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Nowadays, there are still many challenges to overcome in order to enable long-termed human space exploration beyond low Earth orbit (LEO) and metabolic resources management (reliable air, water and food supply for the crew) is of utmost importance. Currently, Environmental Control and Life Support Systems (ECLSS) aim to overcome the challenge of constant re-supply from Earth requirement by revitalization of air and water. Here, we provide an overview of the existing and operating ECLSS on-board the International Space Station (ISS) as well as identify potential areas of technology development for biological ECLSS for long-term human space missions focusing on the inclusion of waste treatment and food production.

The 3-days international virtual MELiSSA conference (November 3 to 5, 2020) about the closed life support systems was organized by the University of Ghent and IDDUP in collaboration with ESA/ESTEC (European Space Agency) and MELiSSA Foundation, and welcomed around 150 papers. The first day addressed the welcomed contributions of the 5 major space agencies, the plants & photosynthetic microorganisms used for life support in space, the simulation of planetary ecosystems as well as MELiSSA inspired circular economy and education. The second day focused on Ground demonstration and analogue testing, Photobioreactors and photosynthetic microorganisms characterization, Modelling and Systems design, Organic wastes process and Metabolome where a real breakthrough was observed as well as in human microbiome in closed environments. The last day addressed: 1) the complex problematics of urine as a major source of nutrients, 2) Terrestrial synergies, and 3) some Physical, Chemical and Microbial contaminants linked to space research.

limnospira indica pcc8005 growth in photobioreactor2020-11-25; International audience; the arthrospira-b experiment is the first experiment in space ever allowing the online measurements of both oxygen production rate and growth rate of limnospira indica pcc8005 in batch photobioreactors running on-board iss. four bioreactors were integrated in the iss biolab facility. each reactor was composed of two chambers (gas and liquid) separated by a ptfe membrane and was run in batch conditions. oxygen production was monitored by online measurement of the total pressure increase in the gas chamber. the experiments are composed of several successive batch cultures for each reactor, performed in parallel on iss and on ground. in this work, a model for the growth of the cyanobacterium limnospira indica pcc8005 (also known as arthrospira or spirulina) in these space membrane photobioreactors was proposed and the simulation results obtained are compared to the experimental results gathered in space and on ground. the photobioreactor model was based on a light transfer limitation model, already used to describe and predict the growth and oxygen production in small to large scale ground photobioreactors. it was completed by a model for ph prediction in the liquid phase allowing assessment of the ph increase associated to the bicarbonate consumption for the biomass growth. a membrane gas-liquid transfer model is used to predict the gas pressure increase in the gas chamber. substrate limitation is considered in the biological model. a quite satisfactory fit was achieved between experimental and simulation results when a suitable mixing of the liquid phase was maintained. the data showed that microgravity has no first order effect on the oxygen production rate of limnospira indica pcc8005 in a photobioreactor operating in space in zero gravity conditions.

The ability of cyanobacterium Arthrospira sp. to assimilate waste nitrogen sources (ammonium and urea) makes it an important candidate for wastewater management. The aim of this work was to evaluate a cultivation approach based on continuous-transitional-feeding regime (nitrate-ammonium-nitrate) in a photobioreactor to assess the effects of ammonium salts on Arthrospira sp. PCC 8005 metabolism. Using a comprehensive biochemical, proteomic and stoichiometric profiling of biomass, this study demonstrated that the proposed cultivation approach could increase the proteins and pigments yields by 20-30%, compared to the respective yields obtained from wild-type Arthrospira sp. strain A light-energy-transfer model was used to predict the biomass and oxygen productivities of Arthrospira sp. cultivated under transitional-feeding regime. 95 ± 2% match was observed between the experimental and simulated productivities. This study thus opened new avenues for use of ammonium rich wastewater for commercial production of high value pigments, biofuel and bioplastics using Arthrospira sp.

