A five-stage treatment train for water recovery from urine and shower water for long-term human Space missions

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 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-kWh p -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

Full-scale validated Air Gap Membrane Distillation (AGMD) model without calibration parameters

Air gap membrane distillation (AGMD) is one of the most widely discussed membrane distillation configurations at the moment and has been regarded as more thermally efficient than direct contact membrane distillation (DCMD), due to the insulation properties of the air gap. Several AGMD models are available in the literature. However, most of the models developed to date are either missing validation or are only validated at lab-scale. A major hurdle in modelling membrane distillation is the lack of information about the condensation that is occurring inside the gap. Often, major parameters such as the average condensate thickness are taken from semi-empirical formulas or are simply estimated based on educated guesses. Moreover, some studies had shown that at certain conditions the gap can be completely flooded with condensate, which raises the question whether the module can be modelled as air gap altogether. In this study, a previously developed and thoroughly validated DCMD model is extended by adding the air gap compartment. In this way the model only needs to be adjusted for the gap-related parameters. A simple technique is demonstrated for observing the condensation in real time, which also allows to experimentally obtain the value of the average condensate thickness parameter and the flooding of the gap. The model is subsequently thoroughly and simultaneously validated with experimental data from two commercially available modules with areas of 7.2 and 24 m(2), showing an excellent fit to the experimental data. Moreover, this work shows a direct comparison between AGMD and DCMD in terms of flux and thermal efficiency at full-scale using modules with identical geometries from the same manufacturer

Calibration and analysis of a direct contact membrane distillation model using the GLUE method

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