Green in More Ways Than One
In addition to being environmentally sound, composting can also bring operations an additional income stream.
Friday, December 31, 2010
By Janis Keating
The old adage, “One man’s trash is another’s treasure,” applies to many items that might arrive at your facility. With scrap metal prices rising, you likely see less of that these days; residents are taking their old washing machines to scrap yards for payment. By the same token, your aluminum recycling may be down, as people learn “there’s cash in them thar cans!”
But what about greenwaste? Homeowners don’t want that, so you’re stuck with it, and as increasing numbers of landfills are prohibited from adding greenwaste, what can you do with it? Plenty, if you’re composting; that greenwaste can become an income stream for you—and often, those same folks who gave you the greenwaste will buy your new product!
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Photo: Harvest Power Inc.
Biofilter pipes draw any odors from the cooking compost. |
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Photo: Harvest Power Inc.
Loaded onto a chain conveyor with an excavator, feedstocks then run across a wide conveyor belt. Laborers watch for, and remove, potential contaminants—anything that will not compost or could be harmful to the compost.
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Aerobic Composting
Using the right recipe, that large pile of grass clippings will break down into something smaller that’s also rich in soil nutrients. As the name aerobic implies, this type of composting requires good airflow for the decomposition process to work. The USEPA offers this recipe for composting:
Feedstock and nutrient balance—Controlled decomposition requires a proper balance of “green” organic materials (e.g., grass clippings, food scraps, manure), which contain large amounts of nitrogen, and “brown” organic materials (e.g., dry leaves, wood chips, branches), which contain large amounts of carbon but little nitrogen. Obtaining the right nutrient mix requires experimentation and patience and is part of the art and science of composting.
Particle size—Grinding, chipping, and shredding materials increase the surface area on which the microorganism can feed. Smaller particles also produce a more homogeneous compost mixture and improve pile insulation to help maintain optimum temperatures (see below). If the particles are too small, however, they might prevent air from flowing freely through the pile.
Moisture content—Microorganisms living in a compost pile need an adequate amount of moisture to survive. Water is the key element that helps transports substances within the compost pile and makes the nutrients in organic material accessible to the microbes. Organic material contains some moisture in varying amounts, but moisture also might come in the form of rainfall or intentional watering.
Oxygen flow—Turning the pile, placing the pile on a series of pipes, or including such bulking agents as wood chips and shredded newspaper all help aerate the pile. Aerating the pile allows decomposition to occur at a faster rate than anaerobic conditions. Care must be taken, however, not to provide too much oxygen, which can dry out the pile and impede the composting process.
Temperature—Microorganisms require a certain temperature range for optimal activity. Certain temperatures promote rapid composting and destroy pathogens and weed seeds. Microbial activity can raise the temperature of the pile’s core to at least 140°F. If the temperature does not increase, anaerobic conditions (i.e., rotting) occur. Controlling the previous four factors can bring about the proper temperature.
Developing a good feedstock balance might be tricky at times. During the growing season, you’re likely pulling in vast amounts of grass clippings, but less “brown” materials. In temperate climates, autumn brings you leaves, leaves, and more leaves. Widening your collection streams might solve these balance problems. For example, during the growing season, wood chips from lumber or tree service operations would come in handy, and during “leaf season,” foodwaste might help level the balance.
Depending upon your setup, oxygen flow can be attained in a variety of ways. Some operations create a venting floor, with air vents below the pile, to infuse it with air. Others choose to physically “churn” their compost piles, to expose all ingredients to more air.
Large-scale, commercial operations usually construct their aerated compost piles in one of two ways: in static piles, or in windrows. A static pile, because it’s not moved, requires more equipment and monitoring. This type pile usually includes forced air or fans, to keep oxygen flowing, and heat sensors, to ensure the pile remains at optimum temperature. Including “bulkier” compostable items, such as wood chips, also allows air pockets inside the pile. To cut down on possible odors, some place a thick layer of finished compost on the pile, which also helps maintain high temperatures throughout. The pile may also require moisture monitors, because visual inspection won’t reveal moisture levels deep inside the pile.
Turned windrow composting doesn’t require installation of air piping, but it does require crews to periodically turn the pile—however, they’ll use motorized equipment you already own. Ideal windrow pile height is between 4 and 8 feet; ideal width is between 14 and 16 feet. These dimensions create a pile large enough to generate sufficient heat and maintain temperatures, yet small enough to allow oxygen to flow to the windrow’s core. As with any aerobic compost pile, windrows also require moisture.
