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Many systems and industries could not function without electricity. Fossil fuels and other non-renewable substances are typically the fuel source for producing electricity (Muda and Pin, 2012). What are some of the negative effects of these resources? Global warming and the rise of carbon dioxide levels are just a few. Because fossil fuels and non-renewable substances are in limited supply, the price of electricity is at the whim of availability (Lucas, 2017).
It is only a matter of time until these non-renewable power sources run out, and as a result, many people are researching new alternative energy sources. MFCs, or microbial fuel cells, are fuel cells capable of producing electric current from respiring microbes (Chaturvedi and Verma, 2016). If MFCs could be used to create electricity on a large-scale, this solution could benefit the environment. It produces no harmful end products and takes nothing but a specific type of microbes and waste fuel to feed them function (Sharma 2015). Interestingly, it may also be a way to provide power in rural areas in which electricity from power plants cannot reach (Planetary Project: Serving Humanity).
Conveniently, the peels of various fruits and vegetables are commonly considered a waste product and are typically thrown away (Munish et al, 2014). Some may be used for fertilizer, but most are left in a landfill to rot (Narender et al, 2017). Banana is globally known to have lots of nutrients and health benefits. It is abundant in Southeast Asian countries in which consumption is very high. The peels are usually discarded, however, different studies conducted on peels revealed the presence of important constituents that could be repurposed.
The research and experimental design for this article were done by Rommer Misoles, Galdo Lloyd, Debbie Grace, and myself. The aforementioned researchers discovered no studies using banana peel sludge as a source of bioelectricity but found that its mineral content consists primarily of potassium, manganese, sodium, calcium, and iron, which can be used to produce electrical charges. Therefore, they hypothesized that there would be a relationship between electrical current and volume of banana sludge. Our team postulated that with more banana sludge, there would be a higher voltage and current output in a given MFC than if there were little to no banana sludge.
How Did We Test Banana Peel Sludge?
The processes and testing were conducted during the month of September in 2019. The experiment was conducted in the Science Laboratory of Daniel R. Aguinaldo National High School (DRANHS) in Matina, Davao City.
Collection of Materials
Ripe bananas (Musa acuminata and Musa sapientum) were procured in Bangkerohan, Davao City. Multimeters and other laboratory equipment were requested procured in the school laboratory. Circular-shaped chambers, copper wire, PVC pipe, unsweetened gelatin, salt, distilled water, gauze pad, carbon cloth, and ethanol were purchased in Davao City.
Preparation of Banana Sludge
Banana peels were coarsely chopped and were kept in 95% ethanol. The entire mixture was homogenized using a blender. This homogenized mixture, also called "slurry", was left at room temperature for about 48 hours. As the reaction proceeded, the yellowish, transparent liquid turned to amber and later to black. The coloration change from yellow to black served as the indicator that the slurry was ready for use (Edwards 1999).
Making a Two-Chamber Microbial Fuel Cell
Two chambers were made using two circular plastic containers for each set-up. The container was connected with 1.5" long PVC pipe making a connection between the anode and cathode chambers. A roof sealant was used to prevent possible leakage (Rahimnejad et al 2015). The lid of the two chambers had 3-millimeter (mm) diameter holes for the positive and the negative wires to go through. A 3-inch copper wire was connected above the container to form the external circuit in which electrons would flow. A carbon cloth was attached to the tip on one side of the wire for a larger surface area for the ions (Logan et al, 2006). Three identical set-ups were prepared in the same way.
Making the Proton Exchange Membrane (Salt Bridge)
The proton exchange membrane (PEM) was prepared by dissolving 100 grams (g) of sodium chloride in 200 milliliters (mL) distilled water. Unsweetened gelatin was added to the solution so that it would congeal. The solution was then heated for 10 minutes and was poured into the PEM compartment. It was then cooled and set aside until further use per the style of Chaturvedi and Verma (2016).
