Cows, as many people know, have four stomachs. Cows also generate lots of methane. So, if your goal is to describe a machine that turns food waste and cardboard into methane gas, the bovine digestive system is an analogy that makes some sense.
The Gas Cube, being developed at the South Dakota School of Mines & Technology, can turn waste products like cardboard, discarded food, agricultural refuse or wastewater from a microbrewery into valuable methane gas for energy generation.
“Our reactor is in some ways a two-stomach cow,” says Jorge Gonzalez-Estrella, a post-doctoral research associate in the Chemical and Biological Engineering Department at Mines.
Gonzalez-Estrella is one of the researchers working on the Gas Cube project. The semi-trailer-sized reactor is much larger than a cow, but it’s still portable. It’s one of the projects in development at Mines aimed at turning a range of remote base waste into energy. This is all thanks to a $4.8 million grant from the United States Air Force, $1.2 million of which funds the Gas Cube. A remote Air Force Base can produce lots of waste. The Air Force seeks to save waste handling and fuel costs at mission-based remote bases. This is a challenge that the Gas Cube is designed to overcome.
How does it work? Back to the cow analogy. At the Gas Cube’s input, or mouth, a shredder grinds up the solid cardboard or food waste and deposits it in chamber number one. This is sort of like a cow chewing and swallowing its food. Then in that first chamber, or stomach number one, hydrolytic microorganisms break down the mix of food waste and cardboard into sugars, and fermenting microbes then break up those sugars into smaller parts called volatile fatty acids. Next, in a vertical chamber or second stomach, methanogenic microbes turn the volatile fatty acids into methane gas. Then in a separate chamber any leftover solids are given more time to react and give off any remaining methane. The gas generated in this reactor can be piped out to run generators or other equipment needed to power a remote base. “This process is well established, it very solid and robust,” says Gonzalez-Estrella.
One challenge in this research is making this reactor portable. Jim Schultze, a chemical engineer, is helping construct the gas cube, “Usually these things take up acres if they’re industrial. We put it in a twenty-by-eight-foot space,” he says. The Gas Cube can be carried on a truck bed, and multiple units can be added together as a remote operation grows.
Another challenge in this project is making it user-friendly. “It’s going to be transported to remote places, and it needs to be easy to run for the operator,” says Gonzalez-Estrella.
Besides being portable and user friendly, researchers must also provide proof of concept. Caitlin Asato, a research scientist and engineer in the Department of Chemical and Biological Engineering at Mines, is helping bring the Gas Cube from the bench scale up to the working prototype. This is no small task. “The nature of scaling up these kind of chemical and biological systems is an imperfect science or engineering exercise,” says Patrick Gilcrease, Ph.D., a professor in the Department of Chemical and Biological Engineering at SD Mines and the principal investigator for the project.
Gilcrease adds that another unique aspect of this project is the interdisciplinary nature. It includes researchers with expertise in agricultural engineering, chemical engineering and civil/environmental engineering. Gilcrease says this diversity brings strength to this team, “A nice learning aspect of this project for me has been being able to see how different disciplines approach the same problem, and the unique advantages of the different approaches we’re bringing to the project,” says Gilcrease.
Like many technologies initially developed for the military, the Gas Cube may have wider applications. The reactor could be deployed to disaster areas or refugee camps, and put into use when waste-handling infrastructure is down. The reactor could also be used for waste generated by agricultural operations. “Microbreweries are often located inside municipalities, and they often can’t dump their wastewater into sewer systems, so they’re looking for ways to treat their wastewater,” says Dave Litzen, a chemical engineer and president of Litzen Process Consulting, Inc. who is helping build and test the working prototype. “But, I can’t think of a better first customer to have than the Air Force,” he adds.
The Gas Cube team is currently undertaking the first testing phase on the prototype. If these tests are successful, the team plans to build a second lighter and more nimble prototype.