In many communities, residents are asked to separate food waste into bins for municipal composting.
In theory, composting can create a circular economy of food: it is grown, it is eaten, the scraps are thrown out and turned into fertilizer sold to farmers, who grow more food. But most consumers are unaware of what the composting process actually involves.
There are two kinds of municipal composting: aerobic (with oxygen) and anaerobic (without oxygen) digestion. In both cases, micro-organisms break down biodegradable material into compost that can later be used as fertilizer.
Aerobic digestion, also known as traditional composting, is the more low-tech, and is done in jurisdictions such as Metro Vancouver and Nova Scotia.
In its simplest form, traditional composting requires making a pile of wet organic matter 一 made up of yard waste, food scraps and occasionally sewage 一 and waiting several months for the waste to break down into humus (which is compost that’s mainly used for conditioning soil). This is something you can do in your backyard.
With anaerobic digestion, food waste is put in an oxygen-free environment, instead of being piled up and left in the open air.
Dianne Saxe, the former environmental commissioner of Ontario who now leads the consultancy Saxe Facts, said that traditional composting doesn’t collect the methane released during the process, which can be used as a source of energy.
As a result, the methane — a potent greenhouse gas — is released into the atmosphere, “which is what happens in the landfill as well,” Saxe said.
Anaerobic digestion is the less common variety of composting in Canada. According to a survey of Ontario municipalities, only about 30 per cent of responding municipalities in the province use it. But they include the biggest city in the country: Toronto.
The facility on Disco Road collects up to 75 per cent of Toronto’s organic waste and converts it into something renewable. The air inside the facility is thick and heavy. The smell of rotting garbage is so strong you can feel it permeating your skin and sticking to your clothes.
During a recent visit, Derek Sawyer, supervisor of organic processing in Toronto, pointed to a towering pile of compost bin waste, all stuffed into bags of various colours and sizes.
The waste, all residential, sat wrapped in layers of plastic before it was piled onto conveyor belts by a large, green excavator, where it will be taken to a large, loud machine called the hydro pulper.
The hydro pulper is a large, whirring machine that uses water to remove non-compostable materials, known as contaminants. Sawyer said contaminants can comprise up to 18 per cent of every batch.
Those contaminants include items that residents are asked to put in the green bin, and that many believe to be compostable — such as disposable diapers, biodegradable bags and sanitary napkins.
The light materials — plastic bags, diapers, compostable forks and straws — float to the top of the pulper, where they are skimmed away by a giant claw machine.
The heavier contaminants — glass, metal, dirt and shells — fall to the bottom, where they are ground up and filtered out before all being shipped to the landfill. Even items that could be recycled, such as metal and glass, end up as garbage.
Recyclables head to dump
The organic waste becomes a sludge, ground up and sopping wet, before being squeezed out and brought to large metal bins called anaerobic digesters. In the digesters, micro-organisms, in the absence of oxygen, break down the material to produce the pre-compost stage — called digester solids — and release biogas, a mix of methane and carbon dioxide.
The digester solids are then sent to a third-party company — in this case, All Treat Farms, about two hours west of Toronto — to be heated, aerated and turned into usable compost.
The biogas is filtered out with big fans, and used to mix and heat the anaerobic digesters, as well as burned to keep the facility warm during the winter months. Some of it is also used to heat the digester tanks in the facility.
Disco Road currently burns the remaining gas. In the future, the City of Toronto hopes to sell it as a more renewable and sustainable type of fuel used for heating and vehicles.
All liquids — liquid digestate, rainwater and all other water used on-site — is collected and purified so that it can supply most of the facility’s water needs, mainly for drinking and to clean instruments.
Aerobic digestion creates nutrient-rich fertilizer without diverting partially decomposed waste to a different facility.
It can still be a complicated, multi-step process, where staff measure how much water, air, carbon and nitrogen-rich materials go into the pile.
Each ingredient does its part in the decomposition process:
Oxygen oxidizes the carbon, which sparks the process.
Carbon produces the energy and heat needed.
Nitrogen encourages the growth and reproduction of micro-organisms.
Water maintains the microbes needed to decompose.
The process is started by shredding yard waste, adding water and regularly stirring or turning the pile. Bacteria and fungi that need oxygen to survive manage the decomposition by converting the materials not only into compost, but also into heat, methane, carbon dioxide and ammonium.
This method can be shortened from months into just two to three weeks.
With both aerobic and anaerobic digestion, the final product — compost — is sold to farms, plant nurseries, grocery stores and garden centres.
But the majority of Canadian organic waste still ends up in the landfill. Ontario alone throws out two million tonnes a year, the Ontario government reports.
According to Saxe, looking at organic waste as a resource can help raise awareness and build an industry based on the principles of the circular economy.