by Claire Eamer
When we urban-dwellers toss stuff into the garbage bin or the compost container, we tend to forget about it. It’s gone – out of our lives and out of our minds.
Except, it isn’t, really. Garbage, compost, and sewage (which we usually try to forget even sooner) live on, changing and decomposing in landfills, municipal composters, and sewage lagoons. And all that decomposing results in greenhouse gases. Lots of them.
Methane, one of the major products of decomposition, is a particularly potent greenhouse gas. It’s also a potential fuel – a nice, clean fuel, in fact. So, is there anything useful we could do with it, rather than releasing it into the atmosphere?
That question took Shannon Mallory to Sweden a few years ago, to study Swedish approaches to using biogas, methane-based fuel produced from various kinds of waste. While looking for answers, Mallory also earned a Master’s degree from a Swedish university.
Sweden, she says, is a world leader in using biogas for vehicle fuel. It’s also a northern country with a sparse population, not unlike most of Canada. She was interested in whether the Swedish approach could transfer to a small, isolated, cold-climate city like Whitehorse.
Climate was one of her questions, Mallory says. Is it simply too cold in Whitehorse to generate biogas efficiently? Size is another issue. Do we generate enough waste? After all, we have no major biowaste-producing industry nearby and our agriculture is small-scale. And how could we use the biogas, assuming we could produce enough to be useful?
Temperature, she discovered, is not a major problem. Industrial-scale biogas production takes place indoors, in large, insulated silos. The chemical process that breaks down the waste generates heat itself, and the resulting biogas can be used as fuel to heat it further, so once you get the facility built and running, it supplies its own warmth.
The chemical process is called anaerobic digestion. Essentially, bacteria munch on the wastes, digesting them and expelling carbon dioxide and methane. The bacteria don’t use oxygen, so the whole process can happen in an enclosed container, making it easy to capture the expelled gases.
Of course, it’s not as simple as pouring all the waste into one big silo and waiting for things to happen. First the waste has to be sorted into organic and non-organic, sifted to remove harmful things, such as plastics, and pulped so that the particle size is small enough to let the bacteria work efficiently. Then it’s turned into a slurry, a mixture that’s about five per cent solids and 95 per cent liquid. The slurry is generally pasteurized to remove harmful bacteria before it’s fed into the processing silo.
Inside the silo, the working bacteria are added to the slurry, much as you’d add sourdough starter to your bread dough. The whole mess is churned by a giant mechanical mixer that prevents the solids from settling to the bottom where the bacteria can’t get at them effectively. Gradually, the bacteria eat away at the waste slurry, producing gas which rises to the top of the silo and is pumped off.
Where do you get the wastes to feed into the process? There are plenty of possibilities: sewage, food wastes, agricultural wastes, and by-products of some industrial processes.
“You design it for what you have available,” says Mallory. One of the three small Swedish cities she studied had an abattoir next door, and abattoir wastes were an important component of its biogas program. Whitehorse doesn’t have that kind of resource, but it does have a municipal compost collection service, and that’s a big advantage, Mallory says. It means that biowastes are already sorted by the homeowner before they even reach the collection service.
In addition, there are sources of biowaste – such as restaurants, grocery stores, and apartment blocks – that aren’t yet part of the municipal compost system. And there’s sewage. Like any community, Whitehorse has a steady supply of sewage, and it can be treated for use in a biogas system.
Developing biogas production in the Yukon would require building processing silos, pre-treatment of the biowaste and transportation to the processor, and construction of infrastructure to distribute biogas or the heat it produces, or to process it further for use as vehicle fuel. Mallory says the Swedish government has invested heavily in the infrastructure required to generate and use biogas.
Turning our biowaste into fuel has advantages beyond fuel. Mallory estimates that the amount of biogas Whitehorse could generate would be the equivalent of heating about 140 houses year-round. That could take some strain off existing energy sources, as well as prolonging the life of the city’s landfill, composting, and sewage treatment facilities, and reducing its greenhouse gas emissions. In addition, a by-product of biogas processing is a dry residue that makes excellent fertilizer for agriculture or reclamation, replacing material currently trucked to the territory.
For more information about biogas, go to this Ontario government site: www.omafra.gov.on.ca/english/engineer/biogas/
This column is co-ordinated by the Northern Research Institute at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.