Calculation of Chlorine Requirement

Task: To calculate how much chlorine is needed to chlorinate a water supply for 20,000 people receiving 15 litres/person/day.

Water demand = 300,000 litres

If water is pumped by a pump at a flow rate of 8 l/s then the total pumping time is about 10.5 hours per day.

In this case the water is of medium quality requireing a dose of 3mg/l of active chlorine to give a residual of 0.2mg/l. This information was obtained by dosing small samples and analysing using a test kit.

For a pumping rate of 8l/s the dosing rate must be 3 x 8 = 24mg/s

Using a 1% chlorine solution, which contains 10g chlorine/litre, the rate of application will be

(24/1000) x (100/1) = 2.4g/s (ml/s) or 144ml/minute

For 10.5 hours pumping per day the amount of 1% chlorine solution required will be

144 x 60 x 10.5/1000 = 90.7 litres per day

Therefore a 200 litre drum of 1% chlorine solution would last two days.

Note:

High Test Hypochlorite (calcium hypochlorite) granules - 70% available chlorine
Sodium Hypochlorite (household bleaches) - 5 - 15% available chlorine

To Make a 1% Solution:

A 1% solution contains 10g of chlorine per litre i.e. HTH would require 14g per litre (1 heaped tablespoon).