Long-term human Space missions depend on regenerative life support systems (RLSS) to produce food, water and oxygen from waste and metabolic products. Microbial biotechnology is efficient for nitrogen conversion, with nitrate or nitrogen gas as desirable products. A prerequisite to bioreactor operation in Space is the feasibility to reactivate cells exposed to microgravity and radiation. In this study, microorganisms capable of essential nitrogen cycle conversions were sent on a 44-days FOTON-M4 flight to Low Earth Orbit (LEO) and exposed to 10−3–10−4 g (gravitational constant) and 687 ± 170 µGy (Gray) d−1 (20 ± 4 °C), about the double of the radiation prevailing in the International Space Station (ISS). After return to Earth, axenic cultures, defined and reactor communities of ureolytic bacteria, ammonia oxidizing archaea and bacteria, nitrite oxidizing bacteria, denitrifiers and anammox bacteria could all be reactivated. Space exposure generally yielded similar or even higher nitrogen conversion rates as terrestrial preservation at a similar temperature, while terrestrial storage at 4 °C mostly resulted in the highest rates. Refrigerated Space exposure is proposed as a strategy to maximize the reactivation potential. For the first time, the combined potential of ureolysis, nitritation, nitratation, denitrification (nitrate reducing activity) and anammox is demonstrated as key enabler for resource recovery in human Space exploration.

The aim of this study was to investigate ammonia load removable by a fixed-bed bioreactor. In this study, high ammonia loads, up to 4.5 kgN/m3 d were applied on a fixed bed reactor colonised by two pures nitrifying bacteria: Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391. The loads were similar to the highest values reported in literature especially with a two bacteria population. The complete ammonia removal efficiency in our installation has reached 2.5 kgN/m3.d for a full nitrification. An N-tank in series model was used to represent the fixed bed reactor and to predict the nitrification in the installation. The developed model was accurate and representative of the nitrification assumed by Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391. This model was also used to predict the biomass and oxygen concentrations during the experiment under various operational conditions. The biofilm fixed on the solid support (polysterene beads 2 mm diameter) was mainly present in the bottom of the reactor where the ammonia load was applied. It is demonstrated that in this region of the column the oxygen concentrations reached the lowest values.

The MELiSSA (MicroEcological Life Support System Alternative) project is developing a closed regenerative life support system for long-term space missions by considering the integration of six biological compartments tested in a dedicated pilot plant. The technological effort of building such a closed and sustainable ecological system can also have relevant applications for intensive circular resources reutilization at terrestrial level. In this work, the continuous operation and gas phase connection of two elements of the loop (83 L air-lift Limnospira indica photobioreactor (PBR) and a rat isolator (mock crew)) is performed and modelled. The model includes PBR hydrodynamic characterization, gas-liquid mass transfer and cyanobacteria growth, crew consumption and a control system adjusting light intensity according to oxygen demand. The model is validated in a series of tests where crew compartment oxygen setpoints are sequentially changed to test the global dynamics. The obtained results show a good model performance, as indicated in the low relative error (≤ 0.06) and the high Pearson correlation coefficient and Willmott-d-index obtained for the main variable of the system (0.98–1.00), oxygen concentration, in all cases.

The aim of the present work was to study the growth of two nitrifying bacteria. For modelling the nitrifying subsystem of the MELiSSA loop, Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25931 were grown separately and in cocultures. The kinetic parameters of a stoichiometric mass balanced Pirt model were identified: μ max = 0.054 h −1 , decay rate b = 0.003 h −1 and maintenance rate m = 0.135 gN-NH 4 + ·gX −1 ·h −1 for Nitrosomonas europaea ; μ max = 0.024 h −1 , b = 0.001 h −1 and m = 0.467 gN-NO 2 − ·gX −1 ·h −1 for Nitrobacter winogradskyi . A predictive structured model of nitrification in co-culture was developed. The online evolution of the addition of KOH is correlated to the nitritation; the dissolved oxygen concentration is correlated to both nitritation and nitratation. The model suitably represents these two variables so that transient partial nitrification is assessed. This is a clue for avoiding partial nitrification by predictive functional control.

