Within the project “Setting the ground for sustainable bioproduction in a Martian settlement”, two doctoral candidates and a postdoctoral researcher will collaborate closely to develop a basis for bioproduction processes on Mars that rely on the planet’s natural resources, in order to increase the sustainability of future settlements. The foreseen approach combines different biological modules including cyanobacterium-, microbial electrosynthesis-, and plant-based modules.
The doctoral project has two main goals: (i) developing the MES-based module which will be fed with cyanobacterium biomass and regolith, produce substrates for plant growth as well as other consumables, and recycle waste from secondary producer (e.g., human metabolic waste and inedible parts of plants) to close the loop; and (ii) model the entire ISRU-based bioproduction concept (centered around the MES, and including cyanobacteria and plants) to guide its optimization and assess its efficiency. More details on those goals, and on the way they will be met, follow.
The MES module is outlined hereafter. It will comprise two half-cells (anodic and cathodic) separated by an ion exchange membrane and connected to an external electrical circuit. Biomass collected from the cyanobacteria grown on site (see Sub-project 1), possibly supplemented with organic waste from plants and humans, will be fed to the anodic compartment, where exoelectrogenic bacteria will (i) oxidize it into gaseous compounds (CO2, and the fuels CH4 and H2); (ii) leave a suspension depleted in organic carbon, and enriched in fixed inorganic nitrogen and other plant-assimilable nutrients; and (iii) transfer electrons, via the anode, to the cathodic compartment. There, electrotrophic bacteria (e.g., Dechloromonas sp.) will use the generated electrons (as well as additional ones from an external power supply), CO2, and some elements from the cyanobacterium biomass (e.g., NH4+) to remove perchlorate from the regolith. An alternative cathodic compartment will rely on Kyrpidia spormannii to produce PHA: polymers of short fatty acids that can be used as bioplastic for 3D printing of tools or structures. This module can be easily adapted to the synthesis of other chemicals (short fatty acids, methane, hydrogen), or to biomining (see APF Seed project 1), by changing the electrotrophic community. Effluents from the MES (plant-assimilable nutrients in solution, and perchlorate-depleted regolith) will be used for plant cultivation (see Sub-project 3).
The present sub-project combines two approaches: a theoretical one (process design and modelling) and an experimental one. The theoretical one will rely on bioreactor- and mass balance-based modelling to guide (i) the design of more efficient pathways (both qualitatively – e.g., adding or removing steps – and quantitatively – e.g., determining the optimal flux towards plants of the various compartments that feed them), and (ii) the determination of the efficiency of the overall ISRU-based bioproduction concept. The costs considered for assessing efficiency include established standards used by space agencies (e.g., mass of imported materials, crew time and power use), but also impact on the Martian landscape (e.g., metal nutrient cycling will be optimized to minimize the need for excavating regolith). This work will draw heavily upon the data generated within the other two sub-projects and within the experimental part of the present one (see below). The effects of reduced gravity study on the system will be assessed theoretically. If relevant, we will aim at confirming or correcting predictions by experiments in the Drop Tower. Separate funding would then be applied for (to DLR), and the experimental setup would be designed by ZARM personnel to keep the workload of the doctoral researcher to a suitable level.
The experimental part will generate data required to develop and confirm the model. Cyanobacterial biomass (which will be used as input for MES) will be collected at the ZARM (at the LASM, and later from the photobioreactor developed as part of the “Living habitat” Seed project). MES experiments will be performed in Prof. Kerzenmacher’s group at UFT, whose experience with MES include, for instance, the production of electricity from wastewater, or the production of bioplastic or biofuel through microbial electrosynthesis. The main scientific questions in this context pertain to the conversion processes (organic carbon oxidation, PHA synthesis, dechlorination) and conversion rates (expressed, e.g., as current density and conversion efficiency) occurring in the anode and cathode compartments of the MES. We will first perform chronoamperometry experiments focusing on the individual electrode processes, before studying the complete MES (in which the transport of ions or small organic molecules between anode and cathode, for instance, can be unveiled). A characterization of the effluents (by HPLC, ion chromatography, NMR as an external collaboration, and colorimetric kits), as well as of the bacterium-weathered regolith (in collaboration with Prof. Thorsten Gesing), will be performed together with the other PhD student (see Sub-project 3). The electroactive biofilm will be characterized using electrochemical, microscopy and molecular biology techniques.
The doctoral researcher will be employed at the Faculty of Production Engineering at the University of Bremen, in the research group Environmental Process Engineering (Prof. Dr. Sven Kerzenmacher). Research activities will be co-supervised by Dr. Guillaume Pillot (Environmental Process Engineering) and Dr. Cyprien Verseux (Laboratory of Applied Space Microbiology, ZARM, University of Bremen). Extensive cooperation is also expected with Dr. Daniel Schubert’s group at the German Aerospace Center (DLR) in Bremen.