Indoor Plant VOC Removal in Sealed Terrariums

ISEF Category: Environmental Engineering

Subcategory: Pollution Control  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

New furniture can release formaldehyde into indoor air for months. That matters because you spend most of your day breathing that air. Your project asks a simple question with real stakes, which plant and substrate combo cleans it best inside a sealed terrarium? A $40 VOC sensor gives you a way to turn that question into numbers.

What Is It?

This project looks at how well different indoor plants, plus the growing material around their roots, remove volatile organic compounds, or VOCs. VOCs are gases released by products like fresh paint, glue, pressed wood, and new furniture. Formaldehyde is one common VOC. Think of your terrarium like a tiny indoor room. You add a pollution source, then see how fast different plant setups lower the sensor reading.

The plant is only part of the system. The substrate, which is the growing medium, can matter too. Soil, coco coir, perlite, and other media change moisture, airflow, root health, and the microbes living around the roots. Those microbes can help break down some pollutants. Your job is to compare setup A versus setup B and see which one changes the VOC signal most.

Why This Is a Good Topic

This makes a strong science fair topic because you can test it with a clear independent variable, a measurable signal, and real-world meaning. Indoor air quality affects homes, classrooms, and offices, and people already look to plants as a low-cost fix. You can learn experimental design, sensor calibration, controls, and data analysis without needing a university lab. You also get room to compare biology and engineering choices, which makes the project more original.

Research Questions

• How does plant species affect VOC removal rate in a sealed terrarium??
• What is the effect of substrate type on VOC removal rate for the same plant species??
• Does adding activated carbon to the substrate change the sensor response over time??
• To what extent do plants reduce VOC levels compared with a no-plant control terrarium??
• Which plant and substrate combination gives the lowest steady-state VOC reading??
• How does terrarium humidity affect the PID-style sensor signal during VOC removal tests??

Basic Materials

• Sealed clear terrarium or airtight storage container.
• $40 PID-style VOC sensor or consumer VOC meter.
• Small indoor plant species with similar starting size.
• Different substrates such as potting soil, coco coir, perlite, and activated carbon mix.
• Identical pots or planting cups.
• Distilled water.
• Digital kitchen scale with 0.1 g accuracy.
• Thermometer and hygrometer.
• Labels and notebook for tracking conditions.
• Phone camera for documenting plant growth and setup.
• Fresh furniture sample, low-VOC wood sample, or a safe formaldehyde source approved by your school.

Advanced Materials

• Gas sampling bag or controlled VOC source chamber.
• Laboratory formaldehyde test kit for confirmation measurements.
• Environmental chamber or incubator for stable temperature and humidity.
• Air pump and tubing for repeatable mixing inside the chamber.
• Data logger for continuous sensor readings.
• Analytical balance.
• pH meter for substrate checks.
• Sterile sampling tools for root-zone or substrate comparisons.
• UV-visible spectrophotometer if you pair sensor readings with a colorimetric assay.
• Microbial plating supplies if you test whether root-zone microbes differ across substrates.

Software & Tools

• Google Sheets: Organizes sensor readings, plots trends, and compares treatment groups.
• ImageJ: Measures plant size or leaf area from photos if you want growth as a second outcome.
• Python: Helps you clean data, fit curves, and compare removal rates across treatments.
• R: Runs statistical tests and makes publication-style graphs for treatment comparisons.
• PubMed: Helps you find review articles on indoor air phytoremediation and VOC removal.

Experiment Steps

1. Define one VOC source, one sensor setup, and one plant growth condition so your comparison stays fair.
2. Choose the main variable you will change first, such as plant species or substrate mix.
3. Build a control plan with at least one no-plant chamber and one empty chamber to separate plant effects from container effects.
4. Set up a way to convert sensor readings into a removal metric, such as percent drop or area under the curve.
5. Plan how you will keep light, humidity, plant size, and chamber sealing consistent across trials.
6. Decide in advance how you will compare groups with graphs and statistical tests, then collect enough repeats to support that plan.

Common Pitfalls

• Using different plant sizes at the start, which makes larger plants look better even if species does not matter.
• Letting the terrarium leak, which lowers VOC readings and hides the real treatment effect.
• Trusting one raw sensor value without calibration, which can confuse humidity changes with VOC changes.
• Changing both plant species and substrate at the same time, which makes it impossible to tell what caused the result.
• Ignoring a no-plant control, which leaves you unable to prove that the drop came from the plant system and not the container.

What Makes This Competitive

A competitive version of this project goes beyond simple before-and-after readings. You would compare multiple plant and substrate pairs, include strong controls, and report removal rate with clear statistics. You could also test whether the sensor signal matches a second measurement method, which makes your claim much stronger. A thoughtful design that separates plant uptake, substrate effects, and humidity effects will stand out.

Project Variations

• Compare pothos, spider plant, and snake plant in the same terrarium setup to see which species lowers VOC readings fastest.
• Test how substrate mixes with and without activated carbon change formaldehyde removal for one plant species.
• Measure VOC removal under different light conditions to see whether plant activity changes the chamber signal.

Learn More

• EPA Indoor Air Quality resources: Search the EPA site for indoor air pollutants, VOCs, and formaldehyde background information.
• NASA technical reports: Search NASA for the classic clean air study and later reviews on indoor plant air cleaning.
• PubMed: Search review articles on phytoremediation, indoor air quality, and volatile organic compounds.
• NOAA learning resources: Use background material on gases, humidity, and environmental measurement concepts.
• Environmental Science & Technology: Search for peer-reviewed studies on plants, substrates, and indoor pollutant removal.