Conclusion and Data Analysis
As stated in one hypothesis of three if bacteria in a MFC metabolize the substrates (in an aqueous solution) found in a MFC then the electrical output will spike significantly from the negative control of autoclaved dirt and the positive control of regular soil. The data was conclusive in relation to this hypothesis. In trial one and two there were spikes after the addition of substrates while the controls did not have spikes at all. In trial one the addition of peptone spiked 430 microamps after the addition of a second substrate. The addition of peptone created the highest spikes in all trials and electrical measurements and this was later highly supported from ANOVA testing and confidence intervals. Through ANOVA testing it was shown with a 99% confidence that each variable was significant. Through confidence intervals it was shown that the addition of the substrate glucose and peptone had significant spikes in both trials highly supporting the hypothesis that the addition of substrates will create significant effects on electrical output. The rationale behind this is that the enzymes in bacteria breakdown substrates on a molecular level (catabolize) which release energy. This is done by fermentation or cellular respiration and the ions generated from these processes generate the electrical flow in a MFC. The use of aqueous solutions of substrates allow bacteria to catabolize and breakdown the substrates faster allowing for the spikes in electrical current to be shown. This hypothesis is strongly supported by the evidence in the data and through the literature of how MFCs make energy and knowledge on bacterial metabolism.
As stated in the second hypothesis of three if a MFC contains isolated bacteria from the electrodes of a MFC then it will produce more electrical output than isolated bacteria not found in a MFC. The data was conclusive in relation to the hypothesis. In trials of the triplicates of the isolated bacteria from the MFC it was shown that each variable was significant to each other with a 99% confidence. In this sets, it was shown that two of the four isolates (spa11, sga21) created a significant result (confidence intervals) in initial spikes produced because of the catabolism on aqueous solution of substrates found in liquid LB broth. In comparison in trials of triplicates of isolated bacteria not found from a MFC it was shown with 99% confidence that each variable was significant. In this set, it was shown that one of the two isolates (Escherichia coli) created a significant result but with considerably high error bars. In terms of spikes the set with isolated bacteria from a MFC had higher percent of increase than the isolates not found in a MFC. Conclusively, the isolates found in a MFC have better spikes in electron flow (current) which suggest that bacteria found in a MFC are adapted to create ions which will later be checked in a future study. It should be also known that the isolates found in the MFC that produced significant results were bacteria from the anode electrode which supports the literature behind electron flow is produced by bacteria in the anode to the cathode.
As stated in the last hypothesis if a MFC contains multiple colonies of bacteria in a MFC then it will produce higher spikes in current of a MFC than isolated bacteria. The data was conclusive in relation to the hypothesis. In comparing the two data sets, statistical analysis was used to determine if spikes created were statistically different. Through the T-Test it was shown that the two data sets of isolated bacteria and multiple colonies were statistically different with a 98% confidence. This shows that there is a difference in data. It was shown that multiple colonies of bacteria generated more electrical output since the concentration of substrates were less than the concentrations added on the isolates. The isolates had 5 mL of broth/100 g of soil giving 5% while the concentration of the multiple colonies was 2%. This shows that the multiple colonies MFC produced more electrical output with less concentrations of substrates.
Some error encountered in this experiment was the variability of the current of a MFC. To mitigate this variability the addition of a resistor should be used. If this project could be reproduced again there would be more trials added creating a bigger sample size. Also, this project could be done on a bigger scale to see if surface area would influence electrical output in a MFC. An interesting future study is to see if gene expression could be applied in order to increase the electrical output of a MFC.
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Basically:
1. Bacteria does impact the electrical output of a MFC
2. Isolated bacteria created a significant spike and creates electrical output
3. The ions in the soil, acidity, and the substrates don't contribute to the electrical output
4. Interesting future steps shall include gene expression to increase the electrical output of a MFC since it is known that bacteria create the electrical output.