7/27/2019 4.09 - Handout - Calculation of Chlorine Dosage

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Kenya WASH Cluster WASH in emergencies training 27-30 Oct 2008

4.09 - Handout - calculation of chlorine dosage.doc1

Kenya WASH Cluster Emergency Water Training

Chlorination calculation of dosage

1% solution has = 10 g active chlorine / litre

10,000 mg / litre

10,000 mg / 1,000 ml

10 mg / ml

So each 1 ml of 1% solution has 10 mg of active chlorine

If you need 3 mg/l of chlorine to leave 0.5 mg/l residual of active chlorine

a) Then for a 20 litre jerry can and using a 1% solution, you will need:

3 mg / litre x 20 litres = 60 mg chlorine needed

60 mg chlorine = 6 x 1 ml of 1% solution

b) If you use a 3% solution this is 10mg x 3 = 30 mg/ml

Then for a 20 litre jerry can and using a 3% solution, you will need:

3 mg / litre x 20 litres = 60 mg chlorine needed

60 mg chlorine = 2 x 1 ml of 3% solution

Quantities of chemical required to make 1 Litre of 1% Chlorine Solution1

Source of chlorine Availablechlorine %

Quantity required(g)

Approx. measure

High Test Hypochloritegranules (HTH)

70 14 g 1 heaped tablespoon

Bleaching powder 34 30 g 2 heaped tablespoons

Stabilized tropicalbleach

25 40 g 3 heaped tablespoons

Liquid householddisinfectant

10 100 ml 7 tablespoons

Liquid laundrydisinfectant

5 200 ml 14 tablespoons

Antiseptic solution (e.g.Milton)

1 1 litre No need to adjust as it isa 1% solution

1Davis & Lambert, Engineering in Emergencies

7/27/2019 4.09 - Handout - Calculation of Chlorine Dosage

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Kenya WASH Cluster WASH in emergencies training 27-30 Oct 2008

4.09 - Handout - calculation of chlorine dosage.doc2

Ascertaining the required dose for HTH powder

To determine how much chlorine to add, the chlorine demand is measured.

1. Prepare a 1% chlorine solution2, the quantity depending upon type ofchlorine used (see the table below).

2. Take 3 or 4 non-metallic containers of known volume (e.g. 20 litre buckets).

3. Fill the containers with some of the water to be treated and check the pH ofthe water.

4. Add to each bucket a progressively greater dose of 1% solution with asyringe:

1st container: 1ml

2nd container: 1.5ml

3

rd

container: 2ml4th container: 2.5ml

5. Wait 30 minutes. (This is essential as this is the minimum contact time forthe chlorine to react. If the pH of the water is high, this minimum time willincrease)

6. Measure the free chlorine residual in reach bucket.

7. Choose the sample which shows a free residual chlorine level between0.2 and 0.5mg/l.

8. Extrapolate the 1% dose to the volume of water to be treated.

9. Pour the solution into the reservoir/dosing vessel, mix well (during filling)and wait 30 minutes before distributing to consumers.

10. Check chlorine demand at several water distribution points and adjust ifrequired.

11. Recheck chlorine demand periodically and when raw water quality isknown to vary, to ensure that the chlorine residual is maintained.

2A 1% solution contains 1% of available chlorine, which is 10g of chlorine per litre, i.e. 10,000 mg/l or 10,000 ppm.