Like an unwanted houseguest, greenwaste has been kicked out of landfills. Stricter air-quality regulations make it hard if not impossible to burn. So what’s to be done with all the greenwaste leaving homes and businesses and heading for local landfills?
The EPA estimates that approximately 13% of the American wastestream is composed of yardwaste. To reduce the volume of material taking up space in landfills, much of the incoming woodwaste has been diverted. In 2005, 62% of greenwaste was recycled. Regardless of the capacity of a solid waste facility, being able to redirect even a portion of the incoming wastestream extends the life of the landfill and helps alleviate the burden of siting a new facility or expanding an existing facility.
The Landfill of North Iowa accepts approximately 400 tons of solid waste per day. Of that, 140 tons of yardwaste are diverted into mulch, animal bedding, and compost that residents can pick up for free. It’s a sought-after commodity that frequently runs out. “Someone just took the last shovelful of our summer compost,” says Bill Rowland, director of the landfill.
While waste diversion is one of the largest drivers in converting yardwaste into mulch and compost, other factors spurred the move. Where recycling goals are mandated or associated with grant money, there is financial incentive to recycle yardwaste. Other drivers include bans, or stricter regulatory requirements, on burning yardwaste. In some instances, a municipality’s effort to divert incoming yardwaste is less about volume and more about reducing methane emissions.
Generally, the greenwaste scene plays out as this: Municipal landfills accept either through curbside collection or through drop-off a variety of greenwaste including yard trimmings, grass cuttings, and even used wooden pallets. The incoming wastestream is sorted with larger bulkier woodwastes going to mulch and the smaller items going to compost. Some facilities have added equipment to process bulkier woodwaste into their compost piles. Mulch is often given out to residents or, while it defeats the efforts of diversion, used as daily cover and erosion control in the landfill. Oftentimes, a minimal amount of effort is used so that it can simply be gotten rid of.
Commercial operations, on the other hand, are run to generate a profit by selling an added-value product. More commonly, they take in yardwaste along with foodwaste, crop residues, wastewater sludges, manure, and other organics and cook up a sellable product.
So, What’s in a Pile?
Turning raked-up leaves or mowed grass clippings into a viable compost relies on the microorganisms biodegrading, or eating, the waste. Microbes require an oxygen level greater than 10% and moisture levels ranging from 40% to 60% to thrive.
It’s important for nutrient levels to be balanced with a carbon-to-nitrogen ratio of 30:1. Leaves, bark, paper, and wood are high in carbon, while grass clippings, sludge, manure, and foodwastes are high in nitrogen. Leaves and wood can decompose on their own, but adding grass clippings will up the rate.
Composting generates heat, and measuring temperature is often used to monitor the process. Nathan O’Connor is the compost product manager for Reotemp Instrument Corp., a company that manufactures industrial thermometers and sells to both municipal and commercial clients. Products range from a simple model for use with backyard composting to more elaborate and even wireless systems with data loggers.
Turning the pile, the temperature can be maintained throughout until decomposition is complete. Reaching sufficient temperature, approximately 140ºF, ensures that weed seeds and such pathogens as salmonella and fecal coliform are killed.
Composting usually takes place in windrows, where aeration is handled through turning and mixing, or aerated static piles, where a perforated pipe pumps air up through the pile. The other option is in-vessel composting, where temperature and oxygen can be monitored continuously. In-vessel is generally saved for commercial operations or those that incorporate wet waste from food, manure, or sludge and are more likely to need odor control and stricter stormwater requirements.
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Photo: Wildcat |
| A fast-screener turns a windrow. |
Sales Are Up
Greenwaste processing requires equipment. And with the push to recycle and utilize greenwaste, it’s a great time to sell not just compost equipment but anything associated with the handling of organic waste.
Bandit Industries Inc. sells The Beast. It’s a cuttermill grinder that can process anything from stumps and logs to brush and wet leaves. Co-owner Jerry Morey has seen the demand for equipment increase here in the US and abroad. “The industry is strong,” Morey says. “Recycling is becoming more important, and someday all greenwaste will be recycled. It’s happening all over the world.”
The biological process of producing compost is highly dependent on the physical process. Grinding reduces material size and generates a consistently sized feedstock, just what the microbes want. The material is then composted for periods ranging from months to a year or more, all while it’s being aerated. After the cooking is done, the compost is screened using a trommel to remove any large un-degraded or nondegradable items (like dog-abandoned tennis balls) and put out to dry, or cure.
Mixers can be used on either the front or the back end of composting. Garland Smith with Roto-Mix explains that the company manufactures mixers that can either combine the incoming material—from grass clippings to woodchips to sludges—for composting or to mix seed into cured compost.
Shredders operate at low speeds and high torque and can be used in the initial breakdown of construction and demolition (C&D) debris. After white goods, steel, and other recognizable contaminants are pulled out of the raw C&D waste, the stream is fed into the shredder, where it’s torn to pieces averaging 12 to 18 inches in size. Their output is splintered, elongated, and fibrous.
