For years, NASA has been committed to finding the most effective and efficient ways to provide filtered and purified recycled water to their astronauts aboard the International Space Station (ISS) (see Figure 1). With over two billion people globally who do not have access to clean drinking water and basic sanitation, this unique new water-treatment technology used by the ISS to filter astronauts’ urine into drinkable water just might have the ability to help fight the global water crisis here on Earth.
    
Water is quite heavy, which means that each pound of water launched into space can cost up to thousands of dollars (DiCicco, 2020). For this reason, nothing is wasted on the International Space Station - every drop of sweat, urine, humidity, and breath moisture is collected, filtered, purified, and reused as drinking water (NASA, 2019). The water filtration system currently used by NASA relies on “filtration beds that weigh down resupply missions and have to be swapped out every 90 days” and is also unable to filter out particular semi-volatile contaminants (NASA, 2019). A newly developed water recovery technology not only has the ability to filter these specific semi-volatile contaminants on the ISS, but also requires much less space and energy in order to operate (DiCicco, 2020).

What is this technology?

With the successful implementation of a new system that mimics the natural process of water filtration through proteins called aquaporins, this space technology might have the ability to add “efficiency to existing wastewater treatment facilities or purifying wastewater that until now has gone untreated, polluting groundwater and waterways” (DiCicco, 2020). Aquaporins are proteins used by all living cells to transfer water through their membranes. By using proteins produced through an industrial fermentation process, this purification system is able to mimic the filtering ability of human kidneys and plant roots (NASA, 2019). In fact, aquaporins are what allow “plant roots to absorb water from soil and human kidneys to filter about 45 gallons of fluid per day” (NASA, 2019). Due to the fact that these proteins have evolved over billions of years to carry out certain tasks, and are highly selective, only water is able to pass through while contaminants cannot (NASA, 2019). Using this protein, water filtration companies have been able to develop a system that removes over 95% of microplastics and micropollutants in wastewater, all while using much less energy than other traditional filtration systems (Moreno, 2020).

How it works

Aquaporins filter water by selectively moving water molecules through plasma membranes at a rapid speed. These transmembrane water channel proteins work as nano-filters to block all other solutes from transporting through plasma membranes within living cells (Xie et al., 2013). Aquaporin membranes can be produced through the apical plasma membrane, which is the cell membrane on the surface of epithelial cells (Apical plasma membrane, 2021). This follows the action of vasopressin, which is responsible for activating protein kinase A (PKA), a holoenzyme, to phosphorylate aquaporin subunits contained in the cytoplasm (Litwack, 2020). Aquaporin channels are then formed as these subunits are inserted into the apical membrane (Litwack, 2020).

Through the use of aquaporins, this water recovery and filtration technology uses forward osmosis to filter specific semi-volatile contaminants on the ISS and exceeds the performance of current water purification and filtration systems onboard (Johnson, 2019). It also operates at a fraction of the cost as well, as forward osmosis driven technologies also “offer a far more resource-efficient means of filtration compared to the more common reverse osmosis techniques” (Johnson, 2019). Forward osmosis is a process that is able to operate on its own without any external influence; much like a kidney, water is recycled in a closed loop (DiCicco, 2020). With “saltwater on one side of the membrane and wastewater on the other, thermodynamics compel the salt to distribute itself evenly throughout all the water in the system”; and since salt is unable to pass through the membrane, fresh water is drawn from the other side (DiCicco, 2020). As the fresh water is extracted, only waste is left behind (DiCicco, 2020). This means that forward osmosis is able to filter extremely dirty and polluted water, which eliminates the reliance on distillation (NASA, 2019). The efficiency of aquaporin technology can offer a more resource-efficient method of water filtration and recycling not only in space, but here on Earth as well (Johnson, 2019).

Benefits of aquaporin technology

Today, about twenty-five percent of the global population do not have access to basic sanitation and water services, meaning that over two billion people on Earth lack access to water that is safe to drink (CDC, 2021). As a result, millions of people, especially those living in developing countries, continue to suffer from preventable sanitation related diseases including diarrhoea, cholera, and typhoid fever; which, without adequate care, can ultimately result in death (CDC, 2021). In fact, unsafe drinking water has contributed to approximately 72% of diarrheal deaths, and unsafe sanitation has contributed to approximately 56% of diarrheal deaths (CDC, 2021). Additionally, according to the Centres for Disease Control and Prevention, “water, sanitation, and hygiene has the potential to prevent at least 9% of the global disease burden and 6% of global deaths” (CDC, 2021). Water scarcity even has the potential to displace 700 million people by 2030, according to the United Nations Department of Economic and Social affairs (United Nations, 2021).

