June 22, 2009

Rubber chips and crumbs are cheaper than most forms of aggregate and their chemical properties aid in treating landfill leachate.

Green Technology

Tires could play role in cleaner landfills

Quebec already using material in treatment of leachate

MARY BAXTER

correspondent

A Goderich engineer’s vision for old tires could gain traction as Ontario’s tire industry powers up its recycling efforts this fall.

Bibek Mondal, a project manager in environmental engineering with B. M. Ross and Associates Ltd., says tire-derived aggregate could be used to treat clear leachate before it is released from landfill sites.

Mondal says landfill sites in Ontario, do a good job in collecting leachate. But once collected, “it’s being discharged into the (sanitary) sewer system” without pretreatment. And that means greater chances of organic materials, ammonia, nitrates and nitrites leaking into a sewer system.

(Leachate at landfills is normally partially treated through a sedimentation process to remove solids before it is released).

While pretreating clear leachate before it enters a sewer system is not mandatory or even recommended in Ontario, Mondal predicts such stricter controls could eventually come into effect as interest in protecting water resources grows.

“If we can go for this kind of treatment as a pretreatment before you are getting into the sewer system, it can help definitely to get rid of the toxicity.”

Rubber chips and crumbs can be cheaper than most aggregates, he says. The tire’s properties make it a strong candidate for leachate treatment methods such as trickle filters.

Compared to aggregates of a similar size, tire-derived aggregate has a greater surface area to house the biological materials involved in the aerobic cleaning process. The aggregate also has greater permeability and the ability to be compressed.

With periodic cleaning, the material could be used effectively for from six to nine months. He says the tire’s carbon which is an inorganic component, either gets stuck on the tire surface or goes down through trickled water, and could be removed through secondary clarification process. With the carbon removed, the tires could be taken to a landfill or processed for yet another use. Either way, a tire won’t pollute “the same way it pollutes now.”

Mondal says the idea is being put to practice in Quebec landfills where it’s used at an earlier stage of leachate treatment. In other parts of North America, wood chips have been used in small-scale industry to pre-treat clear leachate before it enters sewer systems, although he says that material is costlier.

Mondal researched the concept and designed a system while doing post-graduate studies at Ryerson University in Toronto. The university is continuing to study what size of crumb provides the optimum performance for a trickling filter. He says the idea is derived from U.S. research that explored using the material in a filtering process for sludge.

He estimates that adding such filters to small-scale landfills would use one to five tonnes of used tires.

Glenn Maidment, president of the Rubber Association of Canada and chairman of the Ontario Tire Stewardship program, says using tire-derived aggregate is capturing the interest of other provinces, such as Alberta, Manitoba, New Brunswick and Nova Scotia.

The aggregate was used in a recent highway project in New Brunswick. “They used about 1.6 million tires, if I’m not mistaken, because they needed a lightweight fill and it was also going up against an embankment,” he says.

The material was chosen because it offered good drainage and didn’t create the same type of pressure against a retaining wall that sand or soil might. Tire shred’s lack of weight and ability to be compacted are other handy attributes, he adds.

Maidment says the Ontario Tire Stewardship program, which takes effect in September, may provide incentive for using tire-derived aggregate in Ontario for uses such as that which Mondal proposes. Ontario Tire Stewardship, a not-for-profit industry organization.

Under the program, processors will no longer be able to charge tip fees for tires at their gates. Instead, the program will offer a financial incentive of about $55 per tonne for processing tires into new products.

Ontario residents annually discard about 12 million tires.

“Our (the program’s) mandate and vision is we will manage all of the scrap tires here in the province,” says Maidment.

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