September 19, 2011 | General

Tackling Odor Challenges At Organics Recycling Plants

BioCycle September 2011, Vol. 52, No. 9, p. 52
Increased flow of organics from Green Bin programs in the Greater Toronto region tested the mettle of several composting facilities’ odor control systems. The solutions are guiding projects going forward.
Peter Gorrie

LAST summer, two large-scale composting plants near Toronto, Ontario, Canada shut down after nearby residents complained of pervasive odors. Both resumed production a few months later after spending millions of dollars on improvements. One, operated in London, Ontario by Orgaworld Canada Ltd., continues to receive and process organic wastes from the City of Toronto and its northern neighbor, York Region. The other, run by Universal Resource Recovery Inc. in the city of Welland, near Niagara Falls, closed its doors again in May when its odor problems resumed. Its future appears uncertain since much work remains before it can reopen.
While costs are always an issue, odor control has become the expensive Job #1 at all of Southern Ontario’s composting facilities. Neighbors show virtually no tolerance for emissions that offend their sense of smell, and regulators – paying careful heed to their political masters – are increasingly sensitive to the issue. “If it stinks, they tell you,” says Travis Woollings, manager of community relations for Orgaworld, owned by Britain’s Shanks Group plc, an international waste management giant.
The experiences of the two plants have been instructive for Toronto, York and other municipalities in the Greater Toronto Area that now operate or are building their own facilities and placing a heavy emphasis on controlling odors. “We’ve learned from watching the existing processors struggle through the challenges,” says Laura McDowell, York’s director of environmental protection and promotion.

From the time Orgaworld and Universal began operations, neighbors repeatedly and vociferously complained about odors to them and the Ontario Ministry of the Environment (OMOE), and organized to push for improvements. “We had a steep learning curve,” admits Woollings, whose facility opened in 2007.
Both plants faced particular challenges. For one, they were accepting organic wastes that include kitty litter and diapers – items that many composters forbid because of the extra potential for ammonia and related odor-emitting compounds that make precise control of the composting process even more critical than usual. They had little choice since their main customers, Toronto and York, as part of their programs to increase waste diversion rates, allow those items in green bins.
Toronto also operates its own anaerobic digester, which handles part of its green bin stream. That facility can easily cope with diapers and pet wastes, but it wouldn’t be possible to have one organic stream for the digester and another for the private-sector composters the city had to rely on.
As a result, both municipalities were having trouble finding reliable recipients of their wastes. In 2010, Toronto faced a storm of bad publicity because some of the composters it was using, particularly in Quebec, couldn’t handle its green bin material. Thus, they paid a premium price to any facility that would accept their organic wastes and, critics complained, this encouraged the London and Welland plants to take more than they could properly manage.
Finally, Ontario’s regulatory regime complicated matters: Even if a plant is in technical compliance – emitting no more than one odor unit for every cubic meter of air emissions – neighbors can challenge it with the OMOE on the basis of “adverse effects” on them and their enjoyment of their property. “You could perform very well, but have someone very sensitive to odor,” says Orgaworld site manager Greg Mariotti. “It’s very subjective and unclear,” Woollings adds.
Universal faced an additional problem since it had set up shop in a porous former pipe plant rather than a facility purpose-built for composting. That made it difficult to stop air leaks, let alone maintain the structure under negative pressure, a common practice to keep odors trapped inside.
The results in both locations were soon obvious. “The smell was way off the charts,” recalls John Pieterson, a letter carrier and woodworker who lives with his wife and two daughters about half a mile southeast of Orgaworld, in a semirural neighborhood in London’s outskirts. “It’s hard to describe,” neighbor Ted Chojnicki told a public meeting at the height of the odor problem around Universal’s plant. “I have worked in a butcher shop with pig and cow guts in the summer. This is worse. It’s almost like rotting fish.”
After spending more than $5 million to revamp its air handling and odor control systems, Orgaworld reopened in October 2010 at well below its annual capacity of 150,000 tons. It has gradually increased production and by August 2011 was at nearly 90 percent. Pieterson says the odor problem has improved 99 percent: “They’ve really hit the nail on the head. It’s night and day from what it was.” The OMOE has declared Orgaworld to be in compliance with its odor regulation and Woollings hopes the plant will soon return to full capacity. Universal started again last November at much less than its 69,000 tons/year capacity but was unable to overcome its odor challenges, leading to its closure in the spring (see sidebar).

