An unavoidable byproduct generated during the recycling of construction and demolition (C&D) debris, C&D fines—or recovered screen materials—have created a persistent dilemma for recyclers looking to find end markets for the materials they produce.
While some applications have been identified in recent years, such as for use as alternative daily cover (ADC) at landfills, consistent markets for C&D fines have not yet been identified due to heavy contaminants found within the material.
Consisting of primarily soil, wood, concrete, gypsum and other miscellaneous material particles, fines have received increased scrutiny due to their association with hydrogen sulfide (H2S)—a colorless gas that generates toxic emissions, odors and a risk for fires even in low concentrations.
In addition to H2S, concerns over toxic compounds polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) have left recyclers stumped on how to utilize fines in a safe and environmentally friendly way.
For Canada-based Sanexen Environmental Services Inc. (Sanexen), a member of the company Logistec, this challenge posed an opportunity to apply its experience in contaminated soil and residual material management to generate a valuable product from C&D fines.
The close to 40-year-old company has historically focused on environmental remediation projects, such as water rehabilitation, site remediation, regulated materials management, risk assessment and environmental compliance audits. Overall, Sanexen has treatment more than three billion gallons of heavy contaminated water and roughly 15 million tons of contaminated soil.
“Five years ago, we identified internally that there were upcoming issues of disposing C&D fines. So, our group started working on the research of this particular waste stream, identified the characteristics of the C&D fines, and made sure that we had proper analysis and that we understood the difference between regions that will generate the fines,” says Mathieu Germain, director of strategic development at Sanexen.
CREATING END MARKETS
Given the growing percentage of C&D waste created each year, with an estimated 600 million tons generated in the U.S. in 2018, finding a way to develop new materials out of C&D fines in an economically feasible way was Sanexen’s first target.
“There’s millions of tons [of C&D fines] that are being generated in North America every year, so we evolved a solution over the last fived years to ensure that we would answer that particular need to have a large-scale solution that can be applied at an economic cost that would make sense for the operator,” says Germain.
This development transpired into the construction of the first C&D fines recovery plant of its kind in North America. Located in Montreal, Canada, the plant offers large scale processing of up to 150,000 metric tons per year, allowing for millions of tons of C&D debris to now be recycled rather than ending up in landfill.
At the facility, the reclamation process turns accepted debris into byproducts such as aggregate materials, wood residues and compost.
“Our process is a combination of mechanical sorting and biological treatment,” says Germain. “We took the knowledge that Sanexen has develop over almost 40 years now in order to ensure that we would be able to dedicate a solution that will treat the contaminants that are contained in C&D fines.”
According to Sanexen, the process begins with the coarser component of the C&D material residues being mechanically screened to obtain bituminous mix and aggregate materials for road applications. The lighter component of the stream is then directed towards added-value processing for biofuels and renewal chemicals.
As for the ultra-fine components of the C&D material residues, this is biologically treated into compost for mining sites, landfill cover materials and landscaping applications. This material can also be further transformed into additives for manufactured construction or products like foams, composites and plastics.
“The interesting part of our patent-pending solutions that we implemented is that we’re adding the flexibility of the components that enter the biological treatment in order to adapt it to the local market,” says Germain. “So, for instance, if you’re looking for compost that will be used in the northeast, we have a solution in place—namely the one that we have in Montreal—that’s able to fulfill needs throughout the year. So, whether its January or July, we’re able to answer the needs of the market.”
This model of reclaiming C&D fines presents a unique opportunity for creating end markets due to its ability to successfully remove contaminants, which can include metals and asphalt shingle residues.
“After removal of these contaminants, you remain with traces of PAHs—which can be found in asphalt shingles—and gypsum. Gypsum per se is not a contaminant, but if it goes to landfill it leads to all sorts of environmental issues because when it’s buried and interacts with water it generated H2S,” says Martin Bureau, vice president of innovation at Sanexen.
“So, what we did instead of trying to get rid of the gypsum one way or another, we decided to use bio treatments to transform it into nutrients because gypsum is essentially calcium sulfate. You need sulfur for soils, as well as calcium, so we’re transforming it and not getting rid of it, but actually taking advantage of it.”
Depending on where the C&D materials are sourced from, Bureau says bio treatment might be necessary for other contaminants varying by location.
“It depends on what ends up at the C&D facility,” he says. “On a case by case basis, sometimes we need to look at lead and arsenic as well.”
Although there have been several attempts to find value for C&D fines through screening methods over the years, Germain says Sanexen’s approach is unparalleled due to its ability to build upon the characteristics of each byproduct to give them a second life.
“Through this innovation, we’re able to generate revenues that are profitable for something that is the main issue about those residues—the gypsum. So, we’re taking advantage of the presence of gypsum to then create an added value product. If you don’t do that, and you just remove the aggregates and the wood, then you’re stuck with a very fine material and the process is not profitable. It’s actually a loss,” says Bureau.
The C&D fines recovery plant has been in operation since August of this year; however, Germain says Sanexen is already working on new versions of the plant.
“This is the first version of the plant that is fully operational and that has a given use and very cool benefits, but the next version of our plant for the manufacturing of new construction products out of these outputs that we’re creating right now is now a potential reality. It used to be just a thought, or a dream, but now that we have access to an input of material that we’re treating, we made a corporate choice that we can always improve what we’re doing,” he says.
“There’s really endless possibilities being offered now for the C&D world.”