“If a contaminant, like steel or concrete, gets in, the shredder can handle it,” says Aaron Benway, regional sales manager for Continental Biomass Industries Inc. (CBI). CBI manufactures shredders, grinders, and chippers used by C&D facilities, as pulp mills and sawmills.
“Grinders can be used in mill environments as well as mulch yards, land-clearing sites, and any place where felled trees or non-merchantable timber needs to be processed. Dimensional lumber can be fed through a grinder to produce boiler fuel or alternative daily cover,” Benway explains.
Chippers, however, are not as forgiving and need a clean feedstock. They operate using a very sharp knife with close tolerance. CBI manufactures two-knife and four-knife chippers that can produce a consistent and smaller chip size.
DuraTech Industries International Inc. offers grinders that vary in size and include vertical and horizontal systems. Each relies on a hammermill with a spinning cheese-grater effect to rip incoming material apart. “We sell to land-clearing companies looking to use woodwaste as a biomass product and to sawmills that use cut-offs and shorts to make mulch,” explains Al Goehring with Duratech. Generally, he says, municipalities rent equipment rather than purchase it.
At the Landfill of North Iowa, Rowland uses Rotochopper equipment to process branches into mulch that’s given away to residents and sold to commercial landscapers. Grass clippings and leaves are used as compost feedstock. The facility currently composts in seven windrows that are 6 to 7 feet tall, 12 to 15 feet wide, and 60 yards long. To ensure the windrows are properly aerated, they are turned weekly using a Scat pull behind the turner. The turner flattens the piles, which allows the material to absorb extra moisture. It takes approximately 15 months for the material to completely decompose. Before it’s made available to the public, it is run through a trommel.
Rotochopper Inc. manufactures grinders, and its clients include municipalities, urban woodwaste processors, private composting companies, and biomass facilities. “We provide high-performance machines that are targeted to a consistently finished product, whether it’s fuel, mulch, or animal bedding,” says Vince Hundt with Rotochopper. “Our systems are versatile. We provide a machine in a needed configuration with respect to power supply, mobility, and long or short conveyors.” The company also sells woodchip processors that produce colored or uncolored mulch and baggers.
Tim O’Hara is a sales manager with Wildcat Manufacturing Co. Inc. and sells pull-behind and self-operated compost turners, trommel screens, and greenwaste-sorting equipment. “Our compost turners, or aerators, are used on windrowed material. They move through the piles and aerate and fluff.” O’Hara believes most municipalities use composting strictly to avoid costs by diverting the wastestream and have little interest in making any money.
Brian Pugh, with the City of Fayetteville, AR, says the city does sell its compost but admits the city isn’t making a profit. The facility uses a Wildcat turner that produces smaller particles that are very accessible to the microorganisms and can reduce time needed to complete the process. In Fayetteville, it’s three months start to finish.
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Photo: DuraTech |
| A tub grinder processes greenwaste. |
The material is stored in windrows and lined up on a hard-packed base of clay and aggregate that’s graded for drainage. A pull-behind turner is used to aerate the piles. Fayetteville, unlike other municipalities, is able to regain some of its cost by producing a higher-grade compost to a wanting public. In 2006, the city sold 1,000 cubic yards of finished compost for $20 a scoop (1.5 cubic yards).
Samples are collected annually and analyzed for pH, nutrients, metal concentrations, moisture content, and other parameters. Another attribute to Fayetteville’s compost is what’s not there—plastic. Yardwaste is collected curbside in standup paper bags, not plastic. “It used to be brought in plastic bags, but we stopped accepting them in 2001—and we’re still finding leftover plastic. The paper bags are sold in local stores, and we call them to make sure they’re stocked, especially in the fall. I think people have been supportive because they know we produce good-quality compost and it’s cheaper than Wal-Mart.”
Roto-Mix manufactures mixers and spreaders that handle a variety of ingredients. “We carry both horizontal and vertical mixers and can mix in three minutes,” explains Smith. Unlike a windrow turner, Roto-Mix’s equipment works as a blender, mixing raw materials end to end and top to bottom.
Undercover, Under Control
McGill Environmental Systems is in the business of making money making compost. “We take in yardwaste, foodwaste, and wastewater-treatment-plant sludge and blend it all together inside,” says Bill Kish. “It composts for 14 days and then cures for 21 to 28 days. Then it’s done.”
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Photo: Ag-Bag |
| Ag-Bag systems are geared toward high-production operations. |
McGill’s method is sophisticated, with the entire process taking place in a building. The company currently has two facilities in North Carolina, one under construction in Virginia, and three in Ireland. Its feedstock comes from private companies and municipalities looking to get rid of yardwaste without having to process it themselves. Kish says its tipping fees are comparable to landfill tipping fees, and its costs are level with what it would cost a municipality to process yardwaste.
The composting unit is aerated from pipes along the bottom of the pile. A biofilter is located above the pile to treat air before it’s discharged. A Wildcat turner is used to mix the waste. Temperature and oxygen levels are monitored within the compost pile to make sure bacterial growth is maximized.
