Cow eating grass

To improve biodigester efficiency, Michigan researchers look to cows for inspiration

Cows are known for being good at efficiently digesting and extracting nutrients from materials that other animals cannot. That’s why they’re often fed plant byproducts (stems, shells, etc.) left over after grains are harvested for human consumption. A research team led by the University of Michigan, in partnership with institutions including Northwestern University and Argonne National Laboratory, is using their knowledge of cattle digestion to develop a renewable energy production system. 

The scientists believe their renewable methane innovation could offer an alternative to sending organic municipal waste to landfills and could provide 40% more power at a 20% lower cost. The U.S. Department of Energy is providing $5 million for the $6.8 million project. 

“It’s time for us to shift our thinking as a society… We’re throwing away a valuable feedstock. We believe we’ve come up with a highly scalable solution to match the needs of an urbanizing world,” said Steve Skerlos, professor of mechanical engineering at UM, in a news release. “Over the course of the next decade, the technologies, design and operational strategies, and educational programs in this project could lead to a doubling or more of power generated from food waste in the U.S.” 

The technology

Existing bioreactors ingest organic waste and produce methane, the main component in natural gas. But the machines can only handle certain types of organic materials — food wastes or human and animal wastes — and the conversion process isn’t efficient. The research team hopes to expand the categories of waste that bioreactors can break down by carrying over principles from cow digestion.

University of Michigan researchers, including Renisha Karki, a graduate student research assistant, are working on a new biodigester that converts organic solid waste from trash and wastewater into renewable methane. The digester mirrors the ability of a cow’s stomach to efficiently break down substances. Image credit: Robert Coelius/Michigan Engineering

The UM team is developing a two-phase anaerobic bioreactor system — thus named because it doesn’t require oxygen for reactions. The first phase is a “rumen” bioreactor that mimics what happens in a cow’s first stomach, where organic waste is broken down into simpler compounds like acetic acid, vinegar’s key compound. The second phase converts those simple compounds into methane. The two-phase system is smaller than most current bioreactors, which makes it cheaper to build and operate.

The innovation efficiently creates biogas that is a mixture of methane and carbon dioxide. The Argonne and Northwestern researchers are developing a technology that converts the CO2 to methane to create pipeline-ready renewable methane.

What’s next

The researchers will initially work on their portions of the project separately, and then Argonne will host a lab-scale build-out of the system. The Great Lakes Water Authority facility in Detroit eventually will host a pilot project of the full system. GLWA currently does not have technology to convert organic waste and sewage to energy, and the pilot project is expected to demonstrate that such a system is feasible at the utility scale.