Design by Madison Grosvenor

Every few months, the compost bins from the University of Michigan dining halls get picked clean — not by a family of raccoons, but by a team of researchers in the Civil and Environmental Engineering department. 

Engineering professor Lutgarde Raskin and her research team have been gathering samples of food waste from U-M students for their research. The team is working on a $6.8 million dollar project aiming to develop biodigesters inspired by cows with a goal goal to create an efficient and cost-effective way to extract energy from organic waste.

According to Mechanical Engineering professor Steve Skerlos, a co-investigator on the project, the bioreactor is inspired by the cow stomach’s efficient digestion of tough organic materials.

“A cow just grows on grass, and we’re kind of harnessing this bio-inspired design, which is pretty clever and fairly simple,” Skerlos said. 

Renisha Karki, CEE doctoral pre-candidate on the team, says the food waste “smoothie” is fed to bacteria growing inside the bioreactor, a complex series of tubs and tubes stacked on top of tables in the corner of the lab. A single eraser-sized metal box measures the flow rate of the biogas — a mixture of methane and carbon dioxide — produced from the system. At the same time, Raskin’s collaborators outside the University are researching methods to convert biogas into renewable natural gas. 

Organic material is broken down inside the bioreactor using anaerobic digestion, meaning that the bacteria digesting the organic material do not need oxygen to survive, Tim Fairley-Wax, a research lab specialist and CEE alum, said. 

Fairley-Wax said anaerobic technology is useful because it can break down tougher materials like sewage sludge or food waste. Currently, much of the organic waste in the United States is thrown into landfills or compost piles, where it emits large amounts of methane into the atmosphere as it decomposes. 

“We’re very inefficient in dealing with our waste, we just bury and forget about it,” Kuang Zhu, a CEE postdoctoral researcher on the team, said.

Despite the potential usefulness of anaerobic technology in dealing with organic waste, Zhu said anaerobic technology is not widely implemented.

“It’s costly,” Zhu said. “It’s expensive to build and it’s also very demanding to operate. There is also a slow reaction happening within the reactor. The anaerobic process takes days to weeks. So this means that the organic waste just spends a lot of time in the reactor.” 

As such, Fairly-Wax said only the wealthiest investors have the means to implement anaerobic technologies. 

Chevron and Exxon Mobil have financed these anaerobic digesters at some Michigan farms,” Fairley-Wax said. “But right now that technology has to be done with a huge investor because it’s relatively extremely expensive.”

To solve this problem, Zhu said the group hopes to make cost-effective anaerobic technology for widespread use at large industrial facilities as well as smaller operations. 

“We can hopefully use this technology (to) reduce the costs so that smaller-scale users can utilize them … for a variety of waste streams, not limited to just wastewater sludge,” Zhu said. “It could be food waste, could be manure, could be a lot of organic waste streams.”

Raskin’s group is collaborating with researchers at Argonne National Laboratory and Northwestern University who are looking into how biogas can be turned into high-purity methane, a renewable natural gas that can be used to heat homes. 

Heating homes with high-purity methane still emits carbon dioxide into the atmosphere, Skerlos noted, making this research a necessary “short-term win” until a future with no greenhouse gas emissions can be reached. 

“It’s not a perfect win. A perfect win is when you take that methane, and you emit no carbon dioxide to the atmosphere,” Skerlos said. “(But) carbon dioxide has 50 times less greenhouse gas potential than methane.”

Meanwhile, the group said that their first project outside the lab is to retrofit current wastewater treatment plants with their bioreactor system in order to extract and utilize energy from food waste. 

Skerlos said wastewater treatment accounts for roughly 4% of the electricity used in the United States. A large part of energy expenditure at wastewater treatment plants is on the sterilization of the material generated while treating the water, Pedro Puente, a CEE doctoral candidate and a member of Raskin’s team, added. 

“The goal will be for the wastewater treatment plants to include food waste streams into the treatment, so they can recover even more energy,” Puente said. “They can become energy neutral or even generate their own electricity for their operations.”

Skerlos said his team believes their bioreactor can reduce costs of treating sewage by 25% to 50%. 

“What you’re getting is basically free power for the wastewater treatment,” Skerlos said. “And you’re also creating free natural gas that you can put in the pipeline that you didn’t have to frack out of the earth. You’re saving a lot of money.” 

The team at the University is partnering with the Great Lakes Water Authority to run a pilot system at their water treatment plant in Detroit. Skerlos hopes they will have a demonstration project launched in the next five years. 

“We’re doing this with very cost-effective technology that can be deployed, not only in Detroit and in industrialized rich countries, (but also) in developing countries (or) in very rural locations,” Skerlos said.

Zhu said he remembers being shocked when he first learned how waste is dealt with and emphasized the need for better methods of waste disposal. 

“We’re getting surrounded more and more by trash,” Zhu said. “Developing solutions to help us have a better, more efficient management of our waste will help us have a better relationship with our society and our environment. So we don’t leave this legacy to our next generations.”

The researchers also emphasized the importance of recognizing the amount and type of waste humans generate, particularly in Ann Arbor where the collection of waste is highly regulated. 

“It’s just a matter of education on how to separate your waste and be responsible about it because the waste that you generate is yours,” Puente said. “So take advantage of the programs that the city offers because there are not a lot of places that do this separate collection.”

Daily Staff Reporter Elissa Welle can be reached at elissajw@umich.edu.