Disposing of human waste in space missions is a complicated process. It involves storing the waste in containers and loading it off in cargo vehicles where it should be completely burned up before the spacecraft re-enters the Earth's environment.

Researchers from the University of Florida, however, have come up with a more productive way of disposing of fecal waste through a process that turns it into rocket fuel.

In 2006, the National Aeronautics and Space Administration (NASA) announced plans to build a permanently inhabited base on the moon between 2019 and 2024. Aware that carrying back stored waste during long-term missions is impractical and dumping waste on the lunar surface is not an option, the U.S. space agency asked help from UF researchers.

Pratap Pullammanappallil, an associate professor of agricultural and biological engineering, and Abhishek Dhoble, a graduate student at UF at the time, accepted the challenge to look for alternative and better ideas on how to dispose of waste from space.

Using the packaged form of chemically treated human waste supplied to them by NASA, the researchers conducted laboratory tests to determine how much methane would be generated from the waste and for how long with the anaerobic digester technique they used.

The process kills the pathogens that are present in human waste. It also produces biogas, a combination of carbon dioxide and methane produced by the breakdown of organic matter. Biogas is a source of renewable energy that, on Earth, can be used as fuel for transportation, heating and generating electricity.

"We were trying to find out how much methane can be produced from uneaten food, food packaging and human waste," said Pullammanappallil. "The idea was to see whether we could make enough fuel to launch rockets and not carry all the fuel and its weight from Earth for the return journey."

The researchers found that with the process they can produce an equivalent of 290 liters of methane per crew member daily over a period of one week. Methane can be used to fuel rockets and, with a sufficient amount, would allow spacecraft to return from the moon.

The process can also produce about 757 liters of non-potable water per year from all the waste. Through electrolysis, this can be split into hydrogen and oxygen. The latter can be used by astronauts for a back-up breathing system.

The findings were published in the journal Advances in Space Research.

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