Abstract
Long-term human Space missions will rely on regenerative life support as resupply of water, oxygen and food comes with constraints. The International Space Station (ISS) relies on an evaporation/condensation system to recover 74–85% of the water in urine, yet suffers from repetitive scaling and biofouling while employing hazardous chemicals. In this study, an alternative non-sanitary five-stage treatment train for one “astronaut” was integrated through a sophisticated monitoring and control system. This so-called Water Treatment Unit Breadboard (WTUB) successfully treated urine (1.2-L-d−1) with crystallisation, COD-removal, ammonification, nitrification and electrodialysis, before it was mixed with shower water (3.4-L-d−1). Subsequently, ceramic nanofiltration and single-pass flat-sheet RO were used. A four-months proof-of-concept period yielded: (i) chemical water quality meeting the hygienic standards of the European Space Agency, (ii) a 87-±-5% permeate recovery with an estimated theoretical primary energy requirement of 0.2-kWhp-L−1, (iii) reduced scaling potential without anti-scalant addition and (iv) and a significant biological reduction in biofouling potential resulted in stable but biofouling-limited RO permeability of 0.5 L-m−2-h−1-bar−1. Estimated mass breakeven dates and a comparison with the ISS Water Recovery System for a hypothetical Mars transit mission show that WTUB is a promising biological membrane-based alternative to heat-based systems for manned Space missions.
Highlights
With the on-going developments in the commercialization of the space industry, human Space exploration has been attracting renewed attention
The integrated Water Treatment Unit Breadboard (WTUB) testbed facility is composed of a Urine Treatment Unit (UTU) and a shower water treatment unit (SWTU) that is depicted in Fig. 1A and B
The measured reverse osmosis (RO)-permeate quality demonstrates that water re covered with the SWTU from the ED diluate and peracetic acid (PAA) stabilized shower water could meet ESA hygienic water requirements and the WHO drinking water guideline quality on most parameters [40]
Summary
With the on-going developments in the commercialization of the space industry, human Space exploration has been attracting renewed attention. To sustain life in Space, fresh supply of water, oxygen and food is essential. With a metabolic minimum for humans of just over 3 L d−1 [1,2,3], and only 10 L d−1 of shower water for comfort on a 900 days mission to Mars, 4 crew members would already need almost 50 ton of fresh water supplies, which is larger than the mass of O2, CO2capture and food combined [4,5]. Taking into account that the International Space Station (ISS) weighs approximately 400 ton, the current limitations in launcher ca pacity (~1 ton H2O) and the high launching cost [6], recycling of water is essential [7]. The combination of urine (~1.5 L person−1 d−1) and a low flow of shower water (≤10 L person−1 d−1) is challenging due to hardness (30–390 mg Ca2+ L−1, 20–205 mg Mg2+ L−1), salinity (0.3–23 mS cm−1), bioavailable organics (up to 10 g COD L−1) and ammoniacal nitrogen (up to 9 g N L−1) present in urine and the surfactants and bioavailable organics present in shower water [9,10]
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