Watt's Up, Microbes ?

Overview

Microbial Fuel Cells (MFCs) are a promising technology that generate electricity through the metabolic processes of bacteria such as Geobacter and Shewanella. These bacteria release electrons as they break down organic matter under anaerobic conditions. In low‑oxygen conditions, bacteria release electrons from their cells using electron carriers such as NADH and FADH2. These electrons get picked up by electrodes and are harnessed by the MFC to power a device. Since MFCs produce energy from waste materials, they are used in renewable energy production and environmental monitoring. This experiment investigated how different organic substrates affected the electrical output of an MFC. Specifically, we compared a 10% sucrose solution (a simple sugar) and a 10% apple slurry (complex carbohydrates) against a plain soil control. Both the sucrose and the apple were adjusted to 10% sugar concentration using a refractometer. The hypothesis was that the sucrose solution would produce a higher initial power output because bacteria rapidly metabolize simple sugars. In contrast, the apple slurry would generate a lower but longer-lasting output, since its complex organic material broke down more slowly. To test this, nine identical MFC units using carbon felt electrodes connected to a 1 kΩ resistor were divided into three groups: plain soil (control), soil with the 10% sucrose solution, and soil with the 10% sugar apple-slurry. Voltage was recorded daily for 14 days, and electrical power (in microwatts) was calculated using the formula P = V²/R. The results supported the hypothesis. The sucrose MFCs showed a rapid spike in power, peaking at 7.2 microwatts on Day 8 before declining sharply as the sugar was depleted. In contrast, the apple slurry MFCs demonstrated a slower but steadier increase, reaching a peak of 5.5 microwatts on Day 9 and maintaining more consistent output. The control group, without any added substrate, produced no measurable electricity, confirming that an organic substrate was necessary for power generation. These results show that substrate type influences the potential applications of MFCs. Systems fueled by simple sugars are better suited for short-term, higher-power needs such as charging small capacitors or briefly powering sensors. In contrast, MFCs powered by more complex organic materials are better for long-term applications, including wastewater treatment and remote water-quality monitoring systems. Because MFCs use organic waste as fuel, they offer a sustainable way to reduce waste while generating renewable, small-scale energy. Future improvements include constructing a larger MFC or extending the study duration. Additional research could explore different fruits, sugar concentrations, electrode materials, and a two-chamber MFC design with a salt bridge.

Competition history

• CSEF 2026 Biochemistry/ Molecular Biology (Junior Division) · Entry J-04-12

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