In a mining district of northeastern Ontario, biosolids from wastewater treatment plants are being used to revegetate land that had been covered with mine tailings.

The mining reclamation is the result of a public-private partnership between the City of Greater Sudbury and N-Viro Sudbury LP, a wholly owned subsidiary of Walker Environmental Group. The partnership built a $47 million (U.S.) biosolids processing facility, completed in May 2015. It processes all thickened waste activated sludge or solids from the treatment plant in Sudbury and from 10 smaller treatment plants.

The facility uses a proprietary N-Viro advanced alkaline stabilization process to yield a product called N-Rich that can be spread over the tailings, the finely ground waste rock generated by mining. The solids help to establish grass and plants and bring back wildlife.

For about 30 years before the facility was built, the solids from the Sudbury treatment plant were simply dumped into a mine tailings pond. That practice drew complaints about odors, and changing environmental standards required the city to find an alternative.

“This practice is a big step forward — not only for protecting the environment, but also for reclaiming land,” says Akli Ben-Anteur, water and wastewater projects engineer for the city. He managed the design and construction of the city’s largest project to date and oversees the biosolids processing facility, which is operated by N-Viro under Mick Ricci-Lyddiatt, plant manager.

Variety of awards

The project won the 2013 Chuck Willis Award for Innovation and Excellence in a Municipal-Private Partnership from the Canadian Council for Public-Private Partnerships. The award cited the project for commitment to sustainability and for bringing health, environmental and economic benefits to area residents.

The city was also recognized by the Canadian Association of Municipal Administrators in 2014 for excellence and for adapting to changing environmental standards.

The Sudbury treatment facility, also known as the Kelly Lake Wastewater Treatment Plant, uses an activated sludge process. After aeration and clarification, the sludge collected at the end of the process contains about 0.5% solids. Polymer is added to thicken the material to about 3% solids. It is then pumped to the biosolids facility, where it is dewatered in centrifuges and mixed with an alkaline admixture to raise the pH. “When it dries out, it becomes an earthlike product,” Ben-Anteur says.

The alkaline component (lime or cement kiln dust) brings the pH up to 12. Then the material gets moved by conveyor belt to large trailers or bins where it sits for about 12 hours. As it rests, an exothermal reaction occurs, raising the temperature to about 140 degrees F in a process N-Viro calls pasteurization. The high pH and heat kill pathogens. “It’s almost pathogen-free; it’s a Class A biosolid,” Ben-Anteur says.

The plant produces 3,400 dry tons of biosolids per year. It processes the sludge from the Sudbury wastewater facility (42 mgd design) and from 10 other wastewater treatment plants, which are in municipalities that were amalgamated into Greater Sudbury.

Revenue producer

N-Viro sells the final product under a revenue-sharing arrangement with Sudbury. A Walker Environmental Group spokesman says about 80% of the product is used in mining reclamation and the rest in agriculture.

The use of biosolids for mine reclamation is growing in Ontario. One of the reclamations won a 2019 Top Project Award at the Environmental Leader & Energy Manager Conference in Denver in May. It went to Terrapure Environmental, an environmental service provider based in Burlington, Ontario, for its application of the biosolids at the Copper Cliff Central Tailings Area in Sudbury.

The judges liked that the project solved two problems at once, helping to rehabilitate mined land and finding a beneficial use for biosolids in winter, when regulations prevent application to agricultural land. The award noted that Terrapure Environmental had formed a partnership with Sudbury to blend leaves and yard waste with the biosolids to render the mixture nearly odor-free and to provide a better balance of nutrients.

The award announcement also mentioned that the project had covered more than 370 acres of exposed mining waste materials, and vegetative growth was evident wherever the biosolids were applied. Wildlife activity had also increased, with Canada geese and sandhill cranes nesting and white-tailed deer and black bears feeding.