Today, industrial processes tend to generate large amounts of highly concentrated wastewater which they currently do not treat, resulting in prevalent pollution (DiCicco, 2020). Some governments are implementing ‘zero liquid discharge’ requirements, which means that “essentially no liquid waste should leave the premises of an industrial unit” (Perry et al., 2015). As a result of these changes, there is a larger demand for an efficient and effective water treatment system that leaves virtually no waste behind. Several different methods of aquaporin production are being developed and tested for large-scale use and are displaying potential to help

According to the United Nations, “the world will experience a 40% deficit in water supply by 2030”, and the global demand for “blue water” will increase by 55% from 2000 to 2050 (Perry et al., 2015). This is strongly associated with the fact that the global population is expected to reach 9.1 billion by 2050, combined with the idea that more people are entering a wealthier middle class where the “production of water-intensive foods and other nutritional products is increasing” (Perry et al., 2015).

New and improved water treatment technologies using aquaporins have the potential to help manage these increasing demands for water, energy, and food. Due to the protein’s efficiency, water-treatment systems using aquaporins are able to filter water twice as fast as other existing water-treatment systems, and almost double the water recovery rate as well. A higher water recovery rate is crucial, as places that are in need of water purification are also places that tend to experience the highest stresses on water supply (NASA, 2019).

Peter Holme Jensen, founder of a company that specializes in aquaporin technology, specifies that through traditional systems, “It’s not millions, it’s billions of litres of water that are wasted on a daily basis” (NASA, 2019). In fact, in most existing water treatment systems, more than 70% of the water is lost through the process of simply cleaning contaminants off the back of the membrane (NASA, 2019). In desalination, the cost of energy, which is usually 20%-30% the total cost of the water used, is the most substantial factor in the cost of water filtration (Perry et al., 2015). Compared to existing technologies, not only does aquaporin technology require less energy to operate, but it also requires less maintenance and space as well (DiCicco, 2020). This new water treatment technology has the potential to “ensure availability and sustainable management of water and sanitation for all” which resembles the Sustainable Development Goal six (SDG 6).

Challenges and limitations

The largest challenge associated with this technology is the fact that membranes that are capable of hosting transmembrane proteins “must be able to hydrophobically match the proteins” (Perry et al., 2015). Due to this, “the host membrane must be in the order of a few nanometres thick, which again necessitates the use of integrated support materials” (Perry et al., 2015). This requirement in design must also be considered alongside the operational demands for membrane applications including the demand for high selectivity, high permeability, sufficient mechanical stability, chemical stability, and ease of upscaling (Perry et al., 2015).

Future applications

In the future, forward osmosis driven aquaporin technology can be used industrially to treat ‘wastewater in the oil and gas, food and beverage, dairy farming, and textile industries, among other businesses that generate large amounts of highly polluted wastewater’ (NASA, 2019). In animal farming, the high selectivity of aquaporins provides the ability to recapture urea from fertilizer and/or wastewater (NASA, 2019). Additionally, in the healthcare industry, this technology has the potential to improve the quality of life for dialysis patients by making dialysis portable (DiCicco, 2020). Currently, these patients are often required to spend hours travelling back and forth from treatment multiple times every week- where they then must spend three or four hours bedridden (DiCicco, 2020). This is due to the fact that haemodialysis requires approximately 200 litres of water per treatment, all of which turn into wastewater during the process (DiCicco, 2020). It is possible that by implementing forward osmosis driven aquaporin technology, this wastewater can be filtered and reused throughout the treatment, and “dialysis could fit in a backpack” (DiCicco, 2020). Aquaporin technology can also be used to help develop vaccines as the protein can be used to collect virus particles as well (NASA, 2019). In addition, this technology can also be used in the pharmaceutical industry as aquaporins are able to trap active ingredients that other systems fail to capture (NASA, 2019).

Conclusion

As water treatment demands and water pollution/waste increases, it is important to view wastewater and polluted water not as lost resources, but as an opportunity for resource recovery (Perry et al., 2015). While global water demand grows, this new water treatment technology becomes increasingly essential day by day, especially in remote locations where clean drinking water is not easily accessible (see Figure 3).

Now, this unique new water-treatment technology implemented to purify and filter water for astronauts on the International Space Station can help provide millions of people with clean water worldwide. Dines Thornberg, innovation manager of BIOFOS (Denmark's largest state-owned wastewater utility), believes that this new technology has great potential:

"I think [aquaporin technology] could lead the way in actually creating clean, affordable drinking water from wastewater in the future. I am really optimistic that we can meet the challenges of water scarcity in many parts of the world with technologies like this" -Thornberg in Moreno (2020).