Chlorine Demand-HORROCK'S apparatus.pptx

Concept of Chlorine demand and Horrocks Apparatus

1. Concept of Chlorine demand and Horrocks Apparatus Dr. Anuj Singh Asst. Professor Community Medicine Dept UIMS , Prayagraj

2. “If the value is zero, the water is already free of pathogenic microorganisms”.

3. Breakpoint Chlorination

4. Breakpoint chlorination is defined as the point where enough chlorine has been added to a quantity of water to satisfy its disinfecting demand . In other words, it is the point where all undesirable contaminants have been removed from the water .  At breakpoint chlorination, all chlorine added to the solution is consumed by chemical reactions with the contaminants , resulting in no  free available chlorine (FAC)  in the water

5. Breakpoint Chlorination: Combined chlorine (C.C.) is free available chlorine that has combined with wastes containing nitrogen or ammonia (also known as chloramines). Combined chlorine will cause a noticeable "chlorine odour" and can cause skin, eye, and mucous membrane irritation. It also has little disinfecting power. Breakpoint chlorination is used to get rid of combined chlorine.

6. To determine the amount of combined chlorine use the following equation: Combined Chlorine = Total Chlorine - Free Available Chlorine Breakpoint chlorination is a technique used to remove combined chlorine by adding free available chlorine. To reach breakpoint, sufficient chlorine must be added to the pool to raise the free available chlorine level to 10 times the amount of combined chlorine.

7. Horrocks Apparatus

8. Horrock’s apparatus:- used for estimating the dose of bleaching powder needed to disinfect 455 Liters of water. It is used mostly while disinfecting the water in a well.

9. Contents of ‘ Horrocks Apparatus ’ • 6 white cups, each of 200 ml capacity • One black cup with a circular mark on the inside • 2 metal spoons (each holds 2g of bleaching powder when filled up to the brim) • 7 glass stirring rods • One special pipette • Two droppers • Starch - iodide indicator solution • Instruction folder

10. Steps in Estimating the Required Dosage of Bleaching Powder for disinfecting water:- One level spoonful (2g) of bleaching powder is placed in the black cup and made into a thin paste with a little water. More water is added to the paste to bring up the volume up to the circular mark. The solution thus prepared is the ‘Chlorine Stock Solution’ The six white cups are filled with the water to be tested Using the pipette provided with the apparatus, add one drop of the stock solution to the first cup, two drops to the second cup, three drops to the third cup, and so on till adding six drops to the sixth cup.

11. 4. Stir the water in the cups; use a separate rod for each cup 5. Wait for half an hour 6. Add three drops of starch-iodide indicator to each of the white cups 7. Development of blue color indicates the presence of free residual chlorine. 8. The first cup which develops this color gives an estimate of the amount of bleaching powder needed to disinfect 455 L of the sample water.

12. If first cup develops blue colour : 1 spoonful (i.e. 2gm) of bleaching powder would suffice for 455 L of water If the second cup develops blue colour : 2 spoonfuls (4 gm) of bleaching powder for 455 L of water Third cup develops blue colour : 3 spoons (6 gm), so on till the sixth cup when it means 6 spoons (12 gm) of bleaching powder is needed for 455 liter of water If none of the cups develop a blue colour , this means that the chlorine demand of the water is very high and it is better to use some method of clearing the water prior to chlorinating it