Page 357 - Water and wastewater engineering

8-26 WATER AND WASTEWATER ENGINEERING

8-2. A pilot scale ion exchange column was used to develop design data for a softening
system for the Village of Calcite. The data are shown below. The design flow rate is
3
4,000 m /d. The design final hardness is 120 mg/L as CaCO 3 . Regeneration is to be
once per day. The manufacturer’s operating capacity to breakthrough is 60%.
Assume a two-column system: one in service and one in regeneration or standby.
Also assume that there is no leakage before breakthrough. Use the mass balance tech-
nique to determine the mass of resin that will be required.

Raw water data:
2
Ca 444.5 mg/L as CaCO 3
2
Mg 66.7 mg/L as CaCO 3
Operating temperature 10 C
Iron and turbidity concentrations are negligible
Pilot scale column data:
Column diameter 10.0 cm
Column height 150.0 cm
3
Resin density 0.70 g/cm on a moist basis
Moisture content 48%
3
Flow rate through the column 0.25 m /h
Pilot scale breakthrough data for Calcite raw water
3
Volume, m Effluent concentration,
meq/L
0.5 0
1.0 0
1.5 0
2.0 0
2.1 0.05
3.0 0.46
3.5 1.05
4.0 2.00
4.5 3.20
5.0 4.90
5.35 6.00
5.45 6.40
5.5 6.70
5.6 7.00
5.7 7.40
5.8 7.80
5.9 8.20
6.0 8.50
6.4 9.00
7.0 9.70
7.5 10.0