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Conducting Break Point Chlorination Test – Environmental Engineering Lab Experiment

Conducting Break-Point Chlorination Test – Lab Experiment

Chlorination is one of the most widely used methods for disinfection of drinking water. When chlorine is added to water, it reacts with impurities such as ammonia, organic matter, and other reducing substances. The point at which the chlorine demand of water is satisfied and free residual chlorine begins to appear is known as the break-point chlorination.

Conducting a break-point chlorination test helps determine the correct amount of chlorine required for effective water disinfection.

Aim

To determine the break-point chlorination of a water sample by adding different doses of chlorine and measuring the residual chlorine.

Apparatus Required

  • Beakers or conical flasks
  • Measuring cylinder
  • Pipettes
  • Glass rod
  • Comparator or colorimeter
  • Water samples

Chemicals Required

  • Bleaching powder solution or chlorine solution
  • Orthotolidine reagent or DPD reagent
  • Distilled water

Theory

When chlorine is added to water, it first reacts with ammonia and organic compounds. This stage consumes chlorine and produces combined chlorine compounds. As more chlorine is added, these compounds break down and the chlorine demand of water is satisfied.

At a certain point, free residual chlorine starts appearing in the water. This point is called the break point. Beyond this point, any additional chlorine remains in the water as free residual chlorine.

Procedure

  1. Take equal volumes of the water sample in several clean beakers.
  2. Add increasing doses of chlorine solution to each beaker.
  3. Mix the samples thoroughly using a glass rod.
  4. Allow the samples to stand for about 30 minutes.
  5. Add orthotolidine or DPD reagent to each sample.
  6. Measure the residual chlorine using a comparator or colorimeter.
  7. Record the residual chlorine values for each chlorine dose.
  8. Plot a graph between chlorine dose and residual chlorine.

Observation Table

Sample Number Chlorine Dose (mg/L) Residual Chlorine (mg/L)
1 ______ ______
2 ______ ______
3 ______ ______
4 ______ ______
5 ______ ______

Result

The break-point chlorination was determined by plotting a graph between chlorine dose and residual chlorine. The point where the residual chlorine begins to increase sharply represents the break point.

Break-point chlorine dose = ______ mg/L

Precautions

  • Prepare chlorine solution freshly.
  • Use clean glassware to avoid contamination.
  • Allow sufficient contact time for chlorine reaction.
  • Measure residual chlorine accurately.

Conclusion

The break-point chlorination test helps determine the optimum chlorine dosage required for water disinfection. Maintaining chlorine levels beyond the break point ensures effective removal of harmful microorganisms from water.

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