Making the Best of the Rest

MnDRIVE initiative helps Second Harvest Heartland turn inedible food into useful products.

By Mary Hoff

Every day, Second Harvest Heartland gathers more than 100 tons of food from donors across Minnesota and western Wisconsin and redistributes it to food shelves and others who serve people in need. In the process, the food bank—the second largest in the United States—ends up with some 3 tons of bad cabbage, spoiled milk, too-old-to-eat cereal and other “unfit for consumption” bits and pieces left over from this process.

And pays $200,000 per year to have it hauled away.

Now, Second Harvest is looking to turn this waste into a “third harvest” with the help of a MnDRIVE demonstration grant, University of Minnesota agricultural engineers, and an invention that began as a way to reduce problems with pig poop.

It all began when Bob Branham, director of produce strategy for the food bank, began looking for a way to reduce the need to spend money that could be going to feed people on disposing of inedible organics.

“I’m paying people to take away high-value waste,” he recalls thinking. “Why shouldn’t I keep that waste to the benefit of Second Harvest Heartland?”

Branham reached out to the University of Minnesota where, coincidentally, associate professor of bioproducts and biosystems engineering Bo Hu had recently, with the help of a MnDRIVE seed grant, developed an anaerobic digester system for turning another type of organic material—pig manure—into useful materials. Hu and Timothy LaPara, professor of civil, environmental, and geo-engineering, applied for and received a MnDRIVE demonstration grant proposal to apply the concept to meet Second Harvest needs.

With support from MnDRIVE and the help of undergraduate and grad students, Hu and LaPara designed a two-stage system capable of transforming Second Harvest’s highly variable organic waste stream into heat, fertilizer, and a valuable soil amendment.

Anaerobic digestion has some similarities to traditional composting but is miles beyond it in both technical sophistication and value of output. Whereas composting takes place with organic materials exposed to air and produces a soil amendment, anaerobic digestion relies on bacteria that break down materials in the absence of oxygen and produces a gas that can be burned to produce heat.

“Digestion of food waste is actually a very sexy idea right now,” Hu says, noting that some large cities are banning food waste from landfills, and sustainability advocates are pushing to reduce the greenhouse gas contributions of waste while deriving useful products.

To make the process suitable for application at Second Harvest, Hu and his team refined it to work with a variable waste stream, at a relatively small scale, with a minimal need for water, and with a bio-electrochemical system that removes adverse odors. They also did an economic analysis to determine whether a digester would make dollars-and-cents sense for Second Harvest, which operates on a tight budget and aims to put every extra penny into helping allay hunger and reduce food waste.

The project penciled out, so Hu and team built an experimental digester to refine the process. Among other things, they looked at strategies to reduce odor and corrosiveness of the gas it produces, explored how the mix of digesting microbes might be tweaked over time to meet seasonal changes, and identified ways to automate the process.

Now, with many of the bugs worked out of the system, the team is installing a pilot digester at its Brooklyn Park facility to test its performance with the mix of waste the food bank produces. Once the pilot confirms the functionality of the system, Hu will advise Second Harvest on installing a full-scale facility.

Along with the benefits the system will reap from what is currently treated as a liability, Hu envisions a fourth harvest from the project as well: Inspiration and motivation for other food banks, as well as other businesses that manage organic waste.

Hu says MnDRIVE has been “very vital” in making this research possible because federal grants are increasingly hard to come by.

“It’s actually really good seed money to obtain federal support,” he says. “We are doing applied research, but we are also gaining fundamental knowledge at the same time that will help us [pursue funding from] federal agencies like USDA or the National Science Foundation.”

For his part, Branham is delighted to have the opportunity to do an even better job of making the most of the resources his organization stewards. “This is a whole new validation that waste and renewable energy can be great partners,” he says. “I wish there wasn’t organic waste, but there is—it just happens for a variety of reasons and that’s not going to go away. So let’s find a better use for it to fight food insecurity.”


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