Sludge was divided into three categories. "Set-up One" contained the most sludge (500g), "Set-up Two" had a moderate amount of sludge (250g), and "Set-up Three" had no sludge. Musa acuminata sludge was first introduced to the anodic chamber and tap water in the cathodic chamber of the fuel cell (Borah et al, 2013). Recordings of the voltage and current were gathered via multimeter in 15-minute intervals across a period of 3 hours and 30 minutes. Initial readings were also recorded. The same process was repeated for each treatment (Musa sapientum extract). The set-ups were properly washed after every batch of testing and the PEM was kept constant (Biffinger et al 2006).
Results of the Experiment
Voltage: After conducting 15 trials, the highest voltage recorded was 600mV which belonged to Setup 1 (Sapientum). Setup 3 (Sapientum) displayed the lowest voltage with 190mV.
Current: The highest mean current recorded was 0.16533333mA which belonged to Setup 1 (Sapientum) while Setup 2 (Acuminata) has the least with 0.065333333 mA.
Statistical Analysis of the Results
A One-way Analysis of Variance test (One-way ANOVA) was used to determine if there was a significant difference between the results of the three setups (500g, 250g, and 0g).
In testing the hypothetical difference, the p-value, or 0.05 level of significance, was used. All data gathered from the study were encoded using IBM3 SPSS Statistics 21 Software.
Explanation of Figure 1
Figure 1 displays the movement of voltages produced by each setup. The x-axle shows that setups can only produce at the range of 190-600 mV. The lines significantly increase and decrease over time but remained in the given range. Musa sapientum produced more voltage than Musa acuminata. However, even this voltage output could generally power up small light bulbs, doorbells, electric toothbrush, and many more things that requires a low amount of power to function.
What Is Voltage?
Voltage is the electrical force that pushes electrical current between two points. In the case of our experiment, the voltage shows the flow of electrons across the proton bridge. The higher the voltage, the more energy available to power a device.
Explanation of Figure 2
Figure 2 shows the movement of the current produced by each setup. The figure shows that setups can only produce between the range of 0.05–0.28 amperes (or amps). The lines significantly increase and decrease over time but remain in the given range. Musa sapientum has sudden drops but Musa acuminata is constantly increasing. The current produced by the banana sludge shows that its flow of electrons is stable and will not result in overloading.
What Is Current?
Current is the flow of electric charge carriers (electrons), measured in amperes. Current flows through a circuit when a voltage is placed across two points of a conductor.
Results and Conclusion
The results of the One-way ANOVA test showed that there is a significant difference (F=94.217, p < 0.05) between the relationship of sludge volume and produced voltage (Minitab LLC, 2019). We observed that the MFC with the most sludge produces the highest voltage. The medium amount of sludge also produced a significant amount of voltage but is lower than the volume of sludge in Set-up 1. Lastly, in Set-up 3, the least amount of sludge is seen to have produced the least amount of voltage.
Additionally, the results of the ANOVA test showed that there is a significant difference (F=9.252, p < 0.05) between the relationship of sludge volume and current produced (Minitab LLC, 2019). It was observed that Musa sapientum had significantly higher current output than Musa acuminata.
Why is Studying the Voltage and Current Produced by Banana Sludge in MFCs Important?
The generation of electricity via use of MFCs is important for the study of potential small- and large-scale renewable energy sources. Wastewater has limited potential for bioelectricity generation according to recent studies, and, according to our study, Musa acuminata and Musa sapientum perform comparatively better.
This setup can generally power a small light bulb, which is obviously low compared to other renewable energy sources such as hydroelectric power and nuclear power. With the optimization of the microorganism and research on achieving a stable power output, it could provide a promising option for cost-effective bioelectricity generation (Choundhury et, al. 2017).
This research is a small step towards pursuing MFC technology as a biopower generator and it greatly affects the way we see banana sludge as a potential source of electricity.
What Do We Think Future Studies Should Focus On?
Most of the literature is focused on enhancing the performance of the reactor configurations of MFCs, not on the optimized microorganism used and electrode of MFC.
For further research, we recommend:
- Determine how to further increase the current and voltage outcome
- Study to determine optimal microbes used in MFC
- Investigate other variables (size of the wire, size of the chamber, size of carbon cloth, the concentration of banana peels) that may affect the resulting output
- Further analysis of the MFC components Musa acuminata and Musa sapientum
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This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
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