Nitrous oxide is a particularly vile greenhouse gas and one of the unfortunate consequences of processing sewage. But that's not how a team at Stanford University sees it.
In a novel marriage of environmental engineering and rocket science, the nitrous oxide produced at wastewater treatment plants is being used as a propellant for rockets. Rather than blasting off for space though, the idea is to fire up the motors and generate energy to run the plant.
"We definitely have to think differently now. These wastewater treatment plants need to become resource recovery centers," Craig Criddle, a Stanford professor of civil and environmental engineering, told Discovery News.
Rather than limiting nitrous oxide production, Criddle and colleagues are trying to find ways to boost the amount of gas that can be harvested from ammonia, which forms from the amino acids in proteins consumed by people.
Running the gas through a rocket motor converts it into hot air, expelled with with great force. "There's a lot of potential benefit," Criddle said.
There's nothing new about using nitrous oxide in rocket fuel. The engine that boosted SpaceShipOne beyond the atmosphere in 2004 to clinch a $10 million prize consumed a mixture of tire rubber and nitrous oxide. It is a clean-burning propellant, producing only pure nitrogen and oxygen gas -- basically enriched air -- as byproducts.
A graduate student fishing for a thesis subject got curious if the gas could be an emissions-free energy source. He did some research and found there were bacteria that generate nitrous oxide, said Brian Cantwell, a professor of aeronautics and astronautics at Stanford.
"At that point, he began talking to some folks in the Earth sciences division at Stanford who are chemists and they eventually directed him to talk to Criddle, who is an expert in wastewater treatment," Cantwell told Discovery News.
The resulting collaboration not only led to a successful doctoral thesis for the student, but three patents and an ongoing research project now focused on developing a bioreactor that efficiently converts ammonia to nitrous oxide.
The team is aiming to set up a small pilot project at a working waste treatment plant.
"We're committed to bringing this to application," said Cantwell. "This has to get beyond the lab and get out and get used."