Note: This is a guest post by Robert Fares. More about Robert's background below. - David

Credit: Nestle Nespresso

In recent years, disposable coffee pods have grown increasingly popular among coffee enthusiasts. The coffee pod fully encapsulates pre-portioned coffee grounds and flavoring inside a disposable capsule. This unique design allows casual coffee brewers to consistently reproduce their favorite caf beverage at home with minimal preparation and effort. But the ease of the ubiquitous pod has a downside. Pod-based coffee machines produce much more waste on a per-cup basis than the conventional drip coffee maker, and their waste is far more troublesome than simply paper and coffee grounds: Nestl’s Nespresso coffee pods, for example, encase coffee in an aluminum capsule. The additional packaging required for pod-based coffees has triggered criticism from the environmental community.

In response to environmental concerns, some coffee pod manufacturers have made efforts to recycle used pods. In 2009, Nestl launched its AluCycle initiative, which aims to put thousands of dedicated coffee capsule collection points in place to recycle 75% of used Nespresso capsules by 2013. The focus of these collection points is aluminum recycling, which produces enormous energy and greenhouse gas savings compared to aluminum from virgin sources.

Nestl’s aluminum recycling leaves them with an abundance of leftover coffee grounds. Presently, Nestl mixes spent coffee grounds with organic matter to produce compost. Recent work published by researchers at Spain’s Instituto Nacional del Carbn shows that Nestl could potentially further increase the climate benefit of its recycling efforts by repurposing used coffee grounds into carbon capture and storage material.

Carbon capture and storage materials are a vital part of overcoming climate change. The International Energy Agency estimates that about one fifth of required greenhouse gas reductions will come from carbon capture and storage by 2050. An attractive solution is capturing carbon dioxide from a power plant’s exhaust, so that existing facilities can be retrofitted and brought up to modern carbon standards. The Spanish researchers are hoping that their work with spent coffee pods will help develop an inexpensive carbon capture solution that is appealing to the energy industry.

So, how does one turn old coffee grounds into a carbon dioxide scrubber? The key is transforming the plentiful carbon in coffee grounds into activated carbon. Activated carbon is used in a number of filtration applications. It holds onto contaminants via its enormous surface area; small micropores on its surface attract and lock in molecules. If engineered correctly, activated carbon can remove much of the carbon dioxide from the hot gases exiting a coal power plant’s smoke stack.

In their paper published in the journal Applied Energy, Plaza, Gonzlez, Pevida, Pis, and Rubiera from Spain’s Instituto Nacional del Carbn develop two methods to transform grounds from spent Nespresso coffee pods into valuable activated carbon. The first method uses just carbon dioxide and heat. Spent coffee grounds are heated at 600 in the presence of nitrogen gas until they resemble charcoal. Then, the temperature is cranked up to 700 and carbon dioxide is introduced to activate the surface of the charred coffee grounds. Doing so creates micropores that are attractive to errant carbon dioxide molecules.

The second method developed by Plaza and colleagues uses basic potassium hydroxide to create a more intricate surface on the spent coffee grounds. The grounds are heated at 100 to remove excess moisture, and then soaked with potassium hydroxide. The mixture is gradually heated up to 400 with nitrogen gas until the potassium hydroxide melts off and chars with the spent coffee. Finally, the whole charred mixture is heated one last time at 600 and then thoroughly washed and dried. This chemically driven process creates an elaborate pore structure on the charred coffee grounds that is attractive to carbon dioxide.

To test the effectiveness of their low-cost activated carbons, Plaza and colleagues exposed them to both pure carbon dioxide gas and a mix of gases that resembles the flue gas from a coal power plant. With their intricate pore structure, the coffee grounds activated with potassium hydroxide stored more carbon dioxide in the presence of pure carbon dioxide gas. However, the grounds treated with just heat and carbon dioxide filtered the mix of gases resembling coal emissions more selectively. Nitrogen and other elements tended to clog the available pores on the potassium-activated coffee grounds. Thus, Plaza and colleagues have shown that coffee grounds treated with just heat and carbon dioxide could effectively scrub some of the carbon dioxide from coal power plant emissions.

The work by Plaza and others at Spain’s Instituto Nacional del Carbn shows that uniform forms of waste like spent coffee grounds from pod-based coffees could become an inexpensive method of stemming climate change in the future. Both waste heat and carbon dioxide are abundant at any coal power plant. Plaza and colleagues predict that carbon dioxide captured from a coal plant could be repurposed to produce activated carbon from spent coffee on site. If such a process is developed at an industrial scale, three forms of waste (heat, carbon dioxide, and used coffee) could be combined and repurposed to form carbon capture and storage material, a technology vital to the climate and humanity’s future.

Photo Credit: Nestle Nespresso.

Robert Fares is Ph.D. student in the Department of Mechanical Engineering at The University of Texas at Austin. As part of Pecan Street Inc.’s ongoing smart grid demonstration project, Robert’s research looks at how energy storage models can be used with large-scale data and optimization for economic operational management of battery energy storage. Robert hopes to develop novel operational methods and business models that help to integrate distributed energy generation and energy storage technologies with restructured electricity markets and retail electric tariffs. Through his research, he hopes to demonstrate the marketability and technical compatibility of these new technologies.