Montrealers are using compost bags that contaminate organic waste, landfill company says

The bags most Montrealers use to line their compost bins are actually making it more difficult to compost what they contain, according to the director of the landfill that handles most of the city's organic waste.

Many of Montreal's table scraps are sent to Dépôt Rive-Nord, a site about 80 kilometres northeast of the city.

Its director, Gilles Denis, said the biodegradable bags made of material similar to plastic must be removed from the compost pile as early as the day of their arrival on site. They are then put in the garbage pile, and not composted. If they aren't removed from the organic waste, they will contaminate the compost later in the process, he said. 

If left in the compost pile, pieces of those bags are shredded by the machine that turns the compost, and those small pieces of bag have an impact on the quality of the compost, according to organic waste expert Vincent Beaudoin.

City recommends paper bags, or no bags

In a statement, the city said it "recommends limiting the use of compostable bags, by discarding food waste directly in the bins, or by opting for its disposal in paper bags that are more readily degradable."

According to Beaudoin, people should look for the word "compostable" rather than "biodegradable" when purchasing their compost bags.

But both types of plastic-like bags are not ideal, because they decompose slower than the organic waste they contain — bags labelled "compostable" just decompose a bit faster than those labelled "biodegradable." 

Beaudoin also recommends looking for bags that have been certified by the American Society for Testing and Materials or the Biodegradable Products Institute.

According to the city's website, only bags that have been certified by the Bureau de normalisation du Québec are accepted in the compost.

But contaminating bags make their way to composting centres anyway, according to Denis. 

Better options

On top of carefully looking at the label of the bags you purchase, Beaudoin recommends using brown paper bags in your small kitchen bin.

"It's brown paper; we know it's going to compost," he said.

These bags are easy to roll up to create a handle at the top, but won't have a knot at the top, which can also cause problems in some composting facilities, Beaudoin said. 

He says using newspapers is an even cheaper option.

"A lot of people line their small bins with newspaper, or newspaper-like flyers that you get in the mail," Beaudoin said. "That works fine as well; you kind of make a doggy bag."

The city recommends using some sort of bag in home composting for "sanitary reasons," but people aren't actually required to use a bag at all.

Jean-François Parenteau, the executive committee member in charge of the environment, says he's open to looking at new ways of dealing with compost.

"With bags, people are more likely to change their habits," Parenteau said. "But maybe we could simply remove them, because we could do it another way."

In a statement, the city said it would work to communicate the merits of bag-free composting over the next few weeks.