Because the windrows are turned, trained workers will notice if the pile is too dry, and when to add water. By the same token, if your area experiences a lot of rainfall, the pile will likely have to be turned more often, to redistribute the water, to avoid the creation of soggy, rotting pockets within the pile.
Any type of pile will produce some leachate, so it’s advisable (and, in many places, required) to capture and treat the runoff so it doesn’t get into groundwater. Many composting operations place their piles on impervious surfaces to make collection easier.
Thinking of starting a composting area at your facility? Cornell University’s Waste Management Institute offers a range of tools to help you get started, such as a calculator to discover carbon-to-nitrogen ratios of materials or a way to calculate compost’s moisture percentages..
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Photo: Pierce County Recycling, Composting and Disposal, LLC
After grinding, the material is loaded into rows with a loader
equipped with 7-yard tip-out bucket. |
Anaerobic Composting
Add two letters to the name, and you’ve taken all the air out of it. Anaerobic composting works in the absence of oxygen, and it’s likely already happening at your landfill—methane is a common product of anaerobic composting (or digestion). Although they’re different from the microbes that work in aerobic conditions, anaerobic microbes still require organic matter to feed upon; they’re likely chowing down on the food scraps, newspapers, and yardwaste that went into your landfill 30 years ago. Water treatment plants often use anaerobic digestion to break down solids.
Anaerobic bacteria break down or “digest” organic material in three basic stages, and produce biogas as a waste product. The problem with biogas, of course, is that it can be a pollutant, as well as an unpleasant odor. Therefore, to contain the process, one needs either a “digester”—an airtight tank—or a covered lagoon.
Many factors affect the rate of digestion and biogas production; temperature is the most crucial. Anaerobic bacteria communities can survive at temperatures from below freezing to above 135°F (57.2°C), but thrive at 98°F (36.7°C) (mesophilic) and 130°F (54.4°C) (thermophilic). Mesophilc organisms grow best in moderate temperatures; some varieties are used in making cheese, yogurt, beer, and wine. Thermophilic organisms like higher heat; some varieties are found in geothermally heated areas, such as you’d find in Yellowstone National Park’s hot springs.
The Best Result Might Be a Grind, not a Gas
“A faction in the solid waste industry is trying to overturn some landfill bans so they can make more biofuel,” says Craig Coker, of Vinton, VA’s Coker Composting and Consulting. “However, they need to take into account: How does one make the right resource for the right market at the right price? If you’re considering gas extraction, you have to ask—can you make it? Can you sell it to a customer? If both answers are ‘yes,’ then do so—maximize your income. If not, then handle the organics in a different way.”
A board member of the US Composting Council, Coker provides technical support to facilities wanting to develop a composting operation. “Even if yardwaste could still go into landfills, wouldn’t it make more sense to make compost—an income-generating product—rather than take up valuable space?
“On a commercial scale, making compost is relatively simple, when optimizing the production process,” he says. “First, you need a good linear layout, which allows you to move the product out in the minimum amount of time. As handling materials is an economic cost with little offsetting revenue, one should minimize handling. Your layout is important, because every time you move compost you increase your labor and fuel costs.”
Coker stresses the process requires attention to design criteria. “Your compost pile’s carbon-to-nitrogen [C:N] ratio should range between 25:1 and 30:1. The pile’s moisture content should be 50% to 55%. The free air space, or structural porosity, must be sound, so air gets through the pile. Thirty-five to 50% free air space is optimum.” Air space is often created with varied sizes of compostable materials—for example, wood chips mixed with grass clippings would provide air space.
“If yardwaste is uniformly ground, the process moves faster,” he goes on. “In a well-run operation, compost pile temperatures range from 145°F to 155°F, making, essentially, a low-temperature oven. Hold that temperature for 30, perhaps 60, days for best results; the total manufacturing window is 120 to 180 days. That temperature fights vermin attraction; higher temperatures allow faster decomposition of meats, dairy, eggs, et cetera. Covering new yard- or foodwaste with 6 inches of compost will also eliminate vermin. If your pile is inside a building, that also lessens the chance of vermin, but a building makes your capital costs much higher.”
Just as something in the oven, compost has to be checked. “Mix the pile every couple of days, so it ‘cooks’ evenly. If the pile has enough porosity, heat can escape, making a self-regulating pile; the right porosity allows oxygen in, allows heat and carbon dioxide to escape, and maintains optimum conditions inside the pile for microbial growth and activity. Take temperature readings, measure moisture, and check carbon dioxide levels, so you get a quality product.”
