Question

A groundwater supply has the following analysis: Ca2+ = 94 mg/l HCO3- = 317 mg/l Mg2+ = 24 mg/l SO42- = 67 mg/l Na+ = 14 mg/l C1- = 24 mg/l Calculate the quantities of lime and soda ash for excess-lime softening, and the carbon dioxide reacted for neutralization by two-stage recarbonation. Assume that the practical limits of hardness removal for calcium are 30 mg/1 as CaCO3 and for magnesium are 10 mg/1 as CaCO3 and that three-quarters of the final alkalinity is converted to bicarbonate. Calculate the finished hardness and sketch the bar graphs for the raw and finished waters.

Answer 1

Solution:-

Given

= 94 mg/L = 317 mg/L

= 24 mg/L    = 67 mg/L

= 14 mg/L    = 24 mg/L

Total Hardness as mg/L of =

  

= 335 mg/L as

Total Alkalinity =

= 317

(TA) = 259.81 mg/L as

Dose of lime as Cao requires =

= 187.6 mg/L

dose of soda required

i.e.

= 79.7014 mg/L

Given tha practical limits of removal of calcuim = 30 mg/L as

Magnesium = 10 mg/L as

& three quarters of fins Alkalinity converted to bicarbonayes

New Hardness

TH = 335 - 30 - 10

= 295 mg/L as

TA =