The purpose of this study is to estimate the possible effect produced on plant productivity by inedible plant biomass added to soil-like substrate (SLS). Results of the experiments with radish plants grown on the SLS with inedible biomass of carrot and beet plants added in the amounts roughly equal to their yields harvested from the same area showed a significant reduction in productivity of radish plants. The yield of radish plants grown on the SLS with added radish tops was almost the same as the yield of the radish grown on the neutral substrate. Experiments with addition of dry wheat straw to the SLS and growing of wheat and radish plants on that substrate also showed that the productivity of the plants grown in that way was decreased. Attempts to negate the adverse effect of plant wastes proved that the most effective way was to mineralize the wastes using the technique of “wet incineration”.

Scale-up of bioreactors has the intrinsic difficulty of establishing a reliable relationship among physical parameters involved in the design of the new bioreactor and the physiology of the cultured cells. This is more critical in those cases where a more complex operation of the bioreactor is needed, such as in photobioreactors. A key issue in the operation of photobioreactors is establishing a quantification for the interaction between external illumination, internal light distribution and cell growth. In this paper an approach to the scale-up of a photobioreactor for the culture of Spirulina platensis, based on a mathematical model describing this interaction, and the operation of a previous reactor 10 times smaller is presented. The paper describes the approach followed in the scale-up, the analysis of different design constraints, the physical realization of the new bioreactor design, innovative use of plastic material walls to improve reactor safety, and finally the corroboration of its satisfactory operation.

As a part of a natural biological N-cycle, nitrification is one of the steps included in the conception of artificial ecosystems designed for extraterrestrial life support systems (LSS) such as Micro-Ecological Life Support System Alternative (MELiSSA) project, which is the LSS project of the European Space Agency. Nitrification in aerobic environments is carried out by two groups of bacteria in a two-step process. The ammonia-oxidizing bacteria (Nitrosomonas europaea) realize the oxidation of ammonia to nitrite, and the nitrite-oxidizing bacteria (Nitrobacter winogradskyi), the oxidation of nitrite to nitrate. In both cases, the bacteria achieve these oxidations to obtain an energy and reductant source for their growth and maintenance. Furthermore, both groups also use CO2 predominantly as their carbon source. They are typically found together in ecosystems, and consequently, nitrite accumulation is rare. Due to the necessity of modeling accurately conversion yields and transformation rates to achieve a complete modeling of MELiSSA, the present study focuses on the experimental determination of nitrogen to biomass conversion yields. Kinetic and mass balance studies for axenic cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in autotrophic conditions are performed. The follow-up of these cultures is done using flow cytometry for assessing biomass concentrations and ionic chromatography for ammonium, nitrite, and nitrate concentrations. A linear correlation is observed between cell count and optical density (OD) measurement (within a 10 % accuracy) validating OD measurements for an on-line estimation of biomass quantity even at very low biomass concentrations. The conversion between cell count and biomass concentration has been determined: 7.1 × 1012 cells g dry matter (DM)−1 for Nitrobacter and 6.3 × 1012 cells g DM−1 for Nitrosomonas. Nitrogen substrates and products are assessed redundantly showing excellent agreement for mass balance purposes and conversion yields determination. Although the dominant phenomena are the oxidation of NH 4 + into nitrite (0.95 mol mol N−1 for Nitrosomonas europaea within an accuracy of 3 %) and nitrite into nitrate (0.975 mol mol N−1 for Nitrobacter winogradskyi within an accuracy of 2 %), the Nitrosomonas europaea conversion yield is estimated to be 0.42 g DM mol N−1, and Nitrobacter winogradskyi conversion yield is estimated to be 0.27 g DM mol N−1. The growth rates of both strains appear to be dominated by the oxygen transfer into the experimental setups.

Manmade ecosystems differ from their prototype biosphere by the principle of control. The Earth Biosphere is sustainable by stochastic control and very large time constants. By contrast, in a closed ecosystem such as the micro-ecological life support system alternative (MELiSSA system) developed by the European Space Agency for space exploration, a deterministic control is a prerequisite of sustainable existence. MELiSSA is an integrated sum of interconnected biological subsystems. On one hand, all unit operations in charge of the elementary functions constitutive of the entire life support system are studied until a thorough understanding and mathematical modelling. On the other hand, the systemic approach of complex, highly branched systems with feedback loops is performed. This leads to study in the same perspective, with the same degree of accuracy and with the same language, waste degradation, water recycling, atmosphere revitalisation and food production systems prior to the integration of knowledge-based control models. This paper presents the mathematical modelling of the MELiSSA system and the interface between the control strategy of the entire system and the control of the bioreactors.

