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Montreal will digest its garbage – why not Vancouver?

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Spreading garbage at the Vancouver Landfill

There was a small news item in today’s Montreal Gazette: composting to take place across the island of Montreal.  Nice news, sure, but pretty oh-hum, as it were; who doesn’t like composting?

But the real important news are to be found in Montreal’s La Presse: we are talking about 4 large new plants to be built by 2015 to the tune of $250 million, two plants for composting, and – here’s the key part – two for biodigestion.

In this project, green waste (that’s all food residue, plus garden waste, leaf collection, etc) will be collected separately and digested anaerobically.  This produces biogas (about 30% carbon dioxide, the rest mostly methane), which can then be burned to produce energy.  In the Montreal project, the biogas will be filtered and then delivered to the metropolitan natural gas system, replacing the need to purchase fossil fuel.  And we’re not talking about puny amounts: between four and five million cubic metres per year.

After digestion – which is really nothing other than controlled rotting in a sealed vessel – the residue is to be composted.  This means a new source of organic fertilizer and soil amendment.  The compost is expected to be free of food-borne pathogens such as listeria, because the digestion occurs at a high temperature.

This is an excellent project for a number of reasons.  Incinerating garbage works, but garbage is not the best of fuel, and the potential for air pollution is high, which requires fairly sophisticated and costly air pollution control systems.  The Montreal system captures the energy of that portion of the waste which has the best value as fuel and is non-toxic (it was food, remember?).

Further, the left over mass (maybe half of the total before digestion) makes a nice, stable compost.  This retains the fertilizer elements of the waste, which is non-negligable benefit, considering that nutrients like phosphorus are expensive to mine and may well run out in this century – so this system has an important role to play towards future food security.  And the compost itself is made of stable humus compounds, and this reduces the amount of greenhouse gases released as conpared to, say, incineration.

In comparison, landfilling garbage is a waste, in the literal sense; in a landfill, biogas is also generated, but at a much slower rate, and not all of it is captured.  As a result, methane gas is released, and this a greenhouse gas far more potent than the carbon dioxide generated after combustion (whether in an incinerator or following its use as biogas).  To say nothing of the small uncontrolled fires that periodically occur in landfills (and the Vancouver Landfill is no exception) and the leachate problems that landfills generate.

In the Montreal scheme, the gas generated is piped directly into the natural gas grid.  This is a good system, but a great opportunity is missed: district heating.  District heating is common in Europe, and can easily be retrofitted in a dense urban area such as Montreal.  In this system, the fuel source (be it garbage or biogas) is used to generate electricity locally; this also produces low-grade heat (steam or hot water), which is then sent through pipes to heat a whole neighbourhood.  Density need not be excessive; the maion campus of UBC, for instance, is on district heating (though it does not generate its own power).  In BC, most pulp mills now make use of such a system, burning fuel to generate both their own electricity and their process heat (an approach called co-generation; it saves the mills huge amounts of money and reduces their carbon footprint considerably).  This is a missed opportunity for Montreal, for now; the beauty of the system, though, is that district heating could easily be retrofitted in the future.

Metro Vancouver seems mired mired in the past when it comes to systems like this.  We have a handful of municipal politicians who are asking probing questions, but it seems Metro has decided on incineration, period.  What a shame.  Some thoughts are given to composting and green waste collection, but biogas production does not enter into consideration, and that is the missing piece of the puzzle: it brings revenue and energy production to the whole system.  Politicians are leery of going full-compost because the system is costly.  Good on them, but this is a way out right under their noses.

In Metro, compostable waste makes up over 40% of the residential garbage. Add another 16% that is paper (which should be recycled, but isn’t), and  you have a considerable amount that could be diverted to a Montreal type scheme.  Using the 2008 numbers for the residential sector, paper and green waste represent over 440, ooo tonnes.  Assuming that a quarter of that mass can be turned into methane, that represents a heating value of more than four and a half million million kilojoules (which is about as many BTUs, or 1330 GWh).  If half of this value were turned into electrical power, this represents 150 megawatts.  That’s about one sixth of the electricity that is to be produced by the proposed Site-C dam on the Peace. And that’s produced locally, without the line losses.  Not bad!



I spoke to Sarah, a friend at Metro, who set me straight on a couple of things.  Green waste (including food waste) is already collected for composting in a few Metro municipalities (Coquitlam, for instance).  She mentioned that the scheme is quite popular, with a larger number of households participating than originally anticipated.  This is great!  But it also reveals a problem with our governing structure.  Individual municipalities pursue these initiatives; Metro can only suggest and encourage.  So while collecting and composting is already happening in some places, other municipalities are foot-dragging.  This is an even bigger problem if a Montreal-style digestion scheme were to be implemented; for economies of scale to work, centralized facilities are probably essential, but centralized planning is an absolute must.  We’ll get there, maybe, but that is a huge political endeavour.  People have to start loving Metro Vancouver – a pretty tall order given the petty disputes that our municipal politicians promote.



Written by enviropaul

November 2, 2011 at 12:10 pm

Posted in Uncategorized

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