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Jar Test for Determining Optimum Dosage of Coagulant – Environmental Engineering Lab Experiment

Conducting Jar Test for Determining Optimum Dosage of Coagulant – Lab Experiment

Coagulation is an important process in water treatment used to remove suspended particles, turbidity, and impurities from water. Chemicals such as alum (aluminium sulfate) are commonly used as coagulants.

A jar test is performed to determine the optimum amount of coagulant required for effective removal of turbidity and suspended solids from water.

Aim

To determine the optimum dosage of coagulant for the given water sample using a jar test.

Apparatus Required

  • Jar test apparatus with multiple stirrers
  • Beakers (1 L capacity)
  • Measuring cylinder
  • Pipettes
  • Glass rod
  • Turbidity meter (optional)

Chemicals Required

  • Alum (Aluminium Sulfate) solution
  • Distilled water
  • Water sample

Theory

In the coagulation process, chemicals such as alum are added to water to destabilize suspended particles. These particles then combine to form larger particles called flocs, which can settle down during sedimentation.

The jar test helps determine the optimum dose of coagulant by testing different doses and observing the formation and settling of flocs.

Procedure

  1. Fill six beakers with equal volumes of the water sample.
  2. Add different doses of alum solution to each beaker.
  3. Place the beakers in the jar test apparatus.
  4. Mix rapidly for about 1–2 minutes to disperse the coagulant.
  5. Reduce the stirring speed and mix slowly for about 15–20 minutes to allow floc formation.
  6. Stop stirring and allow the flocs to settle for about 30 minutes.
  7. Observe the clarity of the water in each beaker.
  8. Measure turbidity if a turbidity meter is available.

Observation Table

Beaker Number Coagulant Dose (mg/L) Turbidity After Settling Observation
1 ______ ______ ______
2 ______ ______ ______
3 ______ ______ ______
4 ______ ______ ______
5 ______ ______ ______
6 ______ ______ ______

Result

The optimum dosage of coagulant is the dose that produces the maximum clarification and lowest turbidity after settling.

Optimum coagulant dosage = ______ mg/L

Precautions

  • Use equal volumes of water sample in all beakers.
  • Add coagulant doses accurately.
  • Maintain proper mixing speed during the test.
  • Allow sufficient settling time for flocs.

Conclusion

The jar test helps determine the optimum amount of coagulant required for effective water treatment. Using the correct dosage improves water clarity and reduces chemical wastage in treatment plants.

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