Question

Determine the lime and soda ash dose, in mg/L as CaCO3, to soften the following water to a final hardness of 80.0 mg/L as as CaCO3. If the price of lime, purchased as CaO is $100.00 per megagram (Mg), and the price of soda ash, purchased as Na2CO3 is $200.00 per Mg, what is the annual chemical cost required to treat 0.5m^3 /s of this water?

Compound Concentration (mg/L as CaCO3)
CO2 22.0
Ca^2+ 200.0
Mg^2+ 100.0
HCO3^- 150.0

Answer 1

= $ 75811 per annum

Step-by-step explanation:

C02 in water

A = co2 ( mg/l) x cao/co2

= 22 x 56/44

= 28mg/l

Note that co2 = 22mg/l

Ca+2 = 200mg/i

Mg+2 = 100 mg/l

Co3- = 150mg/l

Magnesium ion required during softening process (b)

B = MG+2 X CAO/MG+2

= 00 x ( 56/24.30)

= 230.45 mg/l

Bicarbonate alkalinity removal

= Hco3- x ( cao/ Hco3-)

= 150 x ( 56/61)

137.70mg/l

Lime ion required

Quick lime ( cao) = ( A+ B+ C)/ PURITY OF LIME

= 440.17mg/l

Total hardness = ca+2 + mg +2

= 200 + 100

=300mg/l

Non carbonate hardness = T.H – C .H

= 300 – 150

= 150mg/l

Soda ash dosage = Nch x na2co3/caco3

= 150 x 105.98/100

= 158.97mg/l

Annual chemical cost = lime soda x lime cost per mg

+ soda ash x soda ash per mg

= 440. 17 x 100 + 158.97 x 200

= $ 75811 per annum