By Katherine Holden

Palm Beach Goes First-Class
What About Europe?
What’s Up With Digesters
Edmonton Takes On Co-Composting

Given the Western world’s ongoing addiction to conspicuous consumption and the stunning statistic that our planet is home to six billion humans, it’s no wonder that many MSW managers feel like Sisyphus. He’s the legendary king of Corinth condemned to roll a heavy rock up a hill in Hades only to have it roll down again as it neared the top.

The "rock" of MSW is formidable. According to Steven Morris, president of Waste Recovery Systems Inc., a company that develops, designs, constructs, and operates recycling and composting facilities for the disposal of MSW and biosolids, the annual market for the disposal of MSW in the US is estimated to be about $60 billion.

Over the last decade, methods and attitudes have matured. There are several different and successful composting-facility sites in America and Europe, and this article highlights in a sidebar exciting news about a new MSW composting facility opening at about the same time this issue reaches your mailbox.

Four big obstacles to composting successfully in America include odor generation, flow control, consistent production of a quality product, and creation of product markets. Most facilities contacted for this article now rely on in-vessel procedures.

Palm Beach Goes First-Class

Pat Byer is the assistant director of The Second Nature Compost Facility (SNCF) owned and operated by the Solid Waste Authority of Palm Beach County, FL. Opening a pilot scale in October 1991, it expanded to full-scale three years later.

Using an agitated-bed system developed by IPS (once owned by Waste Management and sold to US Filter about two years ago), this facility’s feedstock includes 50,000 tpy of mulched yardwaste 55,000 tpy of biosolids. The end result is 675,000 tons of finished compost product.

An agitator unit next to compost reactors at Palm Beach County, FL's compost facility.

The facility takes curbside collected yardwaste and landscape debris from contractors, then mulches and screens the material using trommel screens with a mesh size of 1.25 in. minus. Landfill diversion and high-quality finished product are the two purposes for the facility. In 1992, Florida banned yardwaste from lined landfills. Byer says, "Class One, household garbage, and Class Three, trash, both require liners. There are no permanent nonlined landfills in this county. We needed an outlet for yardwaste and biosolids, so we had to go to a higher level of treatment. The state is slowly phasing out many land applications of biosolids, for example, in the Everglades." According to Byer, adding the high-nitrogen biosolids to the high-carbon yardwaste creates the highest-quality compost you can buy.

The SNCF was a turnkey-design and -built operation. Byer says, "We chose the IPS agitated bed because of its ability to process different types of feedstock. It’s a very versatile system. I don’t know of any other technology that produces such a stable product. It’s very forgiving on the type of feedstock you have, plus we needed an odor-controlled system because we have houses within half a mile of our site. We have three bio filters, each is 12,000 square feet. Nine years ago we felt this was the premier facility. This system has become a very popular technology within the last eight years."

SNCF has a year-round supply of yardwaste feedstock. "Mother Nature here in Florida is very kind to us, and you can’t fight Mother Nature. It’s very hard to do quality compost outside, except in really arid areas like California. Most facilities are under roofs."

Byer knows that one key to successful composting programs involves tying in marketing at the beginning. "When you build big projects, you need volume markets right away where you can move lots of compost at a low price. Later on you can look for value markets and make more money. Both are good and serve equal purposes. It’s best to have your product go to value markets, because with volume markets, you are constantly looking for markets."

SNCF sits on a 1,400-ac. site. There are five transfer stations throughout the county. An $850-million bond paid for all capital construction costs, including purchasing the property, site development, closure of landfills, the transfer stations, building the waste energy plant and roads, and so on. Byer says, "We process and market all ferrous material, such as appliances, and our recycling facility is the largest in the United States."

Because more yardwaste arrives than the compost facility can handle, about 60% ends up at the woodwaste-incinerator energy plant, leaving 40% to compost. All 1.25-in.-plus material ends up incinerated. People at the curbside may still put their material in plastic bags. SNCF separates those out of the wastestream.

Processing curbside collected yardwaste into mulch using a tub grinder.

