Human presence in outer Space is currently supported by a regular resupply of water and food from Earth. As this becomes impossible for long distances, deep-space exploration or space habitation will depend on regenerative life support systems (RLSS) for in-situ oxygen, water and food production and waste management. Urine recycling is of key interest in RLSS to recover water and nutrients, which can serve as a fertilizer for plants and microalgae.
Urine source separation and recycling also gains attention on Earth to close and/or shorten the terrestrial nutrient cycles, which play a pivotal role in our food supply, but are currently pushed to their planetary boundaries by extensive synthetic fertilizer production and use.
Urine contains many valuable compounds, but the compositional complexity of urine also presents a challenge for urine treatment and recycling. Different urine treatment trains combining biological and physicochemical processes were explored in this PhD thesis. Three main treatment steps were considered:
(i) Alkalinization through chemical or electrochemical hydroxide addition to prevent urea hydrolysis during collection and storage,
(ii) Biostabilization in a microbial electrolysis cell and membrane-aerated biofilm reactor or moving bed biofilm reactor to transform urine into a stable nitrate-rich urine solution low in organics, suitable for plant or microalgae cultivation,
(iii) Concentration of the nitrified urine through electrodialysis or an electrochemical cell or valorization through microalgae cultivation in a photobioreactor.
These novel resource-efficient urine treatment trains maximize nutrient recovery while minimizing the use of consumables which could advance nitrogen recovery on Earth and could push the development of RLSS for long-term human spaceflights.