But aeration is a costly and energy-intensive process. As an alternative, the Stanford team wants to create a low-oxygen environment in the treatment plant, where nitrous oxide-producing bacteria are favored, while aerobic species die off.
These nitrous oxide producers consume relatively small amounts of organic matter. That's good news for other anaerobic microbes that produce methane gas by feasting on organic compounds. "When bacteria make nitrous oxide, less organic matter is oxidized, so more can be converted into methane potentially two or three times more than is possible in a typical treatment plant," Criddle said. "That extra methane can be used as fuel to run the plant independent of outside power sources."
Using less oxygen also could reduce costs, Cantwell added. "In a typical treatment plant, aeration is responsible for about half of the operating expenses," he said. "So pumping less oxygen could save a lot of money."
In recent experiments, the researchers demonstrated that under laboratory conditions nitrous oxide gas could be produced from wastewater using a low-oxygen technique. But there's a downside to the process. Nitrous oxide is a significant greenhouse gas that's more than 300 times more potent than carbon dioxide.
That's where Cantwell's rocket thruster comes in. Designed for use in spacecraft, the thruster runs on nitrous oxide a surprisingly clean-burning propellant.
"When it decomposes, nitrous oxide breaks down into pure nitrogen and oxygen gas," Cantwell explained. "At the same time, it releases enough energy to heat an engine t
|Contact: Mark Shwartz|