Photo illustration by Dennis Schroeder, NREL

By Phil Pienkos, NREL

When it comes to sustainability in the coffee supply chain, industry members have been finding creative ways to conserve on every level, from the farm to the coffee shop. But what happens to the grounds after the coffee’s brewed?

Many coffee shops already have composting programs, but what if there were a way, not only to divert used grounds from the landfill, but to use those grounds to produce energy? Research at the National Renewable Energy Laboratory (NREL) is exploring this question — and is starting to see some exciting developments with help from the coffee industry.

My research at NREL focuses on algal biofuels, but I also have a personal and scientific interest in waste-to-energy research: “recycling” waste materials to create more efficient (or more efficiently create) energy products. For years, I’ve led projects to develop innovative ways to use algae and waste materials as feedstock to produce biofuels—but these have always been separate processes, until now.

During a recent effort to explore the composition of various waste food products, a couple of unexpected materials stood out, one of which was spent coffee grounds. The grounds turned out to have a composition similar to a biochemical signature I know well: algae. Both have high levels of lipids and reasonable levels of carbohydrates and proteins.

This finding gave me an idea: What if we could use our algal process to make renewable diesel from a mixture of algae and coffee grounds, or even from coffee grounds by themselves? Something like this would be a win-win all around. If a biofuel producer would be willing to pay even a small amount for used grounds, not only would the producer ultimately save costs on algae production, the coffee shop would see a return on its purchase and have an opportunity to boost its sustainable practices—and by diverting waste from the landfill and increasing the percentage of diesel made from renewable sources, the environment would benefit, too.

To test the hypothesis, my team first had to gather samples of coffee grounds for compositional analysis. We compared fresh grounds with spent grounds generated from drip coffee. We also compared spent grounds from regular and decaffeinated coffee. We reached out to the food service company that manages NREL’s cafeteria and instructed its staff to set aside its used grounds. And finally, we received samples from a commercial coffee extraction facility.

We found that all samples, regardless of the source, showed remarkably similar composition — and that the coffee brewing process actually improves the quality of the feedstock for biofuel production because it extracts ash and increases the relative amount of lipid and fermentable carbohydrates. When we tested the spent coffee grounds from our cafeteria for “processibility” (the efficiency of release of sugars and lipids after processing with dilute acid), we obtained nearly 100% yields of both sugars and lipids under fairly mild conditions.

Strategic Project Lead Phil Pienkos in NREL’s algae laboratory. Photo by Dennis Schroeder, NREL

As the team has started to generate feasibility data, I set out to gauge interest in the research by discussing it with members of industry organizations, including NCA President and CEO Bill Murray — who had an idea. Coffee delivery companies deliver fresh grounds to coffee shops and leave empty — but what if they didn’t? What if those vehicles could also pick up the used grounds? This could be another opportunity for profit in the coffee supply chain while also overcoming a key hurdle: the current lack of infrastructure for collecting used grounds and transporting them to a central location for processing.

Meanwhile, a couple of my NREL colleagues who have contacts within in the coffee industry heard about the project and were able to make introductions. One of the companies they put me in touch with happened to have a used-grounds system already in place: It collects the grounds, dries them, and burns them to generate heat and power that feeds back into its coffee-processing facility. The company has indicated it’s also interested in the possibility of using some of its used grounds in biofuel processes, and we are in discussions about the NREL process which could provide higher revenue streams for them.

I have found this pursuit to be very much like a detective novel, encouraging me to keep up the search. While I’ve encountered some closed doors, many windows have opened thanks to enthusiasm from members of the coffee industry, whose perspectives and ideas have been invaluable in guiding this exciting, collaborative research.

I welcome additional ideas and perspectives — please feel free to comment on this post or reach out to me directly at philip.pienkos@nrel.gov.

Philip Pienkos is a strategic project lead for NREL. He helped to start both the Algae Biomass Organization and the Algae Foundation and has served on each organization’s board of directors. He holds four U.S. patents. He received his Ph.D. in Molecular Biology from the University of Wisconsin, Madison.

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