Rendere più efficiente la raccolta di acqua atmosferica è fondamentale nelle regioni aride

Acqua Pulita dall’Aria Rarefatta

In molte regioni del mondo, l’acqua dolce è un bene prezioso. Un’opzione per l’accesso potrebbe essere la desalinizzazione, ma finora è un approccio molto energivoro, anche se alcuni progressi nella tecnologia solare l’hanno resa più vicina alla realtà di recente. La desalinizzazione dell’acqua di mare non è nemmeno un’opzione per molte regioni aride interne, come ad esempio l’Asia centrale, la Mongolia, le montagne cilene o la maggior parte del deserto del Sahara.

Un’altra opzione è catturare l’acqua presente nell’aria. Molti deserti hanno in realtà un’umidità atmosferica piuttosto elevata, ma per ragioni climatiche non formano pioggia né nuvole. Questa è la promessa della raccolta di acqua atmosferica. In precedenza abbiamo trattato come il raffreddamento passivo combinato con un rivestimento di silicio possa aumentare l’efficienza della raccolta d’acqua basata sulla gravità.

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 Transfer¹.”

Adsorbimento dell’Acqua

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.

Fonte: 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.

Desorbimento a Bassa Temperatura

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.

Co-Polimero PEG-PPG

In the latest experiment, the researchers tried to mix a PEG-PPG copolymer with PEG instead.

Fonte: ACS Publication

This mix boosted the HWT effect even further, resulting in the best possible risultato:

• La bassa temperatura di recupero è stata mantenuta
• Il tasso di raccolta dell’acqua è stato effettivamente più alto rispetto al solo PEG, che era normalmente l’elemento che assorbeva meglio l’acqua.

Il copolimero casuale PEG-PPG ha mostrato il più alto tasso di raccolta d’acqua, superiore a quello del PEG. Il miglioramento del recupero d’acqua è derivato dall’effetto sinergico dell’HWT e dal collasso dei cluster d’acqua.

Applicazioni

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.

“Miglioramenti a questa tecnologia sono anche attesi per portare a riduzioni delle emissioni di gas serra e a un uso più efficiente delle risorse idriche. D’ora in poi, mireremo a migliorare l’assorbitore di umidità liquida e ad aumentare l’efficienza dell’intero sistema per renderlo pratico.”

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.).

Regioni più fredde come la Mongolia potrebbero essere più difficili, ma forse un semplice specchio di lamina metallica potrebbe aiutare a raggiungere la soglia di 35°C quando c’è il sole. Questo apre la strada a un sistema completamente passivo, che genera acqua automaticamente con pochissimo sforzo.

The same technology could also be quickly deployed in regions that urgently need clean water.

“Questa tecnologia ha il potenziale di essere applicata non solo all’approvvigionamento idrico in regioni aride e in luoghi con risorse energetiche limitate, ma anche per garantire l’accesso all’acqua in tempi di disastri ed emergenze.”

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.

Azienda che Risolve la Carenza d’Acqua

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.

Fonte: 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.

Fonte: 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.

Riferimento allo Studio:

^{1. Ikegawa, D., Fukatsu, A., Okada, K., & Takahashi, M. (2024). Liquid polyether-based water harvester for near ambient temperature operation via hydrophilicity-difference-induced water transfer. ACS ES&T Water. https://doi.org/10.1021/acsestwater.4c00775} in italiano.