The Great Beyond: A New Journey for Compost at UW-Madison

Gundersen Envision sign.

Food systems are one of the cornerstones of sustainability. That word “systems” is key: the food we eat is part of a vast, interconnected web. To make food sustainable, then, we have to pay attention to its whole lifespan: from production, to consumption, and beyond.

Food waste is a big piece of that “beyond.” It’s the end of the road, the dark and loamy afterlife of our meals. Or is it? Composting provides a means of turning food into soil, from which we can produce more food, so that what we don’t or can’t consume—the “waste”—becomes a resource that nourishes both planet and people.

At UW-Madison, the journey of compost is shifting in exciting ways. Many buildings host compost bins and drop-off points, and the Office of Sustainability is leveraging a Green Fund project to bring its Compost Stewards program to even more locations across campus. But what happens to food scraps once you put them in a compost collection bin on the UW-Madison campus?

The problem of contamination

For the last 10 years, UW-Madison has sent its food scraps to the West Madison Agricultural Research Station (WMARS). WMARS employs a windrow system: long piles of compost material that are turned, or mixed, periodically to encourage oxygen-loving microorganisms to break down food, leaves, and manure into finished compost.

The West Madison Agricultural Research Station is pictured in an aerial view of the University of Wisconsin-Madison campus during an autumn sunset. Photo by Jeff Miller/UW-Madison.
The West Madison Agricultural Research Station is pictured in an aerial view of the University of Wisconsin-Madison campus during an autumn sunset. Photo by Jeff Miller/UW-Madison.

Unfortunately, too many non-compostable items were ending up in the food waste bins sent to WMARS. This problem is widespread; the City of Madison ended its curbside compost pilot program in June 2018 because it could not find a processor that could handle the levels of contamination found in its food waste stream.

Some items were inherently problematic for WMARS—plastic bags, for instance, do not break down in the compost process and can cause entire loads to be sent to the landfill to avoid degrading the final product. Other items, like paper takeout containers and napkins, are technically compostable, but they caused issues in an outdoor windrow system. On windy days, these lightweight objects would take sail and fly away, littering the landscape and creating a headache for both WMARS staff and their neighbors. WMARS even had to make costly repairs to tractor tires punctured by metal cutlery that had been thrown into compost collection bins.

Pile of food waste illustrating contamination issues. Photo by Trina La Susa.
Pile of food scraps illustrating contamination issues. Photo by Trina La Susa.

Recognizing the issues at hand, staff from WMARS, Facilities Planning & Management, the Office of Sustainability, University Housing, and the Union joined together to “clean the stream” of these contaminants. Students conducted trash audits at Union South to collect data on contamination rates. Conclusions from this study contributed to Housing’s decision to replace disposable takeout containers with its Ticket to Takeout program, in addition to training back-of-house staff to sort food waste and send it through a pulper, or chopping machine. Meanwhile, Waste and Recycling staff from FP&M stayed in close communication, sharing observations of the waste stream.

Reusable Ticket to Takeout containers. Photo by University Housing.
Reusable “Ticket to Takeout” containers. Photo by University Housing.

As Ian Aley from the Office of Sustainability related, “we found that the entire chain of food systems at UW-Madison was intimately connected. Purchasing decisions affect staff training, which in turn affects messaging within an organization. That messaging affects waste hauling, which affects compost processing. Through relationship building and regular communication, we have been able to harmonize our efforts across the system.”

Today, WMARS continues to process significant amounts of organic material from campus, including manure and bedding from animal science facilities and plant materials from greenhouses and landscaping. But ongoing contamination in the food waste stream compelled UW-Madison to find another option to divert food scraps from the landfill.

The magical robot

Ten miles west of campus, amidst gentle rolling corn fields, sits a cluster of structures—three very large tanks, a hanger-like space, a holding pond, and assorted smaller buildings—that make up the anaerobic biodigester facility owned by Gundersen Envision. UW-Madison now transports its food waste to their facility to be composted.

The first step in the new process involves dumping food waste into a large machine called a “depackager”—what University Housing sustainability coordinator Breana Nehls fondly dubbed the “magical robot.” The depackager, which makes a terrific racket, pummels its contents with a series of paddles that separate food material from contaminants. The depackager then spits out metals and plastics into one pile and organic material into another.

The depackager machine at Gundersen Envision's compost facility. Photo by Trina La Susa.
The depackager machine at Gundersen Envision’s compost facility. Photo by Trina La Susa.

Gundersen Envision staff combine this clean stream of food waste with food waste from other customers and a much larger quantity of manure from local dairy farms. They store the mixture in a series of three holding tanks. In these tanks, microorganisms digest the material anaerobically, meaning without oxygen. As the organic material breaks down, it releases biogas, which Gundersen Envision captures and burns to generate electricity. In fact, the facility’s biogas yields 16 million kWh of electricity annually—enough to power approximately 1,900 Wisconsin homes.

Indoor windrows maintained by Carbon Cycle Consulting finish the composting process. Photo by Trina La Susa.
Indoor windrows maintained by Carbon Cycle Consulting finish the composting process. Photo by Trina La Susa.

The anaerobic biodigestion process produces liquid fertilizer, which can be applied to farm fields, and also a solid compost product. The latter goes through a final stage of processing in indoor, aerobic windrows, which sit adjacent to the depackager. Carbon Cycle Consulting contracts with Gundersen Envision to maintain the windrows, turning them regularly to further break down the material. When this process is complete, the material is ready to be sold as a high-quality, finished compost that can be used to grow food.

Opportunities ahead

Gundersen Envision’s depackager machine revolutionizes food waste diversion through its ability to sort out contaminants. But there remain significant opportunities for staff, faculty, and students at UW-Madison to influence the sustainability of our food system.

Proper waste sorting is as important as ever. On the one hand, the biodigester can accept items for composting that used to be landfilled, including soiled paper products such as coffee cups and pizza boxes. This is a boon for Badgers.

An entire young kale plant (from one of a several trays) found at the Dane County Landfill. Photo by Nathan Jandl.
An entire young kale plant (from one of a several trays) found at the Dane County Landfill. Photo by Nathan Jandl.

On the other hand, despite its capacity to separate contaminants, the “magical robot” has its limitations. It is unable to discern between recyclable objects and trash, and Gundersen staff can only hand-sort so much of the rejected material. This means that contaminants from the UW-Madison’s food waste stream often end up in a landfill, including plastic bottles, metal cans, and other potentially recyclable items.

In short, the UW-Madison community must continue to work creatively and holistically to optimize our compost system. Part of this work includes helping consumers to think “upstream”: that is, to reduce waste by only taking as much food as they need, and making sure to eat leftovers. Americans toss an average of one pound of food waste per person per day, according to a recent study—which means we are also wasting fuel, water, land, and labor in the production process. Indeed, the Dane County Landfill alone receives about 220,000 tons of waste a year, roughly a quarter of which is food waste.

Ultimately, our new composting process at UW-Madison is an exciting development and an opportunity to engage our entire 60,000-person community. With outreach, education, and encouragement, many more of us can now participate in the great beyond of food—sustainably.

For more information about what you can and cannot compost on campus, where you can find collection bins—and to learn about other composting opportunities in Madison if campus composting is not possible for you—please visit

You can also view our video on the journey of compost at UW-Madison here:


By: Nathan Jandl