For composting, the screened yardwaste and biosolids are mixed together in batch mixers, then go into the compost reactors (bays). The process involves a minimum of 14 days of aerobic composting. After composting, screening the material produces three sizes of compost: 1.25 in. minus, 0.5 in. minus, and 0.25 in. minus. An Erin Star Screen can make both the 0.5 in. minus and 0.25 in. minus.

Markets for the three composts include landscapers and construction site projects for the largest-sized compost. Although it can also be used by the agricultural community, very little ends up there since most farmers add fertilizer to their drip irrigation (a process called "fertigation"). Byer says this means that most Florida farmers don’t build up the organics in their soils. "Some things will drive farmers in that direction, such as protection of the ozone layer and carbon sequestration. You’ll see nitrogen and carbon manufacturers on a worldwide basis in the next century."

The midsize compost, 0.5 in. minus, is used as substrate for potting media and greenhouse plants; on golf courses, to top-dress fairways; and by places like Walt Disney World and housing projects, anxious for nice-looking plants.

The 0.25 in. minus is also used as a substrate for potting soil mix in a bag, in golf courses, and in the construction of golf course greens. "We’re trying to get even a finer product so they can put it on the finest greens. This product is excellent for making faster and faster greens. Golf courses want to mix 15% of this compost with a sand mixture, and they want the compost 4 millimeters or smaller," Byer states.

Right now half of all the facility’s compost is one-half inch and the other two sizes each make up 25% of the finished product.

In 1998, tipping fees were $20/ton. They increased to $25/ton in 1999, primarily because of increased costs of transferring materials to the waste energy plants. The tipping fee pays for processing the yardwaste. Operations and management costs are around $14/ton of feedstock processed.

The facility meets its energy requirements with the electricity produced on site by the waste energy plant. Byer says, "I used 5,870,800 kilowatt hours last year, costing 5.1 cents per kilowatt hour. That’s darn cheap. Retail customers pay eight cents per kilowatt hour." Seven people operate the yardwaste area. "I contract out the grinding operation and do screening and separation here, using temporary labor for separation only." The composting facility has 18 employees, including two mechanics. Some of the equipment used includes Morbark tub grinders, around 14 rubber-tire loaders (different sizes, makes, and models), and a trommel screen by PowerScreen of Florida.

The Weitz Company, a national general contractor, put the turnkey operation together with IPS components and under IPS control. The reactors are 6 ft. wide. BeltDewatering Press built the agitators, which are the mechanical equipment that processes the compost.

Two years ago, SNCF contracted with AllGro Inc. to handle all the marketing of the compost. Byer says, "We get a portion of the revenue; it’s not much right now but they absorb a lot of the process costs, including the screening costs. Future revenue projections are excellent, due to AllGro’s getting into the golf course community. We have more golf courses per person in Palm Beach County than anywhere else in the United States, except for perhaps one place in Arizona. The amount of material we move has really exploded since last January. The potential is for a half-million dollars in another three years."

Continental Biomass Industries (CBI) in Newton, NH is in the process of installing a large yardwaste processing system for the county consisting of a prescreener (4 in. minus), picking stations to remove contaminants, grinder, and a 42-in. wide by 40-ft. long star screen at the back end. According to CBI’s president, Anders Ragnarsson, the system will become operational in May 2000 and will be able to process 400 tpd. "It's the biggest commitment any municipality ever made to grind yardwaste," he says.

What About Europe?

Speaking with several Americans knowledgeable about composting, one hears enthusiasm in their voices when discussing the European composting experience. Many hold the view that Europeans have a more deliberate approach while Americans often look for anther silver bullet.

While people appreciate Europe’s deliberate, decentralized, long-term approach, they also point out the higher tipping fees overseas. That translates to a lot more money to work with, however.

Oley Shermeta (see sidebar) thinks highly of Sorain Cecchini Techno of Italy, which composts 1-5 million tpy of MSW. "Their turning system has a huge advantage over all others. It allows a more uniform temperature gradient regardless of the turning and adds less energy into the pile so it restores and monitors pile porosity."

