Latest Trends in Yard Trimmings Composting

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Courtesy of BioCycle Magazine

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YARD TRIMMINGS composting has come a long way in the almost two decades since states began restricting disposal of leaves, grass and/or brush from solid waste landfills. Public officials, site managers, residents and composters have learned much about cost-effective ways to transform previously-unwanted green feedstocks into useful end products. This article takes a virtual tour of several long-running municipal programs that are successfully diverting hundreds of thousands of tons of yard trimmings annually.

The first stop on this “tour” is Des Moines, Iowa. The city operated a compost site in the southeastern part of town, until Metro Waste Authority (MWA) took it over and implemented a regional yard trimmings collection program. MWA's Metro Compost Center (MCC) accepts yard trimmings from residents who participate in the agency's Compost It! program, a regional bag and/or sticker system created for the Authority's member communities. Currently, 11 of 17 metro-area communities participate, according to Sarah Rasmussen, MWA's public information officer. Prior to implementing Compost It! in 2001, there were at least four city-specific yard trimmings bag/sticker programs in the metro area. “This led to confusion among residents (most of the communities are contiguous) and difficulty in education,” Rasmussen explains. “Compost It! has largely solved these issues.”

MWA began operating the composting facility in March 2001. One of the first steps taken was to place restrictions on availability of free compost. Material was moved within the facility's fenced property, and hours of availability were established to be more efficient with how employees' time was being spent. Until then, residents could come to the Compost Center at any time during the week, including evenings and weekends, load up and haul the compost to their gardens and lawns.

MWA pays $77/ton to the haulers of Compost It! materials (if the yard trimmings are delivered properly bagged/stickered). Bags are sold to residents in bundles of five for $7.50 ($1.50 per bag); stickers are $.90 each. To help cover increasing production and hauling costs and to make the yard trimmings collection program sustainable, MWA implemented a number of changes to its compost policies, including establishing minimum purchase amounts in 2002, and completely ending the free compost program in January 2004.

The same year, MWA established the Compost Distributor Program to allow designated retail outlets to sell its Turf Gold Premium compost. The program is designed to provide central Iowa residents with multiple, convenient locations to purchase compost in small quantities (less than a truckload). The program also has the advantage of removing small quantity compost sales from the MCC, allowing MWA employees to focus on yard trimmings processing, Rasmussen notes.

At the MCC, feedstocks are ground using a Vermeer TG525L tub grinder. Material is put into “trapezoidal piles” that range from 100 to 200 feet long, and from 120 to 150 feet wide. When the piles are new, they are as high as 10 feet. After about a month, they typically reduce to about 6 to 7 feet, and by the time the process is done, piles can be about 5 feet tall, according to Rasmussen. There are six to seven of the piles.

MWA uses a Scat Model 4832 windrow turner that was modified so water can be added at the same time that the material is turned (which is as often as it is needed to maintain temperature levels). The modification has improved efficiency, Rasmussen reports. On average, piles are turned about once a month; it takes two to three days to turn an entire pile. The conversion to compost takes between six and nine months, partly depending on the weather.

The MCC produces half-inch size compost. The site has a Powerscreen 830 half-inch trommel screen. Originally, MCC produced a larger size product as well. “When we started looking at the market price difference compared to the amount of time and effort needed to produce two different products, we found it wasn't coming back to us in sales,” says Rasmussen. “We have talked about adding other products - maybe something specific for golf courses or some other compost mixture, perhaps with sand. We're looking into that to see where the market stands, and find the balance in the amount of time and effort we put into developing that, compared to the demand.”

REDUCED LABOR COSTS, EVALUATING BAGGING

While higher energy costs are obviously an issue for composting operations, labor costs have a more significant impact. So MWA has focused on making its processing operation as efficient and nonlabor-intensive as possible. “The less time we handle the material, the less it costs us to produce the compost - that goes for grinding, screening, adding moisture, turning. So that's where we have focused our efforts.” In addition, only preapproved customers can use the site. This allowed the agency to automate the scale system and focus its labor on processing the material rather than weighing customers in and out. A related improvement was the removal of small-quantity compost sales from the facility, which again allowed employees to focus on processing yard trimmings rather than processing customers.

When MWA took over the facility from the City of Des Moines in 2001, there were five full-time city employees at the site. In 2004, the number of employees was reduced to three, and they are all employed by MWA. “This is a huge advantage to us,” says Rasmussen. “It gives us greater flexibility across our entire organization. When things are slow at the compost facility, we can move the employees around to where they're most needed.”

Although MWA does not have a bagging operation, a pilot project is planned for next spring. By not selling bagged compost, “we lose some retail identification, but with bagging we hope to make that connection in the public's mind, between where the material comes from and how purchasing it helps defray solid waste collection and processing costs,” she notes. Bagged compost also provides a good place to give customers instructions on how to use the compost.

