Scraps to soil: How Princeton’s food waste is recycled on and off campus

Every day, Princeton students eat food in dining halls, dutifully scrape their leftovers into metal chutes labeled “Food Waste & Napkins,” and move on with their days. What journey does this food waste take?

“A food scrap actually has a lot of value when you return it to the earth in a responsible way,” Food Systems Project Specialist Gina Talt ’15 emphasized.

According to Talt, the University sent an average of 70–75 tons of wasted food per month to their off-site energy waste facility, Trenton Biogas, during the Fall 2022 semester; that’s almost one pound of food per meal swipe.

On campus, she manages the composting program at Princeton’s S.C.R.A.P. (Sustainable Composting Research at Princeton) Lab. The lab, affectionately known as “Scrappy,” launched in 2018 through a grant secured by the Office of Sustainability. The project operates year-round, using small-scale composting technology to process food and turn it into nutrient-dense soil to be used as fertilizer on Princeton’s grounds.

Due to the COVID-19 pandemic, however, the composting team was forced to temporarily pause the project in early 2020. For over two years, all of Princeton’s leftovers were sent to Trenton Biogas, until the S.C.R.A.P. Lab reopened last fall. Now, food waste is taken from the Frist Campus Center, campus retail cafés, and both Coffee Club locations and sent to its new location at 300 Washington Road.

Today, 15 percent of overall wasted food at Princeton is processed by the S.C.R.A.P. Lab. Every week, it accepts 200–300 pounds of coffee grounds from Coffee Club and 2000 pounds of food from Frist, according to Talt.

Because the Lab is a small-scale operation with a stated capacity of 5000 pounds per week, the remaining 85 percent of wasted food at Princeton, which comes from dining halls, is sent to Trenton Biogas.

Trenton Biogas General Manager Brian Blair broke down the journey taken by food waste once it leaves the dining halls:

The material is collected by a specialty organics hauler and transported to the Trenton Biogas facility, along with up to 30 trucks a day filled with food waste from other New Jersey establishments.

The facility can process up to 450 tons per day. The waste is first sorted into non-organic and organic materials. All non-organic material is sent to a recycling facility, while the organic portion undergoes anaerobic digestion, in which bacteria break down the food and convert it into acids and gas through a process known as hydrolysis.

The organic waste goes through fermentation, acetogenesis, and methanogenesis processes — which break down substances, create acetate, and create methane, respectively — to together create methane biogas. The biogas is moved out of the digesters and run through a cleaning process to strip it of impurities.

It is then fed into three combined heat and power (CHP) generators, otherwise known as cogeneration, which turn biogas into electricity, helping to power the PSE&G grid that Princeton relies on for much of its energy, according to Blair. The facility also collects heat emitted from the process to warm the digesters and power the facility itself.

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Blair explained, “We recognize that this process is carbon negative. And that’s because we are not just operating in the absence of fossil fuels, but we’re also sequestering greenhouse gas from the environment while doing so.”

Blair added that normally when organic waste is thrown into a landfill, even a well-designed landfill will allow that waste to emit methane into the atmosphere after decomposition. Methane is a greenhouse gas at least 25 times more potent than CO2.

“When you capture that methane, you take it out of the environment and put it to work. We still have emissions from the generators, but it’s a negative emission when you compare it to the greenhouse gas that would otherwise have been emitted,” Blair said.

He also emphasized the unique ability of anaerobic digestion to produce power without fossil fuels while simultaneously sequestering greenhouse gasses from the environment.

“Nuclear doesn’t do it, solar doesn’t do it, wind doesn’t do it. They’re all fantastic technologies and they have their place,” Blair said. “But with a little bit of effort, each individual that contributes wasted food to a container that goes to an energy facility is doing worlds of good for the environment.”

Blair cautioned that there is no “silver bullet” when it comes to solutions for contending with wasted food in an environmentally positive way. However, he believes that the Trenton Biogas solution of anaerobic digestion is a step in the right direction.

“It’s the right thing to do. It takes discipline, and it will probably take many years to get everybody to think this way, but we’re on the right track,” he said.

Back at Princeton, the S.C.R.A.P. Lab’s operation also requires discipline and a dedicated team of workers. Talt detailed the journey of Princeton’s wasted food through “Scrappy.”

Volunteers input food scraps, wood shavings, and oxygen into a drum that rotates every hour. Aerobic bacteria work to break down the material while a blower system aerates the vessel once every 15 minutes. Once the vessel reaches its capacity of 5000 pounds per week, it generates nutrient-dense compost, a process that takes five to seven days.

Assistant Director of Campus Grounds Robert Staudt explained what happens to the compost once it leaves the S.C.R.A.P. Lab.

“We pull it from the lab, put it over in our yard, and then we let it cook a little bit longer to get the right chemistry for what we need,” Staudt explained.

Once that process is complete, the campus grounds team mixes the compost with other soil and uses it as fertilizer for campus green spaces. Through this system, 60 tons of wasted food is recycled into compost and 33 tons of CO2 emissions are saved per year.

Students engage with the facility by working hands-on with the machine to produce compost and by conducting research for classes or independent work using the facility. The composting team is also piloting a program in which the Office of Sustainability’s EcoReps serve as staff at catered campus events, such as the Orange and Black Ball, and monitor compost bins to ensure that leftovers are properly disposed of and can be sent to the lab.

Marissa Bornn ’25 is an operational assistant at the S.C.R.A.P. Lab who helps to make sure all of the food is inserted correctly, catches contamination, and cleans the vessel.

She noted evidence of improper disposal of food waste by students. “Today, we had lots of contamination,” she said. “I caught plastic wrap, three forks, and aluminum foil. Usually, Frist is good at eliminating contamination, but stuff like that does still get in.” Bornn shared that such contamination has occasionally harmed the facility’s equipment.

“It’s so nice to be able to see that the food is going somewhere I know … will be useful and goes back to campus rather than being wasted,” Bornn said.

Adira Smirnov ’23 worked as a S.C.R.A.P. Lab assistant in the fall of 2022. On Friday mornings at 8:30 a.m., she and her fellow volunteers collected compost buckets and loaded them into Talt’s truck before driving down Washington Road to the composting facility.

Smirnov hopes that the lab will raise awareness about the importance of infrastructure for composting campus waste.

Later this month at the “S.C.R.A.P. Lab Relaunch Ribbon-Cutting Ceremony” on March 28, the composting team will be celebrating the lab’s relaunch after the pandemic hiatus with a tour of the facility and compost giveaways for students.

Talt also suggested that students be mindful of the amount they take on their plates in dining venues and read signs on bin receptacles to make sure that they have sorted their wasted food correctly. Sustainability on campus, she said, “boils down to daily actions that you can turn into a habit.”

Raphaela Gold is a staff Features writer for the ‘Prince.’ Please direct any correction requests to corrections[at]dailyprincetonian.com.