A public-private partnership creates a biosolids processing facility that yields a high-quality product for application to Ontario farmland.
Just 10 miles from Niagara Falls, a biosolids treatment plant has managed to take waste and turn it — all of it — into something useful.
A private company operates the Niagara Biosolids Processing Facility in Thorold, Ontario, under contract with the regional government. Eight years after it began, the operation has exceeded its expected output and the operators are looking at more ways to use its product, says Geoff Boyd, general manager - organics for Walker Environmental Group, the plant’s owner.
In spring 2014 the Water Environment Association of Ontario recognized the operation with an Exemplary Biosolids Management Award.
And it all started, Boyd says, when the region’s communities realized they needed an alternative to applying all to farmland in liquid form. “If they didn’t have us as an outlet, they could potentially get themselves into a serious compliance situation,” Boyd says. Although they had “plenty of storage, sometimes it isn’t enough.”
A dozen communities
Ontario’s Niagara Region is a regional municipality, a form of government that takes the place of counties in some parts of Canada. The 715-square-mile region straddles the isthmus between lakes Erie and Ontario. It is bordered on the east by the Niagara River (also the boundary between Canada and the United States at that point). West of the region is the City of Hamilton and Haldimand County.
The region (population 430,000) encompasses five cities, five towns and two townships. It was formed in 1970 in a series of government reforms to consolidate municipal services, one of which is managing the biosolids from municipal wastewater treatment plants.
A little more than a decade ago the Niagara Region undertook a biosolids master planning project. “At the time, 100 percent of biosolids generated in the region were liquid land-applied,” Boyd says. “That can be affected greatly by weather and land availability.” Long winters and wet springs narrowed the opportunities.
Knowing it was time to diversify the use of biosolids, the regional government issued a request for proposals in 2004 for a centralized processing facility. The winning bidder was a 50-50 joint venture between Walker Environmental Group (a division of family-owned Walker Industries) and N-Viro Systems Canada.
The Walker firm came with a background operating landfills and limestone quarries and a product line that includes crushed stone and aggregates, road asphalt and waterproofing emulsions for building products and wallboard. N-Viro provided an alkaline-stabilization process that yields a dried product that in the United States would be considered Class A. The biosolids facility in Thorold became fully operational in 2007.
Since then Walker has acquired N-Viro, making it a wholly owned subsidiary of Walker Environmental. N-Viro also operates plants in Sarnia and Leamington, both about three hours west of the Thorold plant. Additional plants are in Halifax, Nova Scotia, and in Banff National Park in Alberta. A plant in Sudbury will open in 2015.
A composting operation on the Thorold site also takes in Niagara Region food waste and lawn and yard waste.
In addition to Boyd, key personnel involved in the Thorold operation include Walker Environmental Group executives Mike Watt, executive vice president; Robert Crane, biosolids business development manager; and Mike Melinko, Niagara Biosolids plant supervisor. The team also includes Dan Grabell, Kevin White and Jamie Gale, operators, and John Vanderlee, equipment supervisor.
The Thorold biosolids facility is unusual in being operated by a private company rather than by the Niagara Region municipality, Boyd says. The company made the case to municipal officials that it could reduce the risk of liability and bring solid marketing experience. “They felt that we could also operate the plant more cost-effectively than they could,” Boyd says.
The facility takes dewatered biosolids from wastewater treatment plants in Niagara Region and from the City of Toronto. Most of the liquid biosolids are trucked to a central dewatering site owned and operated by the region.
All the region’s treatment plants use anaerobic digestion. Before dewatering, the biosolids are about 3 percent solids. Centrifuges dewater it to about 30 percent solids. The dewatered material is then trucked to the Walker plant, which receives 100 to 165 tons every weekday.
At the Thorold facility, the dewatered biosolids are dumped into two live-bottom bins 15 feet below ground level. Each bin holds 45 tons. Screw augers move the material to a belt conveyer (Serpentix) with a sectional ribbed design that allows for runs that turn extreme corners and go up steep inclines without product falling off.
The conveyor carries material about 30 feet up to the plant’s mixer (Cemen Tech CSP 30), which can process up to 27 wet tons per hour but typically handles about 11 tons per hour.
The kiln dust is transported from the cement plant in trucks with pneumatic blowers used to fill storage silos. During the mixing process, a screw conveyer carries the dust from the storage silos into the plant and to a hopper on the mixer; a second small screw conveyer moves material from the hopper to the mixing box. In the mixing box, a 12-foot-long toothed auger combines the biosolids with highly alkaline (pH13) cement kiln dust.
Kiln dust treatment
The kiln dust, primarily calcium oxide, is added at a ratio of about 30 percent kiln dust to 70 percent wet biosolids. The dust is highly reactive and the resulting alkaline admixture generates heat. The process also raises the pH from neutral pH to about 12.
