What happens with our waste?
Out-of-sight, out-of-mind. Despite our best efforts, and maybe a few new year’s resolutions, a lot of our household waste still goes in the dumpster. From there, most ends up in landfills, some as litter. However, there are a few ways in which waste is being used more productively, like to generate electricity. Some operations use landfill gas (largely methane) to generate electricity. A more common practice is waste-to-energy (WTE) sites that incinerate trash and use the heat generated to spin turbines, much as you would in a coal-burning power plant (a diagram is shown in Figure 1). Although this process is generally cleaner than coal, it has positives and negatives that took a while to be better understood. Being able to pin-point and quantify these plusses and minuses is essential to designing WTE facilities that minimize environmental impact and to evaluating the best waste disposal method. This is just the problem that researchers from the State University of New York and University of California sought to address in their work, recently-published in Environmental Science & Technology.
Separating the Processes
By design, WTE serves two functions: electricity generation and waste management. As seen in Figure 1, a lot of steps contribute to the WTE process. All of these steps, and a few more need to be considered if you’re evaluating the entire “lifespan” of the process. This lifecycle approach is commonly used when comparing the sustainability and/or environmental impacts of products and technologies, in order to account for “hidden” costs and benefits. These can include: waste generation, tradeoffs and opportunity losses from other alternatives, the impact of producing and transporting required materials, etc. For energy technologies, the lifecycle approach is quantified and compared using the life cycle climate change impact (LCCCI), which largely focuses on greenhouse gas emissions.
In order to accurately determine the LCCCI of WTE relative to other electricity-generating technologies, the research team led by Alyssa Pfadt-Trilling sought to better define and separate the WTE process into its energy-generating and waste-management components. Figure 2 depicts how these processes, and the contributing factors in each, were organized. The “electricity scenario” was their primary focus, representing the facility’s energy-generating function. “Process expansion” includes things related to the waste management function, such as avoided landfill emissions and additional recycling possibilities. As indicated in the figure, these activities both add to and remove greenhouse gas emissions, depending on how landfill gas is managed (read more here).
The research team used data from an existing WTE facility in New York to provide a real-world application of their analysis. They found that when only looking at the “electricity scenario”, the LCCCI of electricity from this facility was 0.664- 0.951 kg CO2eq/kWh. This is similar to electricity to fossil fuels, largely because a lot of the combustion emissions are coming from nonbiogenic waste… which doesn’t count as renewable. However, when they considered the additional benefits pertaining to the emissions related to waste management, ie. the “coproduct scenario”, the LCCCI decreased to -0.28-0.593 kg CO2eq/kWh. For comparison, renewable wind energy has a LCCCI ranging from 0.003 to 0.045 kg CO2eq/kWh and natural gas electricity ranges from 0.5 to 0.67 kg CO2eq/KWh. Waste to Energy is only competitive with renewables when the waste-management functions of avoided landfilling and metals recycling are taken into account. However, these advantages are based on the assumption that large amounts of waste are bound for landfills. There are greener ways to achieve better waste management that would not require the generation of greenhouse gases by combustion, as seen with WTE.
What can we do to improve waste management?
Step one in sustainable waste management is to reduce the waste that needs to be managed. This can be accomplished at home by being mindful about your consumption and packaging habits. For your remaining waste, there are still a lot of options, including donating used items, composting organics (like some food waste), and recycling what you can (this varies based on your location). This includes plastics, metals, and paper. While recycling does use energy and create emissions, it is still a lot better than the emissions and energy used to create virgin materials. Plus, plastics still count as fossil-fuel derived energy, and metals have to be separated and transported after incineration in the WTE process.
Source Article: A. Pfadt-Trilling, T. A. Volk, and M-O. P. Fortier. Climate Change Impacts of Electricity Generated at a Waste-to-Energy Facility. Environmental Science & Technology. (2020) https://dx.doi.org/10.1021/acs.est.0c03477
Cover Image Source: Wikimedia Commons