Orgaworld has altered several parts of its operation to effectively control odors, Woollings said during a tour of the revamped, $34 million facility. Initial waste handling and processing, however, remain the same. Trucks unload incoming materials on to the tipping floor. To suit the needs of its own anaerobic digester, Toronto requires residents to put their wastes in regular, nonbiodegradable plastic bags. York insists on biodegradable bags. Thus, waste from both sources goes through a Komptech Terminator 3400 shredder that rips the bags open.
From there, feedstocks – including the plastics, which account for nearly 20 percent by weight – are placed by front-end loader into one of eight tunnels for 12 days of initial composting. The tunnels, open only at the end near the tipping floor, are each nearly 100 feet long and 50 feet wide and high. They are equipped with 2,700 floor-mounted air nozzles that aerate the contents, a ceiling-mounted wetting system, and fans located high on the back wall that pull air into a “technical hall,” the name given to the large, enclosed area behind the tunnels where ventilation fans and ducts start to move the exhaust air toward a series of scrubbers.
The first step in the odor control system is to scrub ammonia – a source of very offensive odor – from the exhaust air. The facility has two roof-mounted ammonia scrubbers. Orgaworld uses a technology that combines sulfuric acid with the exhaust air to create ammonium sulfate, a salt that can be used as farm fertilizer. (The material is permitted for spreading on fields in Europe, but it hasn’t been approved in Canada where undergoing trials are in process, Woollings says.) The scrubbing process reduces the amount of ammonia in the exhaust air to less than 50 parts per million.
In the original system, after ammonia removal, the exhaust air was directed to biofilters (using chipped hardwood media) installed in four tunnels, identical to those used for composting. Bacteria attached to the media oxidize the odor molecules, mainly reduced sulfur compounds. Next, the air, now with a woody smell, was treated in a bioscrubber. The air passes through a plastic mesh, and is sprayed with water to dissolve the water-soluble odor molecules, including those from the biofilter that impart the woody smell. Then, with two huge fans adding outside air for dilution, the treated air was sent up a 131-foot roof-mounted stack.
A “Root Cause Analysis” of its odor problem, conducted in preparation for the repairs by Orgaworld’s technical staff and Boston-based consultant Charles Alix, at the time working with MWH Global, revealed several problems. “They had all the right pieces, but there were little issues with each,” Alix says. For example, the bacteria in the biofilters prefer a temperature below 104°F. However the temperature of the air entering the units fluctuated, harming the bacteria and reducing effectiveness of the treatment.
The water in the bioscrubber should be constantly circulating, with some being removed and some reused. But the sump pump that removes water from the bottom of the unit was located too high, resulting in some water remaining stagnant that contained bacteria and other materials which decomposed and emitted hydrogen sulfide. Rather than removing smells, “there was a bump up in the odor,” Alix explains.
Partly because of those issues, the air going up the stack was warm and very moist. Often, instead of dispersing, the moisture in the exhaust would condense in the cooler outside air and fall to the ground, bringing the remaining odor molecules with it. Finally, a few leaks were found in the ammonia scrubbers.
The major upgrades at Orgaworld included:

Additional biofilter: A fifth biofilter was added, allowing the air to remain with the beneficial bacteria about 50 percent longer.

Air flow modifications: The active composting tunnels are arranged in north and south banks, with separate ventilation for each bank. In the old system, each ammonia scrubber received air from one of the tunnel banks. On occasion, that meant one took in more air than the other, reducing the system’s efficiency. The revamp, which required extensive additional ductwork, combined the two flows in a mixing room, from where equal amounts go to each scrubber. The work also increased the size of the ductwork and added controls to balance the flow and pressure among the many components of the ventilation and odor reduction systems.

