Compost Microbial Fuel Cells and Carbon Sources

ISEF Category: Microbiology

Subcategory: Applied Microbiology  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Trash can become power. In a microbial fuel cell, microbes act like tiny electricians, moving electrons as they eat. That means compost, food waste, and even urine can change how much electricity the system makes. You can test which feedstock gives the best output and whether a special bacterium shifts the current.

What Is It?

A microbial fuel cell, or MFC, uses living microbes to move electrons from food to an electrode. Think of it like a tiny battery powered by bacteria instead of metal. The microbes break down organic matter, then send some of the released electrons to a circuit, which creates measurable voltage and current.

This project asks two main questions. First, how does the carbon source affect power output over time? Cellulose, glucose, urine, and food waste do not look the same to microbes. They differ in how easy they are to break down, which changes the rate of electron release. Second, does adding sourdough-derived Lactobacillus change current production, especially if a redox mediator like neutral red helps shuttle electrons? A redox mediator is a molecule that carries electrons between cells and the electrode, like a ferry boat crossing a river.

Why This Is a Good Topic

This is a strong science fair topic because you can change one input, measure a clear electrical output, and compare results with real statistics. It connects to waste-to-energy, sanitation, and low-cost power generation. You can also build a real model from your data, which raises the project beyond a simple experiment. A student can learn experimental design, microbial ecology, electrode behavior, and curve fitting from one project.

Research Questions

• How does the carbon source affect peak voltage in a compost microbial fuel cell?
• How does the carbon source affect the time needed to reach maximum current?
• What is the effect of sourdough-derived Lactobacillus on current output in a compost microbial fuel cell?
• To what extent does neutral red change current production when Lactobacillus is present?
• Which feedstock, cellulose, glucose, urine, or food waste, gives the highest area under the voltage-time curve?
• How does repeated feeding change power output across successive cycles?
• What is the effect of pH drift on voltage stability in each feedstock condition?

Basic Materials

• Compost inoculum from a stable source
• Small airtight containers or jars for MFC chambers
• Carbon felt, graphite rods, or carbon cloth electrodes
• Copper wire and alligator clips
• Resistors in a known range
• Digital multimeter or data logger
• Distilled water
• Glucose
• Cellulose source such as paper pulp or filter paper
• Food waste slurry prepared in a consistent way
• Urine sample handling supplies with school-approved biosafety procedures
• pH strips or a pH meter
• Graduated cylinders or measuring cups
• Labels and permanent marker
• Notebook or spreadsheet for data logging.

Advanced Materials

• Potentiostat with chronoamperometry and cyclic voltammetry capability
• Multi-channel data acquisition system
• Reference electrode such as Ag/AgCl
• Precision balance
• pH meter with calibration buffers
• Dissolved oxygen probe
• Anaerobic jars or glove box access
• Incubator with temperature control
• Spectrophotometer or plate reader for mediator tracking
• Sterile culture supplies for Lactobacillus isolation or maintenance
• Neutral red reagent with proper safety controls
• Carbon electrodes with defined surface area
• Gas-tight reactor parts
• Image analysis setup for biofilm or electrode surface documentation.

Software & Tools

• Excel: Organizes voltage records, calculates averages, and makes first-pass graphs.
• GraphPad Prism: Fits curves and compares groups with common statistical tests.
• R: Handles repeated-measures analysis, nonlinear fitting, and cleaner figure export.
• Python: Fits Monod and Butler-Volmer style models and automates batch analysis.
• ImageJ: Quantifies electrode surface coverage or biofilm images if you document growth.

Experiment Steps

1. Define the exact response you will measure, such as peak voltage, current density, or area under the curve.
2. Choose one factor to vary first, then lock the rest of the reactor design so your comparison stays fair.
3. Plan a calibration strategy that turns raw voltage data into comparable performance metrics.
4. Build controls that separate substrate effects from pH change, inoculum differences, and electrode behavior.
5. Decide how you will test the model fit, including which parameters come from the data and which stay fixed.
6. Set up a comparison plan for the Lactobacillus and neutral red question so you can tell mediator effects from simple growth effects.

Common Pitfalls

• Using feedstocks with different particle sizes, which changes surface area and makes the carbon-source comparison unfair.
• Letting oxygen leak into one chamber more than another, which steals electrons and lowers measured current.
• Skipping pH tracking, which hides whether the voltage change came from microbes or from acid buildup.
• Treating urine, compost, and food waste as if they have the same nitrogen load, which confuses substrate effects with nutrient effects.
• Changing electrode placement between trials, which alters internal resistance and makes the voltage curves hard to compare.

What Makes This Competitive

A competitive version of this project goes past a simple voltage comparison. You would build a clean model, test whether the fit actually matches the biology, and explain why one feedstock outperforms another. Strong projects also separate direct microbial growth effects from mediator-driven electron transfer. If you can show a real mechanism, not just a higher number, your work looks much stronger.

Project Variations

• Compare kitchen waste, yard waste, and toilet paper as carbon feeds to see which waste stream gives the best electricity output.
• Test whether different electrode materials, such as carbon felt, graphite, and stainless steel mesh, change current more than the feedstock does.
• Compare open-circuit voltage with load-connected power output to see whether the same substrate ranks the same way under both conditions.

Learn More

• PubMed: Search review articles on microbial fuel cells, extracellular electron transfer, and Lactobacillus redox biology.
• NIH NCBI Bookshelf: Find free background chapters on microbial metabolism, biofilms, and anaerobic growth.
• NOAA National Ocean Service: Read about oxygen, water quality, and decomposition to understand environmental context.
• USGS Water Science School: Learn how organic waste, nutrients, and water chemistry interact in real systems.
• MIT OpenCourseWare: Search for free biology, chemistry, and environmental engineering lectures that explain electron transport and reaction kinetics.
• Microbial Biotechnology: Search recent open-access or abstracted review articles on microbial fuel cells and mediator-based electron transfer.