The feasibility of nearly-complete conversion of lignocellulosic waste (70% food crops, 20% faecal matter and 10% green algae) into biogas was investigated in the context of a Life Support Project. The treatment comprised a series of processes, i.e. a mesophilic laboratory scale CSTR (continuously stirred tank reactor), an upflow biofilm reactor and a hydrothermolysis system in near-critical water. By the one-stage CSTR, a biogas yield of 75% with a specific biogas production of 0.37 l biogas g(-1) VSS (volatile suspended solids) added at a HRT (hydraulic retention time) of 20 d was obtained. Biogas yields further increased with 10-15% at HRT20 d, indicating the hydrolysis of lignocellulose to be the rate-limiting conversion step. The solids present in the CSTR-effluent were subsequently treated by hot water treatment (T approximately 310-350 degrees C, p approximately 240 bar), resulting in effective carbon liquefaction (50-60% without and 83% with carbon dioxide saturation) and complete hygienisation of the residue. Subsequent anaerobic digestion of the hydrolysate allowed further conversion of 48-60% on COD (chemical oxygen demand) basis. Thus, the total process yielded biogas corresponding with a COD conversion up to 90% of the original organic matter. It appears that mesophilic digestion in conjunction with hydrothermolysis at near-critical conditions offers interesting features for (nearly) complete, non-toxic and hygienic carbon and energy recovery from human waste in a bioregenerative life support context.

This paper introduces two modeling approaches in consideration for the MELiSSA Higher Plants Compartment. This includes an empirical light response curve modeling approach and the Modified Energy Cascade (MEC) model. The MEC model was translated into EcosimPro and evaluated for its performance under a range of environment conditions. The model demonstrated an adequate response to changes on the environmental conditions (temperature, CO 2 concentration and light flux) predicting the gas exchange (O 2 production, CO 2 consumptions, and water vapor transpiration).

Given the constraints of the current launchers, manned exploration beyond LEO implies long time missions, a high mass of metabolic consumables and consequently regenerative life support technologies developments. To validate their efficiency, as well as their reliability, these technologies need to be tested in the most analog conditions (i.e. isolation, limited spare part, ...). A large number of these conditions are met in the new permanent French-Italian settlement called Concordia, currently being built in the Antarctic continent. Over the last 15 years, ESA developed regenerative life support technologies. Two of these technologies: a Grey Water Treatment Unit and a Black Water Treatment Unit are currently assembled at the size of 15 to 70 persons to fulfill the Concordia crew needs The first technology is a multi step filtration system and will recycle the shower, washing machine, dish washer and cleaning water. The second technology, issued of MELiSSA project development, is composed of three bioreactors and will be used to process the fecal material, the urine and the kitchen wastes generated by the crew. The process is structured in three steps: a liquefaction, a methanogenic and a nitrifying step. Liquid effluents from this unit will then be further treated by the GWTU to produce hygiene water. The long-term life tests of these technologies will allow ESA to test regenerative life support technologies in the most realistic conditions. Technical parameters (i.e. efficiency, reliability,..) as well as human factors issues (i.e. psychology) will be continuously studied.