Reducing leakage, cooling air: The ammonia scrubbers are now made of HDPE plastic, with seams that are less prone to leakage than the joints in the polyvinyl chloride used previously. And a cooler reduces the air temperature to less than 104°F to ensure the bioscrubber and biofilters function properly.

Sequence of biofiltration and bioscrubbing: In the original design, the air was moved from the ammonia scrubbers to the biofilters and then the bioscrubbers. The order of those last two units has been reversed. The biofilter was initially placed ahead of the bioscrubber because that unit could eliminate most of the woody odor, Woollings says. However, in that configuration, if something went wrong in the ammonia scrubber, the biofilter bacteria could be killed. Putting the bioscrubber ahead avoids that hazard, since it can eliminate much of the ammonia, and also ensures that the air entering the biofilter is moist enough that the woody material doesn’t dry out.

Moving sump pump: The bioscrubber sump pump was lowered to near the bottom of the unit.

New stack: The original stack was replaced by a freestanding 196-foot structure, with a third massive fan added to increase dilution of the air before it’s emitted at 7 million cubic feet/hour.

SCADA system: A new Supervisory, Control and Data Acquisition, or SCADA, system keeps tabs on the entire plant and automatically adjusts any part of the composting process or air handling, as required.
Combined, these upgrades have reduced the odor level atop the stack from one odor unit per 35 ft3 of emissions to 0.46 ft3 (OMOE’s standard is 1 m3 or 35.3 ft3), Woollings says. And what comes out is the woody smell from the biofilter rather than anything reeking of rotting organic matter.
The company also consulted with its neighbors – about 80 residences, a variety of retail businesses and a couple of schools in two clusters – through a Zero Odor Advisory Group, or ZOAG. The group, comprised of company and ministry officials and six neighbors, was established, with an independent facilitator after Orgaworld and the residents found they could no longer talk to each other, says Pieterson, who helped to organize the opposition soon after the odor problem began.
ZOAG is set to have a final meeting this fall, but the company will maintain its complaint hotline and continue consultations under a different format. The residents won’t stop paying attention, Pieterson adds. “We have a very knowledgeable group. We’re working together. If it smells, we’ll all be impacted. We’re not going to let it slide.”

None of the experiences in London and Welland have been lost on Toronto, York or Peel Region, a fast-growing area west of the other two municipalities and part of what’s known as the Greater Toronto Area.
Peel operates three facilities worth a combined $37 million – two for composting and a third where the material is cured – where it combines and processes kitchen scraps and yard trimmings. At the composting plants, the two types of incoming materials are combined 50-50 by weight, then put into biocells, concrete boxes that each hold about 260 metric tons of composting material. One plant uses Herfhof technology; the other uses a Christiaens system modified, with a heat exchanger. Aeration trenches on the floor of each box are covered with a layer of wood chips. Air is pumped up through the material; leachate drains into the trenches.
The worst odors come from the tipping floor, says Larry Conrad, Peel’s manager of waste operations. Once the material is in a biocell the smell can be controlled. The plant operators aim to get incoming loads into the boxes within two hours.
Peel uses Mop & Go, a floor cleaner and biological degreaser from Atlanta-based Zep Inc., to wash down the tipping floor and spray the piles of source separated organics and yard trimmings before they’re shredded and put into the biocells. It is also in the third and final year of testing a system that mists the entire tipping area with chemicals that combine with odor molecules to create a pleasant scent. The current product, also from Zep, is called Air Fair Ultra Orange Concentrate.
Air from the biocells first passes through a heat exchanger, in which the moist air cools, forms into drops and falls to the floor, carrying away water-soluble sulfur-bearing compounds. From there, the air is polished in a biofilter from Biorem Technologies Inc., of Guelph, Ontario before being released into the atmosphere. Instead of wood pieces, this system uses inorganic material (clay or aggregate) coated with a proprietary host for bacteria.
After a retention time in the biocells of 7 to 10 days, the compost from both facilities is taken to the curing facility, midway between the two plants. While the composting plants are in rural areas with few close neighbors, the curing facility has people nearby, so “we have to make sure we don’t create an odor issue for them,” says Larry Conrad, Peel’s manager of waste operations. The curing facility originally used open windrows, with front-end loaders for turning the material.
After “a lot of odor complaints,” the Peel Region installed a GORE cover system. The aerated windrows are turned every 14 days with an ALLU turner. “It’s helped tremendously,” notes Conrad, although switching from loaders to turners required smaller windrows and cut capacity by about 15 percent.
Screening of the compost is now the main odor source at the curing facility. If wind conditions are unfavorable, it’s shut down until conditions improve. Still, Conrad says, the best way to keep neighbors happy is to compost and cure correctly. “You can’t control all the odors, but you can properly manage the material to control them.” The curing facility gets a few complaints, he says, “most from the same person.”
Peel’s composting facilities are at their annual capacity of 94,000 tons. A 25-year expansion plan is to be presented to the regional council by the end of this year.


