7 Using the following figure what is the chlorine dose requi

7. Using the following figure, what is the chlorine dose required to attain a combined residual of 0.5 mg/, and a free residual of 0.5 mg/l? What is the combined residual present when a free residual of 0.5 mg/1 exists? Chlorine demand curve 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 16 Chlorine dose, mg/L

Solution

we know that

total residue = 1 mg/l  

then from the graph we taking values

combined residual = total residual - free residual

= 1 - 0.5 = 0.5 mg/l

the chlorine dose required to attain combined residual is 0.5 mg/l is 0.6 mg/l ( From the graph we located on X-axis)