Gillespie of DK Recycling brought us up to date about composting in Baden-Baden, Germany, a country with few landfills and therefore used to composting. Franz Vogel directs composting operations at two sites about seven miles apart from each other. Vogel has approximately DM 2,500,000 invested. The capital is his, and the loans are secured by his long-term contract with the City of Baden-Baden. As part of the land-lease contract, Vogel accepts materials from the city at no charge. Others (and there are many) are charged about $17/ton for horse manure and brush, $60/ton for stumps, $35/ton for hay and straw, and up to $100/ton for unclean (rough) material. Tipping fees at the neighboring household-waste plant run in the $120/ton range.

Feedstock includes about 90,000/tons comprised of 75% green yardwaste (mostly brush and leaves, very little mown grass); 10% hay, straw, and manure; and 15% residential kitchen waste from the nearby municipal biosolids process plant. That plant houses one of the newest and most sophisticated digesters in Europe and came with a $2-million price tag. This first-stage processing plant separates all foreign material, such as metal and glass, from the raw waste, then washes the remaining material in very hot water to remove soluble fats and sugars. A large centrifuge removes excess water, and the "clean" MSW arrives via truck to Vogel’s plants where he incorporates it with the other feedstock in windrows.

Concrete walls surround the actual composting part of each site, acting as push walls as well as some measure of security. Channels underlie the surface of the composting area and carry air, provided by blowers mounted on the outside of the concrete walls, to the composting material, which is in a trapezoidal block or "brick" approximately 120 ft. long, 10 ft. high, and 25 ft. wide. Each brick touches its neighbor to fully utilize the area. A Willibald turner turns each brick only every 30 days, always moving in the same direction to ensure that the oldest material reaches the final composting area in 180 days. There it is screened to 10, 20, and 30-mm sizes and set aside for outdoor curing.

Even though the sites sit in a region world-famous for its health spas, odor has never been a problem. The asphalt surface is graded for drainage, with all surface water directed to a center line drain and then carried to a collection basin for reuse.

Gillespie says, "The air control system is quite precise, controlled by a computer that monitors every block of material for temperature and oxygen-water content on a constant basis." Computers maintain oxygen levels at 18%, water at 55% and hold the temperature at 160 degrees. When oxygen levels fall below 18% the computer turns on the appropriate blower(s) until it measures 18% once again. This system operates 24 hours a day, 7 days a week, all year long.

Vogel creates about 40,000 yd.³ of product annually, and it all sells at prices ranging from about $12 for 1 in. screened to $26 for 3/8 in. screened per yard. Forty-pound bags sell for about $6 in compostable paper sacks. Vogel also sells many mixes at prices ranging from $22 to $60/yd. All prices then have the 16% VAT added.

Gillespie points out that Vogel has worked as a consultant in Bremen, Milan, Tel Aviv, and Saudi Arabia, among other places. "Maybe he and I will do one here in the United States," Gillespie says. "The closest thing I know here to his technology is what Jeff Gage has in Washington."

orty years ago in Rome, Italy, two individual waste companies joined forces creating Sorain Cecchini Techno (SCT). One of the objectives of the merger was to work cooperatively to develop a large-scale composting system. Today more MSW is composted using SCT technology worldwide than any other. SCT has eight plants in Italy and one in France, and the company is deeply involved with the new plant about to go on-line in Edmonton, Canada, where biosolids will be handled along with MSW. SCT’s goal is to divert raw MSW from landfills. End product, while useful, is not the primary focus. SCT’s special machinery and conveyance system are entirely automatic, fully run by PLC.

Throughput at the Italian plants varies from 500 to 1,200 tpd. According to Albereto Carrera, managing director of SCT, "We were among the first to introduce negative aeration in indoor composting plants in order to maintain optimum environmental conditions." SCT extracts air from the bottom of the composting bay and cools it through a heat exchanger. At the same time, it warms winter-cold fresh air coming into the enclosed vessels in order to avoid fog inside the composting plant. Carrera says, "With all indoor plants with biofilters, when cold air enters into a building where biological activity is going on, it hits warm, wet air, causing fog which in turn causes condensation on the walls and the corrosion of machinery." SCT uses the heat produced by the biomass to warm the incoming cold air.

Carrera adds, "When you use negative aeration, you don’t lose too much nitrogen. We recirculate all condensed moisture, so there isn’t a large nitrogen loss." With SCT’s system, augers turn the material. Two nozzles running from a reel on a cable truck take water directly over the augers, automatically injecting the water. "What’s not automatic," says Carrera, "is the checking of when to add water. Operators take samples of the biomass to check the moisture content."

