and purposes is synonymous with SSO. Yet, as a component of mixed MSW, SSO is subject to the Minnesota Solid Waste Management Tax if delivered to a landfill or incinerator. This tax is currently 9.75 percent and 17 percent on residential and commercial billings, respectively. Yard trimmings, on the other hand, are exempt from the tax but are required to be managed (composted) separately from mixed MSW.
The Minnesota Waste Management Act of 1980, among other requirements, legislated that yard trimmings could no longer be disposed in landfills. The ban on yard trimmings dumping came into effect for the Metro Area (the Twin Cities region) in 1990, and 1992 for the Greater Minnesota Area. Counties do not have to report tonnages diverted, but must prove that they have a system in place for handling yard trimmings.
Collecting SSO commingled with yard trimmings is generally more cost-effective than collecting the two compostable waste streams separately. But, under current regulations, commingled SSO and yard trimmings would be considered a solid waste, and if delivered to a landfill or incinerator it would either be rejected outright (due to the yard trimmings) or, if accepted, would be subject to the Minnesota Solid Waste Management Tax (due to the SSO) – a Catch-22.
Four composting facilities in the entire state of Minnesota are allowed to accept SSO; all are permitted as MSW composting facilities. Only one, Resource Recovery Technologies (RRT) in Empire Township, is located in the Minneapolis/St. Paul Metro Area. Though this facility’s tipping fee is comparable to that of local landfills and incinerators, the added cost for collecting the SSO can make it economically challenging to divert these materials without a variety of subsidies and taxes.
By creating an “in-between” category of composting facility for SSO (more protective requirements than a yard trimmings compost site but less restrictive requirements than those found in a solid waste compost facility), the overall cost and ease of siting a facility designed to compost SSO likely will be improved. This also would allow for commingled collection of SSO and yard trimmings, improving efficiencies and costs without any significant impact on environmental protection.
According to statistics from a 2004 report (Commercial Organic Waste Management Marketplace Assessment for the Solid Waste Management Coordination Board Region), about 95,000 tons/year (tpy) of food waste and other organic materials (“organics” excludes fats and grease, wood, and yard trimmings) from the region are being diverted from the trash. Included are approximately 60,000 tons to livestock feed manufacturing; 30,000 tons to livestock feeding; 3,500 tons to backyard composting; 1,000 tons to food rescue; and 600 tons to RRT for composting.
Significant quantities of organics are still being placed in the trash instead of being managed higher on the waste management hierarchy. There are about 200,000 tpy of organics from residential sources and about 180,000 tpy from commercial sources, including institutions. About half of these quantities are food waste; much of the remainder is nonrecyclable paper (which can still be composted). Existing capacity at sites in the area to process these organics include: 36,000 tons for livestock feed manufacturing; 31,600 tons for livestock feeding; 6,500 tons for backyard composting; 3,600 tons for food rescue; and 26,700 tons for source separated composting. Caleb Werth at RRT notes that although their current pad size for SSO is seven acres, which could handle 75 tons/day, they are permitted to take 150 tons/day.
Several jurisdictions have examined collection of residential source separated organics, and one small city, Wayzata, now has a full-scale program. In Wayzata 1,200 households received cart-based collection service for food waste and other separated household organics. Yard trimmings are collected separately and taken to the city’s site. A key feature of the program is that because putrescible wastes are diverted from the trash, residents have the option of a reduction in trash service to every other week, with the associated cost savings. Residents who have shifted to a smaller trash cart size and have gone to every other week trash service have reduced their costs, while costs for other residents have generally increased. About 150 households now have every other week trash service.
The Twin City of St. Paul and its recycling contractor, Eureka Recycling, conducted a pilot in 2001 for a separate collection of food waste and other household organics. The 2002 report regarding this study estimated that about 10,000 tons of SSO could be diverted with a citywide organics curbside collection program. The City and Eureka are planning to implement a residential source separated organics program beginning in mid-2008. The curbside program would be phased in so that it is available to all single-family households within about three years. Bins would be provided to participating residents. Targeted materials are food waste and other household organics wastes, such as soiled paper, dryer lint and pet waste. The increased costs for the program would be paid for by an increase in the City’s recycling service fee that is charged to residents through their property tax bills.
Based on the experience in Carver County’s current pilot (see sidebar), Wayzata and the pilot program in St. Paul, if all of the approximately 800,000 households in the region with curbside trash collection were provided with organics collection, an additional 100,000 tpy or more could be diverted from the trash.
The yard trimmings composting infrastructure in the region consists of 30-35 sites, operated both by municipalities and private contractors. The RRT facility in the region that is permitted to take SSO is below capacity in part due to the restrictions on cocollection, requiring a separate truck and cart. Also, the facility’s south suburban location necessitates longer hauls or use of transfer stations for parts of the region.
Even though separate organics collection is generally exempt from state and county hauler-collected service charges (if going to a composting facility), adding this service has required additional governmental funding to make ends meet. Collection in open hauling communities (i.e., where there are multiple haulers) will have less route density and can be expected generally to be more expensive. The pilot program in Carver County will demonstrate the feasibility of collection in these open hauling communities. A sure way to address issues of cost, and to eliminate the need for an additional truck on the road, would be to have cocollection on a yard trimmings truck. And, where allowed, every-other-week trash pickup could be instated. The use of plastic bags must be addressed on a regional level to make cocollection programs successful.
