By Ty Burke
Greenhouse gases aren’t only emitted from vehicle tailpipes and factory smokestacks. They can also rise into the atmosphere from beneath our feet. Energy projects (e.g., oil and gas development, geological energy storage and carbon sequestration) and landfills can both be potential sources of greenhouse gas emissions through the ground below us. We don’t know the full extent of the problem because these emissions aren’t easy to identify or to measure, but Carleton’s Geoenvironmental Gas and Contaminants Lab is developing innovative ways to pinpoint and mitigate them.
Landfills alone are thought to account for around 20 per cent of Canada’s anthropogenic emissions of methane, a greenhouse gas that is more potent than carbon dioxide. But landfills don’t emit methane evenly over their surface area. Emissions tend to occur at specific locations where methane leaks through to the surface, and locating these “hotspots” can be labour-intensive. Hand-held gas analyzers can determine the concentration of methane at a given location, but landfills can be very large, and walking every square metre of a landfill site can take many hours. However, once the location of those emissions is known, there are ways the emissions can be mitigated.
“Modern landfills are designed with gas collection systems that extract methane and use it for energy, but those systems are not always 100% efficient at removing all the methane,” says Cole Van De Ven, a professor with the Department of Civil and Environmental Engineering who leads the Geoenvironmental Gas and Contaminants Lab.
“There are still fugitive emissions–gas that isn’t collected and is emitted through the landfill cover or along infrastructure associated with the landfill.”
Environmental Engineering Master of Applied Science student Isabella Hearne preparing to collect methane concentration data on a closed landfill site.
Unseen Emissions: A Growing Environmental Challenge
Landfills are covered with an engineered cap that limits the gases they emit, and while most of the methane can be collected by built-in extraction systems, there are inevitably inconsistencies, gaps or cracks through which methane can escape. Van De Ven is collaborating with Niagara Falls-based Walker to address fugitive emissions. Van De Ven and Walker are developing methodologies to detect methane emissions and bio-based technology that aims to neutralize these emissions by creating cover systems that are suitable for microbes that consume methane.
“Traditional landfill cap designs utilize dense soils, and are not optimized for this type of microbes to live,” says Darren Fry, a project director at Walker, which is one of Canada’s largest waste management companies. “We are working together to use organic waste materials, such as the residuals from our food waste composting facilities, to optimize habitat for microbes in the soil.”
Walker already handles organic waste from municipal compost, restaurant grease traps and wood waste from lumber mills. They’re collaborating with Van De Ven’s Lab to transform these waste products into a kind of mulch that is optimized for methane-consuming microbial life and landfill gas transport, and can be placed over known methane leaks on landfill sites.
“We’re letting the science lead the way,” says Fry. “Our main expertise is in landfill operations and landfill gas utilization. Carleton brings the scientific method and laboratory expertise needed to conduct the trial and error aspect.”
“We want to use this waste to create a new product, not only to support our own landfills, but potentially to create a new product that could support other landfills across Canada.”
PhD student Minxuan Wang and Carleton Research Associate Dr. Wameed Alghazali constructing pilot-scale methane oxidation systems in collaboration with Walker Environmental – experiments that look to enhance our understanding of these systems’ performance in Canadian climates.
The Lab’s work isn’t limited to landfills, it is focused on the transport of greenhouse gases from the shallow subsurface into the atmosphere more broadly. This also has applications in the energy sector, including for carbon sequestration and hydrogen storage.
Protecting Aquifers and Water Quality
Carbon sequestration captures carbon dioxide before it is emitted the atmosphere or from the atmosphere and stores it. Sequestration remains an emerging technology, and there are various means by which this might be accomplished. One approach involves pressurizing carbon dioxide gas until it becomes a supercritical fluid, then injecting into porous rock deep below the earth’s surface. But this is only effective if the carbon remains within the rock where it is injected
“Depleted oil and gas reservoirs are one place we might pump super critical carbon dioxide,” says Van De Ven. “These sites already have existing subsurface infrastructure, but they weren’t necessarily designed to prevent carbon dioxide coming back to the surface or could have deteriorated over time. We need to be able to identify the signs and symptoms of a leak.”
That includes into the atmosphere, but also into aquifers, which could reduce groundwater quality.
“Once carbon dioxide is in an aquifer, it could do two things,” says Van De Ven. “The gas could pass through and be emitted into the atmosphere–which would eliminate the climate benefits, but it could also dissolve into the water. That could change water quality and throw off its chemistry, potentially making an aquifer no longer a drinking water resource.”
PhD student Minxuan Wang (right) and Undergraduate Research Assistant Chris Rouse preparing column experiments in Prof. Van De Ven’s lab by filling them with compost.
So, in addition to surface-level gas detection, Van De Ven develops methods to sample groundwater to detect changes in water chemistry and looks at the processes that would occur in groundwater that could indicate a leak. Many parts of the world rely heavily on aquifers for their drinking water, including the U.S. So, leaked gases from sequestration projects could affect large numbers of people, and early detection can help identify leaks before they become a potential public health concern.
A third thrust of the Geoenvironmental Gas and Contaminants Lab’s research is related to the subsurface storage of hydrogen gas. Hydrogen-fuelled vehicles have an important role to play in the energy mix of a green economy, but future underground hydrogen storage facilities also have the potential to contaminate groundwater. With hydrogen leaks, the stakes are even higher. The gas is highly combustible, and can present a threat to public safety.
“Hydrogen is a natural progression of the lab’s work, but it’s a whole different ballgame,” says Van De Ven. “It is a very small molecule, and it can move in different ways. If hydrogen moves through an aquifer and gets into a basement, it could create safety concerns.”
PhD Candidate Madeline Calvert and Prof. Cole Van De Ven preparing experiments to better understand the potential risks of hydrogen release in shallow aquifers and how hydrogen moves in groundwater environments
While hydrogen gas leaks can have severe ramifications, there is broad overlap in the processes controlling its movement in the subsurface and the techniques required to monitor for them.
“There are established techniques to detect leaks from oil and gas wells, and they are transferable to these new problems,” says Van De Ven.
“The group’s goal is to make a difference when it comes to emissions. So, it’s a natural progression to apply these techniques to problems associated with landfills, carbon sequestration, and hydrogen.”
Tuesday, December 10, 2024 in Energy, Environmental, Experiential Learning, Feature Stories, Graduate, Industry Collaboration, Research
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