AUTHOR=Wallentine Tyler , Merkley David , Langenfeld Noah J. , Bugbee Bruce , Seefeldt Lance C. 

TITLE=Approaches to nitrogen fixation and recycling in closed life-support systems

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2023.1176576

DOI=10.3389/fspas.2023.1176576

ISSN=2296-987X

ABSTRACT=<p>N<sub>2</sub> fixation is essential to the sustainability and operation of nitrogen systems but is energetically expensive. We developed a model and used sensitivity analysis to identify the impact of aerobic and anaerobic waste digestion, crop harvest index, rates of recovery of recalcitrant N, and the rate of N<sub>2</sub> fixation in a system combining nitrogen fixation and recycling. The model indicates that the rate of N<sub>2</sub> fixation, loss from reactors, fertilization efficiency, and crop harvest index have the largest impact on maintaining bioavailable N. N recoveries from aerobic and anaerobic digestion, as well as direct-to-soil fertilization, are not well characterized, but the case studies using this model indicate that their efficiencies are critical to N recovery. The findings of this model and its presented case studies can be used as a guide in the design of closed-loop habitats both on Earth and in space. These results reveal a clear need for continued research in the areas of N-efficient digestion, fertilization, and fixation.</p>