In recent years, MWA's compost sales have soared. In fiscal year 2002-2003, the MCC sold only 8,500 cubic yards of compost. The next fiscal year (2003-2004) sales topped 21,000 cubic yards. Sales were down slightly in 2004-2005 to close to 17,000 cubic yards.

MWA sells the unbagged compost wholesale to residents and to four local retailers (one with multiple locations) for $8/cubic yard. “We don't have any control on their mark-up, but I believe they sell the product for about double that,” Rasmussen says. “They're definitely making a profit on it. We might be able to close that gap through bagging our product, keeping operating expenses low, and selling direct to customers rather than through third parties like we are now.”

The commercial end user side is growing as well, she adds. “Over the last year, there's been a lot of public attention in the metro area to the need for green development in residential divisions, commercial areas and parking lots. And cities are looking at how compost can be used to prevent erosion. Metro communities don't have greenscape requirements, but a number of them are looking at doing trial projects.”

CEDAR RAPIDS, IOWA

At the Cedar Rapids/Linn County Solid Waste Agency (SWA), the cost of composting yard trimmings has been defrayed by adding other types of organic materials, thereby increasing the throughput. In fiscal 2004, over 13,000 tons of yard trimmings were collected curbside, but a total of close to 41,000 tons were processed at the city's site, which opened in 1994. This includes over 19,000 tons of industrial organics - paper mill sludge from the nearby Cedar River Paper Co. and by-products from large grain companies and a biotechnology plant - as well fall leaves, grass and brush from commercial landscapers, and storm debris.

The SWA charges a tipping fee of $15/ton. Annual operating costs (before depreciation expense) are slightly over $1 million, or $14.49/ton (FY04). SWA sold 15,382 tons of bulk/bagged finished compost materials. Equipment costs were about $120/hour (fuel and repairs but not depreciation expense). Total capital costs, including buildings, pads, light and heavy equipment were about $5.5 million.

As a general rule, all materials are processed through a Morbark 7600 wood waste recycler. The site uses a Scarab compost turner and a Royer trommel screen for the finished compost. To minimize the amount of odor build-up, SWA staff are instructed to turn the materials on a consistent basis. “However, when atmospheric conditions (wind) are not conducive for turning, we will not turn,” explains Tim Lukan, accounting manager. “Staff is responsive to any complaints we receive due to odor.”

Compost bagging equipment includes a Royer 466 shredder-mixer and a Poly 21-B top sheet dispenser. To increase sales volume of bulk and bagged materials (including bulk compost, erosion control compost, topsoil, packaged potting soils and mulch), SWA entered into a marketing agreement with Ohio-based Garick Corp. in March 2004. On a year-to-year basis, bulk revenues increased 85 percent and bagged revenues increased 10 percent.

“We have been introducing their products to our existing customers and also taking over some of their customers,” says Gary Trinetti, president of Garick. He plans to attend trade shows to do more regional promotion, also employing telemarketing sales and trade magazine advertising. “There is a lot of growth potential in the lawn and garden/landscaping industry, with various niche applications for these types of products - construction, DOT projects, water quality/runoff control, playgrounds, and also the retail market. We plan to continue down that path.”

One new product added in recent years is shredded wood mulch (not colored). SWA also offers an unscreened compost that is useful in erosion control, sold in bulk by the cubic yard.

RAPID CITY, SOUTH DAKOTA

In Rapid City, green waste is composted at the city's 500-acre, $7.2 million site that combines a landfill, yard trimmings composting, materials recovery, and municipal solid waste/ biosolids composting. According to Jerry Wright, superintendent of solid waste operations, Rapid City's Public Works Department (RCDPW) collects about 16,000 tons of yard trimmings, or approximately 150,000 cubic yards per year. About half of the tonnage comes from three drop-off sites, each equipped with 20-cubic yard rolloff containers.

Two full-time employees run the 10-acre yard trimmings composting site. All materials are ground in a Peterson Pacific 5400 horizontal grinder before being placed into windrows for four to six months. There are 20 to 24 windrows, each 12 to 14 feet wide and six to seven feet tall. A Scarab turner mixes and aerates the piles once a week initially, then as needed after that, based on pile temperatures. Finished compost is screened to either three-eighth or three-quarter inches, depending on the end use. The facility has both a Fuel Harvester and a Portec trommel screen.

Annual production is about 4,000 tons of 3/8-inch high-grade yard trimmings compost; 1,000 tons of 3/4-inch high-grade yard trimmings compost; 500 tons of 3/8-inch clean chips; and 1,500 tons of 3-inch reject wood chips. The 3/8-inch compost sells for $30/ton and the 3/4-inch material is $25/ton. About 3,000 to 3,500 tons will be sold for annual, estimated revenues of $100,000 plus, according to Wright. “Sales have improved every year. We also donate compost to city and other public benefit projects at no cost or at a substantially reduced price. This past year, we contracted with a commercial compost bagging operation, and I expect to see sales really increase in the years ahead.”

