University of Michigan explores use of cow-inspired biodigesters for MSW

A proposed energy-production system based, in part, on cow stomachs could generate 40 percent more power from municipal waste stream and provide a viable alternative to sending waste to landfills.

The $6.8 million effort is being led by the University of Michigan (U-M) and includes partnerships with Argonne National Laboratory, Northwestern University and others. The U.S. Department of Energy is providing $5 million of the funding.

“It’s time for us to shift our thinking as a society. These organic materials are only waste in the sense that we bury them at landfills or compost them. 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 U-M and a co-principal investigator on the project.

The endeavor, headed by Lutgarde Raskin, the Vernon L. Snoeyink Distinguished University Professor of Environmental Engineering at U-M, hopes to expand the types of organic waste materials that bioreactors can break down beyond food waste and wastewater sludge.

“A cow’s stomach is really good at degrading lignocellulosic material—things like the grass and hay that cattle eat,” Raskin said. “Those materials can’t be digested by the anaerobic bioreactors commonly used today. We’re looking to develop a new bioreactor that can also digest yard waste and paper waste.”

The cow stomach (rumen) bioreactor represents one part of a two-phase anaerobic bioreactor system, called anaerobic because it doesn’t require oxygen. The first, rumen bioreactor converts organic waste into simpler compounds like acetic acid, the main component in vinegar. The second reactor converts those simpler compounds into methane. Their combined footprint is much smaller than typical bioreactors now in use, making them more affordable to build and operate, the researchers say.

U-M’s system is able to efficiently generate biogas—a mixture of methane and carbon dioxide. Converting that to pipeline-ready renewable methane is the job of researchers at Argonne National Laboratory and Northwestern University. They’re developing a system that converts the carbon dioxide in the biogas to methane as well.

“Argonne’s electrochemical technology provides a pathway of utilizing renewable energy to directly upgrade biogas into cost-effective renewable methane,” said Meltem Urgun-Demirtas, group leader of Argonne’s Bioprocesses and Reactive Separations in Argonne’s Applied Materials Division.

All three aspects of the project will start and progress separately at first. A lab-scale assembly of the integrated system will be hosted by Argonne. Later, a pilot system will be built at the Great Lakes Water Authority (GLWA) water resource recovery facility in Detroit.

Utilities like GLWA’s recovery facility stand to benefit since they do not currently have systems to recover energy from the sewage sludge and organic wastes they produce. In keeping with GLWA’s goal to become energy neutral, the pilot program run by the utility’s personnel will be crucial to establishing that the system can be implemented full scale