Water Purification Using Natural Adsorbents. Using Dried Coffee Grounds and Dried Banana Peels

Access to clean water is one of the most important global challenges. In this simple experiment, I used two common kitchen wastes — banana peels and coffee grounds — to test their ability to filter dirty water. The goal was to compare the filtering performance of each material and discover whether natural waste can be used as a low-cost, eco-friendly water purification method. This project is beginner-friendly, requires only household materials, and demonstrates basic scientific thinking, sustainability, and hands-on creativity.

1. • 1 banana peel (cut and dried)
2. • 2 tablespoons of used coffee grounds (dried)
3. • 1 pouring funnel
4. • 2 cotton pads or 1 piece of cloth
5. • Water with gouache paint (or food coloring)
6. • Scissors
7. • Glass or cup (to collect clean water)
8. • Oven
9. • Baking paper

cut the banana peel into small cubes, as shown above

Dry the Coffee Grounds and Banana Peel:

Spread used coffee grounds in a thin layer on baking paper. Do the same with banana peel. Place both in the oven and dry at 100 °C (212 °F) for 30–45 minutes, stirring or turning occasionally. The coffee grounds should become dry and crumbly, like sand, while the banana peel should turn dry, crispy, and crunchy.

While the adsorbents were being dried, I prepared three samples of contaminated water using gouache paint:

1. The first glass served as a control sample (no adsorbent added).
2. The second glass was treated with used coffee grounds as the adsorbent.
3. The third glass was treated with banana peels as the adsorbent.

Additionally, I constructed a simple filtration setup using a pouring funnel and cotton pads, which were arranged in the following way

This is how dried adsorbents typically appear

Let the Filter Sit

After assembling the filter with banana peel and coffee grounds, I left the adsorbents inside the glasses for about 1 hour to stabilize and settle. This allowed the materials to adjust to the shape of the bottle and become compact.

Filter the Water and Observe

I poured the colored (dirty) water into the filter and waited as it slowly dripped into the glass below. After filtration, I compared the color of the water. The result showed that banana peel removed more color than coffee grounds. This suggests that banana peel is a more effective natural adsorbent.

(You are also welcome to review my presentation, which covers the entire project.)

(You are also welcome to review my presentation, which covers the entire project.)