Introduction
We are Joyce, Chelsea, Xiuting and Natalie. Today we will be sharing with you more about our project. We hope that through our experiment, we will be able to maximise the amount of electricity generated by a microbial fuel cell.
Electrochemical cell
So, what is a microbial fuel cell?
A microbial fuel cell is made up of two electrodes, an anode and a cathode, and is linked by an electrical connection, usually a wire.
Concept of MFC
Bacteria at the anode will hence carry out oxidation reaction, converting the food that it has consumed into electricity and carbon dioxide. The bacteria will hence breathe out electrons onto the anode. This means that there is a loss of electrons, also defined as oxidation, in the anode The electrons are then passed from the anode through the wire to the cathode to complete the electrical circuit to create a kind of battery. As there is a gain of electrons at the cathode, the process involved at the cathode is called reduction. This oxidation-reduction process can also be called redox reaction.
How does bacteria generate electricity
The aim of our experiment is thus to find out whether the material of the electrodes will result in a different amount of electricity produced by the microbial fuel cell and if so, the material that will result in the most amount of electricity being produced by the cell.
Research Questions:
After identifying the aim of our experiment, we came up with research questions to guide us through this project. Our primary research question is:
What material of the electrodes, zinc, copper and aluminum, would allow the maximum amount of electricity to be recorded by the multimeter?
While our secondary questions are:
1. What is the amount of electrical current calculated by the multimeter at every minute over a span of 30 minutes when the electrodes are made up of zinc, copper and aluminum?
2. Does the change in the material of the electrodes result in a different amount of electricity produced by the E. coli (K-12) strain bacteria?
3. If yes, what are the maximum and the average amounts of electrical current calculated by the multimeter when the electrodes are made up of zinc, copper and then aluminum?
4. Which of the materials of the electrodes will allow the highest maximum and average amount of electrical current to be calculated?
Hypothesis:
Our hypothesis is that the materials of the electrodes do affect the amount of electricity calculated by the multimeter and that the aluminum electrodes will allow the most amount of electricity to be generated by the cell.
Experiment:
To build the microbial fuel cell, we used
two 250ml beaker,
two Insulated copper wire of about 30cm with crocodile clips,
a multimeter,
a stopwatch,
2 sheets of metal, made of up either aluminum, zinc or copper, of about 5 x 5cm each,
a salt bridge of about 15 x 4cm
1 vials of E. Coli K12 bacteria,
and 100ml Ethanoic Acid (1M)
Methodology:
Using the materials above, we then connected the crocodile clips of the multimeter to an insulated copper wire each. Next, fold the metal sheet, made of copper into quarters lengthwise. Attach the sheets of copper metal to the crocodile clip of the insulated wire.
Next, pour 100 ml of concentration 1M ethanoic acid into beaker A and put a vial of the bacteria E.Coli K12 into Beaker B. Place each copper metal sheet, which is attached to the copper wire, into Beaker A and vial of bacteria in Beaker B. Next, wet the salt bridge thoroughly with distilled water and fold into vertically into quarters. After that insert one end of the salt bridge into Beaker A, and the other end into the vial of bacteria in beaker B and ensure that the salt bridge and the copper sheet are not touching in both beaker A and the vial of bacteria, turn on the multimeter and switch it to current 200V. Start the stopwatch once the multimeter is turned on and record the voltage produced by the bacteria every minute over half an hour. The experiment was repeated two times more for the copper electrodes to ensure reliable results.
This same set of steps was repeated for the aluminum and zinc electrodes and the control experiment, in which a vial of LB Broth was used instead of bacteria E. Coli.
Here is a picture of our experiment:
Exclusion of Zinc
However, while running a test trial, we found out that the generation of electricity with zinc electrodes was rather unstable and there was a general downward trend in the electricity generated. Furthermore, the amount of electricity produced by the cell using zinc electrodes were negligible. It would hence not be practical in the real-life context. Thus, we decided to exclude zinc from the final comparison as it proved to be an unsuitable material for the electrodes.
Data analysis
This is our graph showing the data collected in our experiment.
The green plotted points on the graph show the electricity generated by the cell when LB broth was used instead of the bacteria. No electricity was generated throughout the experiment when both the aluminum and copper electrodes were used.
The blue plotted points here show, the data collected for the copper electrodes. As can be seen, there is a steady rate of generation of electricity before declining. The rate of generation of electricity is also rather steady. The amount of electricity generated by the cell using the copper electrodes is also quite high, with an average of 126.9 millivolts and an average maximum amount of electricity generated of 141.9 millivolts among the three tests conducted.
The red plotted points are the data for the aluminium electrodes. Compared with the copper electrodes, the aluminium electrodes generate more electricity with the bacteria than with the copper electrodes. Although the rate of generation of electricity fluctuates over time, the general trend is a positive upward trend, and we do not see a decline in the trend. Also, the amount of electricity generated by the cell with the aluminum electrodes is higher than the cell with copper electrodes, with an average of 200.6 millivolts recorded and an average maximum amount of electricity of 235.7 generated among the three tests conducted for aluminum electrodes.
Using the above data collected, we had to prove our null hypothesis, that the bacteria, E. Coli K12 is the cause for the electricity calculated by the multimeter, is correct. As can be seen from the plotted points in green as compared to the points in red and blue, we could see that there were no electricity generated by the cell when no bacteria was present. Hence, we could conclude that the bacteria was the cause of the electricity generated.
Next, using the data, we had to prove our hypothesis, that aluminum electrodes will result in the most amount of electricity generated by the cell, is correct. We thus chose the average electricity generated and the maximum electricity generated by the cell for each material as our two criterias in finding out the material of the electrode that would result in the maximum amount of electricity to be generated by the cell as we wanted to ensure that the material of the electrode could produce high quantities of electricity consistently.
We then found out that aluminum will result in the higher average electricity generated and the higher maximum electricity generated by the cell.
Thus, we concluded that our hypothesis is correct. Aluminum electrodes will result in the most amount of electricity generated by the cell.
Next, using our data collected, we ran a student’s t-test. The null hypothesis is that there will be no statically significant difference between the electricity generated when using the copper electrode and the aluminium electrode. The alternative hypothesis is that there will be a statically significant difference between the electricity generated when using the copper electrode and the aluminium electrode. We found out that the p value was larger than 0.05 at 0.118. This means that we have to accept our null hypothesis.
From the discussion above, we can conclude that the material of electrode does affect the amount of electricity generated by the bacteria. Through this experiment, we have also found that between copper and aluminium, aluminium is the best material for the electrodes as it produces the highest amount of electricity.
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