The ability to charge customers necessitates a consistent and reliable product. “Our compost is considered a Class A compost in accordance with the US Composting Council. So we’re able to market our product to golf courses and organic farms,” Kish says. “With respect to efficiency, our process is more reliable because we operate in a building.” He admits that companies can operate on a different playing field than municipalities, and he notes that because the compost business is a competitive one, the private sector likely has an advantage.
Oftentimes, facilities don’t have the option of processing compost inside. Ag-Bag Systems Inc. manufactures portable enclosures that offer the benefits of indoor or in-vessel composting without the cost.
“The benefits of Ag-Bag are that no turning is required, which reduces the equipment, effort, and fuel costs; the material doesn’t have to be watered because it doesn’t dry out; and there’s no VOCs [volatile organic compounds], or odor, escaping,” says Debbie Linder, who works in environmental sales for Ag-Bag. “Regulators like its contained system. It handles air quality without a building or digester, and stormwater runoff isn’t an issue.”
Linder also helps clients balance their feedstock and have better control over the biological process. “We help make sure the carbon and nitrogen are balanced. Different feedstocks can be analyzed. Say you start with yardwaste and then add some foodwaste or animal manure; you might need to use woodwaste or another carbon source.”
The bags come in 200-foot lengths. The 5-foot-diameter bag holds 76 tons of material, and the 10-foot-diameter bag holds 200 tons of material. The bags are filled using a machine specific to Ag-Bag. The bags and perforated pipes are on two separate rolls. As the machine progresses, the rolls unfurl, placing the pipe on the bottom and filling the bag with waste (like filling a sausage).
The City of Redding in California uses the Ag-Bag system to control odors. “The city is growing really fast, and a lot of custom homes have been put up, with big green lawns,” explains Dennis Carvalho, public works supervisor. “When grass decomposes it really stinks. We tried spray and other treatments, but they didn’t work. Then they built the Big League Dreams Sports Park next door, and I started having nightmares about people watching a national softball championship and getting sick up in the stands.” He knew he needed to stop the complaints and the nightmares.
Carvalho explains that using the Ag-Bags takes longer but is worth it. By California law, compost must have a temperature over 131°F for a period of 15 days to ensure that weed seeds and such pathogens such as salmonella and fecal coliform are killed. Even though the process is legally complete within 15 days, Carvalho believes it takes longer to create good compost. “When we used open windrows, it took three months before we were ready to screen and sell the compost. With the Ag-Bag it takes a little longer. It’s in the bag for three months, and then it goes into windrows for one more month.” Before material goes into the Ag-Bag, it’s put through a grinder and laid out in two rows. Moisture is added by spraying the rows with 30,000 gallons of water. On the last watering pass, Effective Microorganisms (supplemental microbes) are added to increase decomposition. The wet material is then loaded into the Ag-Bag equipment and forced into the 10-foot-diameter bag.
Material comes into the City of Redding’s facility either through the city’s collection program or by being dropped off by the public or businesses. It’s sorted, and larger pieces, such as logs and pallets, are run through the grinder and sent to a biomass facility that burns the waste. The smaller pieces—grass clippings, leaves, and branches—are composted. Due to limited space, the facility can’t compost all of the material that comes in, so a portion is sent to a private compost company. Carvalho says composting costs the city, but the city considers it a public service. “We have a lot of customers, and we have good-quality compost. We get e-mails from people saying they buy only from us.”
The city also takes a hard line when it comes to keeping plastic out of the compost. The city collects yardwaste from city-distributed green carts using an automated side-loader truck. In their rear-view mirrors, the drivers watch the waste being discharged. When plastic or garbage is seen, residents get a written warning. After three strikes, they loose their green cart for six months. When they get it back, they have only one strike before it’s gone for good.
Getting Professional Help
In the municipal sector, those running compost facilities are generally responsible for operating a myriad of other programs, including solid waste collection, disposal, or transfer facilities; recycling; and maybe even household hazardous waste. This leaves little time for handling a compost facility that not only gets along well with its neighbors but also provides a good-quality product to residents. That’s where the professionals come in.
Nicole Chardoul, senior engineer with Resource Recycling Systems Inc., works with municipalities and private clients to develop their yardwaste sites, select equipment, write management and training plans, and incorporate marketing aspects.
Chardoul agrees that most municipal compost operations don’t break even, and her team is working on a model that will help clients better evaluate the cost of processing and dispensing verses disposal. “We cover all the bases; we typically look at the site, the processing, the collection—even as detailed as what type of trucks, the size, what types of material, and permitting requirements,” explains Chardoul. “We also benchmark with communities of comparable size and look at different option scenarios.
“Compost is relatively simple. Typically outdoor windrows are used for yardwaste, but once you incorporate materials like foodwaste you’ll need to use containers either in a tub or a building.” Chardoul also recommends the Ag-Bag because it keeps odor and air-quality issues contained but isn’t high-tech.
Regarding the end product, Chardoul notes that most of the organizations she works with want to sell their final product. And doing that depends not just on the processing capability but also on the market opportunities available. With some investment in process and equipment selection, compost facilities can cope and may even see some revenue in greenwaste.