The kiln dust is a byproduct of a cement plant about three hours away. It previously was landfilled, but N-Viro saw its value and began reclaiming it. Besides 35 percent calcium, it contains about 8 percent potash, a valuable agricultural nutrient.
The biosolids/kiln dust mixture is about 45-50 percent solids, says Boyd. It looks granular and earthy, much as it does when processing is complete. It is discharged onto another conveyer belt that carries it nearly 25 feet and feeds it into a model CSD-6000 direct-fired rotary dryer system (Uzelac Industries).
The dryer pulls about 15,000 cfm of air through the drying chamber and evaporates about 10 tons of water an hour. A tumbling process breaks down clumps of material, reducing particles to about the size of a grain of sand. The retention time in the dryer varies with the solids content of incoming material. The biosolids characteristics can vary with the source. For instance, Toronto biosolids are typically “a lot more pasty” than material from other plants, Boyd says.
What goes into the dryer is “typically about 45 to 50 percent solids,” he says. “After about 10 minutes in the dryer, it comes out at about 58 percent.”
Clearing the air
Dried material is light enough to pass through the center of the dryer drum and through the unit’s cyclone separator, which sends it through an airlock and onto a screw conveyer, which deposits it in one of four 88-ton-capacity concrete cells. Air and fine particulates are drawn off into a baghouse.
The baghouse removes particulate, leaving air high in ammonia. A scrubber (Verantis) then uses a sulfuric acid process to remove the ammonia, producing ammonium sulfate that is collected and sold as liquid fertilizer for its high nitrogen and sulfur content.
The air is then forced through a biofilter (Ambio Biofiltration) that uses shredded wood media for odor removal. The air comes out smelling like damp wood.
Taking the cure
Back in the concrete bunkers the solids cure, typically for 12 to 16 hours. Samples are collected hourly to check the temperature and pH of the batch to make sure pathogen-reduction requirements are met. Solids content is also measured. “If it’s too dry or too wet, we make adjustments to the dryer or mixer,” says Boyd. “If the pH is too high or too low, we make adjustments to the alkaline dosing.”
The facility takes in and treats biosolids during daytime hours; curing takes place overnight and into the next day. The plant typically does not operate on weekends. During the cure the solids dry further. “We’re looking for our final product to have a percent total solids of 60 to 62,” says Boyd. “Anything greater than 64 percent tends to make it a little too dusty; between 60 and 64 percent is ideal for field application.”
To ensure against hazardous substances, municipalities are required to take biweekly samples of their biosolids, checking for all restricted heavy metals and for pathogens. Pretreatment regulations keep heavy metals out and anaerobic digestion keeps the pathogen count low to begin with, Boyd observes.
“Any material coming to us has to meet the guidelines for liquid land application,” he says. “It’s already approved to be spread on land as it is, even before it goes through our process.”
Biosolids safety is regulated under the country’s Fertilizers Act by the Canadian Food Inspection Agency; regulators conduct random spot checks to verify that the material meets or exceeds a minimum guaranteed nutrient level and that it is safe for use.
Walker sells the biosolids straight from its storage building. “It goes out the same way it comes in — in large dump trailers,” says Boyd. “We load it into the customers’ trucks with a front-end loader and off they go.”
The direct customers are large farm fertilizer distributors who sell the material and the direct application service to farmers in Ontario, most of them two hours or farther west of the plant outside the Niagara Region where most of the province’s large cash-crop farms are found.
Total production of the product, branded N-Rich, amounts to about 110 tons per day, or about 33,000 tons per year. Walker has been fetching about $10 (Canadian) per ton. The material has required very little marketing in Ontario, Boyd says.
“We could probably sell three to four times what we’re making,” Boyd says. “We turn people away all the time. The plant was built on the basis that we would do 50 percent of the region’s biosolids. In the past four or five years we’ve been doing closer to 65 percent.”
A closed loop
For now, the operation’s future looks bright. “Our existing customers could take quite a bit more than we’re producing so far,” Boyd says.
At the same time, in anticipation of the Sudbury plant’s opening, the company is looking for more uses for the product, such as mine reclamation. The company is working with a contractor, a mining company and university researchers to apply materials to areas where mine tailings have been deposited. “They will plant vegetation that can be harvested and used as biofuel,” Boyd says. A similar approach is being considered to test usage for reforestation.
Boyd points out that the Thorold operation has achieved the environmental Holy Grail: a closed-loop system. “We’re bringing in biosolids, which are typically a waste to many municipalities, and the alkaline kiln dust, and the plant generates absolutely no waste at all,” he says. “There’s no residual left over — everything that comes in is turned into product.”