Michigan State University’s anaerobic digester turns wasted food into renewable energy.
Leftover food at Michigan State University (MSU) doesn’t become trash.
In many instances, it becomes energy.
The university is one of a handful of higher education institutions in the U.S. to boast an anaerobic digester, a system that converts organic waste —manure and food waste — to renewable energy.
Anaerobic means “without oxygen.” Anaerobic digestion is a naturally occurring, biological process that breaks down organic waste at 100 degrees Fahrenheit, or warmer, in anaerobic conditions, resulting in the production of methane and carbon dioxide. With food waste, the microbes that thrive in such an environment break down proteins, fats and starches to form both the gases.
“It’s what happens in the stomach of a cow,” said Dana Kirk, assistant professor of biosystems and agricultural engineering, and manager of the MSU Anaerobic Digestion Research and Education Center (ADREC). “It’s very similar to what’s happening in our intestines. It’s kind of a natural extension of the body, but we’re doing it in a technical system, so there’s concrete, steel and lots of electronics.”
The south campus anaerobic digester, located at the intersection of College and Bennett roads, near the MSU Dairy Cattle Teaching and Research Center, began operations in 2013. The sealed, airtight tank can hold up to 400,000 gallons and is the largest on-campus digester in the U.S.
Approximately 22,000–25,000 tons of total material comes through the digester each year. About half of it is food waste or food-related byproducts.
Kirk estimates that 5 to 10 percent of the food waste comes from Brody Square, the largest dining hall on campus and the only one currently sending food waste to the digester. The rest comes from Michigan manufacturers, restaurants, retail outlets and distribution centers — nearly every stop on the food supply chain.
“We take food waste from campus and we take food waste from generators all over the state of Michigan,” Kirk said. “It comes in and it is essentially ground up and mixed with dairy manure from the adjacent campus dairy farm.”
The mixture is then held in a mesophilic digester, a part of the anaerobic digester system that operates at 100 degrees Fahrenheit for around 20 days. During this time, microorganisms break the mixture down to form methane, the main component of natural gas, which is used for renewable energy. The digester generates 2.6 million kilowatt hours of electricity per year, roughly enough to power one MSU residence hall, or about 200 houses, for a year.
The byproduct not converted into energy, a nutrient-rich material called digestate, goes into a storage tank and later becomes compost and fertilizer for campus farms.
“The important thing is we’re reducing greenhouse gas emissions and generating energy,” said Kirk. “We’re recovering the nutrients that are in the food so that they can be used as fertilizer. It’s a holistic approach to utilizing food waste.”
The digester, and ADREC’s establishment in 2008, has resulted in beneficial partnerships with Michigan’s food industry.
“MSU has been really heavily engaged with the food sector and food stakeholders,” he said. “Having this research center for the last 10 years, has given us a positive reputation with the industry.”
Kirk, who is co-teaching a new course on food waste solutions this spring, said all of this has positioned MSU as a leader in sustainable food waste solutions.
“We house a tremendous amount of information and knowledge related to food waste,” he said. “When you look across MSU and the number of people that are working on technical solutions to the problem and the assets that we have on campus, you don’t find those on other college campuses.”
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