Drinking water from the atmosphere only costs $3.20?

By: Carolina A. Martinez

Currently, there are almost 13 billion tons of fresh water in the Earth's atmosphere. This source of water above and around us is important to consider when it is a fact that populations are growing rapidly, water sources are being contaminated, and clean water is becoming less abundant. One way that this water can be harvested is through a variety of atmospheric water generators (AWGs). The researchers of this study were able to construct an AWG that was not only affordable (about $3.20 for a usable prototype), but that also worked in low humidity ranges, and that did not need electricity.

The way that Li et al. created their AWG was by creating a hybrid hydrogel that is composed of a polyacrylamide (a water-absorbing gel), carbon nanotubes (for thermal conductivity), and CaCl₂ (an environmentally friendly salt). This hydrogel is formally called PAM-CNT-CaCl₂ and it was made of these components because not only are they low cost, but it was found that the CaCl₂ allowed the gel to sorb water vapor at extremely high rates in places of low humidity. Additionally, it was found that the PAM provided a flexible hydrogel support system that allowed the sorption of those high concentrations of water. Lastly, the CNT was used because it allows the hydrogel to be highly efficient in converting light to heat. This process allows the water to be released from the hydrogel under regular sunlight and, therefore, releases the water it collects from the atmosphere with ease. It was found that 35 g of this hydrogel produced 20 g of fresh water in a period of 2.5 h under regular sunlight.

Conceptual design of the hybrid hydrogel as an AWG. The water vapor has the ability to be captured during the night and it can be released during day time when it is under sunlight (Li et al., 2018).

            The creation of this hybrid hydrogel was important because previous methods of atmospheric water harvesting like the refrigerator method and fog harvesting was only viable in places of high humidity or required a lot of electricity. The hybrid hydrogel can be used to provide clean water to communities located arid regions and land-locked areas in an environmentally sustainable way. Lastly, if produced in a large scale, it has the potential of replacing some human activities like water extraction and water mining.

Reference

Li, R., Shi, Y., Alsaedi, M. W., Shi, L., & Wang, P. 2018. Hybrid Hydrogel with High Water Vapor Harvesting Capacity for Deployable Solar-Driven Atmospheric Water Generator. Environ. Sci. Technol. 52:11367-11377.