The agency's product marketing has been limited to promoting use of compost products as a soil amendment, mulch, or erosion control media. RCDPW has not gotten involved in other processing, such as coloring, to boost sales. To help grow the market, the agency has worked closely with the county extension agency to educate the area's landscapers and gardeners as to the benefits of compost. The high clay and shale content of soils in the area makes compost a valuable tool to improve growing conditions.

Wright estimates Rapid City's annual cost of yard trimmings processing at approximately $287,263, or about $17.95/ton. Equipment costs (not including labor) include: grinder, $118 per hour; loader, $54 per hour; compost turner, $82 per hour plus labor; and trommel screen, $36 per hour plus labor. Capital costs for equipment were about $900,000 total.

ATLANTIC COUNTY, NEW JERSEY

In 1996, the Atlantic County Utilities Authority (ACUA) of Pleasantville, New Jersey discontinued its use of a private contractor and began doing its own yard trimming composting. Over time, ACUA's bottom-line has benefited as a result, according to James Rutala, vice-president of the authority. The ACUA collects about 18,000 tons of yard trimmings per year. It charges a tip fee of $25.75/ton for yard trimmings - a big savings when compared to the tipping fee of $57/ton it had been paying. Approximate annual operating costs, based on feedstock tonnage, are $188,000.

In the equipment category, ACUA uses a Morbark tub grinder for stumps, clean wood and yard trimmings. Material is placed in windrows, which are turned with a Scarab turner. The ACUA facility has had no significant odor control issues since purchasing the turner several years ago, Rutala says. Compost screening is done using a a McCloskey 728 Screener. ACUA only makes compost, topsoil and root mulch on-site; all other products sold at the facility, such as colored wood chips, playground mulch and hardwood mulch are produced elsewhere. Pricing of compost products is $18.50 /cy for “EcoSoil”, $21.50 /cy for EcoTopsoil and $17.50/cy for EcoRootMulch. Rutala estimates total revenue from sale of products in 2004 was about $318,000.

This year, ACUA has been able to absorb higher fuel costs within its current budget by reducing other expenses. “We have switched all of our equipment to B-20 biodiesel to reduce emissions and maintenance costs, and to promote the use of alternative energy,” says Rutala. The ACUA has also purchased hybrid vehicles and powers all of its buildings using a landfill gas-to-energy generator.

MECKLENBURG COUNTY, NORTH CAROLINA

In Charlotte, North Carolina, the Mecklenburg County solid waste facility receives about 80,000 tons of yard trimmings annually, collected by local municipalities, including the city of Charlotte. Total operating costs are about $1.4 million annually, according to operations manager Steve Elliott. Capital equipment costs for 2004 were about $460,000. Product and market development expenses have increased slightly less than five percent, with revenues more than covering the increased costs. The prices of compost products costs have increased 13 percent over the past decade, adds Elliott.

The county has four collection sites. All composting is done at its 25-acre facility near Charlotte Douglas International Airport, on the west side of town. The county charges a $16/ton tipping fee. Because of city zoning restrictions against building near the airport, there is enough of a buffer zone to prevent odor problems near the site. “Composting does produce odors, but being at the end of the runway, we have no neighbors in the area,” Elliott says.

Equipment used to process yard trimmings includes several tub grinders: a Diamond Z, two WHO units and one Morbark with 4-inch screens. “Grinding size is key,” Elliott advises. “If you grind material really fine, there's no air space in the pile; if it's too coarse, it takes a lot longer to decompose. We're tried different sized screens and are currently using 4-inch by 5-inch screens in the grinders; that seems to be the optimum size for windrowing.”

After grinding, material is put in windrows 8-feet high, 20 feet wide and 400 to 800 feet long. The composting pad has an asphalt surface. Windrows are turned weekly with a Scarab to manage heat and moisture, and more frequently if conditions are unusually wet, according to Elliott. “Climate can inhibit the composting process. When we're in drought conditions and don't get enough rain, we have to use water trucks, which is labor-intensive. When there is extra rain in winter, rows can 'die' on you. We have to turn it like crazy to dry it out and get it going again. The main thing is to get the moisture right and turn steadily. That keeps the pile temperatures at a consistent level.”

Mecklenburg County has an Extec Starscreener and a Powerscreen trommel. The county makes and sells a variety of products including topsoil, potting soil, compost, nuggett mulch (made from the “overs” left from the screening of compost), red and black-dyed mulch, and pallet mulch. One of its compost products is an 80-20 mix of compost and ash collected from a Duke Power electrical generating plant about 30 miles away. The agency sells compost to local residents, landscapers and garden/landscaping-product wholesalers. New Solutions, a Charlotte-based retailer, buys product in bulk, mixes and bags it. Compost sales in fiscal year 2004 totalled about $500,000.

North Carolina represents a good market for compost, in part because of its value for improving the region's red-clay soil, Elliott points out. “Compost improves the drainage of clay soils. In the eastern part of the county, where we have sandy soils, compost helps it retain moisture.” To help educate the public about compost and its benefits, Elliott has used weekly gardening programs on local radio stations to get some free advertising.

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