Abstract
Bioregenerative life support systems (BLSS) are currently in development to tackle low recovery efficiencies, high energy demands, as well as food, water, and oxygen production challenges through the regeneration of nutrients from waste streams. The MELiSSA pilot plant has been developed as a testbed for regenerative life support system bioreactor operation and characterization. As nitrogen is a vital resource in such systems, we studied the functional composition of a new packed-bed nitrifying bioreactor inoculated with a co-culture of Nitrosomonas europaea (ATCC 25978) and Nitrobacter winogradskyi (ATCC 25391). After 840 days of autotrophic continuous cultivation, the packed-bed was sampled at five vertical positions, each with three horizontal positions, and the biomass at each position was characterized via qPCR, 16S amplicon sequencing, and liquid chromatography tandem mass spectrometry. The total number of cells within the different sections fluctuated around 8.95 ± 5.10 × 107 cells/mL of beads. Based on 16S amplicons and protein content, N. europaea and N. winogradskyi constituted overall 44.07 ± 11.75% and 57.53 ± 12.04% of the nitrifying bioreactor, respectively, indicating the presence of a heterotrophic population that, even after such a long operation time, did not affect the nitrification function of the bioreactor. In addition, DNA-based abundance estimates showed that N. europaea was slightly more abundant than N. winogradskyi, whereas protein-based abundance estimates indicated a much higher abundance of N. europaea. This highlights that single-method approaches need to be carefully interpreted in terms of overall cell abundance and metabolic activity.
Highlights
IntroductionCrewed long-distance spaceflight and prolonged stay in space, such as on a base on the Moon or Mars, can only be possible provided if autonomy from terrestrial resupply missions is realized
After five days in batch phase, a continuous culture mode was established in the packed-bed reactor at a hydraulic residence time (HRT) of 80 h for 30 days
Our experimental packed-bed bioreactor was exposed to different ammonium loads and hydraulic residence times over a prolonged period and could achieved full nitrification over a period of about 1.5 years, indicating robust and steady nitrifying activity
Summary
Crewed long-distance spaceflight and prolonged stay in space, such as on a base on the Moon or Mars, can only be possible provided if autonomy from terrestrial resupply missions is realized. 20 tons for food and potable water alone for a crew of four, assuming an estimated 1.83 kg of food and 2.50 kg of water per crew member per day [1]. A three-year mission to Mars would require an estimated payload mass of ca. Such a limitation implies the need for the ability to produce food, water, and a breathable atmosphere on the space vessel from waste streams using highly reliable and robust
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