The feasibility of nearly-complete conversion of lignocellulosic waste (70% food crops, 20% faecal matter and 10% green algae) into biogas was investigated in the context of a life support project. The treatment comprised a series of processes, i.e., a mesophilic laboratory scale CSTR (continuously stirred tank reactor), an upflow biofilm reactor, a fiber liquefaction reactor employing the rumen bacterium Fibrobacter succinogenes and a hydrothermolysis system in near-critical water. By the one-stage CSTR, a biogas yield of 75% with a specific biogas production of 0.37 l biogas g(-1) VSS (volatile suspended solids) added at a RT (hydraulic retention time) of 20-25 d was obtained. Biogas yields could not be increased considerably at higher RT, indicating the depletion of readily available substrate after 25 d. The solids present in the CSTR-effluent were subsequently treated in two ways. Hydrothermal treatment (T approximately 310-350 degrees C, p approximately 240 bar) resulted in effective carbon liquefaction (50-60% without and 83% with carbon dioxide saturation) and complete sanitation of the residue. Application of the cellulolytic Fibrobacter succinogenes converted remaining cellulose contained in the CSTR-effluent into acetate and propionate mainly. Subsequent anaerobic digestion of the hydrothermolysis and the Fibrobacter hydrolysates allowed conversion of 48-60% and 30%, respectively. Thus, the total process yielded biogas corresponding with conversions up to 90% of the original organic matter. It appears that particularly mesophilic digestion in conjunction with hydrothermolysis at near-critical conditions offers interesting features for (nearly) complete and hygienic carbon and energy recovery from human waste in a bioregenerative life support context.

The amount of food t o bring and eventually to produce on Mars during a manned mission and the psychological aspect for a human crew to be cut from an earth -like environment and to live and work in an isolated environment are still debated. Design considerations of a greenhous e as part of a Martian human settlement include, beside growing vegetables for consumption, the possibility for astronauts to attend plants and relax in a garden -like area, possibly reminiscent of an earthly environment.. During international simulation c ampaigns of manned Martian missions organized by The Mars Society , several human crews lived and worked in confined isolation. International crews of mixed gender and professional qualif ications conducted various scientific and oper ational tasks as Martian crews would. Operations were conducted as they would be during a Ma rtian mission, including delays in radio comm unications and Extra -Vehicular Activities (EVA) with specially designed unpressurized suits. During a two week simulation of a manned Mars miss ion at the Mars Desert Research St ation (MDRS), four different sort of vegetables have been grown for 12 days in the manned Habitat and in a detached experimental gree nhouse accessible during simulated EVA’s. The six crew members were asked to partici -pate in the observation and reporting of the germin ation and growth process. At the end of the

MELiSSA is a microorganism based artificial ecosystem conceived as a tool for understanding the behavior of ecosystems and developing the technology for future Manned Space Missions. MELiSSA is composed of four compartments colonized by the microorganisms required by the function of this ecosystem : breakdown of waste produced by men, regeneration of atmosphere and biosynthesis of edible biomass. This paper reports the mass balance description of a Biological Life Support System composed of the MELiSSA loop and of a Higher Plant Compartment working in parallel with the photosynthetic Spirulina compartment producing edible biomass. The recycling efficiencies of the system are determined and compared for various working conditions of the MELiSSA loop with or without the HPC.

Following an enthusiastic start in 1985, ESA's life support technology development programme was re-assessed in the mid- to late-1990s to reflect the strong reduction in European manned space ambitions which occurred at that time. Further development was essentially restricted to activities that could constitute ISS upgrades or enhancements, or support ISS utilisation/operations, together with a single, limited, activity (MELISSA) aimed at bioregenerative life support, in the continuing hope that there might be "life after Station". The paper describes the current status of these activities and summarises the main priorities for future development that were identified at the April 1999 Workshop on Advanced Life Support.

MELISSA (Micro Ecological Life Support System Alternative) is a research project for the development of advanced life support systems, conducted by the European Space Agency. Its basic design is based on a loop of bioreactors with the main objective of the regeneration of the wastes generated by a crew into an edible material, with concomitant regeneration of the atmosphere for human respiration. The MELISSA Pilot Plant is a European facility to study and validate advanced life support systems. It has as main objectives the ground demonstration and characterization of a closed loop concept. This includes the development of the associated technology for its successful continuous operation such as water treatment, pathogen detection, food preparation, and other related items. At present time, the main research project developed in the Pilot plant is the MELISSA project. A key point in its development is the collection of experimental data under real operating conditions in order to perform mathematical modeling. This is a key issue in the approximation followed, both for the control and simulation of the individual bioreactors and the complete loop. The state of the art of the pilot plant is discussed, and particular emphasis is made in the description of the continuous operation of the interconnected bioreactors. Also the necessary associated research, required for its successful operation, such as the development of an advanced control system or the analysis of the effect of the malfunction of one compartment, on the subsequent ones are reviewed.