If Bear Grylls has taught us anything, it’s that sometimes, when you’re thirsty, almost anything is going to work. Nowhere is this more evident than on board space stations, where high mission costs make the transport of water very costly. Fortunately for astronauts, scientists Eduardo Nicolau and Carlos Cabrera have devised a way to turn urine into power and clean drinking water.
Currently, each spacecraft is equipped with a unisex toilet that consists of a commode that holds human waste. Because of the weightless environment, the toilet comes equipped with foot restraints to prevent astronauts from floating away. The toilet also has a thigh bar to pull down over your lap, similar to safety bars on rollercoasters. In addition, the toilet uses flowing air instead of water to flush the toilet. After bacteria and odors have been filtered out, the air is returned to the cabin.
Because more than half of total waste from space trips are human emissions — the other half are usually recyclables like paper or various metals — a method to treat and reuse this waste is a necessity. It’s estimated that in future space missions, human liquid waste will make up 54 percent of total waste, and of that 81.4 percent will be urine. There are high launch costs to get fresh water into space, and the urine has to be removed in some way to keep the environment clean for the astronauts. Because of this, it’s practical to look at urine as a source of fresh water. While many purification schemes exist, the proposed Urea Bioreactor Electrochemical unit not only recycles urine into potable water, but also can be used to generate electricity.
Past studies have looked into a process called forward osmosis, a treatment process for wastewater that uses osmosis to separate water from dissolved solutes. The studies found that forward osmosis, in conjunction with a fuel cell, can even generate power. Nicolau and Cabrera decided to build on these studies to find a way to purify urine.
The research combined urea in a bioreactor in the presence of GAC-urease, an enzyme that can turn urea into ammonia. Once the urea was converted into ammonia, the ammonia could be converted into power using an electrochemical cell. This combined system, the bioreactor as well as electrochemical cell, are referred to by the researchers as the Urea Bioreactor Electrochemical (UBE) unit. This research found that over 80 percent of organic carbons were removed from the urea, and approximately 86 percent of urea was converted into ammonia. The ammonia, which is then converted into electricity, can be used for various purposes, and the leftover water is pure enough to drink.
The study, which was funded in part by NASA, was published in ACS Sustainable Chemistry and Engineering, as a paper titled “Evaluation of a Urea Bioelectrochemical System for Wastewater Treatment Processes”. The paper authors are Nicolau, Cabrera, Jose J. Fonseca, Jose A. Rodriguez-Martinez, Tra-My Justine Richardson, Michael Flynn and Kai Griebenow. Since publishing the study, Nicolau and Cabrera have set up a larger-scale UBE system for testing at the NASA Ames Research Center.
Although the UBE system was originally designed for use in space, the paper’s authors note that it could also be used in any wastewater treatment system that contains urea or ammonia. This means that it could have a number of other potential uses, one of which could be treating water in third-world countries.