Residence time for the material varies from four to eight weeks, depending on the plant. In Milan, it’s an eight-week process. Before entering the first vessel (a mass bed 90 m long, 15 m wide, and 2.5 m deep), everything is screened to about a 100-mm size and all ferrous material is taken out. Inside the first vessel, material goes through a three-week thermophilic stage. Then comes the second screening, where it’s now easy to separate to 30 mm, leaving only good material in the second vessel for five more weeks. That’s followed by more refining to sizes ranging from 8 to 12mm. "In Milan, it’s a very, very fine 8 millimeters," Carrera says. "In Rome, some material is 12 mm because of the very high throughput of 1,200 tons per day."

SCT’s Perugia, Italy, plant, now 20 years old, takes up to 600 tpd. In this ancient town, SCT markets compost to vineyards and golf courses. "We have had 20 years to develop a market," Carrera says. "MSW compost is harder to sell to the public because of concerns over heavy metals."

SCT includes MSW paper in its dynamic composting process (which is low in contaminants due to the widespread use of environmentally friendly inks). The paper and fibers are flaked by the augers into very small pieces, and they end up with a reduced heavy-metal content. "Although paper lowers contaminant levels, like heavy metals, the compost is still not the same quality as product made from source-separated waste." Again, Carrera emphasizes that even though the municipalities want a good product, their first goal is landfill diversion, which reduces leachate and methane-gas generation as well as rodent and bird issues.

SCT currently has three sites in Rome and another is under construction to handle source-separated food materials. Carrera says, "Rome has 5,000 tons per day of waste. By 2001, we hope to have the capacity to handle all of Rome’s waste."

currently Rome has 400 wet tons/day of biosolids that now goes into landfills. "Our target is to mix it and be able to handle it in Rome as in Edmonton, Canada."

currently 70% of SCT’s Roman compost ends up as landfill cover, 30% as compost for use in vineyards. Tipping fees at plants in Italy range from $35 to $70/ton.

Europe is ahead of the US in prohibiting raw MSW from landfills. "In 2000 in Italy, only pre-sorted MSW can go into landfills. Every government in Europe is headed in the same direction," Carrera says.

In Canada, with wide-open spaces and a total population less than California’s, the dedication of the City of Edmonton to compost MSW and biosolids comes from an environmental sensitivity that the rest of the developed world would be wise to emulate.

What’s Up With Digesters

Europe offers expertise and insight on how to approach composting from a completely different angle—in-vessel anaerobic composting. Although anaerobic trial sites are underway in America, including N.C. Vasuki’s two test cells now in their 10th year in Delaware landfills, the tests do not include in-vessel digesters. With aerobic composting requires air. With anaerobic composting, air must be removed. Nature creates anaerobic conditions on its own. Consider the bottom of sediment lakes and ponds, swamps, peat bogs, or the forgotten bag of lettuce in plastic at the back of a refrigerator. Such "natural" processes are slow. Modern in-vessel anaerobic processes are lightning fast in comparison.

Steinmuller Valorga (SV) of Germany developed its proprietary anaerobic digestion process and in 1982 began test plant operation in France. With four European plants now under its belt and four additional facilities under design and construction, SV has solid experience with anaerobic composting.

Steven Morris and Mickey Lakos, both with Waste Recovery Systems, filled us in about SV’s newest plant in operation, in Freiburg, Germany, right next to an industrial park and immediately adjacent to a new restaurant.

SV was involved in the design, permitting, and construction of the plant and the training of the operating staff. The company designed the facility to process source separated household organic waste (biowaste). The site represents the state of the art of the SV process and incorporates air locks for all trucks entering the facility to dump waste or pick up compost. This is SV’s first facility to operate its anaerobic digester in the thermophilic temperature range, guaranteeing to meet all protocols for the destruction of harmful pathogens.