York Region was preparing to negotiate a new contract with Universal when the Welland processor shut down this year. As a result, its green bin materials are going to Orgaworld and WeCare, in Marlborough, Massachusetts, a company the Region began dealing with last year when both Ontario plants closed. “We’re not going back to Universal; I can’t see a need,” Laura McDowell says.
The regional government is planning a facility it will share with neighboring Dufferin County, which has provided a rural site far from sensitive noses. The Request for Proposals for the project, which is to process 55,000 tons of green bin materials annually and be expandable to 110,000 tons, requires zero odor emissions, McDowell explains. Among the “strict technical aspects” are a double airlock system, negative pressure and “a lot of air emissions controls.”
York has taken lessons from the troubles at Universal, mainly that a remote site and purpose-built plant are essential. The Welland factory had “large gaps in the roof and elsewhere” and is subject to corrosion, both of which make it difficult to contain odor-laden air, she says. “It’s also important to work with the community so you are a good neighbor and have an operational team to respond quickly to issues at the plant.”
Toronto operates one anaerobic digester for part of its green bin materials at the Dufferin Waste Management Facility and is building a second digester at its Disco Waste Management Facility. The current 44,000 tons/year Dufferin anaerobic digester incorporates a biofilter that forces the odorous air though a field of woody material covered with soil. While it works well, it takes up too much space, according to officials. It is being replaced by an indoor system, a 3,000-square-foot Biorem unit, with six feet of inorganic material (clay or aggregate coated with a proprietary host for the bacteria). This change will open up room for a second digester tank – part of a major upgrade – that will increase Dufferin’s annual capacity to 55,000 tons, says Brian Van Opstal, a manager with Toronto’s Solid Waste Management Services. The new biofilter will contain two cells that can be taken off-line separately for maintenance. A humidifier will moisten the air before it enters the filter.
A similar unit is being installed at the $77.5 million, 83,000 tons/year Disco anaerobic digester facility, scheduled to open next July. The plant will incorporate a biofilter that’s similar to the new one at Dufferin but will cover nearly 5,400 square feet and be divided into six independent cells. The vendor wasn’t confirmed at press time.
Both the Dufferin and Disco digester facilities will have separate ventilation for the overall building and the process areas, allowing every operation except the tipping floor to be fully enclosed. Both will also be under negative pressure, and have 131-foot-tall stacks. Although the air “isn’t very pleasant” on the tipping floor, it’s “really quite fine in the processing area,” Van Opstal says.
All the operators hope their neighbors will decide that things are “really quite fine” for them, too.

Peter Gorrie is a Contributing Editor to BioCycle.
p. 54 sidebar
Universal Composting Update

NEXT steps for the Universal Resource Recovery, Inc. facility in Welland, Ontario are unclear. After restarting in November 2010, the facility closed again this past spring. Officials for both the city and the company would not comment for this article. Ontario Ministry of the Environment spokesperson Kate Jordan offered the following explanation in an email message:
The improvements “were initially effective. But as the company increased its production in March of this year we began to receive odor complaints again. Before it could be determined if … additional Ministry action was needed, the company voluntarily stopped receiving composting materials, removed all materials being processed at the site and ceased operations.”
“The company had applied for approval for additional odor control equipment, including installing fans in the stacks, which was approved, but the equipment has yet to be installed. Before (it) can restart operations, it needs to implement the additional measures.”

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