Mini Wetland Greywater Cleanup Science Project

ISEF Category: Environmental Engineering

Subcategory: Bioremediation  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

A bucket of plants can act like a tiny wastewater plant. That sounds small, but the idea powers real cleanup systems. You can test which plant pulls the most nitrogen and phosphorus out of greywater. That gives you a real environmental engineering project, not just a plant-growing demo.

What Is It?

Constructed wetlands are built systems that clean dirty water using plants, roots, microbes, and soil or gravel. Think of them like a natural filter with living parts. The plants do not work alone. Their roots help trap particles, and microbes on those roots break down waste.

In this project, you compare duckweed, water hyacinth, and cattail in mini wetland setups. Greywater is lightly used household water from sinks or laundry, not toilet water. It often contains nutrients such as nitrogen and phosphorus. Those nutrients can feed algae and harm waterways if they leave homes untreated. Your job is to see which plant setup lowers those nutrients the most over time.

Why This Is a Good Topic

This is a strong science fair topic because you can change one variable, the plant type, and measure real water quality changes. You can collect data over several weeks, compare trends, and use simple test strips to track nitrogen and phosphorus. The project connects to stormwater, wastewater, and home water reuse, so it has clear real-world value. You can also learn experimental design, controls, and data analysis without needing a university lab.

Research Questions

• How does plant species affect nitrogen removal from greywater in a bucket-scale constructed wetland?
• What is the effect of plant species on phosphorus removal from greywater over time?
• Does a planted bucket remove more nutrients than an unplanted control bucket?
• To what extent does duckweed change nutrient levels compared with water hyacinth and cattail?
• Which plant setup keeps water clearer while also lowering nitrogen and phosphorus?
• How does the rate of nutrient removal change across the 6-week trial?

Basic Materials

• Five-gallon buckets or similar opaque containers with lids or covers.
• Duckweed, water hyacinth, and cattail starts from a legal, local source.
• Clean gravel or aquarium substrate for each bucket.
• Dechlorinated water or collected greywater from a safe source.
• Aquarium nitrogen test strips with a known detection range.
• Aquarium phosphorus test strips or a phosphorus color test kit.
• Digital camera or smartphone for photo documentation.
• Measuring cup or graduated pitcher for adding equal water amounts.
• Permanent marker and waterproof labels.
• Notebook or spreadsheet for data tables.
• Gloves and safety glasses.

Advanced Materials

• Dissolved oxygen meter for checking water quality changes.
• pH meter or calibrated pH strips.
• Electrical conductivity meter for salinity tracking.
• UV-Vis spectrophotometer for higher-resolution nutrient assays.
• Glassware for preparing calibration standards.
• Analytical balance for plant biomass measurements.
• Drying oven or food dehydrator for plant dry mass.
• Image analysis setup for root and biomass documentation.
• Soil or substrate nutrient extraction materials.
• Sterile containers for microbial or water sampling, if your lab allows it.

Software & Tools

• Google Sheets: Organizes repeated measurements, calculates averages, and makes trend graphs.
• ImageJ: Measures plant cover, root spread, or color changes from photos.
• Desmos: Helps you inspect curves and compare removal trends across treatments.
• R: Supports stronger statistics if you want to compare multiple plant treatments and controls.
• PubMed: Helps you find review articles on constructed wetlands, greywater, and nutrient removal.

Experiment Steps

1. Define the one question you will test, then pick plant treatments and a no-plant control that match it.
2. Design buckets so each setup starts as similarly as possible, including water volume, container size, and substrate.
3. Choose your measurement plan for nitrogen, phosphorus, and any visual water-quality traits you can score consistently.
4. Build a data table before you start, so each sampling day uses the same labels, units, and record-keeping format.
5. Plan how you will compare changes over time, including averages, percent removal, and simple statistics.
6. Write down the controls and failure checks that will tell you whether a plant effect is real or just random variation.

Common Pitfalls

• Using greywater that changes from one day to the next, which makes nutrient trends hard to compare.
• Letting sunlight and temperature differ between buckets, which changes plant growth and confounds the treatment effect.
• Skipping an unplanted control, which makes it impossible to tell whether plants did the cleanup or the bucket itself did.
• Reading aquarium test strips under different lighting, which can shift the color match and distort nutrient data.
• Starting with uneven plant size or root mass, which gives one treatment an unfair head start.

What Makes This Competitive

A stronger project does more than compare plant names. You can track both nitrogen and phosphorus, add a true control, and analyze removal over time instead of only at the end. You can also compare plant biomass gain, water clarity, and nutrient change together. That kind of multi-metric design shows real engineering thinking, not just plant observation.

Project Variations

• Test greywater from laundry, bathroom sink, or kitchen rinse water to see whether the input source changes removal rates.
• Compare floating plants with rooted emergent plants by adding a fourth treatment such as no-plant gravel only.
• Replace test strips with colorimetry from smartphone photos, then compare whether image-based results match the strip readings.

Learn More

• US EPA Constructed Wetlands resources: Search the EPA site for wetlands and wastewater treatment guidance to learn how real systems are designed.
• NOAA educational wetlands pages: Use NOAA to understand why nutrient runoff matters for algae blooms and coastal water quality.
• USDA NRCS plant fact sheets: Search for duckweed, cattail, and water hyacinth to learn about growth habits and habitat needs.
• PubMed: Search review articles on constructed wetlands, greywater treatment, and nutrient removal for background biology and engineering.
• MIT OpenCourseWare Environmental Engineering materials: Look for free course notes on water quality, treatment, and environmental systems design.