Question

Raw water requires an alum dose of 37 mg/l, as determined by jar testing. if a residual 25 mg/l alkalinity must be present in the water to ensure complete precipitation of alum added, what is the total alkalinity required, in mg/l?

Answer 1

The total alkalinity required in the water after treating it with an alum dose of 37 mg/L, while maintaining a residual alkalinity of 25 mg/L, is 62 mg/L.

Step-by-step explanation:

The question pertains to the total alkalinity required when using an alum dose in water treatment to ensure complete precipitation. When alum (Aluminum sulfate) is used in water treatment, it reacts with the alkalinity of the water to form a precipitate, thereby removing impurities from the water.

The residual alkalinity needed after the addition of alum is important because it ensures that the water does not become too acidic, which can lead to poor coagulation and possible corrosion issues.

In this case, you're told that the raw water requires an alum dose of 37 mg/L and that a residual of 25 mg/L alkalinity must be present. Therefore, the total alkalinity required is the sum of the alum dose and the residual alkalinity, which is 62 mg/L (37 mg/L + 25 mg/L).