Methane produced by manure and food waste in landfills doesn’t have to go to waste. Using anaerobic digesters, the gas can be harnessed for energy.
Methane is far more damaging as a greenhouse gas than carbon dioxide—25 times more so. The gas, which is produced by decomposing organic materials in the absence of air, not only traps heat efficiently but is also a health and safety hazard because it’s so concentrated in landfills. About half of the landfills in the US collect and burn methane, mitigating the danger but still contributing to atmospheric methane and carbon dioxide levels. Animal manure decomposition on farms is the main contributor of methane emissions in agriculture.
Repurposing that wasted gas is the focus of a new study published in the journal Environmental Progress and Sustainable Energy by chemical engineers from Michigan Technological University. Specifically, they examined the carbon footprint of anaerobic digestion—composting organics without air—which can be used to redirect methane into a usable energy source.
“We found that bio-methane produced through anaerobic digestion emits far less than its fossil natural gas equivalent,” says Sharath Ankathi, the paper’s lead author and a PhD student at Michigan Tech. Studying each product’s carbon footprint is a way to assess its social, environmental and economic impact—in other words how sustainable it is—which Ankathi says is “defined as helping current generations without compromising their needs or the needs of future generations.”
Life Cycle Assessment
Ankathi’s faculty advisor is David Shonnard, a professor of chemical engineering who leads the Sustainable Futures Institute on campus. They also collaborated with James Potter from AG Energy USA, and together the team focused on a case study of a biogas facility in Colorado. Their primary tool is a life cycle assessment (LCA).
An LCA can be applied to any human activity in order to determine environmental impacts in a comprehensive manner. In other words, an LCA examines the life of an activity. The activities may include business operations, such as services or goods, and may also be used to understand behaviors and choices at the individual and household levels. Sometimes an LCA is cradle-to-grave, sometimes it looks at just a portion of a product’s life cycle.
In this case, Ankathi and Shonnard dug into the piles of organic waste coming into Colorado’s Heartland Biogas Facility LLC and assessed the process that turns food waste from restaurants in Denver and manure from dairy farms near the facility into bio-methane, an energy source. This is the first study that looks at the entire anaerobic digestion life cycle of both food waste and dairy manure and that includes avoided landfill emissions.
To read the full story, visit https://phys.org/news/2017-10-bio-methane-landfill-energy-source.html.