Typical Atmospheric Water Generators (AWGs) don’t work well in environments with low humidity or temperature. Scientists at Massachusetts Institute of Technology (MIT) found a way to extract water from soil in the driest biome in the world- the desert. Using an air-cooled sorbent-based atmospheric water harvesting device, the research group predicted that over a quarter-liter of water could be extracted per kilogram of metal-organic framework (MOF) each day.
The framework I’m referring to is called MOF-801. It’s the little black square in the photo above that collected heat from the sun during the day. According to the study by Hyunho Kim, Sameer R. Rao, and five others, MOF-801 was created by combining zirconyl chloride octahydrate and fumaric acid, and then it underwent heating, washing, and drying cycles. The result was a microcrystalline powder that could help improve the efficiency of water generation.
At nighttime, the box shown above was opened and cool air caused the MOF to become fully saturated. When the MOF was heated again, water was released. In other words, the apparatus allowed for adsorption during nighttime and water production during the day.
“The system consists of five main components…adsorption and condenser chambers, a glass flask that serves as a reservoir for HPLC water, two temperature-controlled thermoelectric stages, and a vacuum pump.” – Kim and Rao et al.
The purpose of the fan and increased temperature in the apparatus was to mimic weather conditions in an extremely arid location; specifically, Arizona. Copper was used in the condenser for its conductive property. Copper was also found in the resulting water at a concentration of about 2.6 ppm, which is above the EPA regulation of 1.3 ppm for drinking water. Since there was no copper in the MOF, it was determined to have oxidized from the condenser. Although this negatively affected the final water quality, the research group suggested the use of galvanized steel in the future to avoid copper oxidation. Finally, researchers measured efficiency using solar insolation, harvested water, and water temperature. The device had a total thermal efficiency of 14%.
How AWGs Work
AWGs work by cooling a coil, which air then passes over to form water droplets from condensation. Some water generators require electricity, but there are also those that don’t. The downside to this method is that humidity in the air must be at least 40%, and the process is very inefficient. That’s why this research project holds so much promise for the scientific community.
If you want to read more about AWGs, I wrote a post called Water From Air a while ago that covers a similar process performed in Peru. Or, for more information on the study you can read it for yourself here. This is the official citation if you have trouble:
Kim, Hyunho et al. (2018). Adsorption-based atmospheric water harvesting device for arid climates. Nature Communications.