Capital cost of the facility reached $10 million. The plant equipment includes (1) a biowaste-preparation unit: receives waste, removes metals by magnetic separation, and handles size reduction; (2) an anaerobic digestion unit: dilution and mixing of biowaste, pumping into 1- x 4,000-m³ digester, biogas buffer storage, compression and stirring system, digested matter extracted by gravity. Digestion performance occurs under thermophilic conditions, 50-55ºC; (3) digested material treatment: mechanical dewatering of digested matter, suspended solids removal of resulting sludge by flocculation-filtration. A part is used for dilution of the incoming waste. Excess process water is decanted and treated to reduce both chemical and biological content before it is sent to the local sewage treatment plant; (4) an aerobic postcomposting unit: digested material is matured aerobically in a 1-x 300-m³ tunnel by circulating air for two days to produce fresh compost for local farmers. This compost is screened to remove remaining stones and plastic; and (5) an air-treatment unit including: extraction of foul air, ammonia absorption unit, and biofilter.

The facility, which opened in April 1999, produces about 15,000 metric tpy of fresh compost used by local farmers directly on their fields and about 3 million Nm³/yr. of biogas, which is delivered to a gas-powered electricity generating station located next to the facility. Annual throughput capacity ranges from 30,000 metric tpy (126 tpd) to 36,000 metric tpy (153 tpd).

The facility owner, who is also a waste-hauling contractor operating in the City of Freiburg, built the plant to conform to German laws that require that by 2003, any waste going into landfills cannot contain more than 5% biodegradable organic matter. Tipping fees charged at the plant by the owner for his own trucks and for waste delivered by other hauling contractors cover the overall cost of collection, transportation, and processing of the source-separated material and the ultimate disposal of inert materials remaining after passing through the entire process. We were unable to obtain exact tipping fees.

Residence time in the plant includes 20-30 days for the biowaste and 15-25 days for mixed waste. Compost aeration takes 12-24 hours. Fresh compost is stored for two to five days.

currently there is no profit on the compost, which is free to farmers and others. The owner intends to charge 5-10 DM/ton at a later date. A subcontractor receives the biogas and operates the generators under his own responsibility. Profit is calculated per Nm³ transferred to the generators and is paid directly to the owner of the Freiburg plant, BKF Biogas und Kompostbetrieb. The sole owner and shareholder of BKF is Company Meier-Entsorgung (which collects waste for the City of Freiburg and the surrounding area). It is a privately owned, midsize company with about 25-30 million DM turnover per year.

Steve Morris says, "The Freiburg plant represents the state of the art of the SV anaerobic digestion process." Morris explains how it is impossible for the enclosed arrival trucks to emit odors, dust, or litter, and how they enter a delivery pit through a double door air lock. Once the trucks dump their waste, the inside door closes and the air is evacuated for three minutes. This exemplifies the lengths taken to keep odors from reaching even one neighbor’s nostril.

Why is it taking so long for successful anaerobic compost digestion to reach American shores? Flow control, guaranteed waste source, and costs remain issues. Morris says municipalities that own their own MSW even after it’s picked up (thus offering a guaranteed waste source) could specify tipping fees in any contract with private entrepreneurs like Waste Recovery Systems. He adds that it’s less costly to acquire anaerobic composting equipment in the US, so tipping fees here could be far less than in Europe—perhaps around $45-50/ton.

"Laws in Germany are very strict regarding waste disposal. Whatever it costs will be paid, and that leads to processing by composting." With Germany’s 2003 landfill law right around the corner, "Cities have to find ways to dispose of the vast majority of their biodegradable waste.

Morris says 55% of the biogas produced inside the enclosed, anaerobic vessels is methane and 45% is CO₂. If the gas is used to produce electricity or steam, there’s no need to take out the CO2. If it’s to be used as compressed natural gas (CNG) for auto fuel, the CO₂ must come out. "In Los Angeles and Brooklyn, New York, there are some public vehicles on CNG," Morris says.

Clearly in the last decade science, engineering, and individual innovations have made it more and more plausible to turn what most call "waste" into "black gold." Science can surmount odor issues, and municipalities might want to exert more muscle to handle flow-control issues. As the richest nation on earth ever to exist, perhaps we need to rethink the last hurdle, costs. Instead of creating landfill boils, we have the know-how and, increasingly, the environmental incentives to nourish the earth. Looking into the future, some things are worth every penny.

