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

Abstract

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

Toward sustainable space exploration: a roadmap for harnessing the power of microorganisms

“…Symbiotic bacteria are also essential in solubilizing nutrients from the environment and converting them into bioavailable forms, and improving soil fertility 29 , 30 . Nitrogen recovery for food production can, for instance, be accomplished by microbial-mediated nitrogen fixation from the atmosphere, or nitrification of urine, mediated by synthetic microbial communities (see section ‘Human waste processing and reclamation’) 31 .…”

Space Exploration: The Role for Public-Private Research and Development Partnerships

“…Recent advances in bioregenerative life support systems (BLSS) can provide large-scale artificial ecosystems that mimic the environmental conditions on Earth, allowing for the production of key biological mechanisms (e.g. carbon and nitrogen fixation) used as inputs for agricultural production (73). By enhancing regenerative capacity of the carbon reduction cycle and photosynthesis while minimizing oxygenation and photorespiration, yield output can significantly improve (74).…”

Colorimetric determination of urea using diacetyl monoxime with strong acids

“…Monitoring urea concentration in soil leachate or liquid hydroponics helps quantify the hydrolysis rate which can lead to a basis for nitrogen application rates [ 5 ]. Quantification of urea is especially important in regenerative life support systems for long-term space missions to ensure efficient nitrogen recycling and recovery from urine [ 6 ].…”