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.
Highlights
IntroductionTreatment and reuse of human urine is increasingly adopted here on
While separate collection, treatment and reuse of human urine is increasingly adopted here onEarth, on the International Space Station (ISS) it has always been a priority
The results showed a rejection of 61.0 ± 2.8% and 93.3 ± 0.4% of total organic carbon (TOC) and DMSD, respectively [76]
Summary
Treatment and reuse of human urine is increasingly adopted here on. Life Support (ELS) or Bioregenerative Life Support Systems (BLSS) are increasingly investigated for on-site regeneration of water, oxygen and nutrients from urine [3,6,7] These are systems designed to support the biological needs of crew members on board the ISS. The initial capital cost requirements, necessary for an ELS/BLSS to perform reliable high water recovery and high permeate quality, are more relaxed [8] In this context, it is no surprise that space agencies such as NASA and ESA have been spearheading the research and development of technologies to reuse human waste streams from crew members for the last five decades [9,10]. The objective is to outline the current needs to achieve a urine processing unit which is reliable and efficient
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