ANN ARBOR—University of Michigan engineering students have discovered a redeeming quality in junk food: waste grease produced in campus cafeterias that can be used to make biodiesel fuel for U-M buses.

During a term project for a course in environmental sustainability, a four-student team led by Lisa Colosi and Andres Clarens concluded and demonstrated that it is economically and technically feasible to harvest the 10,700 gallons of waste grease produced in the 10 campus dining halls to make an effective biodiesel fuel, which they produced in the lab and tested out on a small U-M tractor.

The students’ vision, “from the fryer to the fuel tank” could save an institution that produces significant amounts of waste grease thousands of dollars in transportation and disposal costs by adopting even a portion of their proposal, said the course instructor, Walter Weber Jr., the Gordon M. Fair and Earnest Boyce Distinguished University Professor of Chemical and Environmental Engineering and director of the College of Engineering Concentrations in Environmental Sustainability (ConsEnSus) Program.

The students tested their theory on the U-M campus, made easier because the University already uses some biodiesel fuel. As part of its commitment to being a green university, U-M recently began purchasing 60,000 gallons of biodiesel fuel from a commercial vendor to blend with regular diesel fuel to make up the 300,000 gallons of combined fuel it uses annually. The principal raw material for regular diesel fuel is petroleum.   The principal raw material for the biodiesel fuel purchased by U-M is oil extracted from soy beans.

“The challenge the students had in this project was to produce a satisfactory or better substitute biodiesel fuel from waste cooking oils,” Weber said. “And they did it.”

The students collected waste grease from deep fryers in the West Quad cafeterial and mixed it in a tank with potassium hydroxide and methanol to create a reaction that produced a glycerine and fatty acid methyl ester solution.   They then separated the glycerine and heated the residual solution to evaporate excess alcohol and water to produce their more than satisfactory biodiesel fuel. The report the students submitted further suggested that the glycerin by-product of the process could be cured and used to make a biodegradable alternative to commercial soaps for use on campus.

By replacing 10,700 gallons of the 60,000 gallons of commercial soy bean oil biodiesel with the students’ product, the report projected that U-M could achieve an estimated $28,000 annual cost savings. Weber said this annual savings could be increased to more than $150,000 by incorporating waste greases from the University Health System cafeterias and area restaurants. The report recommends that the University construct a pilot processing facility on campus to further demonstrate the efficacy of the process.

“The project provides an intriguing idea and presents possible options for increasing our waste recycling while yielding a usable product,” said Dave Miller, director of U-M’s Parking and Transportation Services. “We are exploring the research results and analyzing the potential impact on our existing operations.”

Among the things U-M would need to confirm are the quantity and quality of the grease and the costs involved to create a stable supply, he said.

The potential economic and environmental benefit is huge, Weber said, to any institution, that produces large quantities of waste. For instance, the University produces nearly 11,000 gallons of waste fat annually that is removed at a cost 5 cents a gallon. Even if an institution determined it didn’t want to produce the biodiesel fuel itself, it could still realize significant savings in disposal costs and perform an environmentally friendly deed by harvesting the waste grease and contracting a vendor to convert it to biodiesel fuel.

The U-M College of Engineering is celebrating its 150 th anniversary this year, and is consistently ranked among the top engineering schools in the world. The college is comprised of 11 academic departments: aerospace engineering; atmospheric, oceanic and space sciences; biomedical engineering; chemical engineering; civil and environmental engineering; electrical engineering and computer science; industrial and operations engineering; materials science and engineering; mechanical engineering; naval architecture and marine engineering; and nuclear engineering and radiological sciences. Each year the college enrolls more than 7,000 undergraduate and graduate students and grants about 1,200 undergraduate degrees and 800 masters and doctoral degrees. To learn more, visit www.engin.umich.edu.