Experimental

In order to accomplish the goal of producing oxygen on a martian like environment our team had to look at many different ways of sustaining a bioreaction in conditions akin to those on earth. However, this comes with significant challenges as the martian environment in its current state is nothing near habitable, even for some of the most resilient species. The solution that we settled upon was a modular multistage bioreactor. The bioreactor would consist of five main stages, each of these 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 will 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 the dilution of this solution to the correct concentration. However, before it can be used by the e coli, the solutions need to be cleaned of its other ions mainly include sulphites and many other molecules that do not dissociate in water easily. According to NASA’s baseline assumptions it can be expected to see about 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 which allows this portion of the bioreactor to operate at a lower temperature, reducing the amount of energy required for this subsystem.

While this process is taking 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 place where one does not exist naturally, carbon must be conserved wherever possible. The previous year’s team tested this using “riley broth” which was 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 to greatly reduce the heating cost of this portion of the bioreactor. This system would work similar 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, this begins the bioremediation process. This is one of the most complicated parts of the bioreactor because it is 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). To ensure our design would work as planned the team used mathematical modelling to calculate the efficiency and optimal design for the bioreactor. There are 5 main types of bioreactors that are used commercially. They are stirred tank, bubble column, airlift, fluidised beds, and packed bed. We found the stirred tank bioreactor to be the most efficient due to in shape and large water content. This would be beneficial due to water high specific heat capacity which would lessen the energy consumption. Although seemingly counterproductive to use water in this system, recall that a large percentage of the perchlorate ions were found already dissolved in a briny water. Some of the thing 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. (1) The boiling point of chlorine is -33.97 degrees celsius and the boiling point of oxygen is -183.0 degrees celsius. While this would take a significant amount of energy on earth the average temperature on mars varies around -55 to -60 degrees celsius depending on location. This would work extremely well for the fractional distillation as leaving this subsystem uninsulated would provide a temperature very similar to the one required to separate these two gases. This is another method of reducing energy consumption in the bioreactor.

The culmination of all these processes when executed correctly should include 4 main components, these are:

• -Bioremediated soil
• -E.coli effluent
• -Oxygen Gas
• -Chlorine Gas