Clean Water From Thin Air
In many regions of the world, fresh water comes at a premium. One option for access could be desalination, but this is so far a very energy-intensive approach, even if some progress in solar tech has made it closer to reality recently. Seawater desalination is also not an option for many inland arid regions, like for example central Asia, Mongolia, Chilean mountains, or most of the Sahara Desert.
Another option is to capture the water present in the air. Many deserts actually have rather high atmospheric moisture, but for climatic reasons, they do not form rain and clouds. This is the promise of atmospheric water harvesting. We previously covered how passive cooling mixed with a silicon coating could boost the efficiency of gravity-based water harvesting.
Researchers are now looking at further improving the method, notably by using new types of polymers. Scientists at the Osaka Metropolitan University performed this research, which was published in ACS ES&T Water under the title “Liquid Polyether-Based Water Harvester for Near Ambient Temperature Operation via Hydrophilicity-Difference-Induced Water Transfer.”
Water Adsorption
A method to harvest water from thin air is to use a polymer able to “adsorb” the water. Adsorption is the capacity of solid substances to attract molecules of gases or solutions with which they are in contact with their surfaces – in this case, gaseous water vapors and droplets of water suspended in the air.
In everyday life, we know adsorbent materials like silica gel in commercial packaging. This is actually a rather efficient process, and it can collect a lot of ambient water.
Source: Osaka Metropolitan University
The issue is making the polymer release that water. Usually, heat of around 100°C is required to desorb these polymers, which, of course, makes it very energy-inefficient and costly. In contrast, the new polymer developed in Osaka is different.
Low-Temperature Desorption
The issue with releasing the water from the polymer is that the very characteristics that make a polymer a good adsorbent are also what makes it poor at letting it go, hence the need for high temperature to make it happen.
Previously, the researchers tried to mix together poly(ethylene glycol) (PEG) and oligomeric poly(propylene glycol) (PPG), creating a “hydrophilicity-difference-induced water transfer (HWT)” mechanism.
In simpler terms, the difference in water adsorption between the two types of polymers created a weaker capacity to hold onto the adsorbed water. This allowed for the creation of a liquid moisture adsorbent that requires only a temperature of around 35°C / 95°F to do so.
However, this limited the mixture’s water adsorption capacity, making it less productive even if it was much less energy-intensive.
PEG-PPG Co-Polymer
In the latest experiment, the researchers tried to mix a PEG-PPG copolymer with PEG instead.
Source: ACS Publication
This mix boosted the HWT effect even further, resulting in the best possible result:
- The low temperature of recovery was preserved
- The water harvesting rate was actually higher than PEG alone, which was normally the element adsorbing water the best.
The PEG-PPG random copolymer exhibited the highest water harvesting rate, above that of PEG. The improved water recovery originated from the synergistic effect of HWT and the collapse of water clusters.
Applications
The low temperature required to collect the water and regenerate the polymer radically changes the potential of this technology. First, it removes the need for energy-consuming high temperatures, radically improving the green credentials of the idea.
“Improvements to this technology are also expected to lead to reductions in greenhouse gases and more efficient use of water resources. From now on, we will aim to improve the liquid moisture adsorbent and increase the efficiency of the entire system in order to make it practical.”
Masahide Takahashi – Professor at Osaka Metropolitan University
Secondly, because 35°C / 95°F is much easier to obtain, it could be created just by leveraging the day-night cycle, especially in desert regions where the day is rather hot, like most deserts around the tropical zone (Sahara, Middle East, India, Mexico & South-West of the USA, etc.).
Colder regions like Mongolia could be more tricky, but maybe a very simple metal foil mirror could help reach the 35°C threshold when there is sun. This opens the path for the completely passive system, automatically generating water with very little effort.
The same technology could also be quickly deployed in regions that urgently need clean water.
“This technology has the potential to be applied not only to water supply in arid regions and places with limited energy resources but also to ensuring access to water in times of disaster and emergency.”
Arisa Fukatsu – Assistant professor at Osaka Metropolitan University
Further development could be built on this research as well. For example, nothing proves that the polymer mix discovered here is the optimal combination.
In theory, many other mixes of hydrophilic and slightly less hydrophilic polymers could do the job. So now that the principle has been demonstrated, a systematic exploration of new water adsorbing materials could help improve yield even further, bringing the technique closer to commercial viability.
Company Solving Water Shortages
Xylem Inc.
Together with the European Veolia, Xylem is a global leader in water purification, wastewater treatment, and desalination. It employs 23,000+ (of which 6,000+ engineers) people and operates in 150 countries, with a focus on the USA, with 35,000+ direct industrial customers.
Its main market is municipal drinking and wastewater, but it also provides dedicated solutions to other sectors like healthcare, power, food & beverages, oil & gas, microelectronics, etc.
Source: Xylem
Xylem can provide the critical patented pieces of equipment to clean or produce water like ozone generators, UV lamps, desalination membranes, ultra-pure water generators, etc. But it also provides “simpler” equipment equally critical to water-related operations like turbines, pumps, piping, injection, software, etc. as well as maintenance, repair, and installation services.
Source: Xylem
The water market is still a very fragmented one, with Xylem one of the largest companies in the sector but still holding “only” a 10% market share out of its $80B served addressable market.
The company spends around 4% of its sales on R&D. It should benefit from new regulations regarding PFAS (Per- and polyfluoroalkyl substances, or forever chemicals), with 6,000+ utility facilities needing such PFAS treatment.
Xylem has been growing steadily, with net income growing from $297M in 2012 to $609M in 2023 while keeping a stable 17-219% EBITDA margin.
Overall, this makes the company’s investing profile less like that of an industrial company (often cyclical) and more like that of a utility company growing with the overall economy or a little bit above that rate, like most of its consumers.
