The compost hedge

January 1, 1998

8 Min Read
The compost hedge

Michael Fickes

Just as investors diversify their financial portfolios, municipal solid waste (MSW) managers around the country have diversified their approach to waste management, aiming to meet federal and state diversion goals.

Diversification involves a mixture of recycling and composting strategies. While recycling performs like a high-risk mutual fund - providing great returns one year only to be socked by losses the next, according to the flow and ebb of prices - composting provides steady and reliable diversions and low costs year in and year out.

Composting represents the conservative side of the MSW management portfolio, a low-cost, low-return, stable hedge against recycling's dramatic ups and downs.

While municipalities frequently seem to take investment risks when it comes to high-profile recycling processes, comparatively few seem willing to make unusual financial investments in composting. For example, many forego leasing and rely entirely on outright purchase when they seek to acquire equipment.

Take the Dickerson leaf and grass composting facility in Montgomery County, Md. Montgomery County owns the 10-year-old facility and contracts out day-to-day operations to Maryland Environmental Services (MES), Annapolis, a state agency and non-profit corporation.

The county aims to divert 50 percent of its MSW stream by 2000. County figures show that yard trimmings, leaves and grass account for about 20 percent of the total waste stream, which is why composting is an important investment toward achieving diversion goals.

Important? Yes. Expensive? Not really. Montgomery County acquired the Dickerson facility in the 1980s from the local water company.

Built as a temporary sludge composting station by the water company, the site includes a 55-acre asphalt pad, making it one of the largest composting facilities in the country.

"Most grass and leaf composting facilities don't have an asphalt pad," says Mark Thompson, the county's composting project manager. "It is easy to operate on. While it would have been expensive to build, it has not been too expensive to maintain. Over the years, we've only needed a few minor repairs."

More than 60,000 tons of material arrive annually at Dickerson by truck and by rail from the local transfer station. The rail cars require a high capacity scale, and the facility owns a 130,000-pound capacity model.

Five front end loaders form the material into windrows, which are turned by three self-propelled windrow turners, manufactured by Scarab Manufacturing and Leasing Inc., White Deer, Texas.

It takes about a year of windrowing to compost the volume of material flowing into Dickerson, says Nanci Koerting, the facility's operations manager.

"Our season starts in September and October when the leaves come in to start the windrows," she says. "In April, grass begins to arrive. We mix the grass and leaves, and active composting starts. The turning equipment runs all summer. At the end of the season, the material is pushed into piles and cures."

After curing, two trommel-style screeners sift the material, separating oversized pieces and contaminants from the finished product, which is called "Leaf-Gro," a trademarked brand marketed by MES to landscapers, landscape architects, soil mixing companies and retailers.

The process costs the county $20 to $25 per ton - dramatically less than incineration or landfilling. Incineration costs would be more than $25 per ton and disposing of the ash afterwards would cost $35 per ton, Thompson says. And, landfilling the leaves and grass would cost about $35 per ton.

So, as long as equipment costs remain under control, the county wins on every front.

Old-Fashioned Cash Thompson places the capital value of the facility's equipment at just over $2 million for the scales, loaders, windrow turners and trommel screens as well as two ancillary tub grinders used at the transfer station to pre-process material.

He doesn't like to get fancy with equipment acquisition, preferring straight purchase plans to loans, leasing and renting. "We always have believed that we can get more out of purchase dollars than leasing dollars," he says. "We have a good preventive maintenance program, and we squeeze every bit of life out of the equipment that we can."

"As long as the equipment is well-maintained, life expectancy is very high," Koerting agrees. "For example, we have one windrow turner that is 10 years old and continues to work well."

The Compost Division of the Solid Waste Authority of Palm Beach County, Fla., also favors the purchase of equipment over financing methods.

In Palm Beach, composting occurs at the county landfill and diverts about 500 tons per day of both sludge and vegetation from the solid waste stream.

The composting facilities span two buildings: Building "A" houses 12 bays, and building "B" has 24 bays. The bays run to a length of 250 feet with widths and depths of six feet.

Nine computer controlled and motorized agitators supplied by Knight Industrial Division, Broadhead, Wis., move through the bays, starting the composting process by mixing the sludge and vegetation. It takes between 14 and 21 days for material to travel the length of a bay.

Vegetation arrives by way of the transfer station's trucks or as a commercial drop-off. Arriving vegetation passes through a drum grinder and a trommel screen separator. Sludge comes in on trucks and goes directly to the bays for loading into the mixers.

Front-end loaders deposit the vegetation and sludge into the mixers, which slowly mix and drive the material from the front of the bays to the back. The material drops out of the bay's back, where a front-end loader scoops it onto a tractor trailer for transport to the county's marketing company facilities.

Equipment costs between $1 million and $2 million and is purchased in a conservative manner through a characteristic low-bid process and then is carefully maintained, says Bob Weil, the authority's inventory and maintenance specialist.

"Because of the need for parts interchange ability on the mixers, we go with a sole source provider," he says. "With the loaders, we use an open bid process and deal with several vendors."

Weil manages maintenance to get the most out of the equipment. "We own an extra mixer, so that we can continue to operate if one goes down," he says. "In addition, every Wednesday, we shut down the facility and thoroughly clean and service each machine."

Money Well Spent The Oneida County Solid Waste Department, about three hours north of Green Bay in northern Wisconsin, has purchased about $200,000 worth of equipment for two composting programs operating from the county landfill.

The landfill handles about 18,000 tons of material annually and exports an additional 8,000 tons. The composting efforts divert another 14,000 tons per year from the landfill, says Bart Sexton, the county's solid waste administrator.

"Our largest composting program takes wastewater rejects from a local paper company and composts them in open windrows of fiber cake," he says. "The second program composts source separated organics (paper and food wastes) from grocery stores, restaurants, school cafeterias and other area food service operations."

The open windrows of fiber cake are turned with a Bio System Aeromaster 120, a power-take-off compost turner that attaches to a tractor with a creeper drive.

After the active composting period, the material is spread and mixed into the top layer of soil with a chisel plow.

"The result is a stable product that can be screened and handled with machinery," he says. "It does continue to break down, but not at the rate of the straight compost, which is a kind of pudding that can gum up the screens and other machines."

In the source-separated organics composting program, Sexton shreds the arriving material with a Jenz AZ 35, a horizontal feed rotary drum with swinging hammers and replaceable knives. The shredded material is deposited onto wood chips in static aerated piles under roof. The piles rise to about eight feet. A John Deere 544 loader with a four-in-one bucket turns the material once every one or two months.

Within two to three months, the material has broken down enough to allow combining two piles into one. After another two months, Sexton moves the piles out of the enclosures to a curing pad where it is separated with a Pro-Screen.

"We buy most of our equipment outright," Sexton says. "Our county board is a cash-on-the-barrel-head type of crew, which is a good way to be these days. If you don't have the money, you shouldn't buy the equipment."

The county considered leasing in the past, but rejected the option in favor of spending capital, according to Sexton. "I think that the only time you would lease equipment for composting is if when you don't have the initial capital available, but do have long-term commitments, preferably contractual agreements promising to buy tonnage," he says.

On the other hand, Sexton rents screening equipment. "A screen for our operation would cost a minimum of $110,000," he explains. "At our facility, we screen off about 6,000 cubic yards of compost a year during a six-week period. It's generally a better deal for us to rent the screen."

Except for Sexton's rental of a single piece of equipment, these three different municipal composting operations insist on the financial strategy of acquiring equipment through straightforward purchase plans - and all seem satisfied with the returns on this conservative side of their diversion investments.

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