Part 2. (30 points) The city of Melbourne, Florida has a surface water treatment

Question

Part 2. (30 points) The city of Melbourne, Florida has a surface water treatment plant that produces 20 MGD of potable drinking water. The water source has hardness measured as 94 mg/L as CaCO, and after treatment, the hardness is reduced to 85 mg/L as CaCO (a) Is the treated water, soft, moderately hard, or hard? (b) Assuming all the hardness is derived from calcium ion, what would the concentration of calcium be in the treated water (mg Ca L). (c) Assuming all the hardness is derived from magnesium ion, what would the concentration of magnesium be in the treated water (mg Mg L)

Explanation / Answer

a) The hardness levels classified based on concentration CaCO3 (mg/l) is as follows.

<75 mg/l or ppm - Soft Water,

75-150 mg/l or ppm- Moderately Hard,

150-300 mg/l or ppm - Hard,

>300 mg/l or ppm - Very Hard.

So the Answer is "Moderately Hard".

b) Calcium Hardness = Calcium (mg/l) x (Equivalent weight of CaCO3)/ (Equivalent weight of Calcium)

We Have Calcium hardness = 85 mg/l.

Equivalent weight of CaCO3 = 100,

Equivalent Weight of Calcium = 40,

So Calcium (mg/l) = 85x(40/100) = 34 mg/l,

So Concentration of Calcium in treated water is 34 mg /l.

C) Magnesium Hardness as CaCO3= magnesium (mg/l) x (Equivalent weight of CaCO3)/ (Equivalent weight of magnesium)

We Have Magnesium hardness = 85 mg/l.

Equivalent weight of CaCO3 = 100,

Equivalent Weight of magnesium = 24,

So Magnesium (mg/l) = 85x(24/100) = 20.4 mg/l,

So Concentration of Magnesium in treated water is 20.4 mg /l.

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