What the City of Edmonton’s Waste Management Services wizards do with that banana peel you threw in the garbage last night is almost magic.
In their drive to divert waste from landfills, for 15 years now, they’ve been separating compostable organics from your garbage and not only turning it into saleable, high-demand fertilizer, but also making money – get this! – from the gas NOT produced along the way!
So let’s start at the beginning, when garbage collectors drive into a large building at the huge Edmonton Waste Management Centre and dump loads-of-everything onto the concrete floor.
“Conveyors take the garbage to a sorting area where staff and machines remove virtually all other material except organics,” says Allan Yee, the city’s senior engineer in charge of organics processing.
The organics travel through rotating drums that rip open bags. While the drums nudge the organics along toward the composting facility, different sizes of organic matter are sorted as they drop through different-sized holes.
In another huge, indoor room at the composting plant called the aeration hall, after the addition of partially de-watered biosolids piped from the Gold Bar Wastewater Treatment Plant, the organic material is dumped on a concrete floor in one of three large bays.
“If the material is too dry, we add water. If it’s too wet, we add wood chips to absorb the moisture,” says Allan.
Large wheeled machines continuously mix 27,000 metric tonnes of the piled material in the hall. Air is sucked through it from below to speed the decomposition process.
After two to three weeks in the aeration hall, it’s conveyed to another area of the plant where further size screening happens to remove larger bits, then it’s hauled to an 11-hectare cure site and piled in three-meter high piles.
“We mechanically turn it over at the cure site,” says Allan. “It takes between three and six months to fully ‘cook’ and cure. It’s screened yet one more time before it’s sold as high-quality soil conditioner to farmers, industrial/commercial users and gardening residents.”
The heat produced in the curing process pasteurizes the material, killing pathogens to create a safe product.
Each year, Waste Management Services processes the equivalent of about 180,000 metric tonnes of organic waste that would otherwise be destined for landfill. At a rough disposal cost of $65 per tonne, composting organics avoids the need to spend $11,700,000 annually in landfill costs, and produces something like $500,000 in bulk and retail product revenue.
“And here’s the part that still amazes me,” says Allan.
“Carbon dioxide is produced in the composting process, but if we landfilled the waste, it would produce methane, which has 25 times the global warming potential of carbon dioxide.
“That allows us to sell greenhouse gas offsets under the Alberta Offset System, for which we receive over $1 million a year, twice what the compost product brings in.
The City’s compost is available under the Second Nature brand at many gardening centres and at Eco Stations.
Edmonton operates one of the only municipal composting systems that doesn’t require citizens to separate organics from the rest of their waste.