Food Waste Into Fuel

University project makes an environmental impact

Ohio University feeds thousands of students, faculty, staff and visitors every day, and all of those meals produce a lot of leftovers. A new project led by Dr. Sarah Davis, assistant professor of environmental studies at the Voinovich School of Leadership and Public Affairs, aims to guarantee that those leftovers are used as efficiently as possible.

All campus food waste is already composted at a facility on the Ridges, but the facility receives more and more waste each year. While much of the compost is used in campus landscaping, there is an excess of compost produced.

“After the waste goes through the initial composting it is laid out in windrows behind the composting facility and it continues to decompose. As it decomposes, there are greenhouse gases released,” Davis said.

Davis has a plan to capture those gases. Last fall, she received an 1804 grant from the University for $75,000 to build an anaerobic digester contained in a glasshouse structure next to the current composting facility. The goal is to process the excess food waste and compost, harvest the methane produced and then use that methane as a fuel source.

Usually, compost is made by frequently stirring the food waste to mix it with oxygen and facilitate decomposition. This decomposition process primarily produces carbon dioxide as a by-product. The anaerobic digester Davis is using will eliminate oxygen so that more methane and less carbon dioxide will be produced. The methane will be captured and compressed as fuel.

“Inside the digester, it’s basically a slurry of biomass and water, and then above that, there’s headspace where gas accumulates, so we’ll be drawing off the gas from that headspace and compressing it,” Davis said. “Our plan is then to use the compressed gas to run a generator.”

The generator will power pumps for a hydroponic system in the greenhouse that contains the digester. A hydroponic system conveys nutrients to plants through water instead of through soil. Davis, who also studies the use of plants as biofuel, hopes to use the effluent from the digester to fertilize the plants.

“We’ll also be able to take some of the effluent and apply it to the plots of bioenergy crops that I have planted in the Land Lab at the Ridges,” Davis said.

However, this project involves more than harvesting methane for energy and fertilizer for crops. Working with Dr. Ben Stuart, a professor of civil engineering in the Russ College of Engineering and Technology, Davis will explore ways to improve the digester’s efficiency.

“The research part of the project is looking at what combination of different food waste and composting material leads to the greatest methane production and the highest quality fertilizer,” she said.

Stuart already does research on anaerobic digestion, and has made progress toward understanding the optimum mixtures of food waste components for yielding the greatest methane. Some of his students will work with Davis and Dr. Kim Miller, Voinovich School research scientist, to find better ways to collect rainwater to be used in the digester and to compress the methane from the digester.

Miller is managing the design, construction, and additional lab experiments to optimize methane production. Steve Mack, Director of Facilities Management, is also collaborating with the team.

“For centuries, people lived sustainably,” Stuart said. “It’s only in the last hundred years or so when we’ve industrialized that we waste so much. We’re trying to step back and live in a sustainable manner, but not be afraid to use technology to help us get there.”

Davis estimates that the funding from the 1804 grant will allow her to build and start testing the facility for the first two years, and she plans to look for outside funding after that.

“Essentially we’re talking about making energy out of a resource that we’re generating anyway,” Davis said. “It could be something that would become an asset for the University in the long run, but we’ve got a lot of work to do before we can scale this technology to a level that would address campus energy and greenhouse gas reduction.”