Edmonton Takes On Co-Composting

"The 1,100-ton-per-day Edmonton Co-Composting Facility is one of the largest composting plants in the world," says Oley Sheremeta, a science-driven man. He serves as a composting operations and management consultant to the TransAlta Energy Marketing Corporation, owners of the facility nearing completion in Edmonton, Alberta. "Plenty of eyes across North America are watching to see what happens up here. A unique set of circumstances came together to make this potentially a trend-setting project for the next 20 years."

The project’s major players include TransAlta Energy Marketing Corporation and the City of Edmonton in Alberta. The City of Edmonton will provide 30 years’ worth of residential municipal solid waste (RMSW) and biosolids. Quantities processed will be in the neighborhood of 180,000 tonnes/yr. of RMSW and 22,500 dry tonnes/yr. of biosolids. TransAlta, a Calgary-based corporation with 65 power-generating units worldwide including coal-fired, hydroelectric, and cogeneration plants, is providing a design-build-own-operate service to compost the two materials for the city. TransAlta also provides a major marketing potential to the project in its large surface coal mining reclamation activities just west of Edmonton.

As TransAlta researched the business potential of the project, it did an extensive amount of due diligence into composting technologies. "TransAlta’s philosophy was to design a facility that had a technical right to succeed, a science-based approach to the design and engineering of a plant that would allow the company to predict that they would succeed, rather than to guess or hope to," Sheremeta says. During their due diligence, TransAlta officials attended a week-long course offered by the Washington Organic Recycling Council (WORC) where Sheremeta was an instructor. Later they hired Sheremeta and Phillip Leege, another composting consultant, to teach a similar course in Edmonton to the engineering firm that was hired to provide engineering, procurement, and construction management services on the project. The firm, GKO Engineering with head offices in Edmonton, AB, is a growing multidisciplinary engineering firm now branching out into waste management.

Sheremeta notes, "One of the smartest things TransAlta did was to not go to a turnkey-system provider. Instead they established success criteria for their project, specified equipment that would meet the success criteria, selected individual components that met the equipment specifications, and put them all together. It’s science and engineering for success."

One reason against choosing a turnkey facility in Edmonton is its harsh winter climate, where temperatures fall to -22 to -40°F and waste remains at curbside for two weeks. Sheremeta states that composting in that environment offers special challenges and requires project-specific answers. Another challenge is that unlike most large scale MSW composting plants, the TransAlta facility also has a large dewatering plant to process biosolids. "It’s like having two plants instead of one," adds Sheremeta. Each of the dewatering facility’s three Alfa Laval Sharples centrifuges has a 300-hp main drive plus a 100-hp back drive. They must function to raise the solids content of the biosolids from an average of 4% to approximately 30% prior to composting.

Delivered to the facility’s tipping building, the RMSW waste undergoes manual presorting on the tipping floor in a process referred to as feedstock recovery. "Some items need to be removed from the wastestream because they are ‘nonprocessable,’ such as carpets, bicycles, and dimensional lumber. Materials such as these can damage equipment, cause jam-ups and downtime, or pose hazards to employees. Others items are ‘noncompostable’ and therefore are removed because they can adversely affect compost quality."

After presorting, the RMSW and dewatered biosolids are metered into each of the facilities five mixing drums. The mixing drums prepare the feedstock for the downstream composting process. In the case of the RMSW, a large ram feeder delivers the material into the feed end of the mixing drum. The dewatered biosolids are pumped from a holding tank under the centrifuges with a Schwing pump into the feed end of the mixing drum. The material remains in the mixing drums for 24 hours.

TransAlta selected rotating mixing drums designed, engineered, and fabricated by A-C Equipment Services in Milwaukee, WI. A-C Equipment Services President John Vitas has trademarked his company’s A-C BioMixer composting design. Each of the five mixing drums has a 500-hp electric motor driven by a variable frequency drive allowing for 0-1 rpm of the mammoth drums. "There are a number of composting projects worldwide using a rotating mixing drum in their process. The drums are designed by one of many equipment vendors, such as A-C Equipment Services, who manufacture them. Typically these drums range in size from 8 to 12 feet in diameter and 80 to 180 feet in length. Some facilities have just one mixing drum, while others may have two or three. Sheremeta has seen five used on only one other occasion. But the mixing drums in Edmonton—16 ft. in diameter and 243 ft. long—are the largest he’s ever seen.

