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.

Supplies

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

Step 1:

cut the banana peel into small cubes, as shown above

Step 2:

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.

Step 3:

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

The first glass served as a control sample (no adsorbent added).
The second glass was treated with used coffee grounds as the adsorbent.
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

Step 4:

This is how dried adsorbents typically appear

Step 5:

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.

Step 6:

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.)

Step 7: