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Preliminary Design Considerations

Bioreactor Design Considerations

Over the summer, much thought was put into the design of our bioreactor in order to optimize functionality, expense, and safety. Although many of the details of our design cannot be worked out due to the time constraint of a four-month period, there are still lots of theoretical aspects that we were able to cover.

The first aspect of our design was choosing what type of bioreactor system to use. For lab scale experiments and design, we chose to use a system that is closest to that of a batch system. This system requires all reactants to be added at time zero, with everything being removed at once when the remediation has come to completion. However, our design uses a belt skimmer to continually remove any products (hydrocarbons) formed either emulsified or found on the top layer. This way, we are able to reuse our culture and remove product until all the toxins are converted. We then remove everything in the tank and begin the process again. Our skimmed product goes through UV radiation in order to kill any bacteria that happen to be left in the product. In addition, our bioreactor bacteria will contain kill genes. When our bacteria are in a glucose-free environment (a.k.a. outside the tank) the bacteria are programmed to self-destruct. Since we have three different intermediate steps for remediation (desulphurization, denitrification, decarboxylation) we will need three tanks with the product from the previous tank acting as the reactant for the next tank in line. The product of the last tank will go through distillation to purify our desired alkane. Distillation will also assist in classifying the different hydrocarbons we formed and ensure bacteria do not escape into the environment. The produced hydrocarbons may have different carbon and hydrogen bonds, thus its boiling and condensation temperature will vary. If the bacteria removed by the belt skimmer were to somehow survive UV radiation and thrive in a glucose-free environment, it would be distilled along with the rest of the skimmed material. In distillation the bacteria would be heated to an extremely high temperature and would consequently die as a result.

To improve the growth and environment of our bacteria, we will keep our bioreactor at ideal growth temperature (if E. coli, 37 °; if Pseudomonas, 25°). In addition, we will have an agitator (turbine) and an air sparger supplying filtered air to help mix and oxygenate our solution. In order to help maintain these ideal conditions, our bioreactor will be a closed system with our belt skimmer contained inside the tank.