Urine Treatment on the International Space Station: Current Practice and Novel Approaches

Abstract

A reliable, robust, and resilient water recovery system is of paramount importance on board the International Space Station (ISS). Such a system must be able to treat all sources of water, thereby reducing resupply costs and allowing for longer-term space missions. As such, technologies able to dewater urine in microgravity have been investigated by different space agencies. However, despite over 50 years of research and advancements on water extraction from human urine, the Urine Processing Assembly (UPA) and the Water Processor Assembly (WPA) now operating on the ISS still achieve suboptimal water recovery rates and require periodic consumables resupply. Additionally, urine brine from the treatment is collected for disposal and not yet reused. These factors, combined with the need for a life support system capable of tolerating even dormant periods of up to one year, make the research in this field ever more critical. As such, in the last decade, extensive research was conducted on the adaptation of existing or emerging technologies for the ISS context. In virtue of having a strong chemical resistance, small footprint, tuneable selectivity and versatility, novel membrane-based processes have been in focus for treating human urine. Their hybridisation with thermal and biological processes as well as the combination with new nanomaterials have been particularly investigated. This article critically reviews the UPA and WPA processes currently in operation on the ISS, summarising the research directions and needs, highlighted by major space agencies, necessary for allowing life support for missions outside the Low Earth Orbit (LEO). Additionally, it reviews the technologies recently proposed to improve the performance of the system as well as new concepts to allow for the valorisation of the nutrients in urine or the brine after urine dewatering.

Development of Nitrogen Recycling Strategies for Bioregenerative Life Support Systems in Space

“… Simplified schematic overview of the Environmental Control and Life Support System (ECLSS) currently in use on the International Space Station (ISS; Adapted from Volpin et al, 2020 ). …”

“…The UPA’s position in the ECLSS is shown in Figure 1 . In Figure 2 , a schematic overview of the UPA module is provided ( Bagdigian et al, 2015 ; Volpin et al, 2020 ).…”

“…The remaining waste is stored and destroyed upon re-entry in Earth’s atmosphere. On the ISS, the environmental control and life support systems (ECLSSs) are entirely based on physicochemical processes and are responsible for the production of potable water and oxygen with the help of waste stream recycling ( Bagdigian et al, 2015 ; Volpin et al, 2020 ). As a result, the transport payload of water can be reduced by as much as 96.5% ( Hendrickx et al, 2006 ; Clauwaert et al, 2017 ).…”

Urologic Innovation in the Spaceflight Environment: Challenges, Opportunities, and Future Directions

“…3 On the International Space Station (ISS), urine separated from fecal matter can then be recycled and converted into drinking water. 4 NASA's need for constant innovation and the improvement of existing technology led to the first Space Transportation System (STS) Shuttle Orbiter WCS, followed by the development the Universal Waste Management System (UWMS) for the ISS in 2015 (Figure 1). The development of the UWMS was a partnership between the Advanced Exploration Systems program at NASA headquarters, the Orion Program, the ISS Program, and Collins Aerospace.…”

Membranes for Water, Gas and Ion Separation

“…Lastly, Volpin et al [ 5 ] reported urine treatment applications on the International Space Station (ISS). They focused on membrane-based approaches with current challenges and opportunities.…”