Turning the compost can be labor-intensive. Is there another choice? “If you’re building a new area, you can install a forced air system to make aerated static piles. This aeration system can be negative—pulling air down through the pile—or positive—pushing air up through pile.”
Early systems sometimes included mechanical aeration systems. “Rotating drum systems can still be purchased: a 4-foot-diameter, 6-foot-long drum costs about $30,000,” Coker says. “Vendor-supplied technology can be expensive, because they don’t sell a lot of them.
“Economies of scale are important, due to certain minimum capital costs, such as equipment, paving, permits. If a private company builds a facility, it needs to receive between 50,000 and 80,000 tons of greenwaste a year to send out 25,000 to 35,000 tons of compost. With tipping fees, et cetera, one could maybe pay for equipment. About 60% to 75% of revenues should come from tip fees, the balance from compost sales.”
Incoming waste is crucial. “If you already operate a landfill, you don’t necessarily need additional technology—merely space not used or needed for something else. You might need a windrow turner, a screen, a grinder. Rural landfills that are more distant from people need less technology, because there’s less chance for complaints about any odors or the sight of large compost piles. Of course, the inverse is true: the closer to residential areas, the more technology is needed.”
Compost sales will add revenue, but there are also reasons to hang onto some of the product. “Compost at the top of a final cap helps vegetation to grow. Also, compost can be used as a methane mitigation feature. In one Kentucky landfill, a 3-foot layer of compost soaked up nearly 75% of the methane.”
What would it take to get more landfills to make compost? “Right now, there’s a different mindset for MSW; its core competence is the safe, reliable disposal of solid waste. If a firm gets into composting, it has to make, and sell, that product.”
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Photo: Peterson Pacific
Composting begins with a good grind. |
Yardwaste is the main component of compost, but Coker points out that there’s plenty of other organic waste going to waste. “Overall, 12% to 14% of the MSW stream is food. Foodwaste composting on rise; there are 92 foodwaste collections in the US. One of the nicest is in Toronto, Canada. At the residential level, firms could institute SSO—source-separated organics. Foodwaste could be picked up by compartmentalized trucks.
“There are some entrepreneurial companies starting up, collecting foodwaste. A proper container is important to deter stray dogs and raccoons. Norseman plastics make solid containers that are difficult for scavenger animals to get into. The main industries now composting foodwaste are the ‘ICIs,’ the institutional, commercial, and industrial food processors. I did some research and discovered that foodwaste totals four-tenths of a pound per meal. Amazingly, this research was done in a college environment, where kids seem to eat everything.”
Cooking Compost Full Time
Ken Newman, of Evington, VA’s Royal Oak Farm LLC, is one of Coker’s clients cooking compost as a business. “I’ve been composting eight to 10 years, for agriculture purposes,” he says. “But for nearly three years, I’ve been a licensed facility. By that, I mean, a commercial composting operation in Virginia means you can bring in organic material from other sources and process them out. Agricultural operations can only compost what they produce from spoils on the farm.”
Newman receives foodwaste from retail operations. “A local hauler picks foodwaste up from Wal-Mart, and we compost it. We get mostly vegetable waste, although we’re permitted for everything compostable. We also receive pulp waste from a nearby paper mill. Our compost customers are in the horticultural industry; we also supply top-dressing for athletic fields, wetland restoration, et cetera. We sell in bulk, under the Blueblood brand.”
As he’s in a rural setting, Newman uses turned piles. “We build a windrow of foodwaste like a layer cake: woodwaste, food, short-paper fiber, more food, then wood chips. Then we mix. The way we build our piles, air is drawn through the windrows pretty well. To deter odors, we put finished compost on the top of each windrow. Finished compost acts like a filter. Due to Virginia regulations, composting has to be done on a hardened surface, so we create these windrows on 16 acres of blacktop. We use a Backus 1655 turner to stir the compost, which can turn a pile 15 feet wide by 7 feet tall. Then we let the compost pile sit and cook. It has to get to 131°F for 15 days. We’ll turn the pile up to five times, while taking tab tests for heavy metals, stability, and pathogens. If the compost passes these tests, it goes through a rough screen and then into curing, a stage which lasts three to nine months. After that, compost is screened again, to one-half inch, which is for ‘general purpose’ compost. Other applications want it screened smaller than that. Golf courses want theirs screened to one-eighth of an inch, and athletic fields one-quarter inch. Items that won’t screen down are thrown into a new compost pile and cooked again.”
