Chlorination system sizing involves determining the dosage required. This amount depends on the chlorine demand of the water or waste and on its flow rate.
The following example shows the chlorine dosage required for the effluent from an activated-sludge waste treatment plant. The average flow through the plant is 1.2 million gpd. Table 7.30.2 shows that the average dosage required to produce 0.5 mg/l of combined residual chlorine after 15 min contact time is about 8 mg/l or 8 ppm. The weight of daily waste flow through the plant is as follows:
1,200,000 gal per day X 8.34 lb per gal
= 9,998,000 lb of liquid effluent per day
The weight of chlorine gas needed per day is as follows:
x lb of chlorine 8 parts
9,998,000 lbof effluent = 1,000,000 parts x = 8 X 9.99 = 80 lb of chlorine per day
A typical chlorinator model feeds chlorine gas at rates adjustable from 10 to 200 lb per day.
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