Question

The amount of 38*10 6 gallons/day of raw water enters a water treatment plant to produce potable drinking water. The water source has high turbidity and hardness. The plant’s engineers have decided to use alum to address the turbidity problem and use other appropriate techniques to reduce the hardness. They performed jar tests and an optimum dose for alum was determined as 14.7 mg/L.
a) Calculate the amount of alkalinity consumed (mg/L as CaCO3)
b) Calculate the amount of required alum for this plant per year (kg/year)
The hardness for the raw water is 268 mg/L as CaCO3 and after treatment the hardness is reduced to 103 mg/L as CaCO3.
c) If we assume all the hardness is coming from magnesium ion, what is the concentration of the magnesium in the treated water? (mg Mg 2+ /L)
d) Is the raw water soft, moderately hard, hard, or very hard? How about the treated water?
e) What is the water hardness level in most of the areas in California? (soft, moderately hard, hard, or very hard). How about Oregon State?

Answer 1

note : The equivalent weight of an element is its gram atomic weight divided by its valence.

like for CaCO3 = 100/2 = 50 g , Mg+2 = 24/2 = 12 g

for california--> hard to very hard since average harness is 100 to 300 mg/l

while Oregon State water quality comes under soft to moderate hard on an average is 80 mg/l.

thank you hope you like it.