Turning Human Waste Into Rocket Fuel

Eric Hopton for redOrbit.com – Your Universe Online

What goes in must come out, they say, and though it might not feature in many episodes of Star Trek or Star Wars, disposing of what passes through the crew is a major part of space flight planning. Researchers now think they may have a novel answer.

We all love to recycle don’t we? But this particular green innovation is a little different. It all began back in 2006 when NASA started to make advance plans to create an inhabited “moonbase” facility on the moon’s surface between 2019 and 2024. NASA had a rather difficult problem that they just couldn’t “dump” – what to do with all that human waste.

Bringing it all back to earth would be an expensive and impractical proposition. Leaving it on the moon’s surface is clearly an unacceptable option. So NASA turned to the University of Florida for help and the agency entered into an agreement with UF to develop test ideas.

In the past, waste generated during any spaceflight was just that – by-product to be disposed of with no further use. Until now it seems, the stuff has been collected and disposed of by being burned up on re-entry. The waste is stored in containers then loaded into space cargo vehicles that burn up as they enter the Earth’s atmosphere.

With NASA’s moonbase project in mind, the agency decided to try and reduce the weight of spacecraft leaving Earth. Finding a new way to dispose of the waste would help achieve that goal and, if they could find a new way to use it, there would be a double advantage for NASA. Pratap Pullammanappallil, an associate professor of agricultural and biological engineering at UF, and Abhishek Dhoble, who was a graduate student at the time, took up the challenge.

“We were trying to find out how much methane can be produced from uneaten food, food packaging and human waste,” said Pullammanappallil, who is part of the UF Institute of Food and Agricultural Sciences. “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. Methane can be used to fuel the rockets. Enough methane can be produced to come back from the moon.”

The UF scientists started their research using a packaged form of chemically produced human waste that also included simulated food waste, towels, wash cloths, clothing and packaging materials. The waste material packages were supplied by NASA itself.

Pullammanappallil and Dhoble, who is now a doctoral student at the University of Illinois, carried out laboratory tests on the packages to find out how much methane could be produced from the waste and how quickly. They found that the process could produce 290 liters of methane per crew per day, said Pullammanappallil.

The researchers went on to develop an “anaerobic digester process.” This works by killing the pathogens which are found in human waste. The process produces biogas. This is a mixture of methane and carbon dioxide gases which are given off and collected during the breaking down of the organic matter in waste.

The UF scientists also discovered that the digestion and recycling process could produce up to 200 gallons of water annually from the waste. The organic matter trapped in the waste packages releases water as it is decomposed in the process. Though it has to be said that the resulting water is definitely not for drinking, water is obviously a precious commodity in space and any potential use is highly valuable. The water can be split into hydrogen and oxygen using a process of electrolysis. The oxygen can then be fed into a back-up breathing system for the astronauts. The exhaled carbon dioxide and hydrogen can also be converted to methane and water in the process, said the UF team.

As is so often the case in space research programs, there are many potential applications over and above the immediate intended use. This is definitely a process that could be applied on Earth, said Pullammanappallil. “It could be used on campus or around town, or anywhere, to convert waste into fuel,” he added. Such earth-bound applications would include the production of fuel that could be used for heating, electricity generation or even transportation.

During the research, which was published last month in the journal Advances in Space Research, the effect of stirring, operation temperature, organic loading rate and reactor design on the methane production rate and methane yield was studied. The UF team found that “for the same duration of digestion, the unmixed digester produced 20–50% more methane than mixed system.” They also showed that the two-stage design which separated the soluble components from the solids and treated them separately “had more rapid kinetics than one stage system, producing the target methane potential in one-half the retention time than the one stage system. The two stage system degraded 6% more solids than the single stage system. The two stage design formed the basis of a prototype digester sized for a four-person crew during one year exploratory lunar mission.”

These findings have important implications for waste treatment and management during the planned long term exploratory missions to moon with much longer mission duration.

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