Another of Coker’s clients, Frankford, DE’s Blue Hen Organics, opened its composting facility in 2010. Blue Hen’s founders, Shannon Argo and Robert Tunnell III, realized six years earlier that significant volumes of Delaware’s organic waste were being hauled to landfills and buried. Understanding that composting would reduce landfill methane emissions while also producing a natural, organic soil amendment that could be used in place of synthetic fertilizer, Argo and Tunnell researched a number of techniques to determine the best composting method for the organic waste produced on the Delmarva Peninsula. After receiving final regulatory and zoning approval in early 2009, site construction began later that year, and the Blue Hen Organics Recycling Facility opened to the general public in spring 2010. Capable of processing over 120 tons of debris daily, the facility currently accepts all types of vegetative debris, yardwaste, land-clearing debris, and poultry manure.
“We were all looking for a way to use this yardwaste. Primarily brought to us by commercial haulers and landscaping companies, homeowners also bring yardwaste,” Tunnell says. “We do have a rolloff truck and pick some up, but the majority comes from waste haulers. Blue Hen Organics is a partnership between Blue Hen Disposal, a waste hauler, and Tunnell Companies L.P., a property management company with landscaping, golf course, and construction businesses.”
The operation is sited on asphalt pads, a permitting requirement. “This also keeps any leachate from mixing with groundwater. The pads drain into stormwater ponds. If we need water for the compost, we pump it from there. We build large windrows 280 to 290 feet long, 16 feet wide, 7 feet tall, from material we receive. We grind the material, then blend in some leaves, wood chips, and poultry manure from local farmers. In addition, Sussex County has a large Perdue chicken operation.
“From the time windrows are first formed, EPA guidelines state that in 15 days they must be turned five times, and reach temperatures over 131°F. After that first two weeks, we turn it less and less, maybe once every 10 days. Five to six months from the time raw materials come in, compost goes out as finished product. We use some of the compost, but the majority is sold in bulk to landscaping firms in Delaware and Maryland.”
Since It Was Coming in Anyway...
Puyallup, WA’s Pierce County Recycling, Composting and Disposal LLC was already collecting waste, and since the northwest coast was an early adopter of recycling, composting made equal sense. “This company has been composting about 18 years,” says compost quality manager Carrie Gregory, who’s also a board member of the US Composting Council. “We have two main composting facilities, which have roofs, and aerated, turned mass beds, which allow us more volume in smaller footprint. We physically turn our compost, with special machines. We also have a watering system, so we can add water every time we turn. We wanted to get throughput up, to break down greenwaste as quickly as possible. As forced air tends to dry compost out, we have to add water.”
Gregory explains the process: “Greenwaste comes in, and it’s first checked for contaminants, such as tennis balls, for instance—sometimes odd things come in the waste. Then the greenwaste is run across screens, to remove fines. Larger items go into a grinder, then merged with the fines. As the greenwaste comes off the conveyor, a 3-inch water line gets it back to the water content we want.
“An end loader makes long rows of piles,” she says. “The composting area is a big rectangle, everything moves in one direction. When the compost is ‘cooked,’ it’s moved to a semi-outdoor curing area, which is covered but not enclosed. Cured compost is screened to make it smaller—into either three-eighths of an inch or five-eighths of an inch products—for two different end uses. We sell all our compost in bulk. About 80% goes wholesale, to landscaping firms, DOT jobs, et cetera, and 20% of it is sold retail to the general public.”
One facility, in Purdy, WA, has a floor and some sidewalls. “We use positive aeration only, no air collection,” Gregory reports. “It’s been there 18 years with no odor problems. It accepts only yardwaste. Puyallup Is very built-up, with housing, retail, golf courses, et cetera, and since it takes any type of organic waste, our facility there uses biofiltration to keep odor down. We’re slowly beginning to accept some foodwaste.” How does Pierce County keep piles from going anaerobic? “We run a lot of things with horsepower behind them so compost won’t go anaerobic. And we have no plans for an anaerobic digestion facility, although the Puyallup Energy Recovery Co. Plant—PERC—was constructed in the spring 1999 to utilize methane gas, a product of landfill operations, to produce green power.”
Compost Today, Power Tomorrow
On its Web site, www.harvestpower.com, Waltham, MA’s Harvest Power Inc. likens its operation to “urban mining.” “We use an array of technologies to produce energy and fertilizers in a cost-effective manner,” says Paul Sellew, chief executive officer. “Harvest was formed in 2008 as an organic management company. We work with predominantly organic waste, with a focus on source-separated waste. We think of greenwaste as ingredients for a product, not as ‘waste removal.’ Although some municipalities have set up composting facilities, we think we can do it more efficiently.”
