Optimizing Nitrogen Fixation and Recycling for Food Production in Regenerative Life Support Systems

Nitrogen (N) recycling is essential for efficient food production in regenerative life support systems. Crew members with a high workload need 90–100 g of protein per person day, which about 14 N, or 1 mole day. Most this N excreted through urine 85% as urea. Plants take up predominantly nitrate and ammonium, but direct uptake urea possible small amounts. Efficient requires maintenance pH waste streams below 7 to minimize the volatilization ammonia. In aerobic reactors, continuous conditions are needed nitrous oxide. not well recycled on Earth. The energy intensive Haber–Bosh process supplies most crop terrestrial agriculture. Bacterial fixation dinitrogen ammonium also intensive. Recycling from plant human necessary fixation. Here we review approaches potential Initial estimates indicate that nearly all can be recovered forms usable plants.