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Scraps to compost in 24 hours: Madison College digester diverts waste, cuts emissions

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Nobody eats like "Chester."

In a storage room off the teaching kitchen at Madison Area Technical College, the cabinet-size aerobic digester consumes up to 300 pounds of food scraps per day, turning waste into garden compost.


John Johnson, a culinary arts instructor at Madison Area Technical College, adds food scraps to "Chester," a biodigester that turns organic waste into compost.

Nicknamed Chester by students, the award-winning digester has been gobbling up scraps, leftovers, expired ingredients  just about anything generated by the college’s culinary arts program as well as its cafeteria.

“It could be steaks, it could be sauces, rice, pasta, pasta salad  all that stuff,” said John Johnson, a culinary arts instructor. “Our trash cans are pretty much empty now. If it can go into Chester, it goes in.”


Housed in MATC's teaching kitchen, the biodigester turns about 25 tons of food waste each year into compost, saving space in the landfill and preventing greenhouse gases.

The process is simple: Dump the food scraps in and close the door. The digester slowly churns the material while heating it up to activate the bacteria, which do most of the work. By the next day, all that’s left is a dry, brown powder.

With moisture vented out through a pipe in the ceiling, Chester produces about a pound of compost for every 10 pounds of waste.

Chester especially likes scraps from the baking program, as the bacteria thrive on sugars. Large bones are one of the few things it can’t handle.

“Fat makes Chester sick,” Johnson said.


Compost bins are used to collect food scraps to feed the digester, which runs off of electricity provided by solar power.

Made by the Hong Kong-based company Oklin, Chester requires only electricity, supplied by the college’s rooftop solar array. There’s no need for water; nor does it produce sewage that would need further treatment.

Installed in late 2019  shortly before COVID-19 lockdowns  Chester has digested about 25 tons of food scraps per year, turning that organic waste into nutrient-rich compost rather than sending it to the landfill, where it would take up space and produce methane, a potent greenhouse gas.

Chester received a recycling excellence award this year from the Wisconsin Department of Natural Resources, which has put an emphasis on reducing food waste in landfills as part of a five-year climate action plan.


A control panel monitors conditions in the digester, which uses agitation, heat and bacteria to break down organic waste.

The machine cost a little less than $40,000 to install, paid for with a federal grant.

The college saves about $600 a year in landfill tipping fees and sells the compost for a nominal fee. But Johnson said the motivation was simply minimizing waste and cutting greenhouse gas emissions.

“The philosophy of the college is, ‘What can we do better,’” he said. “This makes perfect sense.”

“Our trash cans are pretty much empty now. If it can go into Chester, it goes in.”

John Johnson, culinary arts instructor with Madison Area Technical College

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