The demonstration project in Carver County seeks to prove that sites shouldn’t have to be permitted to compost MSW when they’re only taking SSO, and therefore a third regulatory designation should be created for SSO. The goal of the pilot is to show that most sites in the area could easily take SSO, as far as available space, staffing and finances are concerned. All that would need to change is the state’s regulation. Carver County will demonstrate that cocollection of SSO with yard trimmings, rather than treating it as MSW, would be environmentally sound and more cost-effective.
The Metro Area plans to sponsor a forum of municipal officials to discuss benefits and any environmental or public health nuisance impacts involved with alternating weeks of trash and organics collection. Finally, it will appoint a team to investigate potential organics composting sites in the region.
Marcus Zbinden is an Environmental Specialist with Carver County, Minnesota. Tim Goodman, of Tim Goodman & Associates in St. Louis Park, Minnesota, conducted the 2004 report for SWMCB.
DURING 2007, Carver County, Minnesota is undertaking a demonstration research project to cocollect food waste and nonrecyclable paper with yard trimmings and compost it at a yard trimmings site. The purpose of the project is to demonstrate to the Minnesota Pollution Control Agency (MPCA), which regulates composting facilities, that food waste/nonrecyclable paper can be efficiently cocollected using the existing yard trimmings collection system and managed in an environmentally safe manner at a composting facility having more environmental protections than a yard waste compost facility, but fewer regulations than a mixed municipal solid waste compost facility. About 600 homes are included in the project in portions of Chanhassen, Chaska, Waconia and Watertown, all of which have Waste Management as their hauler and all of which pay for seasonal yard waste service with a 60-gallon yard waste collection cart.
Collected organics are taken to the University of Minnesota’s Landscape ARBORETUM, which is permitted by MPCA to compost yard waste. The pilot was scheduled to run from April 1, 2007 through October. “Now we are talking with Carver County, the state and Waste Management about extending the pilot through the winter,” says Russ Leistiko of RW Farms, LLC, the contractor who manages the Arboretum’s composting site and is overseeing the pilot. “We also submitted a permit request to MPCA to compost the Arboretum’s food waste as it runs a cafeteria year-round.”
The Arboretum, situated on 1,200 acres, utilizes four acres for its composting site.The operation has been ongoing for 25 years, composting brush, flowers and green waste from the Arboretum. There is neither a pad nor a liner. Leachate from the piles with the SSO is being tested, as is the finished compost. The MPCA provided a $55,000 grant for this project, as well as a waiver to allow for collection and processing.
Waste Management collects the commingled food, soiled paper and yard trimmings – including grass clippings, twigs and other garden materials – on Wednesdays and Fridays. Residents use 60 or 90-gallon carts. They are allowed to use compostable bags (EcoGuard by Husky) that were delivered to households by Carver County. RW Farms uses a Supreme 300 Mixer to blend feedstocks prior to adding them to the windrow. “There is a scale on the mixer, so we know exactly how many tons/week we are processing,” says Leistiko. “About 10-11 yards are mixed at a time. By the time we pull the mixer to the area where we are building the pile, the material is thoroughly blended.” The Friday loads come in late in the day, so that material is processed on Saturday mornings. “By the time we start tracking PFRP temperatures on Monday morning, they are in the 140°-160°F range,” he adds.
The food waste/soiled paper/yard trimmings mix is left on the pad for 10 to 14 days; temperatures are monitored consecutively for seven days to ensure the pile has met PFRP parameters. Leistiko uses static piles that are turned with a 4 cy loader bucket. The piles are about 12-feet high – basically as high as the loader arm can reach. “We’ve learned over the years that you cannot get the piles so high that you have to drive on them,” he says. “In 30 days, the bottom two feet will be settled in. You get into trouble if you drive on them – first with odors and then with pile fires.”
After the initial 10-14 days period, the compost is moved to a curing pile. The first batch of compost made with the commingled materials was screened in July. “None of the EcoGuard bags were visible in the compost,” notes Leistiko. Compost from the pilot project cannot be sold until all the testing to be conducted under the grant project is completed.
Water quality testing is part of the scope of the pilot. Twelve ceramic water collection tubes were installed in one area to capture runoff from the piles. Tom Halbach from the University of Minnesota is conducting the water quality testing.
Leistiko has found that adding source separated organics to the Arboretum’s yard trimming composting operation is fairly straightforward as long as he follows the best management practices he has learned over the years. “If you do what you were taught – to not overload the blend with food waste, just as we learned years ago to not overload the blend with grass clippings – everything works out well. I played with a lot of recipes to identify the best blend of materials. We definitely are spending more man hours, but as long as we work with the materials soon after they arrive at the site and don’t stockpile them, there aren’t any challenges that we can’t manage.”
RW Farms uses a CEC 5-foot by 12-foot deck screen. The middle and overs fraction are added back into the composting process, although Leistiko is starting to identify markets for the middle fraction. The fines are the finished compost product. About 6,000 cy of yard trimmings compost was produced to date this year and the bulk has been sold. The Arboretum uses about 500 cy/year of the compost.
RW Farms recently received a contract to operate another yard trimmings composting site in Carver County in the city of Mayer. The compost site will accept grass, leaves, brush and other organic plant materials from residents of Mayer free of charge. Finished compost will also be made available to the city’s residents each year. RW Farms’ CEC screen is portable and will be brought to that site as well. The company subcontracts its grinding as needed. It also operates a wood grinding site in Moorehead, Minnesota to supply chips to the Fibromin turkey litter boiler fuel plant.

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