Biochar Green Roofs for Stormwater Capture

ISEF Category: Environmental Engineering

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

The Hook

Stormwater can pick up metals and hydrocarbons in minutes. Then it rushes straight into drains and streams. A green roof can act like a sponge, and biochar may help it grab even more pollutants. You can test whether that extra material really improves capture.

What Is It?

This project studies whether a biochar-amended green roof module can trap pollutants during the first flush of stormwater. First flush means the first runoff after a rain, when the water often carries the highest pollutant load. Think of it like the dirty rinse water from a soaked sponge. That first squeeze usually holds the most grime.

Biochar is a carbon-rich material made by heating plant matter with little oxygen. It has lots of tiny pores, so it can adsorb, which means stick to its surface, parts of metals and organic compounds. In this project, you would compare a green roof module with and without biochar, then measure how much lead, zinc, and PAH-type pollutants remain in the runoff or media after exposure. ICP analysis can quantify metals, while PAH tracking may need a partner lab method or a simpler proxy depending on access.

Why This Is a Good Topic

This topic works well for a science fair because you can change one material, measure a clear outcome, and connect your work to real stormwater problems. Cities need better ways to reduce runoff pollution before it reaches rivers and lakes. You can learn sampling design, control setup, and how to compare treatment groups with real data.

Research Questions

• How does adding biochar to a green roof module change Pb retention in first-flush runoff?
• What is the effect of biochar loading on Zn capture in stormwater passing through roof media?
• Does a biochar-amended module reduce total measured metal concentration more than a standard roof mix?
• To what extent does the media depth change pollutant retention in a tote-based green roof model?
• Which roof media blend captures the largest share of dissolved metals after a simulated storm event?
• How does repeated wetting and drying affect pollutant retention in biochar-amended roof modules?

Basic Materials

• Plastic storage tote or shallow planter box.
• Roof media components such as potting soil, sand, and perlite.
• Biochar from a garden supplier or soil supplier.
• Native plants or grass plugs suited to your climate.
• Digital kitchen scale with 0.1 g accuracy.
• Measuring cups or graduated containers.
• Spray bottle or watering can for simulated rainfall.
• Collection trays or containers for runoff.
• Labels, waterproof marker, and notebook.
• Phone camera for documenting module setup.

Advanced Materials

• Prepared green roof trays or custom test modules.
• Sized biochar with known feedstock source.
• Analytical balance.
• Vacuum filtration setup.
• Acid-washed sample bottles.
• ICP-OES or ICP-MS access through a partner lab.
• HPLC access or a certified lab service for PAH analysis.
• Soil pH meter.
• Electrical conductivity meter.
• Desiccator for drying media samples.

Software & Tools

• Google Sheets: Organizes runoff data, calculates means, and makes comparison charts.
• ImageJ: Measures plant cover, surface changes, or photo-based area estimates if you track growth.
• RStudio: Runs statistical tests and helps you compare treatment groups with cleaner plots.
• PubMed: Helps you find review articles on biochar, stormwater, and pollutant retention.
• NIH PubChem: Lets you check chemical properties of PAHs and related compounds.

Experiment Steps

1. Define the pollutant targets, the sample medium, and the one variable you will change first.
2. Design matching control and treatment modules so each test starts with the same roof structure.
3. Plan a rainfall simulation that gives every module the same water exposure and collection method.
4. Build a measurement plan for metals, PAHs, or accepted proxies, and decide how you will compare them across samples.
5. Set up controls that rule out plant-only effects, media-only effects, and contamination from containers.
6. Choose the statistics you will use before data collection so you can test whether biochar changes retention.

Common Pitfalls

• Using different soil depths in each tote, which makes pollutant retention impossible to compare fairly.
• Letting runoff splash between modules, which can move contaminants from one treatment to another.
• Skipping blank samples, which makes it hard to tell whether the lab signal came from your roof media or from contamination.
• Mixing biochar made from different feedstocks, which changes adsorption behavior and adds noise.
• Measuring only one storm event, which hides how retention changes after the media gets saturated.

What Makes This Competitive

A stronger project goes beyond, “Does biochar help?” and asks how much, under what conditions, and with what tradeoffs. You can raise the level by comparing multiple biochar doses, testing more than one pollutant class, or checking whether the effect changes after repeated storm cycles. A careful control design and a clear statistical plan matter as much as the material itself.

Project Variations

• Test whether biochar works better with sedum-based roof modules than with bare media.
• Compare hardwood biochar, crop-residue biochar, and no-biochar controls for metal retention.
• Measure how changing roof slope or tote drainage affects first-flush pollutant capture.

Learn More

• US EPA stormwater resources: Search the EPA site for green roof stormwater basics and runoff pollution background.
• USGS water quality topics: Search USGS for metals in runoff and watershed contamination summaries.
• NOAA Sea Grant stormwater education: Find coastal stormwater explainers and runoff impact resources through NOAA Sea Grant.
• NIH PubMed: Search for review articles on biochar adsorption, stormwater treatment, and PAH retention.
• MIT OpenCourseWare: Search for environmental engineering or water treatment lecture materials to learn basic design concepts.