From trash to treasure: Converting Academy waste into renewable energy

  • Published
  • By Amber Baillie
  • U.S. Air Force Academy Public Affairs
U.S. AIR FORCE ACADEMY, Colo. (AFNS) --  New research here reveals Academy trash might be a treasure.

During August 2013, the Defense Department Environmental Security Technology Certification Program funded CDM Smith, a national engineering and construction firm, to test how the U.S. Air Force Academy can reduce energy use and cost at its wastewater treatment plant, and convert food waste from its dining hall into energy.

Academy professors and engineers toured the Mitchell Hall kitchen and the wastewater treatment plant here July 15, to learn more about the processes and results of the year-long project.

"About 2-3 percent of the nation's energy goes to treating wastewater and water," said Pat Evans, CDM Smith’s vice president. "Most of the energy that's used is for pumping the water and aerating it. We're trying to get wastewater treatment plants to become energy neutral or energy producers instead of energy consumers. One step toward that goal is capturing energy from food waste through anaerobic digestion."

According to Glen Loyche, a Mitchell Hall facility manager, between two to three semitrucks haul food to the Academy every day to feed 4,000 cadets.

"Each trailer carries 20-40 pallets of food," he said.

Leftover food at the dining hall is ran through large grinders, turned into pulp and transferred into dump trucks.

"Waste management picks up 4.5 tons of pulp product here every week," Loyche said.

CDM Smith collects food waste from Mitchell Hall three days a week and converts it into methane and carbon dioxide.

"We're testing on a very small, pilot scale," Evans said. "We transfer the food waste into anaerobic digesters, about 350 gallons in size, that hold about 250 gallons of sludge and food waste. We convert the waste into methane for beneficial uses such as heating boilers, generating electricity and vehicle fuel once it's purified."

Greenhouse gases emitted from food waste takes a toll on the environment, Evans said.

"Some landfills capture the methane released but a lot don't," Evans said. "Methane is a really potent greenhouse gas, much more potent than carbon dioxide. The environmental impact is that it takes up space, emits greenhouse gases and water can go through the waste and generate leaching, which can contaminate ground water."

CDM Smith removes hydrogen sulfide, carbon dioxide and water when converting the waste into methane.

"We purify it," Evans said. "Hydrogen sulfide, or rotten egg gas, is very toxic and can result in corrosion of a lot of equipment. At the end of the process we have pure methane, or natural gas, that can be compressed into vehicle fuel."

Overall, the project has been successful, Evans said.

"We found you get a lot more gas and energy out of fat and protein than you do out of carbohydrates," he said. "We can't control the amount of carbs, fat and protein cadets eat or waste, but now we have a better understanding of how much gas we can get for a given food waste."

Food waste makes up 1-2 percent of the solid waste generated in the U.S., Evans said.

"The Academy's food waste is an energy-rich resource that in going to landfills ends up having an environmental impact," he said. "By converting food waste to methane through anaerobic digestion, we can decrease the impact to the environment, recover energy and help the Defense Department's reach its net zero goals."

Russell Hume, a mechanical engineer with the Academy's directorate of Installations, said converting waste to make energy is a phenomenal step in the right direction for the Academy and beyond.

"I think it has been a great demonstration of the art of the possible," he said. "I would like to see this technology further developed and perfected to the point that it becomes widely available to all."

The project ends Aug. 1.