Nutrient, carbon and water recycling is crucial for life support in long-term Space missions with no or limited opportunity for resupply. Protein (and hence nitrogen) is an essential component of the crew diet (15-17 g N / d / person). The Micro-Ecological Life Support System Alternative (MELiSSA) developed by ESA, aims at providing proteinaceous food via vegetable crops and edible microbes (e.g. cyanobacteria). To produce this phototrophic biomass, it is planned to convert urine, a waste stream containing 85% of the crews' nitrogen intake, into a nitrate fertilizer. Urine pretreatment involving conversion of urea and ammoniacal nitrogen to nitrate, could render this aqueous stream available for water recovery through membrane processes or higher plants, saving considerably on energy consumption. Nitrification of urine hence provides a pivotal role for nutrient and / or water recovery in Space.

Urine nitrification is a process that can only be performed biologically, catalyzed by a consortium

of three functional groups of bacteria, i.e. (i) urease positive heterotrophs responsible for the

hydrolysis of urea to ammonia and for aerobic oxidation of organic compounds in urine, (ii)

ammonia oxidizing bacteria responsible for the aerobic oxidation of ammonia to nitrite

(nitritation), and (iii) nitrite oxidizing bacteria responsible for the aerobic oxidation of nitrite to

nitrate (nitratation). Due to an efficient collaboration of these sub-processes, urine nitrification

can be performed in a single bioreactor system that contains a microbial biomass retention

system, and is fed with urine and oxygen. In contrast to application on Earth, urine nitrification

has not yet been tested in Space, as its development is challenged by some space environment

related aspects which are biological (cfr. reduction of complexity by selection and synthetic

recomposition of the community with only the essential microbial species, stable collaboration of

the three functional groups, biofilm formation and structure under microgravity, effect of

radiation) and technological (cfr. substrate transport to and within the biological community

under microgravity conditions, e.g. oxygen gas transfer from gas to liquid).

The URINIS project aims at providing a proof of principle that urine nitrification, a key process

in the MELiSSA life support system, is possible under Space conditions in the ISS. Its

demonstration would open up future opportunities for advanced nutrient and water recycling in

Space, thus decreasing the need for resupply and/or high energy consumption. The initial ground

studies of URINIS provided preliminary knowledge on aspects such as activities, growth rates,

cell motility and biofilm related organization of these nitrifying bacteria, with and without

simulated gravity. One of the deliverables included the development of an ‘xperiment Scientific

Requirements’document for URINIS A which has been approved by ESA. The present URINISA

Prodex proposal builds on the know-how gathered during the first phase of the project to ensure

the success of the first proof of principle of urine nitrification in space to be conducted at the ISS

in the period 2022-2024. URINIS-A phase 2 lays out an ambitious work plan to address the

existing knowledge gaps and commence the development of adequate hardware for the flight

experiment.