Microplastic Degradation Kinetics in Bacterial Cultures

ISEF Category: Environmental Engineering

Subcategory: Bioremediation  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Plastic lasts a long time in the environment, but not every plastic breaks down at the same speed. Some microbes can chip away at certain polymers, while others barely touch them. That gives you a real research question, not just a cleanup problem. You can measure which film changes fastest and build a kinetics story from the data.

What Is It?

This project asks a simple question with a tricky answer, which plastic does bacteria attack best? You would grow or enrich bacteria from landfill leachate, then expose them to different plastic films such as PET, PLA, and PE. PET is common in bottles, PLA is a compostable plastic, and PE shows up in bags and packaging. Think of the films like three different locks, and the bacteria as keys that may fit one lock better than the others.

The key idea is kinetics, which means how fast a change happens. You are not just asking whether the plastic changes. You are asking how the rate changes over time. Mass loss gives you one signal, and you can pair that with other measures like surface damage, biofilm growth, or pH shifts if your lab setup allows it.

Why This Is a Good Topic

This is a strong science fair topic because you can test a clear variable, the plastic type, and compare real environmental samples against a defined response. The project connects to plastic pollution, landfill management, and biodegradation, so the result has real-world value. You can learn enrichment culture design, measurement quality, controls, and basic kinetics without needing a full molecular biology setup. A good version of this project teaches you how to separate true degradation from simple contamination or handling error.

Research Questions

• How does plastic type affect the rate of mass loss in enrichment cultures from landfill leachate?
• What is the effect of source site on bacterial degradation rate for PET films?
• Does pre-washing or surface roughening change the apparent degradation of PLA films?
• To what extent does incubation time change the mass loss pattern of PE films exposed to the same culture?
• Which plastic shows the greatest surface change after exposure to the enrichment culture?
• How does nutrient availability affect the difference between live cultures and sterile controls?

Basic Materials

• PET, PLA, and PE film samples with known starting masses.
• Sterile or clean glass jars, flasks, or culture containers.
• Soil or leachate samples from a local landfill or waste site, collected with proper permissions.
• Basic growth medium or enrichment medium suitable for environmental bacteria.
• Digital jewelry scale with 0.001 g readability.
• Forceps, gloves, and ethanol for handling samples.
• Permanent marker and labels for sample tracking.
• Camera or smartphone for photo documentation.
• Drying rack or clean covered area for sample drying.
• Notebook or spreadsheet for data logging.

Advanced Materials

• Autoclave or access to sterile prep services.
• Incubator with temperature control.
• Laminar flow hood or clean bench.
• Spectrophotometer or plate reader for culture density checks.
• PCR access for 16S rRNA identification of dominant isolates.
• SEM access for surface imaging of film damage.
• FTIR access for polymer chemistry changes.
• Analytical balance for confirmatory weighing.
• pH meter and dissolved oxygen probe.
• Sterile filtration setup and microbiology consumables.

Software & Tools

• Google Sheets: Organizes mass data, time points, and control comparisons in a simple spreadsheet.
• ImageJ: Measures surface roughness, discoloration, or pitting from photos of the films.
• R: Runs statistical tests and plots degradation curves and confidence intervals.
• Python: Fits kinetics models and automates graphing across multiple plastic types.
• PubMed: Helps you find review articles and primary studies on plastic biodegradation and microbial enzymes.

Experiment Steps

1. Define the exact plastic comparison you will test, then pick one main response variable, such as mass loss or surface change.
2. Design live, sterile, and no-plastic controls so you can tell degradation apart from handling loss and background drift.
3. Plan how you will standardize starting film size, cleaning, drying, and weighing so each sample begins on equal footing.
4. Choose a measurement schedule that lets you compare early, middle, and late changes instead of only a single end point.
5. Build a data plan that turns raw masses into rates, percent loss, or model fits, then compare plastics with the same statistical test.
6. Add a second readout, such as imaging or culture density, so you can check whether mass loss matches biological activity.

Common Pitfalls

• Weighing films before they reach a stable dry mass, which makes water loss look like plastic degradation.
• Skipping sterile controls, which makes it impossible to tell microbial attack from simple physical breakdown.
• Mixing up polymer types or using films with different thicknesses, which distorts the kinetics comparison.
• Using a scale that cannot resolve tiny changes, which hides real differences between treatments.
• Treating dirty landfill samples as direct proof of degradation without checking for biofilm, residue, or particles stuck to the film.

What Makes This Competitive

A stronger version of this project goes beyond one mass-loss chart. You can compare multiple plastics, add sterile and abiotic controls, and test whether the same culture shows different kinetics on each polymer. Strong students also pair the weight data with surface imaging, growth data, or polymer chemistry checks, so the claim has more than one line of evidence. Clear statistics, careful controls, and a well-chosen comparison make the work feel like real research.

Project Variations

• Test compostable packaging films instead of landfill plastics to compare how commercial bioplastics behave in the same culture.
• Compare leachate samples from two waste sites to see whether microbial source changes degradation speed.
• Add surface analysis with smartphone imaging or ImageJ instead of relying on mass loss alone, then compare which signal is most sensitive.

Learn More

• PubMed: Search for review articles on plastic biodegradation, microbial polyester hydrolases, and environmental enrichment cultures.
• NIH NCBI Bookshelf: Find background chapters on microbial metabolism, enzymes, and experimental design.
• NOAA Marine Debris Program: Read accessible material on plastic pollution, degradation, and environmental pathways.
• USGS Water Science School: Use this for background on contamination, sampling, and environmental field methods.
• MIT OpenCourseWare: Search microbiology and environmental engineering lecture notes for free background on culture methods and kinetics.