In 24 hours, the drums meet all of the feedstock-preparation objectives except for particle size. The feedstock’s carbon-to-nitrogen ratio, moisture content, and pH are all set to prescribed levels. Air is forced into each drum to maintain aerobic conditions and to adjust the pH. To achieve the desired particle size, the otherwise prepared feedstocks pass through one of the facility’s large trommel screens.

The trommel screens are designed and manufactured by Triple/S Dynamics in Dallas, TX. They serve to size the feedstock to 80 mm or less before it goes into one of the three agitated bays for composting. The 80-mm-plus residuals are landfilled.

After trommeling, the less-than-80-mm fraction of the prepared feedstock transfers to the 6.2-ac. stressed-skin stainless steel aeration building for a 28 day composting process. TransAlta divided the building into three bays, each 72 ft. wide, 574 ft. long, and 8 ft. deep nearly the size of two football fields. Drawing air down through the compost by negative pressure maintains aerobic conditions and manages the temperatures in each of the bay’s four separate control zones. The negative aeration allows for better odor management reduced worker health and safety concerns and minimizes building and equipment corrosion potential.

TransAlta looked at turning systems in Europe and America for use in the aeration building. The system that met their equipment specifications came from Sorain Cecchini Techno (SCT) in Rome, Italy. Agitated bays using SCT technology turn more MSW than any other turning system in the world. TransAlta purchased three SCT Biomax systems (one for each bay). Essentially the SCT Biomax system is a bridge crane on rails straddling the bay with twin augers hanging from the bridge that affect the turning. The turners also serve to remoisten the compost according to prescribed ranges within the bay.

After 28 days of aeration, the compost goes through a screening and refining system. Designed by Happle Maschinenfabrik of Weissenhorn, Germany, the system separates what is compost from material that never will be, such as stones, glass, metal, and plastic. The system functions to separate the material into three segments based on density. The most dense segment of the material includes the "heavies," such as stones, glass, and some metal. The second-most dense segment is the compost product itself. The least dense segment is the film plastic. Once the compost product passes through the density separators, it passes under overhead magnetic and eddy-current separators to remove any remaining pieces of ferrous and nonferrous metals, respectively.

Now the product is suitable for specific markets, such as mine reclamation, and may be shipped directly to end users. Or it may be further cured at the facility.

Recognizing that odor management is the composting industry’s number-one challenge, Sheremeta says, "TransAlta has gone with a negative-aeration system to aerate the 37,000 cubic yards of compost residing in the aeration hall." To aerate that much compost and keep all the buildings under negative pressure requires around-the-clock movement of between 150,000-300,000 ft.³ of air per minute. Six large fans powered by 400-hp motors are required to move the air.

Sheremeta says, "Everything about this project is done on an unbelievable scale. There are hundreds of motors, pumps, conveyors, and specialized pieces of equipment operating all over the property. That translates into an electrical demand for the whole plant of 3 to 4 megawatts of connected load. That’s a lot of power."

Slated to start wet commissioning in February 2000, the facility will ramp up to full scale operations by June 1, 2000, yielding a net residuals percentage of less than 35% while producing approximately 125,000 tpy of Nutri-Plus compost.

When creating compost from RMSW, Sheremeta says, "Everything goes up—the operating and maintenance costs, the process and product regulations, the testing costs, and so forth." Yet Sheremeta believes that the Edmonton facility is the blueprint for cities like San Francisco, Los Angeles, Chicago, Montreal, New York, Miami, and others. "If we can see these feedstocks successfully composted in these quantities and circumstances, you can certainly do it in other places. We don’t have a choice. We have to do it. Collectively the 5,200 composting facilities in North America are recycling only about 2% of the available organics in the wastestream. We’ve got to do a better job than that. Soil quality, water quality, and related environmental issues can all be improved if we increase composting efforts and return more organics to the soil. Major cities have only held back on projects like this because they haven’t seen the successes promised on this scale with these feedstocks in the past."

MSW
January /February 2000