Team:UrbanTundra Edmonton/Experimental
Experimental
In order to accomplish the goal of producing oxygen on a martian like environment our team considered many different possibilities of sustaining a bioreaction in conditions akin to those on Earth. However, such a project comes with significant challenges as the martian environment in its current state is nearly uninhabitable, even for some of the most resilient species. The solution we settled upon was a modular multistage bioreactor. The bioreactor would consist of five main stages, each of each of which would be responsible for a separate task in the bioremediation process. The bioreactor would initially begin the extraction process with the introduction of the perchlorate rich soil into water.
This first step would cause the dissociation of a positive cation and the negative [ClO4]-1 anion into solution. It is expected that the majority of the positive cations would be Na+ and Mg+2. This subsection would then be responsible for diluting this solution to the correct concentration. However, before it can be used by the E.Coli, the solution needs to be filtered of its other ions including sulphites and many other molecules that do not dissociate easily in water. According to NASA’s baseline assumptions it can be expected that the martian soil will contain 44.84% SiO2, 9.32% Al2O3 and 10.42% FeO all of which are highly insoluble in water and can therefore be separated with a series of simple filters (Anderson et al. 57). The most feasible way to deal with the presence of these few remaining ions is to pass them through a sulphite filter or other filter specifically targeted toward an ion; a technology that has been well developed for winemaking and food processing. The aforementioned salts in the water greatly reduce the freezing temperature of water thereby allowing this portion of the bioreactor to operate at a lower temperature and reduces the amount of energy required for this subsystem.
While this process takes place, the E.Coli will need to be incubated in a separate chamber of the bioreactor; one which is carefully climate controlled. To maintain a carbon cycle in a location where one does not naturally exist, carbon must be conserved wherever possible. The previous year’s team tested this using “Riley broth”, composed of the defecate from Dr. Michael Ellison’s dog. This substance could theoretically be replaced with human fecal matter aboard a long term mission. This chamber would utilize a vacuum sealed double wall system, greatly reducing the heating cost of this bioreactor portion. This system function in a similar fashion to a fed-batch culture, in which nutrients are constantly fed into the system via a controlled feed. This phase is also designed in smaller systems that allow for certain cultures of E.Coli to be left untouched while others are siphoned into the next stage of the bioreactor.
In the third phase of the processing, the E.Coli that has been genetically modified to contain the Ideonella dechloratans metabolic pathway can be combined with the feed from the first part of the bioreactor, thus beginning the bioremediation process. This is one of the most complicated parts of the bioreactor, due to the fact that it is not only responsible for not only maintaining a livable temperature for the E.Coli but also controlling the flow rates of both the feedstock and E.Coli biomass (both in and out of the system). There are five main types of bioreactors that are used commercially: stirred tank, bubble column, airlift, fluidised beds, and packed beds. We found the stirred tank bioreactor to be the most efficient due to its shape and large water content. This would be beneficial due to the high specific heat capacity of water, lessening the energy consumption. Although seemingly counterproductive to use water in this system, recall that a large percentage of the perchlorate ions were already found dissolved in briny water. Some things that must be accounted for in this system are the following:
- -Effluent release
- -Feedstock flow rates
- -Temperature monitoring & control
- -Product monitoring & control
After this process has been completed and the consumed E.Coli cells have been disposed of, the products of the reaction will be in their gaseous phase and pumped into the second last phase of processing. To separate the oxygen and chlorine gas, it will be fractionally distilled. The boiling point of chlorine is -33.97 degrees Celsius and the boiling point of oxygen is -183.00 degrees Celsius. While this would require a significant amount of energy on Earth the average temperature on Mars varies from -55 to -60 degrees Celsius depending on the location. This would function extremely well for fractional distillation, as leaving this subsystem uninsulated would provide a temperature similar to that of the one required to separate these two gases. This is another method of reducing energy consumption in the bioreactor.
When executed correctly the culmination of these processes should include four main components, being:
- -Bioremediated soil
- -E.coli effluent
- -Oxygen Gas
- -Chlorine Gas
Every one of these products has a distinct use in a colony. The first two products can be used in combination for agriculture in a self sustaining colony. The E. Coli strain that was used, DH5-alpha, does not cause any negative effects on humans. In addition, after the E. Coli has died, it will be autoclaved, after which its elemental components can be used as a pseudo-fertilizer for possible agricultural needs. The oxygen gas can be used for breathing by any possible humans and the chlorine gas can be used for a variety of purposes, ranging from manufacturing household cleaners to making rocket fuel. These conservation efforts are incredibly important on a colony that is millions of miles away from earth.
Transportation Concerns: For a system such as ours, a mission to Mars comes with many challenges. While it is fairly easy to transport microorganisms, the bioreactor that will be the housing for process’ such as the concentration and remediation of the perchlorate ion is at least six orders of magnitude larger than the bacteria itself. This is an area in which we would like to employ new and upcoming technologies, such as additive manufacturing, a process that is already being trialed aboard the ISS as well as undergoing preliminary tests for large scale construction here on Earth. This would greatly reduce the space required to transport any materials that may be required for the construction of a self-sustaining colony.
Safety Concerns: The safety of a project on the scale of ours is an incredibly important aspect when looking at its feasibility. For this reason we took into account many possible problems that may arise from this system. The first problem that was looked at was the possibility of the harmful intermediary product rising to higher than normal concentrations, or leaking out of the system. To address this, the bioreactor was designed in a way that allows each of the subsystems to be cut off from one another. This minimizes the risk of any contaminant rising to a level that cannot be dealt with by an independent colony.
The second safety concern has to do with the E.Coli leaking out of the system and into the environment or even worse the colony. This problem was solved with two procedures, the first of these being the choice of E.Coli used in the bioremediation process. We elected to use a laboratory strain of E.Coli that no longer has the potential to cause illness in humans, in the case of a leak. However, it simply isn't enough to just say that it is okay to let these organisms leak out because they aren't harmful to us. To further correct this issue the portion of the bioreactor that is responsible for the incubation of the E.Coli is built in six separate areas that can be monitored and controlled individually.
References Cited
Anderson, Molly S, et al., editors. Life Support Baseline Values and Assumptions Document. NASA TP. NASA/TP-2015-218570. NASA Center for AeroSpace Information, May 2015.
Ratledge, Colin and Bjørn Kristiansen, editors. Basic Biotechnology 3rd ed. 978-0521549585. Cambridge University Press, May 2006.
