Waste and Carbon Emissions

Waste - our most underexploited resource

If I were to choose a single environmental issue that I feel has been able to most successfully capture the public's attention and concern, I would choose waste management. While not without it's controversial elements, most people put their political views aside and partake in improving the management of their household (as well as non-residential) waste. People now invest time and effort to separate their waste streams, and with single-stream recycling, municipalities have facilitated the efforts of their residents. I'm sure that you've heard waste management used as the go-to response for people who are trying to demonstrate their "concerned citizen" bona fides: "Hey, I recycle!" And we should applaud people who make this effort, though it's just a first step in mitigating our environmental impacts.

The climate impact of waste is one that is not only important, but also one that is more readily influenced by cities. As an approximation, landfills contribute roughly 1-5% of Canadian cities' direct emissions. However, the decisions to take action to reduce these emissions are more centralized than, for example, retrofitting buildings. A local government can decide that it wants to divert food scraps from landfils and provide residents with the means to do so. This can lead to a substantial long-term reduction in carbon emissions from waste. My doctoral supervisor Chris Kennedy and I thought it would be worthwhile investigating the Greater Toronto Area's carbon emissions from household waste, examining the entire assortment of treatment methods used in the region in 2005. This was a point in time when the City of Toronto had just started treating household organic waste in large centralized digesters, so there was 5 principal treatment approaches being used: landfilling, incineration, composting, recycling, and anaerobic digestion (AD). The total emissions we calculated from these activities is presented in the pie chart below in kilotonnes (kt) of CO2e.

You might notice that landfills take up the bulk of 509 kt of CO2e emissions; that's because historically most waste has been treated through this means (I'll explain the historically part in a moment). Even though 40% of the GTA's waste was diverted from landfill in 2005 (this includes incinerated waste), households in the GTA still emitted a large amount - that's roughly 90 kg of CO2e per person, with just household waste (non-residential waste would add much more). You might have also noticed that recycling doesn't show up on the figure. It just so happens that recycling prevents so much energy from being released through the replacement of virgin materials that its emissions are a negative figure (the USEPA WARM model suggests the GTA's recycling in 2005 avoided the emissioons of 1,400 kt CO2e). But lets put aside these benefits of recycling for a minute. We still have a problem with greenhouse gas emissions from waste. So where are all these emissions coming from? Well, lets look at each one individually, and put aside emissions from collection and transport to treatment facilities:

  • Landfills - Methane released due to organic matter in buried waste decomposing without the presence of oxygen
  • Composting - Methane and nitrous oxide released from compost facilities that aren't able to completely aerate their compost piles
  • Anaerobic digestion - Methane leaking out of anaerocibic digestion facilities
  • Waste-to-Energy - Fossil carbon (in plastics) oxidized, releasing otherwise "stable" carbon
  • Recycling - Transportation away from sorting facilities to the material supply chain, as well as the disposal of materials unfit for recycling
I mentioned earlier that landfills have an impact because they have historically been used for storing waste - most relevant, storing organic waste. When you throw food scraps of office paper into the landfill, it takes years to break down. But after being buried for about a couple of weeks, the process eats up the limited oxygen available. That doesn't stop it though, as a different set of microbes get involved and these produce methane (which, by the way, is 34 times more powerful in its contribution to climate change than CO2). They work away for quite a while (depending upon the moisture and temperature in your landfill), so waste deposited years ago keeps on producing methane, regardless of how good your organics diversion is this year! So getting back to the list above, all of these alternatives have a climate impact to them. Even backyard composting has a carbon impact, with some studies showing that oxygen-free zones develop within your unturned food/yard scraps, releasing methane. Landfills and AD facilities capture much of this methane and generate electricity and heat, which has the potential to offset electricity generation in the grid or natural gas heating. Traditional waste-to-energy (i.e., incineration) can also generate electricity and heat, but releases fossil carbon - as the electricity grid becomes less carbon-intensive, electricity from these incinerators can become more polluting from a carbon perspective. Even recycling has a climate impact (albiet a lower one when compared to using virgin materials). Much of the recovered materials are unfit to be recycled and end up in landfills. As well, materials are often not processed into new goods locally, so they must be transported further afield (sometimes internationally).

From a carbon perspective, there are many more difficult questions that need answering. Some considerations with respect to greenhouse gas mitigation from waste include:

  • For our existing landfills, should we be trying to reclaim valuable resources that are buried there? What cost/benefit considerations should be made in justifying the capture of methane emissions?
  • What do we do with paper waste when it are no longer suitable for recycling?
  • Which diversion programs are most appropriate food waste - composting, digestion?
  • How do waste-to-energy facilites perform relative to other options, once we consider the co-benefits they provide?

These are just a few of the questions that might come to mind when considering the climate impact of residential waste. But we can take some comfort that we divert a fair amount of our residential waste from landfill, and this continues to improve in most jurisdictions. Waste from our workplaces and the places we go to for entertainment or to purchase our lunches are a different story. Nationally, non-residential waste is roughly 1.7 times (by weight) what is produced by households and 80% of that still goes to landfills (residences did better with around 67% of waste that had been distined for the dump - Stats Can, 2012). All of this landfilled waste represents an opportunity to do better - to capture valuable materials (such as aluminum or steel), to return food waste to the agricultural soil, or at very least, to capture the energy through a number of conversion options available. Waste remains low-hanging fruit not only for carbon emission reductions, but for sustainability in general.

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