Finding out what really happens to wastewater at treatment plants in Water too little to waste – Class 7 Science Experiment

Chapter Name: Water too little to waste

Activity Name: Finding out what really happens to wastewater at treatment plants in Water too little to waste

Activity Description:

Finding out what really happens to wastewater at treatment plants in Water too little to waste - Class 7 Science Experiment

This experiment aims to simulate the wastewater treatment process and observe the changes that occur at each stage.

The process involves adding organic matter, detergent, and coloring to a jar of water, followed by aeration to promote biological processes. Then, the aerated water is passed through a filtration system and finally treated with chlorine, representing chemical treatment.

Required Items:

  1. Large glass jar
  2. Water
  3. Dirty organic matter (e.g., grass pieces or orange peels)
  4. Detergent
  5. Ink or any coloring agent
  6. Test tubes
  7. Aerator (or mechanical stirrer/mixer)
  8. Funnel
  9. Filter paper
  10. Sand, fine gravel, and medium gravel
  11. Chlorine tablet

Step by Step Procedure:

  1. Fill a large glass jar ¾ full of water.
  2. Add dirty organic matter, a small amount of detergent, and a few drops of ink or coloring agent to the jar.
  3. Cap the jar, shake it well, and let the mixture stand in the sun for two days.
  4. After two days, shake the mixture and pour a small sample into a test tube labeled “Before treatment; Sample 1.” Observe and note the smell.
  5. Use an aerator (or mechanical stirrer/mixer) to bubble air through the water in the jar. Leave the aerator attached overnight.
  6. The next day, pour another sample into a second test tube labeled “After aeration; Sample 2.”
  7. Set up a filtration system by folding filter paper to form a cone and placing it in a funnel.
  8. Add layers of sand, fine gravel, and medium gravel to the funnel.
  9. Pour the remaining aerated liquid through the filter into beakers, ensuring the liquid does not spill over.
  10. If the filtered water is not clear, filter it multiple times until you achieve clear water. This represents the physical process in water treatment.
  11. Pour a sample of the filtered water into a third test tube labeled “Filtered; Sample 3.”
  12. Pour another sample of the filtered water into a fourth test tube and add a small piece of a chlorine tablet. Mix well until the water is clear. Label this test tube “Chlorinated; Sample 4.”
  13. Observe the samples in all the test tubes carefully. Do not taste; just smell them.

Experiment Observations:

  • Sample 1 (Before treatment) may have a foul smell due to the presence of organic matter and other impurities.
  • Sample 2 (After aeration) may show some improvement in smell, as aeration helps promote biological processes, breaking down waste material faster.
  • Sample 3 (Filtered) should have a clearer appearance and improved odor after passing through the filtration system.
  • Sample 4 (Chlorinated) should have clear water with a reduction in unpleasant odors, as chlorine helps disinfect and purify the water through a chemical process.


  1. Handle all chemicals and waste materials with care, following safety guidelines.
  2. Avoid direct contact with the wastewater or any samples during the experiment.
  3. Dispose of waste materials properly according to local regulations.

Lesson Learnt from Experiment:

The experiment demonstrates the various stages of water treatment: biological, physical, and chemical processes. Aeration and filtration play crucial roles in removing impurities and enhancing the quality of wastewater, making it safer for the environment and human use. Chlorination further disinfects the water, ensuring it meets acceptable standards for reuse or discharge.

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