Water purification is big business on Earth. Companies offer all kinds of services, from desalination to providing the right pH level for drinking water. But on the Moon there will be no similar technical infrastructure to support astronauts trying to establish a permanent base there. And there is one material in particular that will make water purification even more difficult: lunar dust.
We've reported on the health problems caused by lunar regolith on numerous occasions, so it seems obvious that it's not a good idea to drink it. In addition, the abrasive dust can cause problems with seals, such as those used in electrolysers to create rocket fuel from on-site water resources. It can even negatively affect the water purification equipment itself.
Unfortunately, this contamination is unavoidable. Moon dust is too sticky and electrostatically charged to be kept completely separate from the machinery that would recycle or purify the water. So a group of researchers at the DLR in Germany decided to test what would happen if lunar regolith were intentionally dissolved.
The short answer is, as expected, nothing good. Dissolved lunar regolith causes pH, turbidity and aluminium concentrations to exceed World Health Organisation reference parameters for drinking water. This occurred even with short exposure times (2 minutes) and static pH values, as they used a pH buffer of 5.5 in part of the experiments.
For these experiments, they did not use actual lunar dust, but rather a simulant based on regolith recovered during the Apollo 16 mission. It mimics the regolith believed to be most similar to the Artemis landing sites. In addition to pH changes and exposure time (which reached 72 hours), the authors also varied the amount of dissolved oxygen in the system and the particle size of the simulant.
Those negative results were true for all test variants, no matter which combination of the four control variables was used. Ultimately, that means engineers will have to come up with a system to filter the water from these reservoirs before it can be recycled into the general water system.
Credit: NASA
The article explores some possible solutions for such a water purification system. Each of the limits that were violated requires its own purification methodology. In the author's opinion, reducing turbidity is the first requirement. To achieve this, they suggest performing standard filtration or letting dust particles settle.
The next most important stage is the removal of aluminum, as another experiment showed that plants grown in lunar soil showed signs of aluminum toxicity. Other ions, such as calcium, iron, and manganese, also need to be removed, as they were above acceptable levels in some, but not all, test batches. Removing these ions would require a reverse osmosis or ion exchange process. Ion removal is also vital for the electrolyzer system to function fully.
The authors seemed to want to create a platform for testing and validating water purification processes for future lunar exploration missions. Given the results of their experiments, there will no doubt be more rounds of testing and much technological development to work on solving these technical challenges. Ultimately, astronauts will have to drink water on the Moon, and not just from bottles brought back from Earth.
Learn more:
Freer, Pesch and Zabel – Experimental study to characterize water contaminated by lunar dust
UT – The moon is toxic
UT – Astronauts will follow the trail of dust heading towards the Moon. Is this a problem?
UT – Moon dust remains one of the biggest challenges facing lunar exploration.
Main image:
Turbidity samples of some of the dissolved regolith.
Credit: Freer, Pesch and Zabel
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