Sellew notes that landfill bans are driving this new industry. “In the early 1980s, there were maybe 300 composters in the nation; now there are 4,500. The greenwaste is delivered to us by municipal customers. They pay us to take it at a significantly lower cost than they’d pay for getting rid of municipal solid waste.”
Active on both US coasts, Harvest Power has also moved north for opportunity. “We’re the largest composter in Canada, and we operate a composting facility in Vancouver, BC. The city was ready for this—it’s a progressive part of Canada—and in 2011 we will open an anaerobic digestion plant at the same site.”
Already successful with yardwaste, Harvest is opening its facility to foodwaste. “In most places, foodwaste ends up in the garbage, but with separate waste containers and SSO [source-separated organics] we’re adding this to the mix. We’re using commercial waste as well—foodwaste from restaurants, supermarkets, and coffee shops, for example.” Technology aids the composting process. “Huge aeration fans are situated under the pile to keep air circulated in the compost, then this is exhausted into a biofilter to remove odor. We find the fans provide lower cost and better control.”
“Temperatures run over 55°C to 65°C in a normal compost pile,” says Harvest Executive Vice President Steve Aujla, who runs the Vancouver facility. “We regulate moisture, C:N ratio, and carbon-dioxide levels, to create as close as possible an ideal environment where the greenwaste-degrading organisms can multiply. The heat also kills any possible pathogens, and meat scraps have no problems breaking down with this process.” As they’re made from trees, are paper products also welcome at the facility? “We encourage people to recycle as much at home. Napkins, pizza boxes, shredded paper, old newspaper can be recycled.” Yardwaste must be set at the curb in approved containers: reusable cans or paper bags. “Not in plastic, which is problematic for us. It’s a contaminate,” Aujla says.
“As for foodwaste, we’re trying to educate the public—to find a positive solution for people wanting to use plastic bags,” he goes on. “By the time we get it, wet foodwaste in plastic bags is already starting to ferment, making an odor. We want people to know that kraft bags, and also newsprint, are better for wrapping foodwaste.” To spread the word, Harvest Power is using the media. “We get on TV programs and radio shows. We also do publications, local newspapers—lists of what’s acceptable and what’s not. In addition, each city in the metro area has its own outreach program, whether it be on the Internet, door hangers, et cetera. We’re not trying to tell people we’re the solution for ridding landfills, we are a solution. Just under 50% of all trash is organic waste that can be recycled.”
As yardwaste is the main component in compost production, what happens in the winter months? “You’d be surprised how much greenwaste we still get, even in winter,” Aujla says. “We process compost through the cold weather, albeit less.”
Homeowners who have tried to compost know it can be slow going, but a commercial operation can speed up the process. “From the day materials arrive to when compost goes back to homeowners can be as fast as 12 to 14 weeks,” Aujla states. “Our batch system is a big rectangular block with 21 aeration pipes at floor level. A ‘batch’ is two or three lines of compost material. When a batch is completed, within seven to nine weeks, it goes into curing and screening. With wheel loaders, we’ll stack it, like a big loaf, on pipes. It takes two to three weeks for the rest of the process, then we run it via conveyor belts through a big grinder and screener—gauged at five-sixteenths of an inch or three-eighths of an inch—separating ‘fines’ from ‘overs.’ ‘Overs’ go back into the compost pile, to be worked down. These chunks also ‘inoculate’ the new pile with the microorganisms needed to break it down.”
The facility not only makes compost, but also garden soil. “River sand allows us to make a soil mix. Crews dredge the rivers spring and summer to make sure boats can traverse it. They bring us that sand. We sell the compost and soil both in bulk and in 25-liter field bags. We also sell to larger baggers who sell to Home Depot and other stores under their own labels.
“Last year, over 240,000 metric tons of greenwaste came in, and 500,000 cubic yards of compost and soil went out,” Aujla says proudly. “We’re pleased to see the community embracing organic recycling and proud we can offer assistance. Metro Vancouver, which includes 22 or 23 member cities, has bans on certain things—returnable pop bottles, paper, or cardboard, for instance—from landfills. Three years ago, yardwaste was banned, and now Vancouver is tackling organics and food scraps. In some places, it might be expensive to institute this sort of program; cities may turn a blind eye. However, with our scale, we’re able to lessen tipping fees, which encourages haulers to bring materials to us. We knew where civic and public opinions were headed. We were in the right place at the right time.”
In the coming year, Harvest Power plans to bring new facilities online on both US coasts. The Vancouver facility began construction on its high-solids anaerobic digestion (HSAD) in fall, 2010. MSW
Author's Bio: Janis Keating is a frequent contributor to Forester Media, Inc. publications. |
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